Flooding during the growing season spreads Echinochloa colona seedling emergence towards summer

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Striker, María Crepy, Federico P.O. Mollard This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7158515/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Jan, 2026 Read the published version in Plant and Soil → Version 1 posted 6 You are reading this latest preprint version Abstract Background and aims Floods could promote hydrophyte weed species recruitment in cultivated lowland fields in temperate regions of the world. This study tested whether different flooding regimes change the amount and timing of Echinochloa colona seedling emergence. Methods We did a series of three annual crop-free experiments in mesocosms taken from agricultural wetlands located in the Pampas region and subjected to cultivation during dry years to test if Echinochloa colona (L.) Link. seedling emergence, aboveground biomass and seed production per area could be affected by flood regimes differing in duration and timing. Results Flooding or intermittently flooding-drawdown conditions during the growing season did not increase cumulative emergence compared to drained controls at field capacity; however, flooding affected the seedling emergence pattern by skewing emergency peaks towards mid-summer. Notably, an abundant subaquatic E. colona seedling emergence was observed in spring (≈ 2500 seedlings m − 2 ) in constantly flooded mesocosms. In the second experiment we found that even after prolonged and frequent flood pulses that decreased seedling emergency, E. colona seed production was enough to replenish the soil bank. In a third experiment we revealed that long winter floods, before the growing season, decreased total seedling cumulative emergency yet did not change the emergence pattern of seedlings. Conclusion The extended temporal window of E. colona recruitment due to flooding can complicate its field control and should be included in weed emergency models to accurately forecast E. colona seedling recruitment to advise weed control and management decisions. agricultural wetlands arable weeds flooding Junglerice seedling emergence seed soil bank Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Climate change fosters meteorological conditions suitable for frequent floods as well as drought events. Such events could change the recruitment pattern of arable weed species in extensive crops; however, while the effects of droughts and rainfall events on weed seedling emergence have been thoroughly investigated (Cordeau et al. 2018 ; Singh et al. 2022 ), the effects of floods on weed seedling recruitment have rarely been evaluated (Forcella et al. 2000 ; Ismail et al. 2012 ). Flooding can affect all processes related to seedling emergence and establishment: seed dormancy, germination and seedling pre-emergence growth (Mollard et al. 2007 ; Ismail et al. 2012 ; Echeverry Holguín et al. 2020 ) thus challenging the predictive power of weed seedling emergence models in flood-prone crop fields. Wetlands and poor drainage fields have been put into cultivation in recent years on a global scale (Verhoeven and Setter 2010 ; Fluet-Chouinard et al. 2023 ). Moreover, opportunistic cultivation of lowlands and flood-prone fields leaves non-vegetated areas free to weed colonization and encroachment, particularly once crops have been damaged by floods (Hall et al. 1992 ; Ghersa et al. 2007 ). On the other hand, very few as well as geographically limited studies have been focused on the effect of flood frequency and timing on wetlands plant performance and demography (Webb et al. 2012 ; Rosbakh et al. 2020 ) making it even more difficult to predict if floods can affect weeds seedling emergence or establishment as well as their reproductive output. Echinochloa colona (L.) Link. is an annual C 4 summer grass, native to tropical and subtropical Asia that can severely reduce crop grain yield (Chauhan and Johnson 2010 ; Peerzada et al. 2016 ; Mahajan and Chauhan 2022 ). E. colona is a spring-summer-emerging weed species; however, it has a wide field emergence window in tropical, subtropical and temperate zones (Leguizamón et al. 2009 ; Chauhan 2022 ). Management options for the control of E. colona in different cropping systems are currently limited and further challenged by the emergence of herbicide-resistant biotypes (Peerzada et al. 2016 ; Godar and Norsworthy 2023 ). Moreover, E. colona is expanding its seasonality (Chauhan 2022 ), and an extended emergence period complicates effective weed control (Lutman et al. 1994 ; Brown et al. 2022 ). Therefore, it is crucial to investigate whether flooding regimes may shorten or prolong the window of opportunity for E. colona seedling emergence and establishment. Echinochloa colona has a precocious and plastic reproductive strategy which allows it to produce seeds even in short growing seasons (Hegazy et al. 2005 ) or under water stress (Chauhan and Johnson 2010 ; Mahajan et al. 2019 ). E. colona is a prolific weed able to produce more than 100000 seeds per plant (Chauhan 2022 ) and it can also form persistent soil seedbanks (Peerzada et al. 2016 ). The effects of floods on the reproductive output of extensive crop weeds have not been studied; however, it is expected that E. colona fecundity is changed by flooding events thus potentially affecting its seed rain. The following hypotheses were addressed in this research: 1) Flooding during the growing season significantly increases the number of Echinochloa colona emerged seedlings and modifies the seasonal pattern of emergence, 2) Different flood regimes significantly affect aboveground biomass and seed production of established Echinochloa colona plants, and 3) The duration of winter flooding (short or long) significantly affects Echinochloa colona seedling emergence patterns. Mesocosms have been used to study plant responses to flooding in semi-controlled conditions (Li et al. 2023 ; Yang et al. 2024 ). We used that methodology to address the above-mentioned hypotheses; then, we extracted mesocosms from a crop field subjected to extensive dryland agriculture and, in a series of three experiments, exposed them to different flooding regimes with contrasting duration, frequency and timing. In this contribution we present data from a crop-free series of experiments in where it is mimicked that the crop has been damaged by floods thus creating gaps in the canopy or fields have been left uncultivated because of soil saturation. Materials and Methods Along three years we did a series of crop-free mesocosms experiments to test if Echinochloa colona (L.) Link. seedling emergence patterns, plant aboveground biomass and seed production were changed by floods. Mesocosms were obtained from a seasonal wetland situated in a cropfield located in the cropping region of Buenos Aires province, Argentina (35°33’S, 58°58’W) in the limit of Rolling and Flooding Pampas vegetation units (Soriano 1991 ). The area has a mean annual precipitation of 911 mm (isohydric regime), characterized by significant interannual variation due to ENSO oscillations. The agricultural wetlands, perched on hydromorphic soils, experience seasonal floods during winter in most years, including early spring during El Niño events as well as temporary waterlogging during heavy rains. During La Niña events, the same agricultural wetlands are successfully cultivated. The average monthly temperature ranges from 23ºC in January (summer in the Southern Hemisphere) to 9.1ºC in July (winter). The soils are poorly drained and characterized by a high clay content (28.2% particles < 2 µm) in the surface layer (0–20 cm), with 5.2% organic matter and a pH of 5.9. The cropping system consists of no-till farming with the following crop rotation: sunflower/wheat-soybean/maize. In those wetlands we selected sites for mesocosms extraction where E. colona was the dominant species with plant cover higher than 80%. The accompanying species were: Setaria parviflora (Poir.) Kerguélen, Alternanthera philoxeroides (Mart.) Griseb., and Digitaria sanguinalis (L.) Scop. We assumed that the treatments would be strong enough to override differences in E. colona seed abundance across soil patches. Mesocosms of 30 x 30 cm (15 cm depth) were carefully dig out in winter, placed into plastic containers, and immediately transported to the experimental garden at Faculty of Agronomy, University of Buenos Aires (150 km NE from the source crop site, 34°35′37″S 58°29′03″W). Flooding treatments simulated hydrologic regimes that can happen along different topographic positions on contrasted dry or wet years. Mesocosms were assigned to flooding treatments in a randomized block design; blocks consisted of three parallel rectangular pools (2.4 m x 1.55 m x 40 cm depth). Water level was maintained between 10 to 15 cm above mesocosms soil surface. Drained (control) mesocosms were placed above water surface and irrigated every two days. The emerged E. colona seedlings were marked with plastic toothpicks and recorded twice a week. Seedlings other than E. colona were removed. At the end of the growing season and before seed dispersal, ten representative complete panicles were chosen from every mesocosm (replicate), and the number of seeds on each panicle was tallied. The mean seed number per panicle was computed and then multiplied by the overall number of panicles to assess the seed production per area. Afterwards, E. colona plants were harvested and subjected to oven drying at 80ºC for a minimum of 72 hours and the aboveground plant dry biomass was determined. Oxidation-Reduction Potential (ORP) values in the flooded treatments were registered in the soil-water interface (year 1) and in perforated 50 ml Falcon tubes inserted in the flooded soil (years 2 and 3) as a proxy to identify anaerobiosis (Pezeshki, 2001 ) with a HI98121 (Hanna Instruments, Woonsocket, USA). Experiment 1 This experiment was carried out to test if flooding during the growing season significantly modifies the seasonal pattern of Echinochloa colona seedling emergence. Mesocosms were carefully dig out at the end of winter (August 21, 2019) and immediately transported to the experimental garden at Faculty of Agronomy and placed into the above-mentioned inundation pools. Mesocosms were rotated in the pools. Flood treatments started September 1st (late winter). Mesocosms were maintained flooded to a water level of 10–15 cm and groups of seven mesocosms (replicates) were