Has Invasive Amur Honeysuckle (Lonicera maackii (Rupr.) Maxim) Met its Match? Interspecies Comparisons of Photosynthesis and Shoot Allocation in Heavy Shade

Has Invasive Amur Honeysuckle (Lonicera maackii (Rupr.) Maxim) Met its Match? Interspecies Comparisons of Photosynthesis and Shoot Allocation in Heavy Shade | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Has Invasive Amur Honeysuckle (Lonicera maackii (Rupr.) Maxim) Met its Match? Interspecies Comparisons of Photosynthesis and Shoot Allocation in Heavy Shade Kurt E. Schulz This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2426397/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Sep, 2023 Read the published version in Plant Ecology → Version 1 posted 7 You are reading this latest preprint version Abstract Amur honeysuckle ( Lonicera maackii (Rupr.) Maxim) is a notorious invader of forests and forest edges throughout eastern North America. The species is difficult to exterminate and reestablishes readily. A perpetual presence of Amur honeysuckle in most forests is largely a forgone conclusion. Forests throughout the eastern U.S. are changing due to canopy closure after historical disturbance and long-term fire prevention. Fire intolerant species, especially sugar maple ( Acer saccharum Marshall.), are coming to dominate forest canopies, creating shady understories and forest dynamics that pivot on shade tolerance. Two shade tolerant understory shrubs, pawpaw ( Asimina triloba Adans.) and spicebush ( Lindera benzoin Thunb.) compete with honeysuckle in maple understories. Based on field observations we hypothesized that these native species were more shade tolerant than invasive honeysuckle. We examined shade tolerance in honeysuckle, pawpaw, and spice bush by comparing photosynthetic light responses, leaf characteristics, and allocation to leaf area versus stem mass (leaf area ratio, LAR) in annual shoots. Honeysuckle had comparable light responses measured on a leaf area basis, but mass-based measurements show it is less efficient paying back carbon invested in leaf tissue. This arises because honeysuckle is unable to reduce specific leaf mass to the level of pawpaw and spicebush. LAR is distinctly higher in pawpaw and spicebush, suggesting an advantage in heavy shade. Since the great majority of photosynthesis in these species occurs under a closed canopy, we suggest honeysuckle will diminish in maple-dominated stands. Informal observations of greater height growth in pawpaw and spicebush in the field support this. Lonicera maackii mesofication shade tolerance Asimina triloba Lindera benzoin Figures Figure 1 Figure 2 Introduction Amur honeysuckle ( Lonicera maackii (Rupr.) Maxim.), an introduced shrub native to lowland forests in eastern Asia, has emerged as perhaps the most widespread and problematic invader of forests throughout the eastern United States and adjacent Canada. The body of literature concerning this invasive is large and has been summarized/reviewed by Luken and Thieret ( 1996 ), Lieurance and Landisbergen (2016), and McNeish and McEwan ( 2016 ). The harm Amur honeysuckle inflicts on natural processes and native species populations is extensive, ranging from competitive exclusion of native plants (Collier and Vankat 2002 , Loomis et al. 2015 , Gorchov 2005 , Sena et al. 2021 ), to modification of herbivory patterns (Meiners 2007 , Orrock et al. 2015 ), facilitation of pathogen vectors (Allana et al. 2010 ), modifications of soil (McEwan et al. 2012 , Trammell et al. 2012 ), and modification of stream communities (McNeish et al. 2015 ). Despite an abundance of study, no truly time/cost-effective and ecologically appropriate technique has been devised to eliminate Amur honeysuckle from natural areas. Land managers seem to be resigned to its continued presence. Scope of honeysuckle invasion over the last 30 + years is to a large extent a consequence of forest fragmentation and the degraded nature of regional forests. Commonly honeysuckle establishes in forest edges and damaged stands where the canopy is relatively open (Bartuszevige et al. 2006 , Henken et al. 2013). High light conditions support rapid growth and copious seed production (Luken et al. 1997 , Schulz and Wright 2015 ), with ready populations of animal vectors to disperse seed (Ingold and Craycraft 1983 , Vellend 2002 , Bartuszevige and Gorchov 2006 , Castellano and Gorchov 2013 ). Because honeysuckle has a reasonable level of shade tolerance, it can persist in the understory and capitalize on natural canopy openings for further growth and establishment opportunities (Henken et al. 2013). On mesic sites in eastern North America established honeysuckle are now experiencing a changing understory environment. Canopy closure is occurring in many formerly open canopy stands, reducing light availability. Additionally, throughout much of the eastern United States the process of “mesophication” ( sensu Nowaki and Abrams 2008, Alexander et al. 2021) is under way. This involves replacement of fire tolerant species (e.g., Quercus L. spp., Carya Nutt. spp.) with highly competitive and fire intolerant species, especially sugar maple ( Acer saccharum Marshall.). Active fire suppression has eliminated this constraint on the growth and spread of fire intolerant species. Maple forest understories are exceedingly dark and limit forest floor shrubs to a few shade tolerant species. For this reason, the capacity to survive and prosper in the forest understory will play a larger role for honeysuckle in the future. Part of this scenario is that honeysuckle will compete with other shade tolerant woody species. In southern Illinois we have noticed three woody species are abundant in dark understories where honeysuckle is present: sugar maple, pawpaw ( Asimina triloba Adans.) and spicebush ( Lindera benzoin Thunb.). Maple and pawpaw appear to ultimately overtop honeysuckle, while dense spicebush stands crowd it significantly. This pattern might occur because of shade tolerance in these species, or priority effects. In this study we hypothesized that pawpaw and spicebush had greater shade tolerance than honeysuckle. We focus only on these species because the extreme shade tolerance of maple is well known and has been more widely studied (e.g., Ellsworth and Reich 1992 , Walters et al. 1993 , Walters and Reich 1996 , Sendall et al. 2015 ). Based on the ongoing expansion of pawpaw and spicebush we predicted higher rates of photosynthesis in shade, stronger manifestation of shade acclimation responses in leaf structure, and higher leaf area ratios (LAR, leaf area / plant mass) than in honeysuckle. To provide context for the performance of honeysuckle in shade, we also examined the photosynthetic performance of honeysuckle in edge habitats where it prevails. This was not possible for pawpaw and spicebush because they are absent from forest edges in our region. Photosynthesis is a key aspect of shade tolerance. Early studies tended to treat acclimation or adaptation of photosynthesis to shade as the central element of shade tolerance (Bjorkman 1972, Boardman 1977, Chabot and Chabot 1977). Later work emphasizes patterns of resource allocation, respiratory load, and canopy architecture in conjunction with photosynthetic patterns as important determinants of shade tolerance (Givnish 1988 , Lei and Lechowitz, 1990, Woodward 1990 , Walters et al. 1993 ). Unfortunately, measuring, integrating, and interpreting these aspects is operationally challenging when studying seedlings in controlled environments, much less in the field using pre-existing plants. To make a practical, conceptually robust comparison between species, we interpret photosynthetic light responses in relative to the biomass invested in leaves and shoots. Annual production of leafy shoots by winter-deciduous species is essential to survival. Shoot production not only replaces the essential organs of photosynthesis and reproduction, but also provides the means to overtop and/or overspread competitors. We propose that species-level differences in the biomass costs and photosynthetic returns of shoots are very likely to affect the odds of persistence through time. The background literature for the three study species varies in its depth. Photosynthesis/shade tolerance in Amur honeysuckle has been investigated by Luken et al. ( 1997 ), Fridley ( 2012 ), and Lieurance and Landsbergen ( 2016 ). Luken et al. ( 1997 ) examined the capacity to capitalize on increases in light intensity caused by canopy disturbance by transplanting small shade-grown shrubs to shade structures providing 1, 25, and 100% sunlight. Although the study relied on recently transplanted plants, it clearly showed preexisting leaves can acclimate to increased light. In addition, increased light stimulated production of new light-acclimated leaves and caused modification in tissue allocation patterns. Luken et al. ( 1997 ) conclude that honeysuckle is a habitat generalist with high phenotypic plasticity. Fridley ( 2012 ) compared estimates of carbon gain by native and exotic understory shrubs before the tree canopy expanded in spring and after the canopy opened in fall. Compared to most species, Amur honeysuckle obtained fairly little of its carbon during either period (total C < 15%), while many natives were more reliant on the light windows during early spring and late fall. Notably, shrubs of the genus Lonicera show wide variation in carbon gain patterns in spring and fall. The common tendency to generalize to Amur honeysuckle from the high rates measured by Harrington et al. ( 1989 ) in L. X bella Zabel is inappropriate (Fridley 2012 ). Lieurance and Landsbergen ( 2016 ) examined photosynthesis and allocation patterns across a light gradient (64–12% canopy openness) and concluded that high phenotypic and physiological plasticity allowed honeysuckle to “persist in all habitats”. Pawpaw is an abundant clonal shrub/subcanopy tree distributed across the southeastern U.S. on deep, moist soils. Clones may largely shade the forest floor, and individual ramets can achieve heights of 3–12 m (Immel 2001 ), reaching stem diameters of 25 cm (K. Schulz, pers. obs.). Thus, it is functionally both a large shrub and a subcanopy tree capable of overtopping honeysuckle (maximum height 5.2 m) or spicebush (maximum height 3–5 m) (PLANTS Database 2022). In southwestern Illinois, the location of this study, pawpaw is restricted to the forest interior, where it produces a low canopy of large, horizontally oriented leaves 10–30 cm long (Immel 2001 ). Larger individuals flower and produce banana-like berries 7–16 cm long (Immel 2001 ) in early fall. A number of mammals consume pawpaw fruits and disperse the seeds, although most stands likely consist of large clones (Rogstad et al. 1991 , Larimore et al. 2003 ). White-tailed deer ( Odocoileus virginianus Zimmermann), common understory browsers, do not browse on pawpaw foliage (Slater and Anderson 2014 ). In commercial forests pawpaw is regarded a significant competitor with tree seedlings (Olson and Keeley 2018). Baumer and Runkle (2010) demonstrated strong competitive ability in pawpaw against very tolerant sugar maple and moderately tolerant black cherry ( Prunus serotina Ehrh.). Tree seedlings under pawpaw were less abundant and smaller than in surrounding locations. Accounts of the photosynthetic behavior of pawpaw are seemingly absent in the literature. Spicebush is a dioecious clonal species of moist forest interiors and has a range similar to pawpaw. It achieves height and spread comparable to forest-grown honeysuckle (1–3(5)) m tall, Nesom 2002). The leaves are moderately large, 6–14 cm long. It is an aggressive competitor in the understory, but evidence is mixed concerning its ability to capitalize on canopy gaps (see below). Female shrubs produce shiny red, oily drupes in early fall. These are favored by birds and disappear far earlier than honeysuckle fruits. Spicebush seeds are ca. 3 mm in diameter and germinate easily after stratification. Seeds persist in the litter layer for a number of years (Nesom 2002), but most shrubs arise from clonal reproduction (Nesom 2002). Deer and other mammalian herbivores appear not to browse on spicebush foliage (Schulz, pers. obs.). Luken et al. ( 1997 ) compared light acclimation responses of spicebush to honeysuckle and observed marked differences. Unlike honeysuckle, spicebush transplanted to 25 and 100% sunlight weakly expressed plastic responses to high light (plants grown at 1% sunlight failed to thrive). Davidson (1966) examined growth responses of six shrub species maintained in growth chamber simulating open (14% full sun) and closed canopy (3% full sun) forest light levels. Spicebush was distinctive among species because it gained height faster and produced more leaves under closed canopy, suggesting it was a shade specialist. In contrast to Luken et al. ( 1997 ), Niesenbaum (1992) observed greater leaf area and annual branch growth in spicebush exposed to 20% vs. 1% full sun in natural habitats. Moreover, Veres and Pickett (1982) observed substantially greater leaf area, leaf biomass, branch biomass, and primary stem