Large differences in photorespiration and its temperature response among temperate trees

Large differences in photorespiration and its temperature response among temperate trees | bioRxiv /* */ /* */ <!-- <!-- /*! * yepnope1.5.4 * (c) WTFPL, GPLv2 */ (function(a,b,c){function d(a){return"[object Function]"==o.call(a)}function e(a){return"string"==typeof a}function f(){}function g(a){return!a||"loaded"==a||"complete"==a||"uninitialized"==a}function h(){var a=p.shift();q=1,a?a.t?m(function(){("c"==a.t?B.injectCss:B.injectJs)(a.s,0,a.a,a.x,a.e,1)},0):(a(),h()):q=0}function i(a,c,d,e,f,i,j){function k(b){if(!o&&g(l.readyState)&&(u.r=o=1,!q&&h(),l.onload=l.onreadystatechange=null,b)){"img"!=a&&m(function(){t.removeChild(l)},50);for(var d in y[c])y[c].hasOwnProperty(d)&&y[c][d].onload()}}var j=j||B.errorTimeout,l=b.createElement(a),o=0,r=0,u={t:d,s:c,e:f,a:i,x:j};1===y[c]&&(r=1,y[c]=[]),"object"==a?l.data=c:(l.src=c,l.type=a),l.width=l.height="0",l.onerror=l.onload=l.onreadystatechange=function(){k.call(this,r)},p.splice(e,0,u),"img"!=a&&(r||2===y[c]?(t.insertBefore(l,s?null:n),m(k,j)):y[c].push(l))}function j(a,b,c,d,f){return q=0,b=b||"j",e(a)?i("c"==b?v:u,a,b,this.i++,c,d,f):(p.splice(this.i++,0,a),1==p.length&&h()),this}function k(){var a=B;return a.loader={load:j,i:0},a}var l=b.documentElement,m=a.setTimeout,n=b.getElementsByTagName("script")[0],o={}.toString,p=[],q=0,r="MozAppearance"in l.style,s=r&&!!b.createRange().compareNode,t=s?l:n.parentNode,l=a.opera&&"[object Opera]"==o.call(a.opera),l=!!b.attachEvent&&!l,u=r?"object":l?"script":"img",v=l?"script":u,w=Array.isArray||function(a){return"[object Array]"==o.call(a)},x=[],y={},z={timeout:function(a,b){return b.length&&(a.timeout=b[0]),a}},A,B;B=function(a){function b(a){var a=a.split("!"),b=x.length,c=a.pop(),d=a.length,c={url:c,origUrl:c,prefixes:a},e,f,g;for(f=0;f<d;f++)g=a[f].split("="),(e=z[g.shift()])&&(c=e(c,g));for(f=0;f<b;f++)c=x[f](c);return c}function g(a,e,f,g,h){var i=b(a),j=i.autoCallback;i.url.split(".").pop().split("?").shift(),i.bypass||(e&&(e=d(e)?e:e[a]||e[g]||e[a.split("/").pop().split("?")[0]]),i.instead?i.instead(a,e,f,g,h):(y[i.url]?i.noexec=!0:y[i.url]=1,f.load(i.url,i.forceCSS||!i.forceJS&&"css"==i.url.split(".").pop().split("?").shift()?"c":c,i.noexec,i.attrs,i.timeout),(d(e)||d(j))&&f.load(function(){k(),e&&e(i.origUrl,h,g),j&&j(i.origUrl,h,g),y[i.url]=2})))}function h(a,b){function c(a,c){if(a){if(e(a))c||(j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}),g(a,j,b,0,h);else if(Object(a)===a)for(n in m=function(){var b=0,c;for(c in a)a.hasOwnProperty(c)&&b++;return b}(),a)a.hasOwnProperty(n)&&(!c&&!--m&&(d(j)?j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}:j[n]=function(a){return function(){var b=[].slice.call(arguments);a&&a.apply(this,b),l()}}(k[n])),g(a[n],j,b,n,h))}else!c&&l()}var h=!!a.test,i=a.load||a.both,j=a.callback||f,k=j,l=a.complete||f,m,n;c(h?a.yep:a.nope,!!i),i&&c(i)}var i,j,l=this.yepnope.loader;if(e(a))g(a,0,l,0);else if(w(a))for(i=0;i (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];var j=d.createElement(s);var dl=l!='dataLayer'?'&l='+l:'';j.src='//www.googletagmanager.com/gtm.js?id='+i+dl;j.type='text/javascript';j.async=true;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-M677548'); Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search New Results Large differences in photorespiration and its temperature response among temperate trees View ORCID Profile Rakesh Tiwari , View ORCID Profile Philip David , View ORCID Profile Robert Muscarella doi: https://doi.org/10.1101/2025.11.22.689893 Rakesh Tiwari 1 Plant Ecology and Evolution, Department of Ecology and Genetics, Uppsala University , Sweden Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Rakesh Tiwari For correspondence: shimogarakesh{at}gmail.com Philip David 1 Plant Ecology and Evolution, Department of Ecology and Genetics, Uppsala University , Sweden 2 Ecology and Evolutionary Biology, Department of Biology, University of Turku , Finland Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Philip David Robert Muscarella 1 Plant Ecology and Evolution, Department of Ecology and Genetics, Uppsala University , Sweden Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Robert Muscarella Abstract Full Text Info/History Metrics Supplementary material Preview PDF Summary Photorespiration significantly influences terrestrial carbon fluxes, yet empirical measurements of its variability across tree species and temperature conditions remain limited, constraining predictions of vegetation and climate models. We quantified leaf-level photorespiration rates ( R p ) for seven temperate broadleaf tree species in northern Europe, measuring in situ in Uppsala, Sweden during peak summer. R p was estimated by contrasting net photosynthetic CO 2 assimilation under ambient and O 2 -free conditions at three leaf temperatures (25, 30, and 35°C), encompassing typical and heatwave scenarios. Results reveal pronounced interspecific variation in R p and increasing photorespiration with temperature, consistent with the temperature sensitivity of Rubisco’s oxygenase function. Notably, thermal responses varied substantially among species: some exhibited pronounced Rp increases at higher temperatures, while others maintained stable or even reduced rates, suggesting differences in metabolic and thermal resilience. The photorespiration-to-photosynthesis ratio increased with temperature, surpassing unity at 35°C for some species and indicating reduced photosynthetic efficiency during heat stress. Unexpectedly, the correlation between photosynthesis