monthly drained from October 1st (early spring) to February 1st (midsummer). Thus, the experiment design counted with five monthly flood-drainage treatments plus one control treatment (constant drained and irrigated every two days). Experiment 2 This experiment was carried out to test if intermittently pulsed flooding events can promote E. colona seedling emergence over that produced under well-watered drained conditions. One round of floods per month were applied from August 1st to December 1st, time when all mesocosms were drained so a total of four rounds of floods were applied in the below-mentioned treatments i and ii. Mesocosms were dig out on July 16th and carried to the experimental garden. The experiment consisted in three treatments: i) mesocosm were flooded from the first to the tenth day of the month and then drained and irrigated every two days until next month (10-d flood mo − 1 ), ii) mesocosms were flooded from the first to the twentieth day of the month and then drained and irrigated every two days until next month (20-d flood mo − 1 ), iii) drained mesocosms were irrigated every two days (control treatment). In this experiment, we included two types of mesocosms: with and without E. colona seedling removal. By removing all emerged E. colona seedlings, we created a permanent vacant niche for new seedlings to emerge from the soil seedbank. Both types of mesocosms were analysed independently, each with six replicates. Finally, at the end of the experiment, three soil core samples were taken from the seed soil bank of each replicate using an auger to study the size of the remaining soil bank in those mesocosms where all seedlings were removed. The seed soil bank was averaged from three homogenized and sieved soil samples per mesocosm (i.e. replicate). On December 22, 2021, the photosynthetic photon flux density (PPFD, 400–700 nm) was measured with a Li-118B radiometer (Li-Cor Inc., Lincoln, NE, USA) to study the irradiance reaching the soil under the canopy produced by E. colona established plants in the mesocosms where seedlings were not removed. The Red to Far-Red ratio of light (R:FR) was measured with a Skye SDL 2520 sensor (Skye Instruments Ltd., Llandridrod Wells, UK). The measurements of solar radiation were carried out at midday on a sunny day and with the sensor resting vertically on the soil surface. Experiment 3 This experiment was executed to test if floods during winter affect the emergency pattern of E. colona seedlings during spring. We seized the opportunity of a consecutive series of dry years in the Pampas (La Niña event) that happened from 2019 to 2022 in where agricultural wetlands remained drained most of the year. On May 1st (late autumn), mesocosms were carefully dig out and taken to the experimental garden. The experiment consisted in five treatments: i) a long flood from mid-May to mid-September ii) a flood event from June 1st to September 1st, iii) a flood event from mid-June to mid-August, iv) a short flood during the entire July and v) no flood (mesocosms drained and watered to field capacity). Mesocosms were watered every two days after draining. Each treatment included six replicates, which were randomly assigned to one of three inundation pools. Statistical analysis Cumulative seedling emergence was evaluated by repeated measures analysis of variance (rmANOVA). Significance of the interaction of treatment × time were determined through Wilks’ Lambda multivariate tests. Aboveground dry biomass and seed production per square meter were analysed through one-way ANOVAs. Normality and homogeneity of variances were verified before each analysis. ANOVAs were followed by post hoc Tukey tests with α = 0.05. All statistical analyses were conducted using STATISTICA version 10 (StatSoft Inc. Tulsa, OK). All results are presented as untransformed means of replicates ± standard error. Results Experiment 1: effects of floods during the growing season on E. colona seedling emergence, aboveground biomass and seed production The repeated-measures ANOVA (rmANOVA) of cumulative E. colona seedling emergence revealed a significant interaction between time and flooding regime (p < 0.0001; Fig. 1 a). In well-watered, constantly drained mesocosms, seedling emergence followed an early-season distribution (Fig. 1 b). In contrast, simulated flooding not only delayed the initial spring emergence peak by approximately two weeks but also shifted the emergence distribution toward later dates in the growing season (Fig. 1 b). A pronounced emergence peak occurred in all treatments during the first week of November (mid-spring; Fig. 1 b). In the control and early drained treatments (drainage in October or November), emergence ceased by December (Fig. 1 a,b). In contrast, the longest flooding treatments (drained in December, January, or February) exhibited a bimodal emergence pattern: an initial emergence phase occurred underwater (representing approximately 50% of total emergent seedlings), followed by a notable gap and then a delayed midsummer emergence peak after drainage (Fig. 1 a,b). Mesocosms flooded during the early growing season acquired higher E. colona aboveground dry biomass than continuously drained (control) mesocosms (p 0.05; Fig. 2 a). Flooding regimes did not significantly change E. colona seed production per area (p > 0.05; Fig. 2 b); however, the longer the floods during the growing season the higher the variability shown within treatments in seed production (Fig. 2 b). Mesocosms ORP values in the soil-water interface indicated that oxygen was lost after one month of flooding (ORP < < 100 mV) and reduction progressed towards negative values during spring (Fig. S1). Experiment 2: effects of intermittently pulsed floods during the growing season on E. colona seedling emergence, aboveground biomass and seed production In the experiment carried out during the second year, the rmANOVA of cumulative seedling emergence revealed a significant time x flooding regimes interaction (p < 0.0001, Fig. 3 a). A bimodal E. colona seedling emergence distribution was observed in the constantly drained, well-watered mesocosms where seedlings were not eliminated (Fig. 3 b). Interestingly, a second and discrete main emergence peak was noticeable during November in all treatments. Intermittent flooding pulses during 10 days per month (10-d flood mo − 1 ) did not change the overall pattern of seedling emergence compared to the drained condition (Fig. 3 b). Irradiance data indicated that the soil was shaded in December in both the drained and 10-d flood mo − 1 treatment (Fig. S2), coinciding with the cessation of seedling emergence in these treatments (Fig. 3 a,b). In contrast, intermittent flooding pulses lasting 20 days per month (20-d flood mo − 1 ) resulted in a multimodal emergence pattern, with seedling emergence events extending into late summer (February) (Fig. 3 b). Intermittently pulsed flooding regimes did not change aboveground dry biomass production nor seed production per square meter (Fig. 4 a,b). The removal of emerged E. colona seedlings allowed the occurrence of additional cohorts in both constantly drained and 10-d flood mo − 1 (Fig. 3 c,d). Moreover, the mesocosms where E. colona seedlings were removed allowed us to study the potential depletion of the soil seedbank during the treatments without seed additions caused by accidental seed rain (Fig. 4 c). Notably, at the end of the growing season, the final seed bank was four times larger than total emergence in the drained and 10-d flood mo − 1 treatments, and eight times larger than in the 20-d flood mo − 1 treatment (Fig. 4 c). ORP values indicated that anaerobiosis was noticeable both in the 10-d flood mo − 1 and the 20-d flood mo − 1 treatments at the end of spring (Fig. S3) Experiment 3: effects of winter floods on E. colona seedling emergence, aboveground biomass production and fecundity The rmANOVA of cumulative E. colona seedling emergence revealed a significant time x flooding regime interaction (p < 0.0001; Fig. 5 ). Most of the winter flooding regimes and the drained mesocosms brought about similar step-wise cumulative emergence patterns during the growing season excepting the longest (i.e. 4 months) flooding regime that had the poorest total seedling emergence (Fig. 5 b). Aboveground dry biomass was significantly higher in those winter flooding regimes subjected to the largest floods than in the drained mesocosms (p < 0.05; Fig. 6 a). Seed production per area was higher and more variable in the treatment flooded for a longer period in winter (flooded 4 months) than in the drained control (p < 0.05; Fig. 6 b). ORP values in the soil water showed strong reduction potential and anaerobiosis in the long-lasting winter flooding treatments (Fig. S4) Discussion In this research, we tested through a crop-free experiment whether different flood regimes -both before and during the growing season- facilitate or inhibit Echinochloa colona encroachment by evaluating seedling emergence from the soil seed bank, as well as biomass accumulation and seed production of the established plants. We found scarce evidence for the promotion or inhibition of E. colona by diverse flood treatments compared to drained, well-watered conditions; however, we found that floods change the seedling emergence pattern, an effect that could challenge weed management practices. The effects of flooding regimes on E. colona seedling emergence timing Primarily, our results for the first-year experiment show that even relatively short periods (1 month) of continuous flooding at the beginning of the growing season delayed E. colona seedling emergence. Moreover, flooding increased the asymmetry of emergence as a second emergence peak was observed in mesocosms drained during late spring or summer. For some weeds with protracted emergence, multiple weed seedling emergence peaks are common during part of the growing season, mainly related to precipitation events after drought periods (Brown et al. 2022 ) giving rise to multiphasic cumulative emergence curves. Here, we show that late emergence peaks may result from drawdown periods following flooding events, particularly in the lowest topographic areas of lowland crop fields, where prolonged flooding can persist throughout the growing season in rainy years. Unexpectedly, those mesoscosms drained either in January or February (summer) had produced copious E. colona subaquatic emergence in November (mid-spring): around 2500 seedling per square meter. Laboratory