production in high light (4300 foot candles, estimated as ca. 43% full sun) vs. low light (300 foot candles, estimated as 3% full sun) habitats. Methods And Materials Studies were conducted in late midsummer (August and early September) in a ca. 50 year-old upland successional forest and a south-facing forest edge on the Campus of Southern Illinois University (38.78 o N, 90.00 o W), in Madison County, southwestern Illinois USA. The soils are moderately acid Menfro Silt loam, containing ca. 22% clay in the surface horizons (Leeper 2004 ). Dominant forest trees include sugar maple, several oak species ( Quercus rubra L., Q. michauxii Nutt., Q. macrocarpa Michx.), walnut ( Juglans nigra L.), slippery elm ( Ulmus rubra Muhl.), green ash ( Fraxinus pennsylvanica Marshall.), and persimmon ( Diospyros virginiana L.). The tree canopy is somewhat broken, supporting a heavy subcanopy of maple seedlings and pawpaw ca. 3–6 m tall. Mean (SD) midsummer light levels in the forest understory estimated from canopy photographs were < 13.3 (0.06)% of available photosynthetically active radiation. The edge site was dominated by cottonwood ( Populus deltoides Marshall.), green ash, and sycamore ( Platanus occidentalis L.). No light measurements of were made at the edge site but an appropriate sun path diagram shows the site received ca. 10 h. direct sunshine daily during summer. Understory study shrubs were selected as sets of adjacent honeysuckle, spicebush, and pawpaw shrubs 0.7–1.2 m tall and < 1.5 m apart. All individuals were apparently healthy and unstressed. Sets were located under similar, representative canopy conditions. We chose this approach to ensure comparable environments among study plants and for use as a blocking variable. Although this is not per se a random sample, it follows widespread practice in plant ecophysiology. Edge habitat shrubs were selected haphazardly at intervals of 5 m along the shrub line. Photosynthetic light response curves were measured on eight individuals of each species during midsummer (late July and August 2016) at midday with a LI-COR Li6400XT gas exchange system (LI-COR Biosciences, Lincoln, NB USA). Chamber conditions (means with SD) were maintained at levels typical for forest conditions in summer. CO 2 concentration in the chamber was 396 (2.78) ppm. Leaf temperature was 30.0 (0.0844) o C and leaf to air vapor pressure deficit (VPD) was 1.12 (0.198) kPa, corresponding to ca. 70–75% relative humidity, which approaches the operating limit of the photosynthesis system. Before light curves were taken leaves were acclimated to a previously determined saturating light intensity (500 µmol m − 2 s − 1 in the understory site; 1600 µmol m − 2 s − 1 for edge shrubs). PAR levels were then stepped downward: 400, 300, 250, 200, 150, 100, 75, 50, 25, and 0 µmol m − 2 s − 1 for understory shrubs; 1600, 1400, 1200, 1000, 800, 600, 400, 300, 200, 150, 100, 50, and 0 µmol m 2 s − 1 for edge shrubs. Measurements were recorded after stable gas exchange rates were achieved at each light level. Respiratory rates at PAR 0 µmol m − 2 s − 1 are means of four samples because respiratory measurements are of low magnitude and in practice have greater temporal variability. Leaf areas were determined from photographs of pressed leaves using ImageJ. Leaf mass was measured to a resolution of 0.0001 g on specimens dried at 65 o C. Rates of gas exchange are expressed on both a leaf area basis and a leaf dry weight basis. Leaf chlorophyll contents were measured from leaf disks using the DMSO method (Hiscox and Israelstam 1979 ). To assess the leaf area and biomass allocation in shoots of shaded shrubs, 12–14 leafy shoots were collected from the study plants and other comparable individuals in the study area. Leaf areas and the masses of leaves and stems were determined as above. Photosynthetic light responses were compared using repeated measures ANOVA. Comparisons of leaf traits and biomass allocation in shade were made by 1-way ANOVA followed by Tukey’s HSD. In some cases, biomass data did not conform to theoretical assumptions and Kruskal-Wallis nonparametric ANOVA followed by the Dwass-Steel-Chritchlow-Fligner Test for all pairwise comparisons were substituted. Comparisons of honeysuckle leaf traits in sun and shade were made using unequal variance t-tests. All analyses were conducted using Systat 13 (Systat Software, San Jose, CA USA). Results Understory Photosynthesis, leaf area basis Light response curves were similar across species (Fig. 1 a), saturating at ca. 150 µmol m − 2 s − 1 with maximum rates of photosynthesis (A max ) ranging 3.4 µmol m − 2 s − 1 in pawpaw to 4.2 µmol m − 2 s − 1 in spicebush. Repeated measures ANOVA showed that overall photosynthetic rates were significantly higher in spicebush, but the patterns of light response (PAR x species interaction) were the same among species (Table 1 ). A max and respiratory rate (R) did not differ significantly among species (Table 1 ). Stomatal conductance (g w ), intrinsic water use efficiency (A max /g w , with g w measured in µmol), and internal CO 2 concentration were tested by 1-way ANOVA, with and without VPD as a covariate. Neither stomatal conductance (mean = 75.4, SE = 5.81 mmol m − 2 s − 1 ), intrinsic water use efficiency (mean = 54.1, SE = 3.24), nor internal CO 2 (mean = 299, SE = 5.09 ppm) varied significantly. Understory Photosynthesis, leaf mass basis Photosynthesis calculated on a leaf mass basis presented a different picture. Repeated measures ANOVA showed that honeysuckle had markedly lower rates of photosynthesis overall (Fig. 1 b, Table 1 ) and responded to increasing light (0–100 µmol m − 2 s − 1 ) much more slowly than spicebush and pawpaw (Fig. 1 b, Table 1 ). The light responses of spicebush and pawpaw were nearly identical. A max in honeysuckle was 45% lower than in the two other species (Fig. 1 b, Table 2 ). Respiratory CO 2 release in pawpaw was significantly (ca. 20%) smaller in honeysuckle and spicebush (Table 2 ). Table 1 Repeated measures ANOVA for photosynthetic light response curves. PAR is photosynthetically active radiation Leaf Area Basis Between Subjects Source SS df MS F-Ratio P Species 24.1526 2 12.0763 3.96 0.0334 Error 70.2114 23 3.0527 Within Subjects Source SS df MS F-Ratio P PAR 425.4770 10 42.5477 314.97 0.0000 PAR*Species 5.5950 20 0.2798 2.07 0.0057 Error 31.0693 230 0.1351 Leaf Mass Basis Between Subjects Source SS df MS F-Ratio P Species 0.3469 2 0.1735 32.28 0.0000 Error 0.1236 23 0.0054 Within Subjects Source SS df MS F-Ratio P PAR 0.6920 10 0.0692 373.94 0.0000 PAR*Species 0.0687 20 0.0034 18.56 0.0000 Error 0.0426 230 0.0002 Shade Leaf Characteristics All three species exhibit similar levels of chlorophyll measured on a leaf area basis and have statistically indistinguishable chlorophyll a:b ratios (Table 2 ). Leaf mass per unit area (specific leaf mass, SLM) in honeysuckle is nearly twice that in pawpaw and spicebush (Table 2 ). This results in significantly lower levels of total chlorophyll per unit mass in honeysuckle. Table 2 Characteristics of sun and shade-grown honeysuckle, pawpaw, and spicebush. A max , maximum light-saturated photosynthetic rate; R, dark respiration rate; QUE, quantum use efficiency (slope of light response curve 0 to 50 µmol photons m − 2 s − 1 ); LAR, leaf area ratio. Comparisons of sun and shade honeysuckles are denoted by capital letters (unequal variance t-test); comparisons of shade honeysuckle, pawpaw, and spicebush are denoted by lower case letters (1-way ANOVA followed by Tukey’s HSD). Values followed by the same letter do not differ at P < 0.05. Honeysuckle (sun) Honeysuckle (shade) Pawpaw Spicebush Leaves Mean SE Mean SE Mean SE Mean SE Total chlorophyll (g m − 2 ) 0.378 0.025 A 0.258 0.009 B a 0.242 0.013 a 0.241 0.010 a Total chlorophyll (g g − 1 ) 3.94 0.18 A 6.58 0.45 B a 12.67 0.76 b 11.01 0.79 b Chlorophyll a:b ratio 11.86 1.77 A 3.11 0.33 B a 4.00 0.38 a 4.63 0.57 a Specific leaf mass (g m − 2 ) 96.3 6.8 A 40.3 2.3 B a 19.3 0.9 b 22.3 0.9 b A max (µmol m − 2 s − 1 ) 16.58 0.82 A 3.56 0.26 B a 3.44 0.20 a 4.23 0.29 a A max (µmol g − 1 s − 1 ) 0.1760 0.0157 A 0.0916 0.0092 B a 0.1808 0.0116 b 0.1903 0.0120 b R (µmol m − 2 s − 1 ) -1.29 0.07 A -0.34 0.06 B a -0.31 0.07 a -0.25 0.03 a R (µmol g − 1 s − 1 ) -0.0137 0.0014 A -0.0083 0.0015 B a -0.0157 0.0033 b -0.0114 0.0011 a QUE (µmol C (µmol photons) −1 ) 0.0230 0.0005 A 0.0339 0.0032 B a 0.0396 0.0016 a 0.0421 0.0016 a Light Compensation Point (µmol m − 2 s − 1 ) 23.9 4.0 A 6.6 4.7 B a 3.1 2.4 a 1.5 0.8 a Shoots Leaf area (m 2 ) 0.0234 0.0019 a 0.0792 0.0094 b 0.0385 0.0038 c Stem mass (g) 0.291 0.036 a 0.279 0.071 a 0.204 0.034 a Leaf mass (g) 0.995 0.081 a 1.567 0.203 b 1.031 0.108 a,b LAR (m 2 g − 1 ) 0.02369 0.00065 a 0.05460 0.00760 b 0.03755 0.00073 c Edge vs. Understory Photosynthesis for Honeysuckle Forest edge and understory honeysuckle showed large and statistically significant differences in photosynthetic measures and leaf characteristics (Table 2 ). A max in high light honeysuckle was 4.5-fold greater than in shade honeysuckle; R was 3.5-fold greater; LCP was 3.6-fold higher; QUE (quantum use efficiency: the slope of light response curve 0 to 50 µmol photons m − 2 s − 1 ) was 0.7 of the value in shade. Total chlorophyll on an area basis was 1.5-fold higher, but only 0.6-fold as high on a mass basis. Chlorophyll a:b ratio was 3.8-fold higher and SLM was 2.4-fold higher. When A max and R are expressed on a mass basis, high light shrubs have 1.9 and 1.6-fold higher rates, respectively. Comparison of potential carbon gain by shoots Comparisons of biomass and leaf area allocation were complicated by widely differing variances between species which precluded standard ANOVA, even after multiple attempts to transform the data. Kruskal-Wallis nonparametric ANOVA (KW) followed by the Dwass-Steel-Chritchlow-Fligner Test for all pairwise comparisons were substituted. The ratio of leaf to stem biomass was similar for pawpaw and spicebush (6.5 and 6.9, respectively), but significantly less for honeysuckle (3.5, both comparisons significant at P < 0.0200). Leaf area per shoot differed among the three species (Table 2 ). Leaf areas were greatest for pawpaw, followed by spicebush, and then honeysuckle. Consequently, leaf area ratio (LAR), the ratio of leaf area per unit shoot mass, varied greatly across species in the order spicebush = pawpaw, > honeysuckle (Table 2 ). If photosynthetic rates (area basis) at a representative PAR level are multiplied by LAR, one obtains an approximation of potential daytime carbon gain per gram of biomass investment in shoots. Figure 2 a illustrates the approximate photosynthetic “payback” across PAR levels typical of forest understories. In all cases honeysuckle obtains far less carbon per unit of biomass investment than spicebush and pawpaw. A problem with this analysis is that nighttime respiration is a drain on carbon gain. To partially correct this, payback estimates were adjusted by subtracting an estimate of dark respiration. Leaves and stems were assumed to have the same mass-based respiratory rate which was adjusted to typical cooler conditions at night (25 o C, using Q 10 = 2). We assumed that the duration of the daily photosynthetic period under a canopy would be ca. 12h. This attempt to account for respiration overnight reveals much lower levels of carbon gain (Fig. 2 b), but species differences and the pattern of response to light remain. Discussion Area-based photosynthetic rates for honeysuckle in this study can be compared with the more detailed work of Lieurance and Landsbergen ( 2016 ). Honeysuckle in our study achieved half their maximum photosynthetic rate in shade, and 10% higher rates in the sun. Patterns in the light response and leaf characteristics were concordant with greater acclimation to shade, suggesting our shade site was darker and the sun site brighter than in that published account. Luken et al. ( 1997 ) observed about 10% lower maximum rates for sun honeysuckle, but twice the maximum rate for spicebush, again suggesting our sites were more extreme. Until this study is replicated in brighter shade environments, our conclusions are limited to deep shade. Studies of shade tolerance and photosynthesis have traditionally measured photosynthetic rates on a leaf area basis, not a mass or shoot basis as was done here. Here, different impressions were gained depending on whether measurements were area-based or mass/shoot-based. On an area basis all three species show comparable light responses and rates of photosynthesis. This would suggest that honeysuckle has the acclimation capacity to sufficient compete with native woody understory plants. In a short survey of studies examining invasive understory shrub photosynthesis [e.g., Harrington et al. 1989 , Luken et al. 1997 , Pattison et al. (1998), Lieurance and Landsbergen ( 2016 ),, Dornbos et al. (2016)], none except Xu (2007) deviate from area-based measurements. This is significant because mass-based measurements reference photosynthesis to the to the approximate carbon cost of leaf construction and the “profitability” of leaves; area-based