and photorespiration strengthened at elevated temperatures. Our results reveal high variability and temperature sensitivity in photorespiration among temperate trees. Compared to crop-based model parameters, tree values are substantially higher, with important implications for dynamic vegetation model predictions. Introduction Photorespiration, the second largest biological flux on Earth, has major impacts on terrestrial carbon fluxes but we have limited understanding of how this process varies across environmental conditions and among species ( Bauwe et al ., 2010 ; Busch & Sage, 2017 ). The photorespiration process occurs when Rubisco, the key enzyme responsible for catalysing photosynthesis by binding CO 2 to its substrates, catalyses the binding of O 2 ( Lorimer & Andrews, 1973 ). This oxygenation reaction produces glycolate (2-phosphoglycolate), a toxic intermediate that is subsequently recycled through the photorespiratory pathway ( Ogren & Bowes, 1971 ). During this process, a portion of the previously assimilated carbon is released as CO 2 at a rate known as the photorespiration rate ( Wingler et al ., 2000 ). Despite the large impact of photorespiration on overall photosynthetic yield and the global carbon cycle, empirical studies quantifying variation in photorespiration rates at the leaf level remain scarce. Most dynamic global vegetation models (DGVMs) integrate photorespiration theoretically through the Farquhar–von Caemmerer–Berry (FvCB) model for C3 plants ( Farquhar et al ., 1980 ). In part due to a lack of empirical data, this approach does not explicitly incorporate variation of photorespiration rates across species or climate conditions ( Oberpriller et al ., 2022 ; Beauclaire et al ., 2024 ). In practice, DGVMs that use the FvCB model typically adopt a fixed value for the ratio of photorespiration ( R p ) to photosynthesis ( A net ) – expressed as Φ = R p / A net (Box 1). Notably, the empirical basis for the Φ parameter relies primarily on crop plant data—namely rice, wheat, and soybean—with only a limited number of studies on trees ( Keys et al ., 1977 ; Yeo et al ., 1994 ; Epron et al ., 1995 ; Valentini et al ., 1995 ; Hochberg et al ., 2013 ; Huang et al ., 2015 ; Zhang et al ., 2016 ; Tomeo & Rosenthal, 2018 ; Ye et al ., 2019 ). Consequently, the FvCB model may inadequately represent photorespiration in forest ecosystems and lead to inaccurate estimations of other critical parameters (e.g., maximum rubisco carboxylation rate and electron transport rates – V cmax and J max ), thereby reducing accuracy of vegetation–climate feedback projections ( Ye et al ., 2025b , a ; Lochocki & McGrath, 2025 ). Empirical constraints, particularly for long-lived plants, could help improve model fidelity and provide key insights to the role of photorespiration in the global carbon cycle ( van Bodegom et al ., 2014 ). Photorespiration consumes a substantial fraction of the chemical energy generated during the light reactions of photosynthesis, thereby reducing photosynthetic light-use efficiency and has thus been considered a major inefficiency in plant productivity ( Zhu et al ., 2010 ). However, under stress conditions when photosynthesis is suppressed (e.g., high temperature), photorespiration serves as an essential alternative sink for the light reactions products ( Streb et al ., 2005 ; Huang et al ., 2019 ; Osei-Bonsu et al ., 2021 ), alleviates photoinhibition of photosystem I ( Wada et al ., 2020 ; Shi et al ., 2022 ), and prevents the accumulation of reactive oxygen species ( Foyer et al ., 1994 , 2009 ; Jiang et al ., 2023 ), thereby providing thermal protection ( Kozaki & Takeba, 1996 ; Wingler et al ., 2000 ; Chuang & Ling, 2005 ; Hu et al ., 2020 ; Cavanagh et al ., 2022 ). The protective role of photorespiration is supported by studies on Arabidopsis , tobacco, rice, and maize mutants deficient in photorespiratory enzymes ( Zelitch et al ., 2009 ; Timm et al ., 2012 ). The loss of photorespiratory function in these mutants led to increased heat sensitivity, impaired growth, leaf necrosis, and reduced survival. Thus, photorespiration is recognized as a key component of plant thermal tolerance, maintaining redox and energy balance and supporting cellular homeostasis during thermal stress ( Noctor et al., 2002 ; Bauwe et al., 2010 ; Voss et al., 2013 ; Roze et al., 2025 ). However, our knowledge of the temperature sensitivity of photorespiration remains limited, particularly for perennial plants. Box 1: Values for the ratio of photorespiration (R p ) and photosynthesis (A net ) rates. Letter annotations indicate significant differences between means of the groups. Download figure Open in new tab Compared with photosynthesis (A net ), in situ, leaf-level measurements of photorespiratory CO 2 release (R p ) rates are relatively rare and have been reported for only a limited number of species. Two main approaches are commonly used to estimate R p : (a) comparing photosynthetic CO 2 assimilation rates under ambient and low-oxygen conditions to suppress photorespiration ( Sharkey, 1985 , 1988 ; Sharkey et al., 1988 ), and (b) using simultaneous measurements of photosynthetic electron transport rates with a fixed partitioning ratio between photorespiratory and non-photorespiratory pathways ( Peterson, 1989 ; Valentini et al., 1995 ; Yoshimura et al., 2001 ). Both methods have notable limitations and require corrections for alternative CO 2 release pathways ( Sharkey, 1988 ; Busch, 2013 ; Busch et al., 2017 ; Xu et al., 2021 ). The figure above compiles data from both approaches, including