experiments predicted that E. colona seeds from the same accession can be induced to geminate when submerged under hypoxic conditions (Echeverry Holguín et al. 2024 ). Underwater germination of weeds such as E. crus-galli and weedy rice is common in paddy-fields (Ismail et al. 2012 ) yet it is not expected to occur in lowland temperate agroecosystems where rice has not been introduced so far due to short growing seasons. While flooding stress may negatively affect seedling emergence and establishment, a following drawdown period that leaves soil in optimal moisture conditions may successfully help emergence of wetland species (Casanova and Brock 2000 ). So, we hypothesized that intermittent pulsed flooding regimes -mimicked during the second-year experiment- would promote further seedling emergence of a facultative wetland weed such as E. colona . That did not happen as the 10-d flood periods per month (10-d flood mo − 1 ) did not increase emergence over the drained well-watered control treatment. Moreover, 20-d flood periods per month decreased total cumulative seedling emergence and produced two late emergence peaks in summer. In crops, successful weed recruitment must occur within a few weeks before crop canopy closure (Ghersa and Holt 1995 ; Brown et al. 2022 ). However, already closed canopies may reopen during flooding in flood-susceptible crops such as rapeseed and pulses due to extensive leaf senescence (Ploschuk et al. 2020 ); such canopy openings may potentially cause further emergence late in the season (Brown et al. 2022 ). The second-year seedling removal experiment revealed that the absence of summer emergence peaks observed in the non-removal experiment for both the drained control and the 10-d flood mo − 1 flooding treatment was due to environmental changes (e.g., light intensity and quality) imposed by early-established E. colona plants. Thus, the 20-d flood mo − 1 treatment, by decreasing cumulative seedling emergence, inhibited competitive exclusion by early E. colona recruiters upon late cohorts. In dry years, episodes of warm season weed recruitment may not coincide with floods because E. colona seedling emergence occurs in spring and floods during winter, season where summer weeds accumulate seeds in the soil bank (Cavers and Benoit 1989 ). However, seeds in the soil bank may be subjected to changes in dormancy level due to flooding (Mollard et al. 2007 ; Peralta Ogorek et al. 2019 ). As dormancy is the most important component of emergency periodicity from soil seedbanks (Grundy 2003 ), we hypothesized that flooding during winter would change the E. colona seedling emergence pattern early in the season. Winter flooding treatments did not alter the seasonal pattern of emergence; however, the longest winter flooding—ending just before the onset of the recruitment season—markedly reduced the seedling emergence rate of E. colona . This inhibition may result from either the induction of secondary dormancy or seed decay. Although these mechanisms differ, both have important and contrasting implications for weed management. Therefore, further research and modelling are needed, as soil seed bank depletion is a key objective in weed management (Gallandt 2006 ; Schwartz-Lazaro and Copes 2019 ). The effects of flooding regimes on E. colona aboveground dry biomass Spring E. colona cohorts produce the highest aboveground plant biomass while autumn cohorts produce lower biomass and the lowest number of leaves and tillers compared to spring emergents (Chauhan 2022 ). On the other hand, prolific weed seedling emergence early in the season can cause an important intraspecific competition, which can affect individual plant growth rates (Mohler 1996 ). Our first-year results revealed a trade-off between density-dependent competition among early-emerging seedlings in the drained treatments and the constraints imposed by a shortened growing season on cohorts emerging later in summer. Consequently, the treatments drained in mid-spring exhibited the highest aboveground dry biomass. In the second year, light irradiance and quality data suggested that the early-recruiters from the drained and 10-d flood mo − 1 were competing for light during summer so the less abundant plants in the 20-d flood mo − 1 produced similar aboveground dry biomass than the afore-mentioned treatments. Strong self-thinning is expected at the levels of crowding shown in our experiments (Watkinson et al. 1983 ). Our results show that E. colona early and numerous cohorts - with a putative competitive advantage over crops (Bosnic and Swanton 1997 ; Hock et al. 2006 )- emerging in drained soils or after short flooding periods, experienced strong density-dependent effects. In contrast, treatments with longer flooding, which delayed emergence and led to later cohorts, did not exhibit penalties in aboveground dry biomass. The effects of flooding regimes on E. colona seed production Echinochloa colona plants have high fecundity and propagule pressure (Chauhan 2022 ) so we wondered whether flooding regimes could reduce total E. colona seed rain. Notably, most of the different flooding regimes did not change mean seed production per square meter across the three experiments, resulting in sufficient seed output to replenish depleted soil seed banks. Moreover, in the third experiment, which simulated floods during the fallow period, the longest flooding treatment—despite producing the fewest seedlings—resulted in higher seed production per square meter than the drained control. These results suggest the density-dependent control of fecundity in those early-drained treatments with plentiful E. colona recruiters. On the other hand, E. colona forms long viable seed banks (Walker et al. 2010 ). Seed soil bank samples collected at the end of the second-year seedling removal experiment showed that E. colona maintained a persistent seed soil bank regardless of the flooding regime. In conclusion, flooding did not reduce E. colona total seed input nor seed reserves of the soil bank. Conclusions This study shows that flooding—whether before or during the growing season—reshapes Echinochloa colona emergence dynamics in agricultural wetlands. Longer floods reduced overall emergence but delayed it into mid or late summer, extending the recruitment window beyond drained conditions and complicating early-season weed control. Despite fewer seedlings, seed production per area remained stable, likely due to reduced density-dependent competition. Thus, all flooding regimes produced enough seeds to replenish the soil bank. A persistent seed soil bank was observed regardless of flooding intensity or timing, indicating that seed soil bank depletion remains a major challenge in poorly drained fields. These findings highlight the need to incorporate hydrological variability into weed emergence models and support adaptive management approaches. Monitoring phenology and adjusting control practices to target delayed cohorts may be crucial to limiting the long-term impact of E. colona in flood-prone agroecosystems. Declarations Financial Support This work was supported by Universidad de Buenos Aires (UBACyT 20020170200034BA and 20020220400218BA) and National Scientific and Technical Research Council (CONICET) (Grant number PIP 11220150100041CO). Conflicts of Interest Authors declare no conflicts of interest. Data Availability Statement The data that supports this study will be shared upon reasonable request to the corresponding authors. Author Contribution Statement Juliana Echeverry Holguín: Conceptualization, methodology, investigation, writing—original draft, Gustavo Striker: Conceptualization, methodology, writing-review & editing, María Crepy: Resources, review & editing, Federico Mollard: Conceptualization, methodology, supervision, writing-review & editing, funding acquisition. References Bosnic AC, Swanton CJ (1997) Influence of barnyardgrass ( Echinochloa crus-galli ) time of emergence and density on corn ( Zea mays ). Weed Science 45:276–282. https://doi.org/10.1017/S0043174500092833 Brown B, Gallandt ER, DiTommaso A, Salon P (2022) Improving weed management based on the timing of emergence peaks: A case study of problematic weeds in northeast USA. Front Agron 4:Article 888664. https://doi.org/10.3389/fagro.2022.888664 Casanova MT, Brock MA (2000) How do depth, duration and frequency of flooding influence the establishment of wetland plant communities? 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AoB Plants 2012:pls019. https://doi.org/10.1093/aobpla/pls019 Leguizamón ES, Rodríguez N, Rainero H, Pérez M, Pérez L, Zorza E, Fernández-Quintanilla C (2009) Modelling the emergence pattern of six summer annual weed grasses under no tillage systems in Argentina. Weed Res 49:98–106. https://doi.org/10.1111/j.1365-3180.2008.00669.x Li YL, Ge ZM, Xie LN, et al. (2023) Effects of waterlogging and elevated salinity on the allocation of photosynthetic carbon in estuarine tidal marsh: a mesocosm experiment. Plant Soil 482:211–227. https://doi.org/10.1007/s11104-022-05687-9 Lutman PJW, Dixon FL, Risiott R (1994) The response of four spring sown combinable arable crops to weed competition. Weed Res 34:137–146. https://doi.org/10.1111/j.1365-3180.1994.tb01981.x Mahajan G, Chauhan BS (2022) Interference of junglerice ( Echinochloa colona ) in mung bean. Weed Sci 70:481–487. https://doi.org/10.1017/wsc.2022.38 Mahajan G, Mutti NK, Walsh M, Chauhan BS (2019) Effect of varied soil moisture regimes on the growth and reproduction of two Australian biotypes of junglerice ( Echinochloa colona ). Weed Sci 67:552–559. https://doi.org/10.1017/wsc.2019.32 Mohler CL (1996) Ecological bases for the cultural control of annual weeds. J Prod Agric 9:468–474. https://doi.org/10.2134/jpa1996.0468 Mollard FPO, Insausti P, Sánchez RA (2007) Flooding induces secondary dormancy in Setaria parviflora seeds. Seed Sci Res 17:55–62. https://doi.org/10.1017/S0960258506006157 Peerzada AM, Bajwa AA, Ali HH, Chauhan BS (2016) Biology, impact, and management of Echinochloa colona (L.) Link. Crop Prot 83:56–66. https://doi.org/10.1016/j.cropro.2016.04.002 Peralta Ogorek L, Striker GG, Mollard FPO (2019) Echinochloa crus-galli seed physiological dormancy and germination responses to hypoxic floodwaters. Plant Biol 21:1159–1166. https://doi.org/10.1111/plb.12993 Pezeshki SR (2001) Wetland plant responses to soil flooding. Environ Exp Bot 46:299–312. https://doi.org/10.1016/S0098-8472(01)00107-1 Ploschuk RA, Miralles DJ, Colmer TD, Striker