measurements reference photosynthesis to the efficiency of the receptive surface of whatever carbon cost. Evaluated, on a leaf mass or shoot basis, honeysuckle in deep shade is distinctly inferior to the two native species. Higher allocation to leaf mass per unit area is a well-known trait of plants in high light environments (e.g., forest edge honeysuckle in this study), however this is a liability when light is very limiting and mass per unit area cannot be sufficiently adjusted downward to support larger leaf areas. SLM for honeysuckle in sun was about twice that for shade honeysuckle, but SLM for shade honeysuckle is still twice as large as for pawpaw and spicebush. Plastic responses in honeysuckle clearly cannot duplicate the behavior of the more shade-specialized pawpaw and spicebush. The profoundly higher performance for honeysuckle leaves in sun suggests its presence in the forest understory is an expression of wide niche breadth, not adaptation to shade per se as seen in pawpaw and spicebush. Based on gas exchange data and leaf characteristics, honeysuckle clearly finds near optimal habitat along forest edges. This supports Schulz and Wright’s ( 2015 ) suggestion that control of edge shrubs should be a conservation priority. From the perspective of shoot allocation, the lower capacity of honeysuckle to adjust SLM in shade is reinforced by a greater allocation to stem tissue and lower LAR. Presuming leaf orientation is similar between the species, in a very shady environment honeysuckle shoots cannot repay the cost of shoots as quickly as pawpaw and spicebush. Naturally, it would be informative to compare whole plant respiratory costs, but obtaining these data is out of practical reach. A concern in any photosynthesis study involving Lonicera spp. is the relative importance of summer photosynthesis under a closed canopy versus spring/fall photosynthesis under more open canopies. There is a tendency to generalize from Harrington et al. ( 1989 ) that high spring photosynthetic rates seen in L. X bella apply to Amur honeysuckle. Fridley ( 2012 ), using photosynthesis measurements in a model, showed that spring photosynthetic gains for L. X bella were clearly meaningful, but that Amur honeysuckle achieved low gains in spring and modest gains in fall. Phenological observations like those made by McEwan et al. ( 2009 ) are fertile ground for speculation, but do not include photosynthesis measurements in light of photosynthetic capacity, or considerations of low leaf area and near-vertical leaf orientation for much of spring (Schulz, pers. obs.). Photosynthesis in fall might be significant (Fridley 2012 ), but frequent phenological mismatches between tree canopy senescence (last half of October), hard frost which causes honeysuckle leaves to senesce, and generally declining photosynthetic capacity are also probable. Records of fall weather patterns in nearby St. Louis, MO USA show high interannual variation in the first date of frost. The mean date is November 1, but one standard deviation from this date spans the period October 16 to November 17 (NOAA 2022a). Anecdotally, in 2020 we noted honeysuckle leaf senescence at the start of November; in 2022 leaf senescence was delayed into early December (Schulz, pers. obs.). For these reasons the value of the fall light window may be quite intermittent for understory shrubs. In the long term, phenological differences between the three species are probably of limited importance given the large performance gap between honeysuckle and the two natives. Any phenological advantage would be difficult to overcome in a few weeks of a mean 208 day (range 159–260) growing season (NOAA 2022b). This finding should be taken as a suggestion that pawpaw and spicebush may replace honeysuckle over time in forest types driven by shade tolerance. Naturally the abundance and distribution of pawpaw and spicebush in any given situation will affect this process. Ironically, management plans which seek the re-imposition of fire will greatly reduce the abundance of maple, pawpaw, and likely spicebush, however they may only top kill honeysuckle and, absent repeated fire, leave stands more invasible (Nyboer and Edgin 2017 ). We have noticed that both pawpaw and spicebush are increasing in local forests. This may be caused by higher shade tolerance as regional forests recover from anthropogenic disturbance, but it also reflects the fact that deer do not browse either species and competitors have declined (Slater and Anderson 2014 ). We note that honeysuckle is subject to moderate deer browsing, which is a disadvantage. Nonetheless, we periodically observe that honeysuckle overtopped by pawpaw shows signs of decline, as do honeysuckle under closing maple canopies. Certainly, this analysis of photosynthetic patterns and the structure of shoots is not a comprehensive study of whole plant shade tolerance. However, we submit that the capacity to produce shoots that have a higher level of net primary production in shade is a meaningful element of the larger problem. A recent visit back to the study site several years after this work supports these findings. Pawpaw and spicebush, which were originally comparably sized, are now almost twice as tall as honeysuckle. Declarations Gas analyzer calibration and maintenance were supported by a Seed Grant for Transitional and Exploratory Projects awarded to Kurt Schulz by the Graduate School of Southern Illinois University Edwardsville. The author has no relevant financial or non-financial interests to disclose. Kurt Schulz conceived the project, collected, and analyzed the data, and wrote the manuscript. Special thanks to Anh Nguyen (Southern Illinois University Edwardsville) for considerable assistance with field data collection. References Allana BF, Dutra HP, Goessling LS, Barnett K, Chasea JM, Marquis RJ, Pang G, Storch GA, Thach RE, Orrock JL. 2010. Invasive honeysuckle eradication reduces tick-borne disease risk by altering host dynamics. Proceedings of the National Academy of Sciences of the United States of America 107: 18523-18527. https://doi.org/10.1073/pnas.1008362107. Bartuszevige AM, Gorchov DL. 2006. Avian seed dispersal of an invasive shrub. Biological Invasions 8: 1013-1022. https://doi.org/10.1007/s10530-005-3634-2. Bartuszevige AM, Gorchov DL, Raab L. 2006. The relative importance of landscape and community features in the invasion of an exotic shrub in a fragmented landscape. Ecography 29: 213-222. https://doi.org/10.1111/j.2006.0906-7590.04359.x Castellano SM, Gorchov DL. 2013. White-tailed deer ( Odocoileus virginianus ) disperse seeds of the invasive shrub, Amur honeysuckle ( Lonicera maackii ). Natural Areas Journal 33: 78-80. https://doi.org/10.3375/043.033.0109 Collier MW, Vankat JL. 2002. Diminished plant richness and abundance below Lonicera maackii , an invasive shrub. American Midland Naturalist 147: 60-71. https://doi.org/10.1674/0003-0031(2002)147[0060:DPRAAB]2.0.CO;2 Ellsworth DS and Reich PB. 1992. Water relations and gas exchange of Acer saccharum seedlings in contrasting natural light and moisture regimes. Tree Physiology 10: 1-20. https://doi.org/10.1093/treephys/10.1.1 Fridley JD. 2012. Extended leaf phenology and the autumn niche in deciduous forest invasions. Nature 485: 359-362. https://doi.org/10.1038/nature11056 Givnish TJ. 1988. Adaptation to sun and shade: A whole-plant perspective. Australian Journal of Plant Physiology 15: 63-92. https://doi.org/10.1071/PP9880063 Gorchov DL. 2005. Control of forest invasives and responses of native forest-floor plants: case studies of garlic mustard and Amur honeysuckle. Paper presented at Ohio Invasive Plant Research Conference: Bridging the Gap Between Land Management and Research. Gould AMA, Gorchov DL. 2000. Effects of the exotic invasive shrub Lonicera maackii on the survival and fecundity of three species of native annuals. American Midland Naturalist 144: 36-50. https://doi.org/10.1674/0003-0031(2000)144[0036:EOTEIS]2.0.CO;2 Harrington RA, Brown BJ, Reich PB. 1989. Ecophysiology of exotic and native shrubs in southern Wisconsin I. Relationship of leaf characteristics, resource availability, and phenology to seasonal patterns of carbon gain. Oecologia 80: 356-367. https://doi.org/10.1007/BF00379037 Henkin MA, Medley KE, Abbitt RJ, Patton JM. 2013. Invasion dynamics of nonnative Amur honeysuckle over 18 years in a southwestern Ohio forest. The American Midland Naturalist 170: 335-347. https://doi.org/10.1674/0003-0031-170.2.335 Hiscox JD, Israelstam. GF. 1979. A method for the extraction of chlorophyll from leaf tissue without maceration. Canadian Journal of Botany 57: 1332-1334. https://doi.org/10.1139/b79-163 Immel DL. 2001. Pawpaw Asimina triloba (L.) Dunal.: USDA, NRCS, National Plant Data Center. https://plants.sc.egov.usda.gov/DocumentLibrary/plantguide/doc/cs_astr.docx. Last access 20 December 2022. Ingold JL, Craycraft M. 1983. Avian frugivory on honeysuckle ( Lonicera ) in southwestern Ohio in fall. Ohio Journal of Science 83: 256-258. http://hdl.handle.net/1811/22964 Larimore RL, Busemeyer DT, Ebinger JE. 2003. Pawpaw, Asimina triloba (L) Dunal (Annonaceae), in the Prairie Peninsula of Illinois, USA. Natural Areas Journal 23: 356-361. Leeper RA. 2004. Soil Survey of Madison County, Illinois. United States Department of Agriculture, Natural Resources Conservation Service and Illinois Agricultural Experiment Station. https://www.nrcs.usda.gov/Internet/FSE_MANUSCRIPTS/illinois/IL119/ 0/madison_IL.pdf. Last access 20 December, 2022. Lei TT, Lechowicz MJ. 1990. Shade adaptation and shade tolerance in saplings of three Acer species from eastern North America. Oecologia 84: 224-228. DOI: 10.1007/BF00318275 Lieurance D, Landsbergen K. 2016. The influence of light habitat on the physiology, biomass allocation, and fecundity of the invasive shrub Amur honeysuckle ( Lonicera maackii , Caprifoliaceae). Journal of the Torrey Botanical Society 143: 415-426. https://doi.org/10.3159/torrey-d-15-00056.1 Loomis JD, Matter SF, Cameron GN. 2015. Effects of invasive Amur honeysuckle ( Lonicera maackii ) and white-tailed deer ( Odocoileus virginianus ) on survival of sugar maple seedlings in a southwestern Ohio forest. American Midland Naturalist 174: 65-73. https://doi.org/10.1674/0003-0031-167.2.256 Luken JO, Thieret JW. 1996. Amur honeysuckle, its fall from grace. Bioscience 46: 18-24. https://doi.org/10.2307/1312651 Luken JO, Kuddes LM, Tholemeier TC. 1997. Response of understory species to gap formation and soil disturbance in Lonicera maackii thickets. Restoration Ecology 5: 229-235. https://doi.org/10.1046/j.1526-100X.1997.09727.x McEwan, RW, Birchfield, MK, Schoergendorfer, A., & Arthur, MA. 2009. Leaf Phenology and Freeze Tolerance of the Invasive Shrub Amur Honeysuckle and Potential Native Competitors. The Journal of the Torrey Botanical Society, 136(2), 212–220. https://doi.org/10.3159/08-ra-109.1 McEwan RW, Arthur MA, Alverson SE. 2012. Throughfall chemistry and soil nutrient effects of the invasive shrub Lonicera maackii in deciduous forests. American Midland Naturalist 168: 43-55. https://doi.org/10.1674/0003-0031-168.1.43 McNeish RE, McEwan RW. 2016. A review on the invasion ecology of Amur honeysuckle ( Lonicera maackii , Caprifoliaceae) a case study of ecological impacts at multiple scales. The Journal of the Torrey Botanical Society 143: 367-385. https://doi.org/10.3159/torrey-d-15-00049.1 McNeish RE, Moore EM, Benbow ME, McEwan RW. 2015. Removal of the invasive shrub, Lonicera maackii , from riparian forests influences headwater stream biota and ecosystem function. River Research and Applications 31: 1131-1139. https://doi.org/10.1002/rra.2808 Meiners SJ. 2007. Apparent competition: An impact of exotic shrub invasion on tree regeneration. Biological Invasions 9: 849-855. https://doi.org/10.1007/s10530-006-9086-5 Miller KE, Gorchov DL. 2004. The invasive shrub, Lonicera maackii , reduces growth and fecundity of perennial forest herbs. Oecologia 139: 359-375. https://doi.org/10.1007/s00442-004-1518-2 NOAA (National Oceanic and Atmospheric Administration). 2022a. NOWData - NOAA Online Weather Data for St. Louis, MO 1875-2021. https://www.weather.gov/wrh/climate?wfo=lsx. Last access 20 December, 2022. NOAA (National Oceanic and Atmospheric Administration). 