only studies that reported R p and A net with sufficient information on corrections for alternative pathway CO 2 release (Supplementary Section 1). From these data, we calculated the ratio of R p to A net (Φ) at a leaf temperature of 25°C, highlighting the variation in Φ values across species. The data is separated based on short duration species and long duration species that include trees and woody perennials. Species average values from the current study are also presented at each of three temperature points. Variation among tree species in terms of photorespiration rates may be related to other aspects of life-history. For example, photosynthetic capacity has been shown to vary systematically across successional stages: early-successional species tend to exhibit higher net photosynthesis and Rubisco carboxylation rates, prioritizing rapid carbon acquisition, whereas late-successional species adopt more conservative metabolic strategies ( Zhang et al ., 2018 ; Ziegler et al ., 2020 ). Thermal responses also differ markedly, with early-successional trees maintaining stable performance under warming while late-successional species tend to show greater heat vulnerability ( Mujawamariya et al ., 2023 ). Given the critical role of photorespiration in thermal protection, it remains unclear whether species with higher photosynthetic rates also exhibit proportionally higher photorespiration or if these processes are decoupled, particularly under thermal stress. Photosynthesis and photorespiration are closely linked, as both are co-regulated and catalysed by Rubisco ( Bauwe et al ., 2012 ; Timm et al ., 2016 ). Photorespiration also protects plants by dissipating excess energy and minimizing photodamage, meaning species with higher photosynthetic capacities often exhibit higher rates of photorespiration ( Kozaki & Takeba, 1996 ; Busch et al ., 2018 ). The coupling between photosynthesis and photorespiration is, however, temperature dependent. As leaf temperature rises, CO 2 solubility decreases, favouring Rubisco oxygenation and thus increasing photorespiration relative to photosynthesis. Photosynthetic rates increase with temperature up to an optimum, then decline due to reduced Rubisco activation and higher susceptibility to photodamage ( Yamori et al ., 2014 ). In contrast, photorespiration generally continues to rise as temperatures increase ( Sharkey, 1988 ; Schuster & Monson, 1990 ; Busch & Sage, 2017 ). As a result, at supra-optimal temperatures, the sharp decline in net photosynthesis is largely due to accelerated photorespiration and impaired carboxylation, which may weaken the A net – R p relationship observed at moderate temperatures ( Sharkey, 2005 ). Beyond Rubisco kinetics, heat stress introduces several factors that may disrupt the coupling between photosynthesis and photorespiration. At temperatures above ∼42ϑ°C, PSII reaction centre proteins rapidly dephosphorylate and destabilize, reducing electron transport and increasing photoinhibition ( Rokka et al ., 2000 ; Salvucci & Crafts-Brandner, 2004 ). Stomatal conductance may remain high or even rise under heat to enhance transpiration cooling, yet net photosynthesis often declines due to biochemical limitations, resulting in a decoupling between stomatal behaviour and carbon assimilation ( Marchin et al ., 2023 ; Diao et al ., 2024 ). Additionally, heat-driven reactive oxygen species production activates antioxidant defences that preferentially support photorespiratory pathways ( Kuppusamy et al ., 2023 ). Consequently, under higher temperatures, the shifting metabolic and energetic costs of photosynthesis and photorespiration is likely affecting their relative rates. In this study, we measured photorespiration among a diverse set of temperate tree species, including variation across three temperature points. Given the short growing seasons and long daylight hours typical of northern temperate regions, photorespiration likely plays a key role in photoprotection and thermal regulation functions that are increasingly important as air temperatures rise and extreme heat events become more frequent ( Walker et al ., 2016 ; Perkins-Kirkpatrick & Lewis, 2020 ). We selected a set of seven widely distributed broadleaf tree species from the northern temperate region and conducted in situ measurements of R p and A net at three leaf temperatures: 25°C (typical summer conditions in the study area), 30°C (occasional summer highs), and 35°C (heat wave conditions, which are now increasingly common in the study area). We addressed the following questions: How do photorespiration rates vary across a set of temperate tree species? How do photorespiration rates vary with temperature? How does the correlation between photosynthetic CO 2 assimilation rates and photorespiratory CO 2 release rates vary with temperature? Based on existing studies, we hypothesized that photosynthesis and photorespiration rates would generally increase with temperature due to the temperature sensitivity of Rubisco oxygenation activity. Additionally, we hypothesized that photosynthesis and photorespiration rates would exhibit a positive correlation at moderate temperatures, but this relationship would weaken at elevated leaf temperatures due to differential physiological sensitivities and stress responses. Alternatively, it is possible that a positive correlation between photosynthesis and photorespiration could be maintained ( Walker et al ., 2017 ; Tomeo & Rosenthal, 2018 ) as was observed in Arabidopsis ecotypes or even strengthened at higher temperatures. Materials and Methods Study