GG (2020) Waterlogging differentially affects yield and its components in wheat, barley, rapeseed and field pea depending on the timing of occurrence. J Agron Crop Sci 206:493–505. https://doi.org/10.1111/jac.12396 Rosbakh S, Phartyal SS, Poschlod P (2020) Seed germination traits shape community assembly along a hydroperiod gradient. Ann Bot 125:67–78. https://doi.org/10.1093/aob/mcz130 Schwartz-Lazaro LM, Copes JT (2019) A review of the soil seedbank from a weed scientist’s perspective. Agronomy 9:369. https://doi.org/10.3390/agronomy9070369 Singh M, Thapa R, Kukal MS, Irmak S, Mirsky S, Jhala AJ (2022) Effect of water stress on weed germination, growth characteristics, and seed production: A global meta-analysis. Weed Sci 70:621–640. https://doi.org/10.1017/wsc.2022.51 Soriano A (1991) Río de la Plata grasslands. In: Coupland RT (ed) Natural grasslands: Introduction and Western Hemisphere . Elsevier, pp 367–407. Verhoeven JTA, Setter TL (2010) Agricultural use of wetlands: Opportunities and limitations. Ann Bot 105:155–163. https://doi.org/10.1093/aob/mcp276 Walker SR, Wu H, Bell K (2010) Emergence and seed persistence of Echinochloa colona , Urochloa panicoides and Hibiscus trionum in the subtropical environment of north-eastern Australia. Plant Prot Q 25:127–132. Watkinson AR, Lonsdale WM, Firbank LG (1983) A neighbourhood approach to self-thinning. Oecologia 56:381–384. https://doi.org/10.1007/BF00379798 Webb JA, Wallis EM, Stewardson MJ (2012) A systematic review of published evidence linking wetland plants to water regime components. Aquat Bot 103:1–14. https://doi.org/10.1016/j.aquabot.2012.06.003 Yang J, Gao Y, Zhao C, et al. (2024) Leaf phenotypic plasticity and integration balance plant adaptation to water table decline: a mesocosm experiment. Plant Soil 497:611–627. https://doi.org/10.1007/s11104-023-06418-4 Supplementary Files Supplementaryfigures.docx Cite Share Download PDF Status: Published Journal Publication published 06 Jan, 2026 Read the published version in Plant and Soil → Version 1 posted Editorial decision: Major revisions 21 Sep, 2025 Reviewers agreed at journal 01 Aug, 2025 Reviewers invited by journal 01 Aug, 2025 Editor invited by journal 21 Jul, 2025 Editor assigned by journal 21 Jul, 2025 First submitted to journal 18 Jul, 2025 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. 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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-7158515","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":494168285,"identity":"7d0417c2-de88-4544-b3fc-4c76a4ed176e","order_by":0,"name":"Juliana Echeverry Holguín","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/klEQVRIiWNgGAWjYBACxgYGNiiT+QCEliBeC1sCcVpASqE0jwFxWpjbm589+Nhmk28+I+fjx697bBgMbjc/YPi5B4/Deo6ZG85sS7OccyN3s7TMszQGgzvHDBh7nuHRMiOHTZrnzGEDCYncDdISBw4zGNxIMGDgOYBHy/w3bNJ/zvwHasl5/BuiJf0D4x98WmbwsEkzVBwAaWGT/ADWkmPAjNeWnjQzyZ6KZAMJnmdm1gwH0ngk75wpOCyDR4th++FnEj8M7Awk2JMf3/xxwEaO73b7xodv8GlpgLEEEhiYeYCxA2Lj0cDAIA9n8R9gYPyBT+koGAWjYBSMWAAA4vBTKx0HpTQAAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0008-0051-5676","institution":"University of Buenos Aires Faculty of Agronomy: Universidad de Buenos Aires Facultad de Agronomia","correspondingAuthor":true,"prefix":"","firstName":"Juliana","middleName":"Echeverry","lastName":"Holguín","suffix":""},{"id":494168286,"identity":"c1573910-50b6-489a-9a48-85b15a403df6","order_by":1,"name":"Gustavo G. Striker","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Gustavo","middleName":"G.","lastName":"Striker","suffix":""},{"id":494168287,"identity":"4448d719-3514-4e21-9842-6447dab2205b","order_by":2,"name":"María Crepy","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"María","middleName":"","lastName":"Crepy","suffix":""},{"id":494168288,"identity":"33fe09dd-4fa8-4541-8115-826416571158","order_by":3,"name":"Federico P.O. Mollard","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Federico","middleName":"P.O.","lastName":"Mollard","suffix":""}],"badges":[],"createdAt":"2025-07-18 14:19:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7158515/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7158515/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11104-025-08237-1","type":"published","date":"2026-01-06T15:58:26+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":88321420,"identity":"f510b976-d0e0-4013-9edc-73b55e6f534f","added_by":"auto","created_at":"2025-08-05 08:59:12","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":340841,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e seedling emergence timing in flooded mesocosms monthly drained in the first-year experiment and schemes of treatments application(a) cumulative seedling emergence (b) percent seedling emergence per treatment. Data are presented as means ± SE (N=7). Inserted vertical bars represent the LSD of rmANOVA treatment x time interaction.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7158515/v1/d9fbed53bc39eeab914c7fd5.png"},{"id":88321423,"identity":"b3c9f276-ffa6-42eb-b431-02bc66158262","added_by":"auto","created_at":"2025-08-05 08:59:12","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":172702,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e aboveground dry biomass (a) and seed production (b) per area at the end of the first-year experiment. Data are presented as means ± SE (N=7). Bars not sharing the same letter are significantly different after Tukey tests (p \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7158515/v1/a971bdba6752c87e9f2d7ef9.png"},{"id":88321422,"identity":"b94d2922-a021-4bb8-b673-ad357b3f49f7","added_by":"auto","created_at":"2025-08-05 08:59:12","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":513457,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e seedling emergence timing in mesocosms flooded once a month during either 10 days (10-d flood mo\u003csup\u003e-1\u003c/sup\u003e) or 20 days (20-d flood mo\u003csup\u003e-1\u003c/sup\u003e) in the second-year experiment and schemes of treatments application: (a,b) mesocosms without \u003cem\u003eE. colona\u003c/em\u003e seedling removal and (c,d) mesocosms with \u003cem\u003eE. colona\u003c/em\u003e seedling removal. (a,c) cumulative seedling emergence and (b,d) percent seedling emergence per treatment. Data are presented as means ± SE (N=6). Inserted vertical bars represent the LSD of rmANOVA treatment x time interaction.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7158515/v1/7ea5f3a27e2f62f01d81abb6.png"},{"id":88321424,"identity":"76cef31f-29f0-4da6-a85f-f869f3eea93c","added_by":"auto","created_at":"2025-08-05 08:59:12","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":251695,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e aboveground dry biomass (a), seed production (b), and seed soil bank (c) per area at the end of the second-year experiment. (a,b) without \u003cem\u003eE. colona\u003c/em\u003e seedling removal and (c) with \u003cem\u003eE. colona\u003c/em\u003e seedling removal. Data are presented as means ± SE (N=6). Bars not sharing the same letter are significantly different after Tukey tests (p \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7158515/v1/af0d89dca658691ddc6c159e.png"},{"id":88321755,"identity":"d8daa14a-8dcd-4294-bf07-a80893687cf8","added_by":"auto","created_at":"2025-08-05 09:07:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":363176,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e seedling emergence timing in mesocosms flooded during winter -before the growing season- in the third-year experiment and schemes of treatments application(a) cumulative seedling emergence (b) percent seedling emergence per treatment. Data are presented as means ± SE (N=6). Inserted vertical bars represent the LSD of rmANOVA treatment x time interaction.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7158515/v1/f17bfcc1db4a44177b3a8d78.png"},{"id":88321428,"identity":"3ac91b80-9dcb-4de0-81b6-802beb3973f3","added_by":"auto","created_at":"2025-08-05 08:59:12","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":175361,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e aboveground dry biomass (a) and seed production (b) per area at the end of the third-year experiment in where mesocosms were flooded during winter and drained at the start of the growing season. Data are presented as means ± SE (N=6). Bars not sharing the same letter are significantly different after Tukey tests (p \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7158515/v1/851e6ed3d35e5541ed443e87.png"},{"id":100069313,"identity":"f778f283-0867-47cc-b3ad-2384d94230a2","added_by":"auto","created_at":"2026-01-12 16:12:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2354899,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7158515/v1/1a86368c-02cf-4ee1-8920-12b6cae428c1.pdf"},{"id":88321418,"identity":"28b39ed7-b316-4820-867a-d1f5631be4b3","added_by":"auto","created_at":"2025-08-05 08:59:12","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":289392,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryfigures.docx","url":"https://assets-eu.researchsquare.com/files/rs-7158515/v1/de8d707ce275974729d0710a.docx"}],"financialInterests":"","formattedTitle":"Flooding during the growing season spreads Echinochloa colona seedling emergence towards summer","fulltext":[{"header":"Introduction","content":"\u003cp\u003eClimate change fosters meteorological conditions suitable for frequent floods as well as drought events. Such events could change the recruitment pattern of arable weed species in extensive crops; however, while the effects of droughts and rainfall events on weed seedling emergence have been thoroughly investigated (Cordeau et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Singh et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), the effects of floods on weed seedling recruitment have rarely been evaluated (Forcella et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Ismail et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Flooding can affect all processes related to seedling emergence and establishment: seed dormancy, germination and seedling pre-emergence growth (Mollard et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Ismail et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Echeverry Holgu\u0026iacute;n et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) thus challenging the predictive power of weed seedling emergence models in flood-prone crop fields.