2022b. Latest spring freeze - first fall freeze - length of growing season Saint Louis, Mo (1873 - present). https://www.weather.gov/media/lsx/climate/stl/temp/temp_stl_grow_season.pdf. Last access 20 December, 2022. Nyboer R, Edgin R. 2017. Bush Honeysuckles: Tartarian, Morrow's, Belle, and Amur Honeysuckle ( Lonicera tatarica L., L. morrowii Gray, L. x bella Zabel, and L. maackii (Rupr.) Maxim.). Illinois Nature Preserves Commission, Vegetation Management Guideline 6(1). https://www2.illinois.gov/dnr/INPC/Pages/INPCManagementGuidelines.aspx Last access 20 December, 2022. Orrock JL, Dutra HP, Marquis RJ, Barber N. 2015. Apparent competition and native consumers exacerbate the strong competitive effect of an exotic plant species. Ecology 96: 1052-1061. https://doi.org/10.1890/14-0732.1 Rogstad RH, Wolff K, Schaal BA. 1991. Geographical variation in Asimina triloba Dunal (Annonaceae) revealed by the M13 "DNA fingerprinting" probe. American Journal of Botany 78: 1391-1396. https://doi.org/10.2307/2445277 Schulz KE, Wright J. 2015. Reproduction of invasive Amur honeysuckle ( Lonicera maackii ) and the arithmetic of an extermination strategy. Restoration Ecology 23: 900-908. https://doi.org/10.1111/rec.12260 Sena K, Gauger L, Johnson T, Shirkey F, Caldbeck W, Hammock J, Kim A, Mazza B, Pethtel I, Leuenberger W. 2021. Honeysuckle ( Lonicera maackii ) presence is associated with reduced diversity and richness of flowering spring flora in central Kentucky. Natural Areas Journal 41: 249-257. https://doi.org/10.3375/20-41 Sendall KM, Lusk CH, Reich PB. 2015. Becoming less tolerant with age: sugar maple, shade, and ontogeny. Oecologia 179: 1011-1021. https://doi.org/10.3375/20-41 Slater MA, Anderson RC. 2014. Intensive selective deer browsing favors success of Asimina triloba (Paw Paw) a native tree species. Natural Areas Journal 34: 178-187. https://doi.org/10.3375/043.034.0207 Trammell TLE, Ralston HA, Scroggins SA, Carreiro MM. 2012. Foliar production and decomposition rates in urban forests invaded by the exotic invasive shrub, Lonicera maackii . Biological Invasions 14: 529-545. https://doi.org/10.1007/s10530-011-0093-9 Vellend M. 2002. A pest and an invader: White-tailed deer ( Odocoileus virginianus Zimm.) as a seed dispersal agent for honeysuckle shrubs ( Lonicera L.). Natural Areas Journal 22: 230-234. Walters MB, Kruger EL, Reich PB. 1993. Growth, biomass distribution and CO 2 exchange of northern hardwood seedlings in high and low light: relationships with successional status and shade tolerance. Oecologia 94: 7-16. https://doi.org/10.1007/BF00317294 Walters MB, Reich PB. 1996. Are shade tolerance, survival, and growth linked? Low light and nitrogen effects on hardwood seedlings. Ecology 77: 841-853. https://doi.org/10.2307/2265505 Woodward FI. 1990. From ecosystems to genes: the importance of shade tolerance. Trends in Ecology and Evolution 5: 111-115. https://doi.org/10.1016/0169-5347(90)90164-9 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 09 Sep, 2023 Read the published version in Plant Ecology → Version 1 posted Editorial decision: Major revision 20 Mar, 2023 Reviews received at journal 11 Mar, 2023 Reviewers agreed at journal 27 Feb, 2023 Reviewers invited by journal 27 Feb, 2023 Editor assigned by journal 01 Jan, 2023 Submission checks completed at journal 29 Dec, 2022 First submitted to journal 29 Dec, 2022 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2426397","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":163756731,"identity":"471670f4-01d3-44c6-9830-f77aa09fb1f6","order_by":0,"name":"Kurt E. Schulz","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYBACCQYGNgaGAgY5BmYwn5lYLQYMxqRrSWxgIFaLZP/hZ495DOrS57fzGD5gqLCG6cUNpCXSzI15DNhyNxzmMTZgOJNOWIucBA+bNI8BT+4GZh4zCca2w0Ro4T8D0iKRLt/MY/6D8R8RWqQZckBaDBIYDvOYMTA2EKFFckaameQcgwTDDYfZiiUSjqUbE9Qicf7wM4k3FXXy8v2HN374UGMtS1ALKkggTfkoGAWjYBSMAlwAADInMOllKvb2AAAAAElFTkSuQmCC","orcid":"","institution":"Southern Illinois University Edwardsville","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Kurt","middleName":"E.","lastName":"Schulz","suffix":""}],"badges":[],"createdAt":"2022-12-29 19:44:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2426397/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2426397/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11258-023-01347-9","type":"published","date":"2023-09-09T15:01:37+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":31110012,"identity":"cb097b0c-fdf1-468c-98ce-75d0f213649f","added_by":"auto","created_at":"2023-01-04 17:51:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":51560,"visible":true,"origin":"","legend":"\u003cp\u003ea,b. Photosynthetic light response curves (means and SEs) of honeysuckle, pawpaw, and spice bush. a) measured on a unit leaf area basis; b) measured on a leaf mass basis. For leaf area-based comparisons spicebush has significantly higher rates of photosynthesis. For leaf mass-based comparisons honeysuckle has significantly lower rates of photosynthesis and a differently shaped response curve (Table 1.)\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-2426397/v1/71d38f3618ac5e81680bbeaa.png"},{"id":31110011,"identity":"b7c6aa44-b7aa-4b4c-ae5d-5b5c59dc9728","added_by":"auto","created_at":"2023-01-04 17:51:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":48692,"visible":true,"origin":"","legend":"\u003cp\u003ea,b. Photosynthetic gains per unit shoot mass at common understory light levels. a) daytime only, no adjustment for dark respiration; b) adjustment for dark respiration assuming all shoot tissue respires at the rate of leaves.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-2426397/v1/de00f427a1f0c21e7f8ec348.png"},{"id":42947582,"identity":"3f9aad77-668a-4d0b-9b70-6d95e2f3be71","added_by":"auto","created_at":"2023-09-11 15:09:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":370861,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2426397/v1/bf5f3d5d-bd82-4548-b431-44ef66d14d31.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Has Invasive Amur Honeysuckle (Lonicera maackii (Rupr.) Maxim) Met its Match? Interspecies Comparisons of Photosynthesis and Shoot Allocation in Heavy Shade","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAmur honeysuckle (\u003cem\u003eLonicera maackii\u003c/em\u003e (Rupr.) Maxim.), an introduced shrub native to lowland forests in eastern Asia, has emerged as perhaps the most widespread and problematic invader of forests throughout the eastern United States and adjacent Canada. The body of literature concerning this invasive is large and has been summarized/reviewed by Luken and Thieret (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1996\u003c/span\u003e), Lieurance and Landisbergen (2016), and McNeish and McEwan (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The harm Amur honeysuckle inflicts on natural processes and native species populations is extensive, ranging from competitive exclusion of native plants (Collier and Vankat \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2002\u003c/span\u003e, Loomis et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2015\u003c/span\u003e, Gorchov \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2005\u003c/span\u003e, Sena et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), to modification of herbivory patterns (Meiners \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e, Orrock et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), facilitation of pathogen vectors (Allana et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), modifications of soil (McEwan et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2012\u003c/span\u003e, Trammell et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), and modification of stream communities (McNeish et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Despite an abundance of study, no truly time/cost-effective and ecologically appropriate technique has been devised to eliminate Amur honeysuckle from natural areas. Land managers seem to be resigned to its continued presence.\u003c/p\u003e \u003cp\u003eScope of honeysuckle invasion over the last 30\u0026thinsp;+\u0026thinsp;years is to a large extent a consequence of forest fragmentation and the degraded nature of regional forests. Commonly honeysuckle establishes in forest edges and damaged stands where the canopy is relatively open (Bartuszevige et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, Henken et al. 2013). High light conditions support rapid growth and copious seed production (Luken et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1997\u003c/span\u003e, Schulz and Wright \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), with ready populations of animal vectors to disperse seed (Ingold and Craycraft \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e1983\u003c/span\u003e, Vellend \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2002\u003c/span\u003e, Bartuszevige and Gorchov \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2006\u003c/span\u003e, Castellano and Gorchov \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Because honeysuckle has a reasonable level of shade tolerance, it can persist in the understory and capitalize on natural canopy openings for further growth and establishment opportunities (Henken et al. 2013).\u003c/p\u003e \u003cp\u003eOn mesic sites in eastern North America established honeysuckle are now experiencing a changing understory environment. Canopy closure is occurring in many formerly open canopy stands, reducing light availability. Additionally, throughout much of the eastern United States the process of \u0026ldquo;mesophication\u0026rdquo; (\u003cem\u003esensu\u003c/em\u003e Nowaki and Abrams 2008, Alexander \u003cem\u003eet al.\u003c/em\u003e 2021) is under way. This involves replacement of fire tolerant species (e.g., \u003cem\u003eQuercus\u003c/em\u003e L. spp., \u003cem\u003eCarya\u003c/em\u003e Nutt. spp.) with highly competitive and fire intolerant species, especially sugar maple (\u003cem\u003eAcer saccharum\u003c/em\u003e Marshall.). Active fire suppression has eliminated this constraint on the growth and spread of fire intolerant species. Maple forest understories are exceedingly dark and limit forest floor shrubs to a few shade tolerant species. For this reason, the capacity to survive and prosper in the forest understory will play a larger role for honeysuckle in the future. Part of this scenario is that honeysuckle will compete with other shade tolerant woody species.\u003c/p\u003e \u003cp\u003eIn southern Illinois we have noticed three woody species are abundant in dark understories where honeysuckle is present: sugar maple, pawpaw (\u003cem\u003eAsimina triloba\u003c/em\u003e Adans.) and spicebush (\u003cem\u003eLindera benzoin\u003c/em\u003e Thunb.). Maple and pawpaw appear to ultimately overtop honeysuckle, while dense spicebush stands crowd it significantly. This pattern might occur because of shade tolerance in these species, or priority effects. In this study we hypothesized that pawpaw and spicebush had greater shade tolerance than honeysuckle. We focus only on these species because the extreme shade tolerance of maple is well known and has been more widely studied (e.g., Ellsworth and Reich \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1992\u003c/span\u003e, Walters et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1993\u003c/span\u003e, Walters and Reich \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e1996\u003c/span\u003e, Sendall et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Based on the ongoing expansion of pawpaw and spicebush we predicted higher rates of photosynthesis in shade, stronger manifestation of shade acclimation responses in leaf structure, and higher leaf area ratios (LAR, leaf area / plant mass) than in honeysuckle. To provide context for the performance of honeysuckle in shade, we also examined the photosynthetic performance of honeysuckle in edge habitats where it prevails. This was not possible for pawpaw and spicebush because they are absent from forest edges in our region.\u003c/p\u003e \u003cp\u003ePhotosynthesis is a key aspect of shade tolerance. Early studies tended to treat acclimation or adaptation of photosynthesis to shade as the central element of shade tolerance (Bjorkman 1972, Boardman 1977, Chabot and Chabot 1977). Later work emphasizes patterns of resource allocation, respiratory load, and canopy architecture in conjunction with photosynthetic patterns as important determinants of shade tolerance (Givnish \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1988\u003c/span\u003e, Lei and Lechowitz, 1990, Woodward \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1990\u003c/span\u003e, Walters et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e1993\u003c/span\u003e). Unfortunately, measuring, integrating, and interpreting these aspects is operationally challenging when studying seedlings in controlled environments, much less in the field using pre-existing plants. To make a practical, conceptually robust comparison between species, we interpret photosynthetic light responses in relative to the biomass invested in leaves and shoots. Annual production of leafy shoots by winter-deciduous species is essential to survival. Shoot production not only replaces the essential organs of photosynthesis and reproduction, but also provides the means to overtop and/or overspread competitors. We propose that species-level differences in the biomass costs and photosynthetic returns of shoots are very likely to affect the odds of persistence through time.