site We conducted this study during the summer of 2024 (June–August) in Stadsskogen nature reserve, Uppsala, Sweden (59.842563N, 17.621133E; 40 m a.s.l.). The site experiences a temperate continental climate, with an average annual temperature of approximately 7 °C and average annual precipitation of 576 mm. During the study period, daytime temperatures (8-17h) ranged from 4.2 °C to 33.3 °C, with a mean of 20.1 °C. Notably, the area holds the Swedish record for the highest observed summer temperature, reaching 38 °C in nearby Ultuna. Study species Measurements were conducted on seven common broadleaf tree species: silver birch ( Betula pendula Roth.), downy birch ( Betula pubescens Ehrh.) European beech ( Fagus sylvatica L.), Swedish whitebeam ( Scandosorbus intermedia (Ehrh.) Sennikov), Norway maple ( Acer platanoides L.), small-leaved linden ( Tilia cordata Mill.) and common hazel ( Corylus avellana L.). The study species encompass a large portion of the common non-conifer trees found in the deciduous forests of Sweden and most are common across Europe ( Rydin et al ., 1999 ). The study area represents the northern range edge of F. sylvatica, S. intermedia , A. platanoides , T. cordata , and C. avellana , whereas it represents a more central part of the geographic distribution for the B. pendula and B. pubescens ( de Rigo et al ., 2016 ). The seven study species represent a range of life-histories, with distinct resource acquisition strategies and successional associations. B. pendula is an early successional species with an acquisitive resource strategy characterized by high photosynthetic rates under high light conditions and rapid biomass growth rates ( Õunapuu-Pikas et al ., 2025 ). Five species, B. pubescens , A. platanoides , T. cordata , C. avellana and S. intermedia are more typically associated with mid-successional stages, exhibiting intermediate shade tolerance and demonstrating flexible resource strategies that allow rapid response to canopy gaps while maintaining modest performance under moderate shade conditions ( Hagemeier & Leuschner, 2019a ). F. sylvatica represents a typical late-successional species with conservative resource strategies, featuring shade-tolerance mechanisms including high specific leaf area plasticity, efficient light capture at photon flux densities as low as 1-3% of full sunlight, and high competitive ability through efficient shade production that reduces understory light availability ( Desotgiu et al ., 2012 ; Hagemeier & Leuschner, 2019b ; Leuschner & Hagemeier, 2020 ). Gas exchange measurements We measured light-saturated photosynthetic CO₂ assimilation rate ( A net ) using a Li-6800 infrared gas analyser (IRGA) with a Li-6800-01A leaf chamber (Li-Cor, Lincoln, Nebraska). Leaf environmental conditions included a CO 2 concentration of 420 μ mol mol −1 , 50% relative humidity, and an irradiance of 1500 μ mol m −2 s −1 . Steady-state measurements were conducted on three different fully mature healthy leaves from the canopy strata for at least 5 individual trees per species. We made measurements at three leaf temperatures: 25°C (typical summer conditions in Uppsala), 30°C (occasional summer highs), and 35°C (heat wave conditions, now increasingly common in the region) ( SMHI, 2024 ) (See Supplementary Section 2). Measurements were taken between 10:00 and 16:00. For each leaf, A net was first measured under ambient O 2 conditions (21% O 2 ) to record photosynthesis rate including photorespiration ( A net, ambient ) and then in an O 2 -free environment to record photorespiration inhibited A net ( A net, N2 ). The difference in A net recorded in the two different O 2 conditions ( A net , N2 – A net, ambient ) was corrected for CO 2 release to calculate photorespiration rates. To achieve an O 2 -free environment, we used nitrogen gas (99.8% purity; O 2 <0.01% from Air Liquide) as IRGA input at a flow rate of ∼1.6 L min −1 . We exposed leaves to the O 2 -free conditions for 1–5 minutes prior to measurements such that O 2 in the leaf was completely flushed out, thereby inhibiting photorespiration. Upon reaching a steady state, we recorded A net under non-photorespiratory conditions as A net , N2 . Before the next measurement, we flushed the chamber with ambient air and allowed the CO 2 flux from the leaf to stabilise under the desired conditions. Photorespiration rate calculations We calculated photorespiratory CO 2 release ( R p ) by comparing CO 2 assimilation rates under photorespiration-inhibiting nitrogen ( A net, N2 ) and ambient ( A net, ambient ) conditions, adjusted for CO 2 release: Here, λ (CO 2 released per oxygenation reaction) is assumed fixed at 0.5 ( Hanson & Peterson, 1985 , 1986 ). However, λ varies depending on whether additional CO 2 during photorespiration is released via glycine (below 0.5) or methylene tetrahydrofolate CH 2 -THF (above 0.5) pathways ( Busch, 2020 ; Kleczkowski & Igamberdiev, 2024 ). Furthermore, λ increases with temperature based on studies of tobacco, wheat, and soybean ( Walker et al ., 2017 ). For our measurement, we make three assumptions. First, we assume the specific CO 2 release pathway across species to be similar and constant. Second, we assume mitochondrial respiration to be similar under the ambient and nitrogen environments ( Brooks & Farquhar, 1985 ; Villar et al ., 1995 ; Yin & Amthor, 2024 ). Third, that and the temperature function of λ from Walker et al., (2017) applies to tree species. We use the following temperature function for λ from Walker et al., (2017) ( Equation 2 ) We applied this temperature function