\u003c/p\u003e\u003cp\u003eWetlands and poor drainage fields have been put into cultivation in recent years on a global scale (Verhoeven and Setter \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Fluet-Chouinard et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Moreover, opportunistic cultivation of lowlands and flood-prone fields leaves non-vegetated areas free to weed colonization and encroachment, particularly once crops have been damaged by floods (Hall et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1992\u003c/span\u003e; Ghersa et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). On the other hand, very few as well as geographically limited studies have been focused on the effect of flood frequency and timing on wetlands plant performance and demography (Webb et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Rosbakh et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) making it even more difficult to predict if floods can affect weeds seedling emergence or establishment as well as their reproductive output.\u003c/p\u003e\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e (L.) Link. is an annual C\u003csub\u003e4\u003c/sub\u003e summer grass, native to tropical and subtropical Asia that can severely reduce crop grain yield (Chauhan and Johnson \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Peerzada et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Mahajan and Chauhan \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). \u003cem\u003eE. colona\u003c/em\u003e is a spring-summer-emerging weed species; however, it has a wide field emergence window in tropical, subtropical and temperate zones (Leguizam\u0026oacute;n et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Chauhan \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Management options for the control of \u003cem\u003eE. colona\u003c/em\u003e in different cropping systems are currently limited and further challenged by the emergence of herbicide-resistant biotypes (Peerzada et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Godar and Norsworthy \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Moreover, \u003cem\u003eE. colona\u003c/em\u003e is expanding its seasonality (Chauhan \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), and an extended emergence period complicates effective weed control (Lutman et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Brown et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Therefore, it is crucial to investigate whether flooding regimes may shorten or prolong the window of opportunity for \u003cem\u003eE. colona\u003c/em\u003e seedling emergence and establishment.\u003c/p\u003e\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e has a precocious and plastic reproductive strategy which allows it to produce seeds even in short growing seasons (Hegazy et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) or under water stress (Chauhan and Johnson \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Mahajan et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). \u003cem\u003eE. colona\u003c/em\u003e is a prolific weed able to produce more than 100000 seeds per plant (Chauhan \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) and it can also form persistent soil seedbanks (Peerzada et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The effects of floods on the reproductive output of extensive crop weeds have not been studied; however, it is expected that \u003cem\u003eE. colona\u003c/em\u003e fecundity is changed by flooding events thus potentially affecting its seed rain.\u003c/p\u003e\u003cp\u003eThe following hypotheses were addressed in this research: 1) Flooding during the growing season significantly increases the number of \u003cem\u003eEchinochloa colona\u003c/em\u003e emerged seedlings and modifies the seasonal pattern of emergence, 2) Different flood regimes significantly affect aboveground biomass and seed production of established \u003cem\u003eEchinochloa colona\u003c/em\u003e plants, and 3) The duration of winter flooding (short or long) significantly affects \u003cem\u003eEchinochloa colona\u003c/em\u003e seedling emergence patterns. Mesocosms have been used to study plant responses to flooding in semi-controlled conditions (Li et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Yang et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). We used that methodology to address the above-mentioned hypotheses; then, we extracted mesocosms from a crop field subjected to extensive dryland agriculture and, in a series of three experiments, exposed them to different flooding regimes with contrasting duration, frequency and timing. In this contribution we present data from a crop-free series of experiments in where it is mimicked that the crop has been damaged by floods thus creating gaps in the canopy or fields have been left uncultivated because of soil saturation.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eAlong three years we did a series of crop-free mesocosms experiments to test if \u003cem\u003eEchinochloa colona\u003c/em\u003e (L.) Link. seedling emergence patterns, plant aboveground biomass and seed production were changed by floods. Mesocosms were obtained from a seasonal wetland situated in a cropfield located in the cropping region of Buenos Aires province, Argentina (35\u0026deg;33\u0026rsquo;S, 58\u0026deg;58\u0026rsquo;W) in the limit of Rolling and Flooding Pampas vegetation units (Soriano \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1991\u003c/span\u003e). The area has a mean annual precipitation of 911 mm (isohydric regime), characterized by significant interannual variation due to ENSO oscillations. The agricultural wetlands, perched on hydromorphic soils, experience seasonal floods during winter in most years, including early spring during El Ni\u0026ntilde;o events as well as temporary waterlogging during heavy rains. During La Ni\u0026ntilde;a events, the same agricultural wetlands are successfully cultivated. The average monthly temperature ranges from 23\u0026ordm;C in January (summer in the Southern Hemisphere) to 9.1\u0026ordm;C in July (winter). The soils are poorly drained and characterized by a high clay content (28.2% particles\u0026thinsp;\u0026lt;\u0026thinsp;2 \u0026micro;m) in the surface layer (0\u0026ndash;20 cm), with 5.2% organic matter and a pH of 5.9. The cropping system consists of no-till farming with the following crop rotation: sunflower/wheat-soybean/maize. In those wetlands we selected sites for mesocosms extraction where \u003cem\u003eE. colona\u003c/em\u003e was the dominant species with plant cover higher than 80%. The accompanying species were: \u003cem\u003eSetaria parviflora\u003c/em\u003e (Poir.) Kergu\u0026eacute;len, \u003cem\u003eAlternanthera philoxeroides\u003c/em\u003e (Mart.) Griseb., and \u003cem\u003eDigitaria sanguinalis\u003c/em\u003e (L.) Scop. We assumed that the treatments would be strong enough to override differences in \u003cem\u003eE. colona\u003c/em\u003e seed abundance across soil patches. Mesocosms of 30 x 30 cm (15 cm depth) were carefully dig out in winter, placed into plastic containers, and immediately transported to the experimental garden at Faculty of Agronomy, University of Buenos Aires (150 km NE from the source crop site, 34\u0026deg;35\u0026prime;37\u0026Prime;S 58\u0026deg;29\u0026prime;03\u0026Prime;W). Flooding treatments simulated hydrologic regimes that can happen along different topographic positions on contrasted dry or wet years. Mesocosms were assigned to flooding treatments in a randomized block design; blocks consisted of three parallel rectangular pools (2.4 m x 1.55 m x 40 cm depth). Water level was maintained between 10 to 15 cm above mesocosms soil surface. Drained (control) mesocosms were placed above water surface and irrigated every two days.\u003c/p\u003e\u003cp\u003eThe emerged \u003cem\u003eE. colona\u003c/em\u003e seedlings were marked with plastic toothpicks and recorded twice a week. Seedlings other than \u003cem\u003eE. colona\u003c/em\u003e were removed. At the end of the growing season and before seed dispersal, ten representative complete panicles were chosen from every mesocosm (replicate), and the number of seeds on each panicle was tallied. The mean seed number per panicle was computed and then multiplied by the overall number of panicles to assess the seed production per area. Afterwards, \u003cem\u003eE. colona\u003c/em\u003e plants were harvested and subjected to oven drying at 80\u0026ordm;C for a minimum of 72 hours and the aboveground plant dry biomass was determined. Oxidation-Reduction Potential (ORP) values in the flooded treatments were registered in the soil-water interface (year 1) and in perforated 50 ml Falcon tubes inserted in the flooded soil (years 2 and 3) as a proxy to identify anaerobiosis (Pezeshki, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) with a HI98121 (Hanna Instruments, Woonsocket, USA).\u003c/p\u003e\u003cp\u003e\u003cem\u003eExperiment 1\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThis experiment was carried out to test if flooding during the growing season significantly modifies the seasonal pattern of \u003cem\u003eEchinochloa colona\u003c/em\u003e seedling emergence. Mesocosms were carefully dig out at the end of winter (August 21, 2019) and immediately transported to the experimental garden at Faculty of Agronomy and placed into the above-mentioned inundation pools. Mesocosms were rotated in the pools. Flood treatments started September 1st (late winter). Mesocosms were maintained flooded to a water level of 10\u0026ndash;15 cm and groups of seven mesocosms (replicates) were monthly drained from October 1st (early spring) to February 1st (midsummer). Thus, the experiment design counted with five monthly flood-drainage treatments plus one control treatment (constant drained and irrigated every two days).