\u003c/p\u003e \u003cp\u003eThe background literature for the three study species varies in its depth. Photosynthesis/shade tolerance in Amur honeysuckle has been investigated by Luken et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1997\u003c/span\u003e), Fridley (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), and Lieurance and Landsbergen (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Luken et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1997\u003c/span\u003e) examined the capacity to capitalize on increases in light intensity caused by canopy disturbance by transplanting small shade-grown shrubs to shade structures providing 1, 25, and 100% sunlight. Although the study relied on recently transplanted plants, it clearly showed preexisting leaves can acclimate to increased light. In addition, increased light stimulated production of new light-acclimated leaves and caused modification in tissue allocation patterns. Luken et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1997\u003c/span\u003e) conclude that honeysuckle is a habitat generalist with high phenotypic plasticity. Fridley (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) compared estimates of carbon gain by native and exotic understory shrubs before the tree canopy expanded in spring and after the canopy opened in fall. Compared to most species, Amur honeysuckle obtained fairly little of its carbon during either period (total C\u0026thinsp;\u0026lt;\u0026thinsp;15%), while many natives were more reliant on the light windows during early spring and late fall. Notably, shrubs of the genus \u003cem\u003eLonicera\u003c/em\u003e show wide variation in carbon gain patterns in spring and fall. The common tendency to generalize to Amur honeysuckle from the high rates measured by Harrington et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1989\u003c/span\u003e) in \u003cem\u003eL.\u003c/em\u003e X \u003cem\u003ebella\u003c/em\u003e Zabel is inappropriate (Fridley \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Lieurance and Landsbergen (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) examined photosynthesis and allocation patterns across a light gradient (64\u0026ndash;12% canopy openness) and concluded that high phenotypic and physiological plasticity allowed honeysuckle to \u0026ldquo;persist in all habitats\u0026rdquo;.\u003c/p\u003e \u003cp\u003ePawpaw is an abundant clonal shrub/subcanopy tree distributed across the southeastern U.S. on deep, moist soils. Clones may largely shade the forest floor, and individual ramets can achieve heights of 3\u0026ndash;12 m (Immel \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), reaching stem diameters of 25 cm (K. Schulz, pers. obs.). Thus, it is functionally both a large shrub and a subcanopy tree capable of overtopping honeysuckle (maximum height 5.2 m) or spicebush (maximum height 3\u0026ndash;5 m) (PLANTS Database 2022). In southwestern Illinois, the location of this study, pawpaw is restricted to the forest interior, where it produces a low canopy of large, horizontally oriented leaves 10\u0026ndash;30 cm long (Immel \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Larger individuals flower and produce banana-like berries 7\u0026ndash;16 cm long (Immel \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) in early fall. A number of mammals consume pawpaw fruits and disperse the seeds, although most stands likely consist of large clones (Rogstad et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1991\u003c/span\u003e, Larimore et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). White-tailed deer (\u003cem\u003eOdocoileus virginianus\u003c/em\u003e Zimmermann), common understory browsers, do not browse on pawpaw foliage (Slater and Anderson \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In commercial forests pawpaw is regarded a significant competitor with tree seedlings (Olson and Keeley 2018). Baumer and Runkle (2010) demonstrated strong competitive ability in pawpaw against very tolerant sugar maple and moderately tolerant black cherry (\u003cem\u003ePrunus serotina\u003c/em\u003e Ehrh.). Tree seedlings under pawpaw were less abundant and smaller than in surrounding locations. Accounts of the photosynthetic behavior of pawpaw are seemingly absent in the literature.\u003c/p\u003e \u003cp\u003eSpicebush is a dioecious clonal species of moist forest interiors and has a range similar to pawpaw. It achieves height and spread comparable to forest-grown honeysuckle (1\u0026ndash;3(5)) m tall, Nesom 2002). The leaves are moderately large, 6\u0026ndash;14 cm long. It is an aggressive competitor in the understory, but evidence is mixed concerning its ability to capitalize on canopy gaps (see below). Female shrubs produce shiny red, oily drupes in early fall. These are favored by birds and disappear far earlier than honeysuckle fruits. Spicebush seeds are ca. 3 mm in diameter and germinate easily after stratification. Seeds persist in the litter layer for a number of years (Nesom 2002), but most shrubs arise from clonal reproduction (Nesom 2002). Deer and other mammalian herbivores appear not to browse on spicebush foliage (Schulz, pers. obs.).\u003c/p\u003e \u003cp\u003eLuken et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1997\u003c/span\u003e) compared light acclimation responses of spicebush to honeysuckle and observed marked differences. Unlike honeysuckle, spicebush transplanted to 25 and 100% sunlight weakly expressed plastic responses to high light (plants grown at 1% sunlight failed to thrive). Davidson (1966) examined growth responses of six shrub species maintained in growth chamber simulating open (14% full sun) and closed canopy (3% full sun) forest light levels. Spicebush was distinctive among species because it gained height faster and produced more leaves under closed canopy, suggesting it was a shade specialist. In contrast to Luken et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1997\u003c/span\u003e), Niesenbaum (1992) observed greater leaf area and annual branch growth in spicebush exposed to 20% vs. 1% full sun in natural habitats. Moreover, Veres and Pickett (1982) observed substantially greater leaf area, leaf biomass, branch biomass, and primary stem production in high light (4300 foot candles, estimated as ca. 43% full sun) vs. low light (300 foot candles, estimated as 3% full sun) habitats.\u003c/p\u003e"},{"header":"Methods And Materials","content":"\u003cp\u003eStudies were conducted in late midsummer (August and early September) in a ca. 50 year-old upland successional forest and a south-facing forest edge on the Campus of Southern Illinois University (38.78\u003csup\u003eo\u003c/sup\u003e N, 90.00\u003csup\u003eo\u003c/sup\u003e W), in Madison County, southwestern Illinois USA. The soils are moderately acid Menfro Silt loam, containing ca. 22% clay in the surface horizons (Leeper \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Dominant forest trees include sugar maple, several oak species (\u003cem\u003eQuercus rubra\u003c/em\u003e L., \u003cem\u003eQ. michauxii\u003c/em\u003e Nutt., \u003cem\u003eQ. macrocarpa\u003c/em\u003e Michx.), walnut (\u003cem\u003eJuglans nigra\u003c/em\u003e L.), slippery elm (\u003cem\u003eUlmus rubra\u003c/em\u003e Muhl.), green ash (\u003cem\u003eFraxinus pennsylvanica\u003c/em\u003e Marshall.), and persimmon (\u003cem\u003eDiospyros virginiana\u003c/em\u003e L.). The tree canopy is somewhat broken, supporting a heavy subcanopy of maple seedlings and pawpaw ca. 3\u0026ndash;6 m tall. Mean (SD) midsummer light levels in the forest understory estimated from canopy photographs were \u0026lt;\u0026thinsp;13.3 (0.06)% of available photosynthetically active radiation. The edge site was dominated by cottonwood (\u003cem\u003ePopulus deltoides\u003c/em\u003e Marshall.), green ash, and sycamore (\u003cem\u003ePlatanus occidentalis\u003c/em\u003e L.). No light measurements of were made at the edge site but an appropriate sun path diagram shows the site received ca. 10 h. direct sunshine daily during summer.\u003c/p\u003e \u003cp\u003eUnderstory study shrubs were selected as sets of adjacent honeysuckle, spicebush, and pawpaw shrubs 0.7\u0026ndash;1.2 m tall and \u0026lt;\u0026thinsp;1.5 m apart. All individuals were apparently healthy and unstressed. Sets were located under similar, representative canopy conditions. We chose this approach to ensure comparable environments among study plants and for use as a blocking variable. Although this is not \u003cem\u003eper se\u003c/em\u003e a random sample, it follows widespread practice in plant ecophysiology. Edge habitat shrubs were selected haphazardly at intervals of 5 m along the shrub line.\u003c/p\u003e \u003cp\u003ePhotosynthetic light response curves were measured on eight individuals of each species during midsummer (late July and August 2016) at midday with a LI-COR Li6400XT gas exchange system (LI-COR Biosciences, Lincoln, NB USA). Chamber conditions (means with SD) were maintained at levels typical for forest conditions in summer. CO\u003csub\u003e2\u003c/sub\u003e concentration in the chamber was 396 (2.78) ppm. Leaf temperature was 30.0 (0.0844) \u003csup\u003eo\u003c/sup\u003eC and leaf to air vapor pressure deficit (VPD) was 1.12 (0.198) kPa, corresponding to ca. 70\u0026ndash;75% relative humidity, which approaches the operating limit of the photosynthesis system. Before light curves were taken leaves were acclimated to a previously determined saturating light intensity (500 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the understory site; 1600 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for edge shrubs). PAR levels were then stepped downward: 400, 300, 250, 200, 150, 100, 75, 50, 25, and 0 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for understory shrubs; 1600, 1400, 1200, 1000, 800, 600, 400, 300, 200, 150, 100, 50, and 0 \u0026micro;mol m\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for edge shrubs. Measurements were recorded after stable gas exchange rates were achieved at each light level. Respiratory rates at PAR 0 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are means of four samples because respiratory measurements are of low magnitude and in practice have greater temporal variability. Leaf areas were determined from photographs of pressed leaves using ImageJ. Leaf mass was measured to a resolution of 0.0001 g on specimens dried at 65 \u003csup\u003eo\u003c/sup\u003eC. Rates of gas exchange are expressed on both a leaf area basis and a leaf dry weight basis. Leaf chlorophyll contents were measured from leaf disks using the DMSO method (Hiscox and Israelstam \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1979\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo assess the leaf area and biomass allocation in shoots of shaded shrubs, 12\u0026ndash;14 leafy shoots were collected from the study plants and other comparable individuals in the study area. Leaf areas and the masses of leaves and stems were determined as above.\u003c/p\u003e \u003cp\u003ePhotosynthetic light responses were compared using repeated measures ANOVA. Comparisons of leaf traits and biomass allocation in shade were made by 1-way ANOVA followed by Tukey\u0026rsquo;s HSD. In some cases, biomass data did not conform to theoretical assumptions and Kruskal-Wallis nonparametric ANOVA followed by the Dwass-Steel-Chritchlow-Fligner Test for all pairwise comparisons were substituted. Comparisons of honeysuckle leaf traits in sun and shade were made using unequal variance t-tests. All analyses were conducted using Systat 13 (Systat Software, San Jose, CA USA).\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eUnderstory Photosynthesis, leaf area basis\u003c/h2\u003e \u003cp\u003eLight response curves were similar across species (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), saturating at ca. 150 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with maximum rates of photosynthesis (A\u003csub\u003emax\u003c/sub\u003e) ranging 3.4 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in pawpaw to 4.2 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in spicebush. Repeated measures ANOVA showed that overall photosynthetic rates were significantly higher in spicebush, but the patterns of light response (PAR x species interaction) were the same among species (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A\u003csub\u003emax\u003c/sub\u003e and respiratory rate (R) did not differ significantly among species (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Stomatal conductance (g\u003csub\u003ew\u003c/sub\u003e), intrinsic water use efficiency (A\u003csub\u003emax\u003c/sub\u003e/g\u003csub\u003ew\u003c/sub\u003e, with g\u003csub\u003ew\u003c/sub\u003e measured in \u0026micro;mol), and internal CO\u003csub\u003e2\u003c/sub\u003e concentration were tested by 1-way ANOVA, with and without VPD as a covariate. Neither stomatal conductance (mean\u0026thinsp;=\u0026thinsp;75.4, SE\u0026thinsp;=\u0026thinsp;5.81 mmol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), intrinsic water use efficiency (mean\u0026thinsp;=\u0026thinsp;54.1, SE\u0026thinsp;=\u0026thinsp;3.24), nor internal CO\u003csub\u003e2\u003c/sub\u003e (mean\u0026thinsp;=\u0026thinsp;299, SE\u0026thinsp;=\u0026thinsp;5.09 ppm) varied significantly.