to derive the final R p values. To facilitate comparison of our results of photorespiration rates with the literature, we also calculated the ratio of photorespiration to net photosynthesis, denoted as Φ (phi), where Φ = R p / A net . For this comparison, we compiled studies that performed leaf-level measurements and included appropriate methodological corrections (See Box 1). Under a nitrogen (N 2 ) atmosphere, where external oxygen is absent, the light reactions of photosynthesis still generate O 2 locally within the leaf through water splitting at PSII under saturating irradiance ( Braun, 2020 ). This internally produced O 2 allows Rubisco oxygenation and consequently photorespiration to persist even in nominally anoxic conditions. To minimize exogenous O 2 availability and thereby suppress photorespiration, a 0% N 2 environment is preferable to one containing 1–2% O 2 , since higher O 2 concentrations would increase oxygenation reaction rates and reduce measurement accuracy. However, this approach cannot eliminate photorespiration because O 2 , which is continuously generated by the light reaction, sustains residual oxygenation at the site of Rubisco. The occurrence of photorespiration under nominally anoxic conditions is well-documented in photosynthetic microorganisms, where microoxic zones enable O 2 -dependent pathways to function even under overall anoxic conditions ( Holert et al ., 2011 ; Milrad et al ., 2023 ), demonstrating that this phenomenon is not unique to vascular plant leaves. Two critical limitations remain unresolved by this methodology. First, we cannot quantify whether, or to what extent, mitochondrial respiration is suppressed under low (1–2%) or zero O 2 conditions in vivo . If mitochondrial suppression occurs, it could alter electron flow and carbon allocation, confounding photorespiration estimates. Second, because O 2 is continuously generated internally via the light reactions even under N 2 , our measured photorespiration rates likely underestimate actual in vivo photorespiration. This underestimation stems from incomplete suppression of Rubisco oxygenation at the subcellular level, compounded by the complexity of photorespiratory CO 2 release through multiple metabolic pathways—particularly the variable contribution of glycerate metabolism via glycerate kinase and differential CO 2 release via glycine versus methylene tetrahydrofolate pathways ( Kleczkowski & Igamberdiev, 2024 ). Despite these limitations, the 0% N 2 method is a reliable approach for estimating the oxygenation component of Rubisco activity under our measurement conditions. Data analysis To address the first two research questions–examining the variation of R p across species and temperature–we used ANOVA models, including species, temperature, and their interaction as fixed effects. Replicates (individual trees) were also included as fixed effects to account for systematic differences among replicates (Supplementary Section 3). Pearson correlation coefficient was calculated for the A net – R p relationship, separately for the three temperature points (Supplementary Section 4). To visualise the slope of the A net ∝ R p relationship, linear models were fitted to assess the temperature responses of both A net and R p (Supplementary Section 5). For the third question on the relationship between A net and R p , we computed the Pearson correlation coefficient combining all species data for each temperature point. All analyses were conducted using R version 4.5.1 ( R Core Team, 2025 ). Results Rates of photosynthesis, A net , significantly varied across species ( F =17.7, p <0.001), with values ranging between 5.8–17.2 μ mol CO 2 m −2 s −1 (pooling across temperatures). B. pendula had the highest observed mean value for A net (17.2 ± 1.30 μ mol CO 2 m −2 s −1 at 25 °C) whereas C. avellana had the lowest (5.82 ± 0.57μ mol CO 2 m −2 s −1 at 35 °C) ( Figure 1 , top row). Across species, the effect of temperature on A net was not significant ( F =0.01, p =0.93) (Supplementary Section 6). Download figure Open in new tab Figure 1: Temperature-dependent variations in photosynthetic CO 2 assimilation (A net ), photorespiration (R p ) rates, and their ratio (Φ = R p /A net ) across seven temperate broadleaf tree species during peak summer conditions measured in situ in Uppsala, Sweden. Measurements were taken under saturating irradiance of 1,500 μ mol m −2 s −1 , ambient CO 2 concentration (420 μ mol mol −1 ) and 50–60% RH. Dark horizontal lines represent medians across at least 5 individual trees, box edges show first and third quartiles, whiskers show minima and maxima, and points are outliers. p-values indicate significance of linear temperature responses – regression lines shown where significant. Note that data for S. intermedia at 25°C is missing due to problems during measurement. (See Supplementary Sections 6 and 7). Letter annotations indicate statistical significant differences between means of temperature points within species. Letters are omitted when there was no significant trend with temperature Photorespiration rates ( R p ) showed significant variation among species ( F =5.34, p <0.001) and temperature treatments ( F =37.14, p <.001) ( Figure 1 , middle row). Across the three temperature points measured, R p values ranged from 3.3–12.9 μ mol CO 2 m −2 s −1 . F. sylvatica had the highest species-mean value for R p (12.9 ± 1.3 μ mol CO 2 m −2 s −1 at 35 °C) and the lowest value was measured for A. platanoides (3.3 ± 0.48 μ mol CO 2 m −2 s −1 at 25 °C). The interaction of species and temperature was also