\u003c/p\u003e\u003cp\u003e\u003cem\u003eExperiment 2\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThis experiment was carried out to test if intermittently pulsed flooding events can promote \u003cem\u003eE. colona\u003c/em\u003e seedling emergence over that produced under well-watered drained conditions. One round of floods per month were applied from August 1st to December 1st, time when all mesocosms were drained so a total of four rounds of floods were applied in the below-mentioned treatments i and ii. Mesocosms were dig out on July 16th and carried to the experimental garden. The experiment consisted in three treatments: i) mesocosm were flooded from the first to the tenth day of the month and then drained and irrigated every two days until next month (10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), ii) mesocosms were flooded from the first to the twentieth day of the month and then drained and irrigated every two days until next month (20-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), iii) drained mesocosms were irrigated every two days (control treatment). In this experiment, we included two types of mesocosms: with and without \u003cem\u003eE. colona\u003c/em\u003e seedling removal. By removing all emerged \u003cem\u003eE. colona\u003c/em\u003e seedlings, we created a permanent vacant niche for new seedlings to emerge from the soil seedbank. Both types of mesocosms were analysed independently, each with six replicates. Finally, at the end of the experiment, three soil core samples were taken from the seed soil bank of each replicate using an auger to study the size of the remaining soil bank in those mesocosms where all seedlings were removed. The seed soil bank was averaged from three homogenized and sieved soil samples per mesocosm (i.e. replicate). On December 22, 2021, the photosynthetic photon flux density (PPFD, 400\u0026ndash;700 nm) was measured with a Li-118B radiometer (Li-Cor Inc., Lincoln, NE, USA) to study the irradiance reaching the soil under the canopy produced by \u003cem\u003eE. colona\u003c/em\u003e established plants in the mesocosms where seedlings were not removed. The Red to Far-Red ratio of light (R:FR) was measured with a Skye SDL 2520 sensor (Skye Instruments Ltd., Llandridrod Wells, UK). The measurements of solar radiation were carried out at midday on a sunny day and with the sensor resting vertically on the soil surface.\u003c/p\u003e\u003cp\u003e\u003cem\u003eExperiment 3\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThis experiment was executed to test if floods during winter affect the emergency pattern of \u003cem\u003eE. colona\u003c/em\u003e seedlings during spring. We seized the opportunity of a consecutive series of dry years in the Pampas (La Ni\u0026ntilde;a event) that happened from 2019 to 2022 in where agricultural wetlands remained drained most of the year. On May 1st (late autumn), mesocosms were carefully dig out and taken to the experimental garden. The experiment consisted in five treatments: i) a long flood from mid-May to mid-September ii) a flood event from June 1st to September 1st, iii) a flood event from mid-June to mid-August, iv) a short flood during the entire July and v) no flood (mesocosms drained and watered to field capacity). Mesocosms were watered every two days after draining. Each treatment included six replicates, which were randomly assigned to one of three inundation pools.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eCumulative seedling emergence was evaluated by repeated measures analysis of variance (rmANOVA). Significance of the interaction of treatment \u0026times; time were determined through Wilks\u0026rsquo; Lambda multivariate tests. Aboveground dry biomass and seed production per square meter were analysed through one-way ANOVAs. Normality and homogeneity of variances were verified before each analysis. ANOVAs were followed by \u003cem\u003epost hoc\u003c/em\u003e Tukey tests with α\u0026thinsp;=\u0026thinsp;0.05. All statistical analyses were conducted using STATISTICA version 10 (StatSoft Inc. Tulsa, OK). All results are presented as untransformed means of replicates\u0026thinsp;\u0026plusmn;\u0026thinsp;standard error.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cem\u003eExperiment 1: effects of floods during the growing season on E. colona seedling emergence, aboveground biomass and seed production\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThe repeated-measures ANOVA (rmANOVA) of cumulative \u003cem\u003eE. colona\u003c/em\u003e seedling emergence revealed a significant interaction between time and flooding regime (p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). In well-watered, constantly drained mesocosms, seedling emergence followed an early-season distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). In contrast, simulated flooding not only delayed the initial spring emergence peak by approximately two weeks but also shifted the emergence distribution toward later dates in the growing season (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). A pronounced emergence peak occurred in all treatments during the first week of November (mid-spring; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). In the control and early drained treatments (drainage in October or November), emergence ceased by December (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea,b). In contrast, the longest flooding treatments (drained in December, January, or February) exhibited a bimodal emergence pattern: an initial emergence phase occurred underwater (representing approximately 50% of total emergent seedlings), followed by a notable gap and then a delayed midsummer emergence peak after drainage (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea,b).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eMesocosms flooded during the early growing season acquired higher \u003cem\u003eE. colona\u003c/em\u003e aboveground dry biomass than continuously drained (control) mesocosms (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea) while mesocosms drained in mid-summer (January, February) had the lowest aboveground dry biomass yet non statistically different from the continuously drained treatment (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Flooding regimes did not significantly change \u003cem\u003eE. colona\u003c/em\u003e seed production per area (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb); however, the longer the floods during the growing season the higher the variability shown within treatments in seed production (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). Mesocosms ORP values in the soil-water interface indicated that oxygen was lost after one month of flooding (ORP\u0026thinsp;\u0026lt;\u0026thinsp;\u0026lt;\u0026thinsp;100 mV) and reduction progressed towards negative values during spring (Fig. S1).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eExperiment 2: effects of intermittently pulsed floods during the growing season on\u003c/em\u003e E. colona \u003cem\u003eseedling emergence, aboveground biomass and seed production\u003c/em\u003e\u003c/p\u003e\u003cp\u003eIn the experiment carried out during the second year, the rmANOVA of cumulative seedling emergence revealed a significant time x flooding regimes interaction (p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). A bimodal \u003cem\u003eE. colona\u003c/em\u003e seedling emergence distribution was observed in the constantly drained, well-watered mesocosms where seedlings were not eliminated (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Interestingly, a second and discrete main emergence peak was noticeable during November in all treatments. Intermittent flooding pulses during 10 days per month (10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) did not change the overall pattern of seedling emergence compared to the drained condition (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Irradiance data indicated that the soil was shaded in December in both the drained and 10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e treatment (Fig. S2), coinciding with the cessation of seedling emergence in these treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ea,b). In contrast, intermittent flooding pulses lasting 20 days per month (20-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) resulted in a multimodal emergence pattern, with seedling emergence events extending into late summer (February) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). Intermittently pulsed flooding regimes did not change aboveground dry biomass production nor seed production per square meter (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003ea,b).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe removal of emerged \u003cem\u003eE. colona\u003c/em\u003e seedlings allowed the occurrence of additional cohorts in both constantly drained and 10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003ec,d). Moreover, the mesocosms where \u003cem\u003eE. colona\u003c/em\u003e seedlings were removed allowed us to study the potential depletion of the soil seedbank during the treatments without seed additions caused by accidental seed rain (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). Notably, at the end of the growing season, the final seed bank was four times larger than total emergence in the drained and 10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e treatments, and eight times larger than in the 20-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). ORP values indicated that anaerobiosis was noticeable both in the 10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the 20-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e treatments at the end of spring (Fig. S3)\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eExperiment 3: effects of winter floods on E. colona seedling emergence, aboveground biomass production and fecundity\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThe rmANOVA of cumulative \u003cem\u003eE. colona\u003c/em\u003e seedling emergence revealed a significant time x flooding regime interaction (p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001; Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Most of the winter flooding regimes and the drained mesocosms brought about similar step-wise cumulative emergence patterns during the growing season excepting the longest (i.e. 4 months) flooding regime that had the poorest total seedling emergence (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). Aboveground dry biomass was significantly higher in those winter flooding regimes subjected to the largest floods than in the drained mesocosms (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). Seed production per area was higher and more variable in the treatment flooded for a longer period in winter (flooded 4 months) than in the drained control (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). ORP values in the soil water showed strong reduction potential and anaerobiosis in the long-lasting winter flooding treatments (Fig. S4)\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this research, we tested through a crop-free experiment whether different flood regimes -both before and during the growing season- facilitate or inhibit \u003cem\u003eEchinochloa colona\u003c/em\u003e encroachment by evaluating seedling emergence from the soil seed bank, as well as biomass accumulation and seed production of the established plants. We found scarce evidence for the promotion or inhibition of \u003cem\u003eE. colona\u003c/em\u003e by diverse flood treatments compared to drained, well-watered conditions; however, we found that floods change the seedling emergence pattern, an effect that could challenge weed management practices.