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eUnderstory Photosynthesis, leaf mass basis\u003c/h2\u003e \u003cp\u003ePhotosynthesis calculated on a leaf mass basis presented a different picture. Repeated measures ANOVA showed that honeysuckle had markedly lower rates of photosynthesis overall (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and responded to increasing light (0\u0026ndash;100 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) much more slowly than spicebush and pawpaw (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The light responses of spicebush and pawpaw were nearly identical. A\u003csub\u003emax\u003c/sub\u003e in honeysuckle was 45% lower than in the two other species (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Respiratory CO\u003csub\u003e2\u003c/sub\u003e release in pawpaw was significantly (ca. 20%) smaller in honeysuckle and spicebush (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRepeated measures ANOVA for photosynthetic light response curves. PAR is photosynthetically active radiation\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeaf Area Basis\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBetween Subjects\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF-Ratio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecies\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24.1526\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.0763\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0334\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eError\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70.2114\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.0527\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWithin Subjects\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF-Ratio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePAR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e425.4770\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e42.5477\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e314.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePAR*Species\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.5950\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.2798\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0057\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eError\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.0693\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e230\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1351\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLeaf Mass Basis\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBetween Subjects\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF-Ratio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecies\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.3469\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1735\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e32.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eError\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.1236\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.0054\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWithin Subjects\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF-Ratio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePAR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.6920\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.0692\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e373.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePAR*Species\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0687\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.0034\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eError\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0426\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e230\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.0002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eShade Leaf Characteristics\u003c/h2\u003e \u003cp\u003eAll three species exhibit similar levels of chlorophyll measured on a leaf area basis and have statistically indistinguishable chlorophyll a:b ratios (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Leaf mass per unit area (specific leaf mass, SLM) in honeysuckle is nearly twice that in pawpaw and spicebush (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This results in significantly lower levels of total chlorophyll per unit mass in honeysuckle.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of sun and shade-grown honeysuckle, pawpaw, and spicebush. A\u003csub\u003emax\u003c/sub\u003e, maximum light-saturated photosynthetic rate; R, dark respiration rate; QUE, quantum use efficiency (slope of light response curve 0 to 50 \u0026micro;mol photons m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e); LAR, leaf area ratio. Comparisons of sun and shade honeysuckles are denoted by capital letters (unequal variance t-test); comparisons of shade honeysuckle, pawpaw, and spicebush are denoted by lower case letters (1-way ANOVA followed by Tukey\u0026rsquo;s HSD). Values followed by the same letter do not differ at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"13\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eHoneysuckle (sun)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e \u003cp\u003eHoneysuckle (shade)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c10\" namest=\"c8\"\u003e \u003cp\u003ePawpaw\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c13\" namest=\"c11\"\u003e \u003cp\u003eSpicebush\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eLeaves\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eMean\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSE\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eMean\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSE\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eMean\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSE\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eMean\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSE\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal chlorophyll (g m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.378\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.258\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.009\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.242\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.013\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.241\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal chlorophyll (g g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e12.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e11.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChlorophyll a:b ratio\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e4.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e4.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecific leaf mass (g m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e96.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e40.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e19.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e22.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA\u003csub\u003emax\u003c/sub\u003e (\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e4.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA\u003csub\u003emax\u003c/sub\u003e (\u0026micro;mol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.1760\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.0916\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0092\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.1808\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.0116\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.1903\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.0120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eR (\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-1.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-0.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-0.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-0.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eR (\u0026micro;mol g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-0.0137\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0014\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-0.0083\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e-0.0157\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.0033\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e-0.0114\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.0011\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQUE (\u0026micro;mol C (\u0026micro;mol photons)\u003csup\u003e\u0026minus;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.0230\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.0005\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.0339\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0032\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.0396\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.0016\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.0421\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.0016\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLight Compensation Point (\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e6.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eB a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eShoots\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeaf area (m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.0234\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.0019\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.0792\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.0094\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.0385\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.0038\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ec\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStem mass (g)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.291\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.036\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.279\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.071\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.204\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.034\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeaf mass (g)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.995\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.081\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1.567\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.203\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e1.031\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.108\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ea,b\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLAR (m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.02369\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.00065\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003ea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.05460\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.00760\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.03755\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e0.00073\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ec\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eEdge vs. Understory Photosynthesis for Honeysuckle\u003c/h2\u003e \u003cp\u003eForest edge and understory honeysuckle showed large and statistically significant differences in photosynthetic measures and leaf characteristics (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). A\u003csub\u003emax\u003c/sub\u003e in high light honeysuckle was 4.5-fold greater than in shade honeysuckle; R was 3.5-fold greater; LCP was 3.6-fold higher; QUE (quantum use efficiency: the slope of light response curve 0 to 50 \u0026micro;mol photons m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was 0.7 of the value in shade. Total chlorophyll on an area basis was 1.5-fold higher, but only 0.6-fold as high on a mass basis. Chlorophyll a:b ratio was 3.8-fold higher and SLM was 2.4-fold higher. When A\u003csub\u003emax\u003c/sub\u003e and R are expressed on a mass basis, high light shrubs have 1.9 and 1.6-fold higher rates, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eComparison of potential carbon gain by shoots\u003c/h2\u003e \u003cp\u003eComparisons of biomass and leaf area allocation were complicated by widely differing variances between species which precluded standard ANOVA, even after multiple attempts to transform the data. Kruskal-Wallis nonparametric ANOVA (KW) followed by the Dwass-Steel-Chritchlow-Fligner Test for all pairwise comparisons were substituted. The ratio of leaf to stem biomass was similar for pawpaw and spicebush (6.5 and 6.9, respectively), but significantly less for honeysuckle (3.5, both comparisons significant at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0200). Leaf area per shoot differed among the three species (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Leaf areas were greatest for pawpaw, followed by spicebush, and then honeysuckle. Consequently, leaf area ratio (LAR), the ratio of leaf area per unit shoot mass, varied greatly across species in the order spicebush\u0026thinsp;=\u0026thinsp;pawpaw, \u0026gt; honeysuckle (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIf photosynthetic rates (area basis) at a representative PAR level are multiplied by LAR, one obtains an approximation of potential daytime carbon gain per gram of biomass investment in shoots. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea illustrates the approximate photosynthetic \u0026ldquo;payback\u0026rdquo; across PAR levels typical of forest understories. In all cases honeysuckle obtains far less carbon per unit of biomass investment than spicebush and pawpaw.\u003c/p\u003e \u003cp\u003eA problem with this analysis is that nighttime respiration is a drain on carbon gain. To partially correct this, payback estimates were adjusted by subtracting an estimate of dark respiration. Leaves and stems were assumed to have the same mass-based respiratory rate which was adjusted to typical cooler conditions at night (25 \u003csup\u003eo\u003c/sup\u003eC, using Q\u003csub\u003e10\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;2). We assumed that the duration of the daily photosynthetic period under a canopy would be ca. 12h. This attempt to account for respiration overnight reveals much lower levels of carbon gain (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb), but species differences and the pattern of response to light remain.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eArea-based photosynthetic rates for honeysuckle in this study can be compared with the more detailed work of Lieurance and Landsbergen (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Honeysuckle in our study achieved half their maximum photosynthetic rate in shade, and 10% higher rates in the sun. Patterns in the light response and leaf characteristics were concordant with greater acclimation to shade, suggesting our shade site was darker and the sun site brighter than in that published account. Luken et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1997\u003c/span\u003e) observed about 10% lower maximum rates for sun honeysuckle, but twice the maximum rate for spicebush, again suggesting our sites were more extreme. Until this study is replicated in brighter shade environments, our conclusions are limited to deep shade.\u003c/p\u003e \u003cp\u003eStudies of shade tolerance and photosynthesis have traditionally measured photosynthetic rates on a leaf area basis, not a mass or shoot basis as was done here. Here, different impressions were gained depending on whether measurements were area-based or mass/shoot-based. On an area basis all three species show comparable light responses and rates of photosynthesis. This would suggest that honeysuckle has the acclimation capacity to sufficient compete with native woody understory plants. In a short survey of studies examining invasive understory shrub photosynthesis [e.g., Harrington et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1989\u003c/span\u003e, Luken et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1997\u003c/span\u003e, Pattison \u003cem\u003eet al.\u003c/em\u003e (1998), Lieurance and Landsbergen (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2016\u003c/span\u003e),, Dornbos \u003cem\u003eet al.\u003c/em\u003e (2016)], none except Xu (2007) deviate from area-based measurements. This is significant because mass-based measurements reference photosynthesis to the to the approximate carbon cost of leaf construction and the \u0026ldquo;profitability\u0026rdquo; of leaves; area-based measurements reference photosynthesis to the efficiency of the receptive surface of whatever carbon cost.\u003c/p\u003e \u003cp\u003eEvaluated, on a leaf mass or shoot basis, honeysuckle in deep shade is distinctly inferior to the two native species. Higher allocation to leaf mass per unit area is a well-known trait of plants in high light environments (e.g., forest edge honeysuckle in this study), however this is a liability when light is very limiting and mass per unit area cannot be sufficiently adjusted downward to support larger leaf areas. SLM for honeysuckle in sun was about twice that for shade honeysuckle, but SLM for shade honeysuckle is still twice as large as for pawpaw and spicebush. Plastic responses in honeysuckle clearly cannot duplicate the behavior of the more shade-specialized pawpaw and spicebush. The profoundly higher performance for honeysuckle leaves in sun suggests its presence in the forest understory is an expression of wide niche breadth, not adaptation to shade \u003cem\u003eper se\u003c/em\u003e as seen in pawpaw and spicebush. Based on gas exchange data and leaf characteristics, honeysuckle clearly finds near optimal habitat along forest edges. This supports Schulz and Wright\u0026rsquo;s (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) suggestion that control of edge shrubs should be a conservation priority.\u003c/p\u003e \u003cp\u003eFrom the perspective of shoot allocation, the lower capacity of honeysuckle to adjust SLM in shade is reinforced by a greater allocation to stem tissue and lower LAR. Presuming leaf orientation is similar between the species, in a very shady environment honeysuckle shoots cannot repay the cost of shoots as quickly as pawpaw and spicebush. Naturally, it would be informative to compare whole plant respiratory costs, but obtaining these data is out of practical reach.\u003c/p\u003e \u003cp\u003eA concern in any photosynthesis study involving \u003cem\u003eLonicera\u003c/em\u003e spp. is the relative importance of summer photosynthesis under a closed canopy versus spring/fall photosynthesis under more open canopies. There is a tendency to generalize from Harrington et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1989\u003c/span\u003e) that high spring photosynthetic rates seen in \u003cem\u003eL.\u003c/em\u003e X \u003cem\u003ebella\u003c/em\u003e apply to Amur honeysuckle. Fridley (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), using photosynthesis measurements in a model, showed that \u003cem\u003espring\u003c/em\u003e photosynthetic gains for \u003cem\u003eL.\u003c/em\u003e X \u003cem\u003ebella\u003c/em\u003e were clearly meaningful, but that Amur honeysuckle achieved low gains in spring and modest gains in fall. Phenological observations like those made by McEwan et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) are fertile ground for speculation, but do not include photosynthesis measurements in light of photosynthetic capacity, or considerations of low leaf area and near-vertical leaf orientation for much of spring (Schulz, pers. obs.). Photosynthesis in fall might be significant (Fridley \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), but frequent phenological mismatches between tree canopy senescence (last half of October), hard frost which causes honeysuckle leaves to senesce, and generally declining photosynthetic capacity are also probable. Records of fall weather patterns in nearby St. Louis, MO USA show high interannual variation in the first date of frost. The mean date is November 1, but one standard deviation from this date spans the period October 16 to November 17 (NOAA 2022a). Anecdotally, in 2020 we noted honeysuckle leaf senescence at the start of November; in 2022 leaf senescence was delayed into early December (Schulz, pers. obs.). For these reasons the value of the fall light window may be quite intermittent for understory shrubs. In the long term, phenological differences between the three species are probably of limited importance given the large performance gap between honeysuckle and the two natives. Any phenological advantage would be difficult to overcome in a few weeks of a mean 208 day (range 159\u0026ndash;260) growing season (NOAA 2022b).\u003c/p\u003e \u003cp\u003eThis finding should be taken as a suggestion that pawpaw and spicebush may replace honeysuckle over time in forest types driven by shade tolerance. Naturally the abundance and distribution of pawpaw and spicebush in any given situation will affect this process. Ironically, management plans which seek the re-imposition of fire will greatly reduce the abundance of maple, pawpaw, and likely spicebush, however they may only top kill honeysuckle and, absent repeated fire, leave stands more invasible (Nyboer and Edgin \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). We have noticed that both pawpaw and spicebush are increasing in local forests. This may be caused by higher shade tolerance as regional forests recover from anthropogenic disturbance, but it also reflects the fact that deer do not browse either species and competitors have declined (Slater and Anderson \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). We note that honeysuckle is subject to moderate deer browsing, which is a disadvantage. Nonetheless, we periodically observe that honeysuckle overtopped by pawpaw shows signs of decline, as do honeysuckle under closing maple canopies.\u003c/p\u003e \u003cp\u003eCertainly, this analysis of photosynthetic patterns and the structure of shoots is not a comprehensive study of whole plant shade tolerance. However, we submit that the capacity to produce shoots that have a higher level of net primary production in shade is a meaningful element of the larger problem. A recent visit back to the study site several years after this work supports these findings. Pawpaw and spicebush, which were originally comparably sized, are now almost twice as tall as honeysuckle.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eGas analyzer calibration and maintenance were supported by a Seed Grant for Transitional and Exploratory Projects awarded to Kurt Schulz by the Graduate School of Southern Illinois University Edwardsville.\u003c/p\u003e\n\u003cp\u003eThe author has no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003eKurt Schulz conceived the project, collected, and analyzed the data, and wrote the manuscript. Special thanks to Anh Nguyen (Southern Illinois University Edwardsville) for considerable assistance with field data collection.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAllana BF, Dutra HP, Goessling LS, Barnett K, Chasea JM, Marquis RJ, Pang G, Storch GA, Thach RE, Orrock JL. 2010. Invasive honeysuckle eradication reduces tick-borne disease risk by altering host dynamics. Proceedings of the National Academy of Sciences of the United States of America 107: 18523-18527. https://doi.org/10.1073/pnas.1008362107.\u003c/li\u003e\n \u003cli\u003eBartuszevige AM, Gorchov DL. 2006. Avian seed dispersal of an invasive shrub. Biological Invasions 8: 1013-1022. https://doi.org/10.1007/s10530-005-3634-2.\u003c/li\u003e\n \u003cli\u003eBartuszevige AM, Gorchov DL, Raab L. 2006. The relative importance of landscape and community features in the invasion of an exotic shrub in a fragmented landscape. Ecography 29: 213-222. https://doi.org/10.1111/j.2006.0906-7590.04359.x\u003c/li\u003e\n \u003cli\u003eCastellano SM, Gorchov DL. 2013. White-tailed deer (\u003cem\u003eOdocoileus virginianus\u003c/em\u003e) disperse seeds of the invasive shrub, Amur honeysuckle (\u003cem\u003eLonicera maackii\u003c/em\u003e). Natural Areas Journal 33: 78-80. https://doi.org/10.3375/043.033.0109\u003c/li\u003e\n \u003cli\u003eCollier MW, Vankat JL. 2002. Diminished plant richness and abundance below \u003cem\u003eLonicera maackii\u003c/em\u003e, an invasive shrub. American Midland Naturalist 147: 60-71. https://doi.org/10.1674/0003-0031(2002)147[0060:DPRAAB]2.0.CO;2\u003c/li\u003e\n \u003cli\u003eEllsworth DS and Reich PB. 1992. Water relations and gas exchange of \u003cem\u003eAcer saccharum\u003c/em\u003e seedlings in contrasting natural light and moisture regimes. Tree Physiology 10: 1-20. https://doi.org/10.1093/treephys/10.1.1\u003c/li\u003e\n \u003cli\u003eFridley JD. 2012. Extended leaf phenology and the autumn niche in deciduous forest invasions. Nature 485: 359-362. https://doi.org/10.1038/nature11056\u003c/li\u003e\n \u003cli\u003eGivnish TJ. 1988. Adaptation to sun and shade: A whole-plant perspective. Australian Journal of Plant Physiology 15: 63-92. https://doi.org/10.1071/PP9880063\u003c/li\u003e\n \u003cli\u003eGorchov DL. 2005. Control of forest invasives and responses of native forest-floor plants: case studies of garlic mustard and Amur honeysuckle. Paper presented at Ohio Invasive Plant Research Conference: Bridging the Gap Between Land Management and Research.