significant ( F = 4.2, p <0.001), indicating that the temperature response of R p differed among species. In general, the rates of photorespiration tended to increase with temperature but the temperature response of R p was species-specific. Four species showed significant increase in R p with leaf temperature namely F. sylvatica , B. pendula, A. platanoides , and T cordata. While F. sylvatica recorded an increase in R p of 9.0 μ mol CO 2 m −2 s −1 between 25°C and 35°C, T cordata recorded lowest yet significant increase of 2.4 μ mol CO 2 m −2 s −1 . For B. pubescens and C. avellana, R p did not significantly vary across the temperature treatments (Supplementary Section 6). The ratio of R p and A net (Φ) ranged from 0.35 to 1.16 (median of 0.7). In most species, Φ increased with temperature, often exceeding 1.0 at 35°C (e.g., A. platanoides, C. avellana, and F. sylvatica). In B. pubsescens and T cordata, Φ did not vary significantly with temperature. Pooling all species, the increase in Φ increase from 0.52 to 0.926 between 25 – 35°C with a slope of 0.038 ± 0.006 per °C and an intercept of – 0.4 ± 0.19 (adjusted R 2 = 0.21, p<0.001) ( Figure 1 , Bottom Row; Supplementary Section 7). A net and R p tended to be positively correlated, but the strength of this relationship was temperature dependent. At 25°C, the correlation between R p and A net was weak and not statistically significant (Pearson’s R=0.18, p=0.34). However, at higher temperatures (30°C and 35°C), the correlation was strong and statistically significant (30°C: R=0.70, p<.001; 35°C: R=0.69, p<.001), indicating that photosynthetic rates were more strongly associated with higher photorespiratory rates at elevated temperatures ( Figure 2 ). Download figure Open in new tab Figure 2. Relationship between photosynthesis and photorespiration rates at leaf temperatures of 25, 30, and 35°C under saturating irradiance for seven tree species in Uppsala, Sweden. Points represent species means ± SE. Data for S. intermedia at 25°C are absent due to measurement error. For each panel, Pearson’s correlation coefficient (R) quantifies the relationship. Linear regression lines with confidence intervals depict the direction and strength of associations (Supplementary Sections 4 and 5). Discussion Our study reveals previously uncharacterized diversity in leaf-level in situ photorespiration rates (R p ) among a set of seven temperate broadleaf tree species. Our key findings include substantial interspecific variation in R p , a general increase in R p with rising leaf temperature, and a positive correlation between net photosynthesis (A net ) and R p that strengthened at elevated temperatures, consistent with enhanced Rubisco oxygenase activity and lower CO 2 solubility under heat ( Yamori et al., 2014 ; Busch et al., 2018 ). Notably, several species exhibited divergent thermal responses, suggesting distinct Rubisco properties and metabolic strategies. Photorespiration rates vary across temperate trees species Our results demonstrate previously underrecognized interspecific diversity in photorespiratory metabolism among temperate trees. This variation directly challenges the current practice of parameterizing vegetation models with uniform, crop-derived photorespiration values and suggests that species-specific constraints on Rubisco oxygenation may represent a critical source of functional diversity in forest photosynthetic capacity ( Bernacchi et al ., 2001 ; Archontoulis et al ., 2012 ; Han et al ., 2020 ; Walker et al ., 2021 ). Photosynthesis and photorespiration rates among the study species were largely consistent with predictions based on the successional associations documented in the literature ( Hagemeier & Leuschner, 2019b ; Leuschner & Hagemeier, 2020 ). In particular, rates were mostly higher for acquisitive, early successional species and lower for mid- and late-successional species. However, F. sylvatica – a shade-tolerant, late-successional species – exhibited photorespiration rates comparable to the early-successional B. pendula , particularly under heat stress. This deviation suggests that photorespiration is influenced by factors beyond successional status and hints at underlying functional diversity in Rubisco properties among species. We speculate that genetically determined variation in Rubisco’s relative affinity for carboxylation versus oxygenation may underlie these interspecific differences. Understanding how Rubisco kinetics vary phylogenetically and constrain thermal acclimation capacity could be valuable for improving predictions of species’ responses to warming. The ratio of photorespiration to photosynthesis (Φ = R p / A net ), equivalent to the ratio of rubisco oxygenation and carboxylation, provides a proxy metric for integrating photorespiration into physiology models ( Trudeau et al ., 2018 ; Fernie & Bauwe, 2020 ). At moderate temperatures, Φ values ranged from 0.35 to 0.66 (0.52 ± 0.05), comparable to the literature average for woody species (0.56 ± 0.05, Box 1). However, species-level variation was substantial, with the lowest values indicating efficient carbon assimilation and the highest reflecting greater proportional investment in photorespiration. Particularly, Φ increased markedly with temperature, reaching values exceeding unity at 35°C in three species, meaning photorespiratory CO 2 release surpassed net photosynthetic uptake under heat stress. This temperature-driven variation in Φ has direct implications for FvCB photosynthesis model, foundational to dynamic global vegetation models. The FvCB framework typically