\u003c/p\u003e\u003cp\u003e\u003cem\u003eThe effects of flooding regimes on E. colona seedling emergence timing\u003c/em\u003e\u003c/p\u003e\u003cp\u003ePrimarily, our results for the first-year experiment show that even relatively short periods (1 month) of continuous flooding at the beginning of the growing season delayed \u003cem\u003eE. colona\u003c/em\u003e seedling emergence. Moreover, flooding increased the asymmetry of emergence as a second emergence peak was observed in mesocosms drained during late spring or summer. For some weeds with protracted emergence, multiple weed seedling emergence peaks are common during part of the growing season, mainly related to precipitation events after drought periods (Brown et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) giving rise to multiphasic cumulative emergence curves. Here, we show that late emergence peaks may result from drawdown periods following flooding events, particularly in the lowest topographic areas of lowland crop fields, where prolonged flooding can persist throughout the growing season in rainy years. Unexpectedly, those mesoscosms drained either in January or February (summer) had produced copious \u003cem\u003eE. colona\u003c/em\u003e subaquatic emergence in November (mid-spring): around 2500 seedling per square meter. Laboratory experiments predicted that \u003cem\u003eE. colona\u003c/em\u003e seeds from the same accession can be induced to geminate when submerged under hypoxic conditions (Echeverry Holgu\u0026iacute;n et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Underwater germination of weeds such as \u003cem\u003eE. crus-galli\u003c/em\u003e and weedy rice is common in paddy-fields (Ismail et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) yet it is not expected to occur in lowland temperate agroecosystems where rice has not been introduced so far due to short growing seasons.\u003c/p\u003e\u003cp\u003eWhile flooding stress may negatively affect seedling emergence and establishment, a following drawdown period that leaves soil in optimal moisture conditions may successfully help emergence of wetland species (Casanova and Brock \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). So, we hypothesized that intermittent pulsed flooding regimes -mimicked during the second-year experiment- would promote further seedling emergence of a facultative wetland weed such as \u003cem\u003eE. colona\u003c/em\u003e. That did not happen as the 10-d flood periods per month (10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) did not increase emergence over the drained well-watered control treatment. Moreover, 20-d flood periods per month decreased total cumulative seedling emergence and produced two late emergence peaks in summer. In crops, successful weed recruitment must occur within a few weeks before crop canopy closure (Ghersa and Holt \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Brown et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, already closed canopies may reopen during flooding in flood-susceptible crops such as rapeseed and pulses due to extensive leaf senescence (Ploschuk et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e); such canopy openings may potentially cause further emergence late in the season (Brown et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The second-year seedling removal experiment revealed that the absence of summer emergence peaks observed in the non-removal experiment for both the drained control and the 10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e flooding treatment was due to environmental changes (e.g., light intensity and quality) imposed by early-established \u003cem\u003eE. colona\u003c/em\u003e plants. Thus, the 20-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e treatment, by decreasing cumulative seedling emergence, inhibited competitive exclusion by early \u003cem\u003eE. colona\u003c/em\u003e recruiters upon late cohorts.\u003c/p\u003e\u003cp\u003eIn dry years, episodes of warm season weed recruitment may not coincide with floods because \u003cem\u003eE. colona\u003c/em\u003e seedling emergence occurs in spring and floods during winter, season where summer weeds accumulate seeds in the soil bank (Cavers and Benoit \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). However, seeds in the soil bank may be subjected to changes in dormancy level due to flooding (Mollard et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Peralta Ogorek et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). As dormancy is the most important component of emergency periodicity from soil seedbanks (Grundy \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2003\u003c/span\u003e), we hypothesized that flooding during winter would change the \u003cem\u003eE. colona\u003c/em\u003e seedling emergence pattern early in the season. Winter flooding treatments did not alter the seasonal pattern of emergence; however, the longest winter flooding\u0026mdash;ending just before the onset of the recruitment season\u0026mdash;markedly reduced the seedling emergence rate of \u003cem\u003eE. colona\u003c/em\u003e. This inhibition may result from either the induction of secondary dormancy or seed decay. Although these mechanisms differ, both have important and contrasting implications for weed management. Therefore, further research and modelling are needed, as soil seed bank depletion is a key objective in weed management (Gallandt \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Schwartz-Lazaro and Copes \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cem\u003eThe effects of flooding regimes on E. colona aboveground dry biomass\u003c/em\u003e\u003c/p\u003e\u003cp\u003eSpring \u003cem\u003eE. colona\u003c/em\u003e cohorts produce the highest aboveground plant biomass while autumn cohorts produce lower biomass and the lowest number of leaves and tillers compared to spring emergents (Chauhan \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). On the other hand, prolific weed seedling emergence early in the season can cause an important intraspecific competition, which can affect individual plant growth rates (Mohler \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Our first-year results revealed a trade-off between density-dependent competition among early-emerging seedlings in the drained treatments and the constraints imposed by a shortened growing season on cohorts emerging later in summer. Consequently, the treatments drained in mid-spring exhibited the highest aboveground dry biomass. In the second year, light irradiance and quality data suggested that the early-recruiters from the drained and 10-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were competing for light during summer so the less abundant plants in the 20-d flood mo\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e produced similar aboveground dry biomass than the afore-mentioned treatments. Strong self-thinning is expected at the levels of crowding shown in our experiments (Watkinson et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1983\u003c/span\u003e). Our results show that \u003cem\u003eE. colona\u003c/em\u003e early and numerous cohorts - with a putative competitive advantage over crops (Bosnic and Swanton \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Hock et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2006\u003c/span\u003e)- emerging in drained soils or after short flooding periods, experienced strong density-dependent effects. In contrast, treatments with longer flooding, which delayed emergence and led to later cohorts, did not exhibit penalties in aboveground dry biomass.\u003c/p\u003e\u003cp\u003e\u003cem\u003eThe effects of flooding regimes on E. colona seed production\u003c/em\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eEchinochloa colona\u003c/em\u003e plants have high fecundity and propagule pressure (Chauhan \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) so we wondered whether flooding regimes could reduce total \u003cem\u003eE. colona\u003c/em\u003e seed rain. Notably, most of the different flooding regimes did not change mean seed production per square meter across the three experiments, resulting in sufficient seed output to replenish depleted soil seed banks. Moreover, in the third experiment, which simulated floods during the fallow period, the longest flooding treatment\u0026mdash;despite producing the fewest seedlings\u0026mdash;resulted in higher seed production per square meter than the drained control. These results suggest the density-dependent control of fecundity in those early-drained treatments with plentiful \u003cem\u003eE. colona\u003c/em\u003e recruiters. On the other hand, \u003cem\u003eE. colona\u003c/em\u003e forms long viable seed banks (Walker et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Seed soil bank samples collected at the end of the second-year seedling removal experiment showed that \u003cem\u003eE. colona\u003c/em\u003e maintained a persistent seed soil bank regardless of the flooding regime. In conclusion, flooding did not reduce \u003cem\u003eE. colona\u003c/em\u003e total seed input nor seed reserves of the soil bank.