\u003c/li\u003e\n \u003cli\u003eGould AMA, Gorchov DL. 2000. Effects of the exotic invasive shrub \u003cem\u003eLonicera maackii\u003c/em\u003e on the survival and fecundity of three species of native annuals. American Midland Naturalist 144: 36-50. https://doi.org/10.1674/0003-0031(2000)144[0036:EOTEIS]2.0.CO;2\u003c/li\u003e\n \u003cli\u003eHarrington RA, Brown BJ, Reich PB. 1989. Ecophysiology of exotic and native shrubs in southern Wisconsin I. Relationship of leaf characteristics, resource availability, and phenology to seasonal patterns of carbon gain. Oecologia 80: 356-367. https://doi.org/10.1007/BF00379037\u003c/li\u003e\n \u003cli\u003eHenkin MA, Medley KE, Abbitt RJ, Patton JM. 2013. Invasion dynamics of nonnative Amur honeysuckle over 18 years in a southwestern Ohio forest. The American Midland Naturalist 170: 335-347. https://doi.org/10.1674/0003-0031-170.2.335\u003c/li\u003e\n \u003cli\u003eHiscox JD, Israelstam. GF. 1979. A method for the extraction of chlorophyll from leaf tissue without maceration. Canadian Journal of Botany 57: 1332-1334. https://doi.org/10.1139/b79-163\u003c/li\u003e\n \u003cli\u003eImmel DL. 2001. Pawpaw\u003cem\u003e\u0026nbsp;Asimina triloba\u003c/em\u003e (L.) Dunal.: USDA, NRCS, National Plant Data Center. https://plants.sc.egov.usda.gov/DocumentLibrary/plantguide/doc/cs_astr.docx. Last access 20 December 2022.\u003c/li\u003e\n \u003cli\u003eIngold JL, Craycraft M. 1983. Avian frugivory on honeysuckle (\u003cem\u003eLonicera\u003c/em\u003e) in southwestern Ohio in fall. Ohio Journal of Science 83: 256-258. http://hdl.handle.net/1811/22964\u003c/li\u003e\n \u003cli\u003eLarimore RL, Busemeyer DT, Ebinger JE. 2003. Pawpaw, \u003cem\u003eAsimina triloba\u003c/em\u003e (L) Dunal (Annonaceae), in the Prairie Peninsula of Illinois, USA. Natural Areas Journal 23: 356-361.\u003c/li\u003e\n \u003cli\u003eLeeper RA. 2004. Soil Survey of Madison County, Illinois. United States Department of Agriculture, Natural Resources Conservation Service and Illinois Agricultural Experiment Station. https://www.nrcs.usda.gov/Internet/FSE_MANUSCRIPTS/illinois/IL119/ 0/madison_IL.pdf. Last access 20 December, 2022.\u003c/li\u003e\n \u003cli\u003eLei TT, Lechowicz MJ. 1990. Shade adaptation and shade tolerance in saplings of three \u003cem\u003eAcer\u003c/em\u003e species from eastern North America. Oecologia 84: 224-228. DOI: 10.1007/BF00318275\u003c/li\u003e\n \u003cli\u003eLieurance D, Landsbergen K. 2016. The influence of light habitat on the physiology, biomass allocation, and fecundity of the invasive shrub Amur honeysuckle (\u003cem\u003eLonicera maackii\u003c/em\u003e, Caprifoliaceae). Journal of the Torrey Botanical Society 143: 415-426. https://doi.org/10.3159/torrey-d-15-00056.1\u003c/li\u003e\n \u003cli\u003eLoomis JD, Matter SF, Cameron GN. 2015. Effects of invasive Amur honeysuckle (\u003cem\u003eLonicera maackii\u003c/em\u003e) and white-tailed deer (\u003cem\u003eOdocoileus virginianus\u003c/em\u003e) on survival of sugar maple seedlings in a southwestern Ohio forest. American Midland Naturalist 174: 65-73. https://doi.org/10.1674/0003-0031-167.2.256\u003c/li\u003e\n \u003cli\u003eLuken JO, Thieret JW. 1996. Amur honeysuckle, its fall from grace. Bioscience 46: 18-24. https://doi.org/10.2307/1312651\u003c/li\u003e\n \u003cli\u003eLuken JO, Kuddes LM, Tholemeier TC. 1997. Response of understory species to gap formation and soil disturbance in \u003cem\u003eLonicera maackii\u0026nbsp;\u003c/em\u003ethickets. Restoration Ecology 5: 229-235. https://doi.org/10.1046/j.1526-100X.1997.09727.x\u003c/li\u003e\n \u003cli\u003eMcEwan, RW, Birchfield, MK, Schoergendorfer, A., \u0026amp; Arthur, MA. 2009. Leaf Phenology and Freeze Tolerance of the Invasive Shrub Amur Honeysuckle and Potential Native Competitors. The Journal of the Torrey Botanical Society, 136(2), 212\u0026ndash;220. https://doi.org/10.3159/08-ra-109.1\u003c/li\u003e\n \u003cli\u003eMcEwan RW, Arthur MA, Alverson SE. 2012. Throughfall chemistry and soil nutrient effects of the invasive shrub \u003cem\u003eLonicera maackii\u003c/em\u003e in deciduous forests. American Midland Naturalist 168: 43-55. https://doi.org/10.1674/0003-0031-168.1.43\u003c/li\u003e\n \u003cli\u003eMcNeish RE, McEwan RW. 2016. A review on the invasion ecology of Amur honeysuckle (\u003cem\u003eLonicera maackii\u003c/em\u003e, Caprifoliaceae) a case study of ecological impacts at multiple scales. The Journal of the Torrey Botanical Society 143: 367-385. https://doi.org/10.3159/torrey-d-15-00049.1\u003c/li\u003e\n \u003cli\u003eMcNeish RE, Moore EM, Benbow ME, McEwan RW. 2015. Removal of the invasive shrub, \u003cem\u003eLonicera maackii\u003c/em\u003e, from riparian forests influences headwater stream biota and ecosystem function. River Research and Applications 31: 1131-1139. https://doi.org/10.1002/rra.2808\u003c/li\u003e\n \u003cli\u003eMeiners SJ. 2007. Apparent competition: An impact of exotic shrub invasion on tree regeneration. Biological Invasions 9: 849-855. https://doi.org/10.1007/s10530-006-9086-5\u003c/li\u003e\n \u003cli\u003eMiller KE, Gorchov DL. 2004. The invasive shrub, \u003cem\u003eLonicera maackii\u003c/em\u003e, reduces growth and fecundity of perennial forest herbs. Oecologia 139: 359-375. https://doi.org/10.1007/s00442-004-1518-2\u003c/li\u003e\n \u003cli\u003eNOAA (National Oceanic and Atmospheric Administration). 2022a. NOWData - NOAA Online Weather Data for St. Louis, MO 1875-2021. https://www.weather.gov/wrh/climate?wfo=lsx. Last access 20 December, 2022.\u003c/li\u003e\n \u003cli\u003eNOAA (National Oceanic and Atmospheric Administration). 2022b. Latest spring freeze - first fall freeze - length of growing season Saint Louis, Mo (1873 - present). https://www.weather.gov/media/lsx/climate/stl/temp/temp_stl_grow_season.pdf. Last access 20 December, 2022.\u003c/li\u003e\n \u003cli\u003eNyboer R, Edgin R. 2017. Bush Honeysuckles: Tartarian, Morrow\u0026apos;s, Belle, and Amur Honeysuckle (\u003cem\u003eLonicera tatarica\u003c/em\u003e L., \u003cem\u003eL. morrowii\u003c/em\u003e Gray, \u003cem\u003eL.\u003c/em\u003e x \u003cem\u003ebella\u0026nbsp;\u003c/em\u003eZabel, and \u003cem\u003eL. maackii\u003c/em\u003e (Rupr.) Maxim.). Illinois Nature Preserves Commission, Vegetation Management Guideline 6(1). https://www2.illinois.gov/dnr/INPC/Pages/INPCManagementGuidelines.aspx Last access 20 December, 2022.\u003c/li\u003e\n \u003cli\u003eOrrock JL, Dutra HP, Marquis RJ, Barber N. 2015. Apparent competition and native consumers exacerbate the strong competitive effect of an exotic plant species. Ecology 96: 1052-1061. https://doi.org/10.1890/14-0732.1\u003c/li\u003e\n \u003cli\u003eRogstad RH, Wolff K, Schaal BA. 1991. Geographical variation in \u003cem\u003eAsimina triloba\u003c/em\u003e Dunal (Annonaceae) revealed by the M13 \u0026quot;DNA fingerprinting\u0026quot; probe. American Journal of Botany 78: 1391-1396. https://doi.org/10.2307/2445277\u003c/li\u003e\n \u003cli\u003eSchulz KE, Wright J. 2015. Reproduction of invasive Amur honeysuckle (\u003cem\u003eLonicera maackii\u003c/em\u003e) and the arithmetic of an extermination strategy. Restoration Ecology 23: 900-908. https://doi.org/10.1111/rec.12260\u003c/li\u003e\n \u003cli\u003eSena K, Gauger L, Johnson T, Shirkey F, Caldbeck W, Hammock J, Kim A, Mazza B, Pethtel I, Leuenberger W. 2021. Honeysuckle (\u003cem\u003eLonicera maackii\u003c/em\u003e) presence is associated with reduced diversity and richness of flowering spring flora in central Kentucky. Natural Areas Journal 41: 249-257. https://doi.org/10.3375/20-41\u003c/li\u003e\n \u003cli\u003eSendall KM, Lusk CH, Reich PB. 2015. Becoming less tolerant with age: sugar maple, shade, and ontogeny. Oecologia 179: 1011-1021. https://doi.org/10.3375/20-41\u003c/li\u003e\n \u003cli\u003eSlater MA, Anderson RC. 2014. Intensive selective deer browsing favors success of \u003cem\u003eAsimina triloba\u003c/em\u003e (Paw Paw) a native tree species. Natural Areas Journal 34: 178-187. https://doi.org/10.3375/043.034.0207\u003c/li\u003e\n \u003cli\u003eTrammell TLE, Ralston HA, Scroggins SA, Carreiro MM. 2012. Foliar production and decomposition rates in urban forests invaded by the exotic invasive shrub, \u003cem\u003eLonicera maackii\u003c/em\u003e. Biological Invasions 14: 529-545. https://doi.org/10.1007/s10530-011-0093-9\u003c/li\u003e\n \u003cli\u003eVellend M. 2002. A pest and an invader: White-tailed deer (\u003cem\u003eOdocoileus virginianus\u003c/em\u003e Zimm.) as a seed dispersal agent for honeysuckle shrubs (\u003cem\u003eLonicera\u003c/em\u003e L.). Natural Areas Journal 22: 230-234.\u003c/li\u003e\n \u003cli\u003eWalters MB, Kruger EL, Reich PB. 1993. Growth, biomass distribution and CO\u003csub\u003e2\u003c/sub\u003e exchange of northern hardwood seedlings in high and low light: relationships with successional status and shade tolerance. Oecologia 94: 7-16. https://doi.org/10.1007/BF00317294\u003c/li\u003e\n \u003cli\u003eWalters MB, Reich PB. 1996. Are shade tolerance, survival, and growth linked? Low light and nitrogen effects on hardwood seedlings. Ecology 77: 841-853. https://doi.org/10.2307/2265505\u003c/li\u003e\n \u003cli\u003eWoodward FI. 1990. From ecosystems to genes: the importance of shade tolerance. Trends in Ecology and Evolution 5: 111-115. https://doi.org/10.1016/0169-5347(90)90164-9\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"plant-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"vege","sideBox":"Learn more about [Plant Ecology](https://www.springer.com/journal/11258)","snPcode":"11258","submissionUrl":"https://submission.nature.com/new-submission/11258/3","title":"Plant Ecology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Lonicera maackii, mesofication, shade tolerance, Asimina triloba, Lindera benzoin","lastPublishedDoi":"10.21203/rs.3.rs-2426397/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2426397/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAmur honeysuckle (\u003cem\u003eLonicera maackii\u003c/em\u003e (Rupr.) Maxim) is a notorious invader of forests and forest edges throughout eastern North America. The species is difficult to exterminate and reestablishes readily. A perpetual presence of Amur honeysuckle in most forests is largely a forgone conclusion. Forests throughout the eastern U.S. are changing due to canopy closure after historical disturbance and long-term fire prevention. Fire intolerant species, especially sugar maple (\u003cem\u003eAcer saccharum\u003c/em\u003e Marshall.), are coming to dominate forest canopies, creating shady understories and forest dynamics that pivot on shade tolerance. Two shade tolerant understory shrubs, pawpaw (\u003cem\u003eAsimina triloba\u003c/em\u003e Adans.) and spicebush (\u003cem\u003eLindera benzoin\u003c/em\u003e Thunb.) compete with honeysuckle in maple understories. Based on field observations we hypothesized that these native species were more shade tolerant than invasive honeysuckle. We examined shade tolerance in honeysuckle, pawpaw, and spice bush by comparing photosynthetic light responses, leaf characteristics, and allocation to leaf area versus stem mass (leaf area ratio, LAR) in annual shoots. Honeysuckle had comparable light responses measured on a leaf area basis, but mass-based measurements show it is less efficient paying back carbon invested in leaf tissue. This arises because honeysuckle is unable to reduce specific leaf mass to the level of pawpaw and spicebush. LAR is distinctly higher in pawpaw and spicebush, suggesting an advantage in heavy shade. Since the great majority of photosynthesis in these species occurs under a closed canopy, we suggest honeysuckle will diminish in maple-dominated stands. Informal observations of greater height growth in pawpaw and spicebush in the field support this.\u003c/p\u003e","manuscriptTitle":"Has Invasive Amur Honeysuckle (Lonicera maackii (Rupr.) Maxim) Met its Match? Interspecies Comparisons of Photosynthesis and Shoot Allocation in Heavy Shade","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-01-04 17:50:57","doi":"10.21203/rs.3.rs-2426397/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-03-20T14:08:22+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-03-11T14:05:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"d1bdbba7-522d-40d0-938d-1d8c969d9322","date":"2023-02-28T01:26:33+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-02-27T18:41:59+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-01-01T05:17:49+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2022-12-30T01:16:32+00:00","index":"","fulltext":""},{"type":"submitted","content":"Plant Ecology","date":"2022-12-29T19:31:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"plant-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"vege","sideBox":"Learn more about [Plant Ecology](https://www.springer.com/journal/11258)","snPcode":"11258","submissionUrl":"https://submission.nature.com/new-submission/11258/3","title":"Plant Ecology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e68824b8-d6ce-42b7-a278-bfd918f06edd","owner":[],"postedDate":"January 4th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-09-11T15:08:13+00:00","versionOfRecord":{"articleIdentity":"rs-2426397","link":"https://doi.org/10.1007/s11258-023-01347-9","journal":{"identity":"plant-ecology","isVorOnly":false,"title":"Plant Ecology"},"publishedOn":"2023-09-09 15:01:37","publishedOnDateReadable":"September 9th, 2023"},"versionCreatedAt":"2023-01-04 17:50:57","video":"","vorDoi":"10.1007/s11258-023-01347-9","vorDoiUrl":"https://doi.org/10.1007/s11258-023-01347-9","workflowStages":[]},"version":"v1","identity":"rs-2426397","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2426397","identity":"rs-2426397","version":["v1"]},"buildId":"-HB7Z8yhvgn0wM9Nzuekk","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}