assumes fixed photorespiration parameters derived from crop data, yet our results demonstrate this fails to capture interspecific variation and strong temperature sensitivity in temperate trees. Since photorespiration parameters are among the most influential in FvCB predictions, and uncertainty propagates to errors in estimating V cmax and J max , incorporating species-specific and temperature-sensitive Φ values is essential to improve model fidelity and reduce systematic biases in projecting forest carbon dynamics under warming ( Walker et al ., 2017 ; Han et al ., 2020 ; Ye et al ., 2025b ; Lochocki & McGrath, 2025 ). Temperature sensitivity of photorespiration Temperate species tend to exhibit photosynthetic responses that remain efficient across a wide range of temperatures, reflecting physiological adaptations to variable thermal environments that allow them to maintain high photosynthetic rates over a broader temperature range ( Charles-Edwards & Charles-Edwards, 1970 ; Crous et al ., 2022 ). In our study, A net typically declined slightly or remained unchanged with increasing temperature, which may indicate that the thermal optimum was either already exceeded at 25°C or not reached at 35°C. With only three temperature points, it is not possible to precisely determine the thermal optimum. However, although not statistically significant, three species – F. sylvatica , A. platanoides , and T. cordata – displayed higher A net rates at 30ϑ°C – than at 25ϑ°C or 35ϑ°C. Nonetheless, leaves generally maintained fairly high A net rates even at 35ϑ°C. Further experiments are required to clarify the shape of these temperature response curves. In contrast to the largely invariant temperature response of A net across species, R p increased with temperature in four species, while in three species it did not change. In C. avellena , the trend of increasing R p with temperature was apparent but not statistically significant. Thus, some species showed a clear temperaturezldriven increase in photorespiration, consistent with a protective role under thermal stress conditions ( Jordan & Ogren, 1984 ; Brooks & Farquhar, 1985 ; Morales et al ., 2020 ; Ciereszko & Kuźniak, 2024 ), whereas in others the increase was weak or absent, and in B. pubescens there was no temperature effect on photorespiration. The physiological significance of this insensitivity remains unclear, but it may reflect interspecific differences in thermal stress responses, in the contribution of photorespiration to protection, or in the use of alternative protective mechanisms that are not yet understood. In our study, the average ratio of photorespiratory CO 2 release to net photosynthesis ( R p / A net ) increased from 0.52 at 25ϑ°C to 0.93 at 35ϑ°C. In vitro enzyme kinetic studies show that the oxygenation to carboxylation ratio ( V O / V C ) of Rubisco in wheat rises from 0.25 at 10ϑ°C to 0.56 at 35ϑ°C, under conditions simulating sub-atmospheric CO 2 concentrations ( Hall & Keys, 1983 ; Brooks & Farquhar, 1985 ). If the enzymatic Rubisco oxygenation rate reflects leaf-level photorespiratory flux, the temperature sensitivity (slope) of V O / V C is 0.0124ϑ°C −1 (from 0.25 to 0.56 across 10–35ϑ°C), while the increase in R p / A net observed in our measurements is steeper, at 0.038ϑ°C⁻¹ (from 0.52 to 0.93 between 25–35ϑ°C). This suggests that the leaf-level photorespiratory response to temperature may be more sensitive than indicated by isolated Rubisco enzyme kinetics. While the slope of the R p / A net varied among species studied, distinctly, the late-successional species F. sylvatica showed a pronounced increase in R p at elevated temperatures, exceeding that of mid-successional species such as T. cordata and A. platanoides . Also, B. pubescens exhibited no measurable increase in R p with temperature. Considering the role of photorespiration in thermal protection, fast-growing, acquisitive species appear to prioritize carbon acquisition rather than heat defence, whereas slow-growing, late-successional species must prioritise photorespiration and thermal tolerance to safeguard longevity ( Bazzaz, 1979 ; Slot & Winter, 2017 ; Mujawamariya et al ., 2023 ). Our measured photorespiration rates generally support this trade-off, with the notable exceptions of F. sylvatica (a late-successional species with unexpectedly high thermal response) and B. pubescens (which showed no temperature effect). Whether these divergent responses reflect differing degrees of thermal stress tolerance or genetic adaptation of Rubisco remains to be determined ( Hall & Keys, 1983 ; Kozaki & Takeba, 1996 ). Incorporating species-specific and temperature-sensitive photorespiration parameters will help refine predictions of forest carbon dynamics ( van Bodegom et al ., 2014 ; Cavanagh & Matthews, 2025 ; Lochocki & McGrath, 2025 ). Coordinated regulation of photosynthesis and photorespiration Contrary to our original expectations, we found a significant positive relationship between photosynthesis and photorespiration rates, especially at higher leaf temperatures. This coincides with a previous study on A. thaliana ecotypes grown in environmentally-controlled growth chambers ( Tomeo & Rosenthal, 2018 ). This study demonstrated a positive relationship between photosynthetic capacity (maximum rubisco carboxylation rate) and photorespiratory CO 2 efflux suggests that these two processes are physiologically coordinated, likely through common regulatory mechanisms governing carboxylation and oxygenation reactions. Although photosynthesis and photorespiration demonstrate strong