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis study shows that flooding\u0026mdash;whether before or during the growing season\u0026mdash;reshapes \u003cem\u003eEchinochloa colona\u003c/em\u003e emergence dynamics in agricultural wetlands. Longer floods reduced overall emergence but delayed it into mid or late summer, extending the recruitment window beyond drained conditions and complicating early-season weed control. Despite fewer seedlings, seed production per area remained stable, likely due to reduced density-dependent competition. Thus, all flooding regimes produced enough seeds to replenish the soil bank. A persistent seed soil bank was observed regardless of flooding intensity or timing, indicating that seed soil bank depletion remains a major challenge in poorly drained fields. These findings highlight the need to incorporate hydrological variability into weed emergence models and support adaptive management approaches. Monitoring phenology and adjusting control practices to target delayed cohorts may be crucial to limiting the long-term impact of \u003cem\u003eE. colona\u003c/em\u003e in flood-prone agroecosystems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFinancial Support\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by Universidad de Buenos Aires (UBACyT \u0026nbsp; 20020170200034BA and 20020220400218BA) and National Scientific and Technical Research Council (CONICET) (Grant number PIP 11220150100041CO).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthors declare no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that supports this study will be shared upon reasonable request to the corresponding authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJuliana Echeverry Holgu\u0026iacute;n: Conceptualization, methodology, investigation, writing\u0026mdash;original draft, Gustavo Striker: Conceptualization, methodology, writing-review \u0026amp; editing, Mar\u0026iacute;a Crepy: Resources, review \u0026amp; editing, Federico Mollard: Conceptualization, methodology, supervision, writing-review \u0026amp; editing, funding acquisition.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBosnic AC, Swanton CJ (1997) Influence of barnyardgrass (\u003cem\u003eEchinochloa crus-galli\u003c/em\u003e) time of emergence and density on corn (\u003cem\u003eZea mays\u003c/em\u003e). \u003cem\u003eWeed Science\u003c/em\u003e 45:276\u0026ndash;282. https://doi.org/10.1017/S0043174500092833\u003c/li\u003e\n\u003cli\u003eBrown B, Gallandt ER, DiTommaso A, Salon P (2022) Improving weed management based on the timing of emergence peaks: A case study of problematic weeds in northeast USA. \u003cem\u003eFront Agron\u003c/em\u003e 4:Article 888664. https://doi.org/10.3389/fagro.2022.888664\u003c/li\u003e\n\u003cli\u003eCasanova MT, Brock MA (2000) How do depth, duration and frequency of flooding influence the establishment of wetland plant communities? \u003cem\u003ePlant Ecol\u003c/em\u003e 147:237\u0026ndash;250. https://doi.org/10.1023/A:1009875226637\u003c/li\u003e\n\u003cli\u003eCavers PB, Benoit DL (1989) Seed banks in arable land. 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Link. \u003cem\u003eCrop Prot\u003c/em\u003e 83:56\u0026ndash;66. https://doi.org/10.1016/j.cropro.2016.04.002\u003c/li\u003e\n\u003cli\u003ePeralta Ogorek L, Striker GG, Mollard FPO (2019) \u003cem\u003eEchinochloa crus-galli\u003c/em\u003e seed physiological dormancy and germination responses to hypoxic floodwaters. \u003cem\u003ePlant Biol\u003c/em\u003e 21:1159\u0026ndash;1166. https://doi.org/10.1111/plb.12993\u003c/li\u003e\n\u003cli\u003ePezeshki SR (2001) Wetland plant responses to soil flooding. \u003cem\u003eEnviron Exp Bot\u003c/em\u003e 46:299\u0026ndash;312. https://doi.org/10.1016/S0098-8472(01)00107-1\u003c/li\u003e\n\u003cli\u003ePloschuk RA, Miralles DJ, Colmer TD, Striker GG (2020) Waterlogging differentially affects yield and its components in wheat, barley, rapeseed and field pea depending on the timing of occurrence. \u003cem\u003eJ Agron Crop Sci\u003c/em\u003e 206:493\u0026ndash;505. https://doi.org/10.1111/jac.12396\u003c/li\u003e\n\u003cli\u003eRosbakh S, Phartyal SS, Poschlod P (2020) Seed germination traits shape community assembly along a hydroperiod gradient. \u003cem\u003eAnn Bot\u003c/em\u003e 125:67\u0026ndash;78. https://doi.org/10.1093/aob/mcz130\u003c/li\u003e\n\u003cli\u003eSchwartz-Lazaro LM, Copes JT (2019) A review of the soil seedbank from a weed scientist\u0026rsquo;s perspective. \u003cem\u003eAgronomy\u003c/em\u003e 9:369. https://doi.org/10.3390/agronomy9070369\u003c/li\u003e\n\u003cli\u003eSingh M, Thapa R, Kukal MS, Irmak S, Mirsky S, Jhala AJ (2022) Effect of water stress on weed germination, growth characteristics, and seed production: A global meta-analysis. \u003cem\u003eWeed Sci\u003c/em\u003e 70:621\u0026ndash;640. https://doi.org/10.1017/wsc.2022.51\u003c/li\u003e\n\u003cli\u003eSoriano A (1991) R\u0026iacute;o de la Plata grasslands. 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Elsevier, pp 367\u0026ndash;407.\u003c/li\u003e\n\u003cli\u003eVerhoeven JTA, Setter TL (2010) Agricultural use of wetlands: Opportunities and limitations. \u003cem\u003eAnn Bot\u003c/em\u003e 105:155\u0026ndash;163. https://doi.org/10.1093/aob/mcp276\u003c/li\u003e\n\u003cli\u003eWalker SR, Wu H, Bell K (2010) Emergence and seed persistence of \u003cem\u003eEchinochloa colona\u003c/em\u003e, \u003cem\u003eUrochloa panicoides\u003c/em\u003e and \u003cem\u003eHibiscus trionum\u003c/em\u003e in the subtropical environment of north-eastern Australia. \u003cem\u003ePlant Prot Q\u003c/em\u003e 25:127\u0026ndash;132.\u003c/li\u003e\n\u003cli\u003eWatkinson AR, Lonsdale WM, Firbank LG (1983) A neighbourhood approach to self-thinning. \u003cem\u003eOecologia\u003c/em\u003e 56:381\u0026ndash;384. https://doi.org/10.1007/BF00379798\u003c/li\u003e\n\u003cli\u003eWebb JA, Wallis EM, Stewardson MJ (2012) A systematic review of published evidence linking wetland plants to water regime components. \u003cem\u003eAquat Bot\u003c/em\u003e 103:1\u0026ndash;14. https://doi.org/10.1016/j.aquabot.2012.06.003\u003c/li\u003e\n\u003cli\u003eYang J, Gao Y, Zhao C, et al. (2024) Leaf phenotypic plasticity and integration balance plant adaptation to water table decline: a mesocosm experiment. \u003cem\u003ePlant Soil\u003c/em\u003e 497:611\u0026ndash;627. https://doi.org/10.1007/s11104-023-06418-4\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":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"plant-and-soil","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"plso","sideBox":"Learn more about [Plant and Soil](https://www.springer.com/journal/11104)","snPcode":"11104","submissionUrl":"https://submission.nature.com/new-submission/11104/3","title":"Plant and Soil","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"agricultural wetlands, arable weeds, flooding, Junglerice, seedling emergence, seed soil bank","lastPublishedDoi":"10.21203/rs.3.rs-7158515/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7158515/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground and aims\u003c/h2\u003e\u003cp\u003eFloods could promote hydrophyte weed species recruitment in cultivated lowland fields in temperate regions of the world. This study tested whether different flooding regimes change the amount and timing of \u003cem\u003eEchinochloa colona\u003c/em\u003e seedling emergence.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eWe did a series of three annual crop-free experiments in mesocosms taken from agricultural wetlands located in the Pampas region and subjected to cultivation during dry years to test if \u003cem\u003eEchinochloa colona\u003c/em\u003e (L.) Link. seedling emergence, aboveground biomass and seed production per area could be affected by flood regimes differing in duration and timing.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eFlooding or intermittently flooding-drawdown conditions during the growing season did not increase cumulative emergence compared to drained controls at field capacity; however, flooding affected the seedling emergence pattern by skewing emergency peaks towards mid-summer. Notably, an abundant subaquatic \u003cem\u003eE. colona\u003c/em\u003e seedling emergence was observed in spring (\u0026asymp;\u0026thinsp;2500 seedlings m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) in constantly flooded mesocosms. In the second experiment we found that even after prolonged and frequent flood pulses that decreased seedling emergency, \u003cem\u003eE. colona\u003c/em\u003e seed production was enough to replenish the soil bank. In a third experiment we revealed that long winter floods, before the growing season, decreased total seedling cumulative emergency yet did not change the emergence pattern of seedlings.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eThe extended temporal window of \u003cem\u003eE. colona\u003c/em\u003e recruitment due to flooding can complicate its field control and should be included in weed emergency models to accurately forecast \u003cem\u003eE. colona\u003c/em\u003e seedling recruitment to advise weed control and management decisions.\u003c/p\u003e","manuscriptTitle":"Flooding during the growing season spreads Echinochloa colona seedling emergence towards summer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-05 08:59:07","doi":"10.21203/rs.3.rs-7158515/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revisions","date":"2025-09-21T04:26:36+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-08-01T10:04:54+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-01T08:36:48+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Plant and Soil","date":"2025-07-22T00:45:04+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-21T10:29:06+00:00","index":"","fulltext":""},{"type":"submitted","content":"Plant and Soil","date":"2025-07-18T10:15:45+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"plant-and-soil","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"plso","sideBox":"Learn more about [Plant and Soil](https://www.springer.com/journal/11104)","snPcode":"11104","submissionUrl":"https://submission.nature.com/new-submission/11104/3","title":"Plant and Soil","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"51f9ad78-0b1c-40f5-b0f9-9d1d72bba7f1","owner":[],"postedDate":"August 5th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-01-12T16:04:04+00:00","versionOfRecord":{"articleIdentity":"rs-7158515","link":"https://doi.org/10.1007/s11104-025-08237-1","journal":{"identity":"plant-and-soil","isVorOnly":false,"title":"Plant and Soil"},"publishedOn":"2026-01-06 15:58:26","publishedOnDateReadable":"January 6th, 2026"},"versionCreatedAt":"2025-08-05 08:59:07","video":"","vorDoi":"10.1007/s11104-025-08237-1","vorDoiUrl":"https://doi.org/10.1007/s11104-025-08237-1","workflowStages":[]},"version":"v1","identity":"rs-7158515","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7158515","identity":"rs-7158515","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}