phenotypic correlation through their interconnected biochemical pathways and molecular crosstalk, the absence of genetic correlation across natural variation suggests that these processes are maintained through distinct regulatory mechanisms that operate independently at the genetic level despite their tight physiological integration. The absence of genetic correlation across species, despite tight phenotypic correlation, suggests that species may have evolved independent genetic control systems for these processes that converge at the biochemical level ( Tomeo & Rosenthal, 2018 ). We found that photorespiration rates could reach near, or surpass 100% of photosynthetic rates (e.g., A. platanoides , C. avellana , and F. sylvatica) under heat wave conditions (i.e., 35°C) and that they even reached upwards of 60% under normal summer conditions (25°C). The ratio of photorespiration to photosynthesis rates being positively correlated at higher temperatures indicates that photorespiration has a vital role in controlling the flow of energy under conditions that would otherwise disrupt or inhibit photosynthesis. In other words, in stressful conditions, photorespiration may enable plants to maintain similar or higher photosynthesis rates than under normal conditions, at the cost of having a larger percentage of that photosynthesis allocated to photorespiration ( Huang et al ., 2019 ; Osei-Bonsu et al ., 2021 ). In this case, the role of photorespiration becomes clear, as it serves as a necessary sink for excess energy and removal of toxins, albeit at the cost of decreasing the overall efficiency of photosynthesis ( Ort & Baker, 2002 ; Foyer et al ., 2009 ; Hochberg et al ., 2013 ; Erel et al ., 2015 ). Our results provide evidence for a positive relationship between photorespiration and photosynthesis rates across temperature and posit that photorespiration is critical in the upkeep of photosynthesis, particularly under high temperature conditions. Conclusion We studied leaf-level photorespiration rates across seven temperate broadleaf tree species, measured in situ under ecologically relevant temperatures. The results show substantial species wide variation in photorespiration and a generally strong positive response of photorespiration to increasing leaf temperature, along with changes in the ratio of photorespiration to net photosynthesis. Although species displayed diverse thermal responses while maintaining stable photosynthesis, most showed increased photorespiration at higher temperatures, with some exceptions where photorespiration did not increase. The evidence of both strengthened coupling and occasional decoupling between photosynthesis and photorespiration under heat stress highlights complex regulatory and protective processes. These findings are important for vegetation models that largely rely on crop-based photorespiration parameters, which tend to underestimate the variation and temperature sensitivity seen in forest species. Competing interests The authors declare no conflicts of interest. Author contributions RT conceived the study, developed the methodology, carried out the analysis and led the writing of the original draft. PD and RT collected the data. RM supervised the study. All authors contributed to the writing and revision of the manuscript. Data availability Data available in article supplementary material. Acknowledgement Research was funded by grants from the Wenner-Gren Foundation (to RT and RM), the Birgitta Sintring Foundation (to RT and RM), the Swedish Phytogeographical Society (to RT and RM), the J.W Palmstruch Scholarship fund (to PD), and the Swedish Research Council, Formas (2020-00921 to RM). We thank Christoffer Bergvall, Adriana Puentes, Gustaf Granath for valuable assistance. We thank H S Shankaranarayana Bhatta, Somashekhara Achar KG for the help with Sanskrit and Kannada language version of the article. We thank Shankaranarayana Bhatta HS, Vasudeva HR, Chethan TR and Pragya Rakesh Tiwari for their help with the Sanskrit, Kannada and Hindi language versions of the manuscript. RT thanks Shāradā-Chandramaulishwara and Ubhaya Jagadgurus of the Dakshinamnāya Sri Sharadā Peetham, Sringēri for their guidance. 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Share Large differences in photorespiration and its temperature response among temperate trees Rakesh Tiwari , Philip David , Robert Muscarella bioRxiv 2025.11.22.689893; doi: https://doi.org/10.1101/2025.11.22.689893 Share This Article: Copy Citation Tools Large differences in photorespiration and its temperature response among temperate trees Rakesh Tiwari , Philip David , Robert Muscarella bioRxiv 2025.11.22.689893; doi: https://doi.org/10.1101/2025.11.22.689893 Citation Manager Formats BibTeX Bookends EasyBib EndNote (tagged) EndNote 8 (xml) Medlars Mendeley Papers RefWorks Tagged Ref Manager RIS Zotero Tweet Widget Facebook Like Google Plus One Subject Area Plant Biology Subject Areas All Articles Animal Behavior and Cognition (7629) Biochemistry (17660) Bioengineering (13881) Bioinformatics (41910) Biophysics (21436) Cancer Biology (18576) Cell Biology (25480) Clinical Trials (138) Developmental Biology (13368) Ecology (19887) Epidemiology (2067) Evolutionary Biology (24302) Genetics (15598) Genomics (22482) Immunology (17726) Microbiology (40360) Molecular Biology (17163) Neuroscience (88534) Paleontology (666) Pathology (2830) Pharmacology and Toxicology (4821) Physiology (7637) Plant Biology (15129) Scientific Communication and Education (2045) Synthetic Biology (4290) Systems Biology (9817) Zoology (2269)