Subtropical shallow lakes often experience monospecific succession of submerged macrophytes, resulting in two typical community structures: canopy-forming (associated with eutrophic stages) and rosette-forming (associated with post-restoration conditions). However, current understanding of how these two community structures influence subsequent plant colonization remains limited. This study employed a mesocosm experiment with different plant community structures (PCSs): canopy-forming communities (CAs), rosette-forming communities (ROs), and no-plant controls (CK), combined with two water depths, to examine the effects of PCSs on the growth of eight submerged macrophyte species. Based on the key functional trait—plant height, these eight typical species were classified into two growth forms: long species and short species, with a focus on elucidating consistent patterns of plant responses under the combined effects of PCSs and water depth. The results showed that: (i) The effects of PCSs on plant growth varied and were modulated by water depth: CAs inhibited subsequent plant colonization through intense competition for light resources, with this inhibitory effect intensifying with increasing water depth; ROs homogenized underwater environmental heterogeneity, effectively alleviating deep-water stress, reducing plant biomass differences induced by water depth treatment, and weakening competitive imbalance between long and short species. (ii) Functional classification based on plant height effectively predicted species responses: long species exhibited between performance in shallow water, or under the background of CAs, and CK, but these advantages were context-dependent, significantly diminishing or disappearing in deep water and under the background of ROs. Notably, Potamogeton maackianus, despite morphological similarity to long species, displayed response patterns characteristic of short species, highlighting the importance of ecological functional classification. This study demonstrated that PCSs regulated subsequent species colonization through microenvironmental filtering and that plant height could serve as a key functional indicator for predicting coexistence patterns among submerged macrophytes. Our findings provide experimental evidence for community assembly of submerged macrophytes, and this knowledge can be used in natural lake restoration to improve the plant diversity.

Vallisneria are submerged macrophytes characterized by linear or banded leaves, and the capacity for both bicarbonate (HCO3−) use and crassulacean acid metabolism (CAM). A notable feature of Vallisneria leaves is the presence of a maturity gradient from the tip to the base. However, detailed studies on the variation of CO2-concentrating mechanisms (CCMs) within Vallisneria leaves from the tip to the base remain scarce. In this study, two common Vallisneria plant, Vallisneria natans and V. spinulosa, were selected to investigate how the tip and the base of the leaves respond to variable CO2. The pH-drift data showed that the tip and the base of both V. natans and V. spinulosa could use HCO3− under high CO2 (HC) and low CO2 (LC) treatments. Notably, the capacity for HCO3− use was significantly higher in the leaf tip compared to the base in both species, regardless of the [CO2]. Moreover, the mode of HCO3− utilization was identical between the tip and the base in both V. natans and V. spinulosa and was independent of [CO2]. Titratable acidity results indicated that both the tip and the base of V. natans and V. spinulosa performed CAM metabolism under LC treatment. Compared to the base, the diurnal acidity change was significantly higher at the tip under LC in both V. natans and V. spinulosa. The chlorophyll contents of V. natans and V. spinulosa in the tip region under HC treatments were significantly higher than those in the base under LC treatments. These findings reveal the spatial heterogeneity of CCMs within Vallisneria leaves, enhancing our understanding of how these species acclimate to CO2-fluctuating freshwater.

Emergent and floating-leaved plants share similar root system, but emergent plants extend their leaves above water like terrestrial plants, while floating leaves remain on the surface. Previous studies have demonstrated coordinated variation among photosynthetic traits in terrestrial plants, e.g. vein traits and leaf mass per area (LMA). Nonetheless, the co-ordination of these traits in aquatic plants remains unclear, especially for the emergent and floating-leaved plants. We conducted correlation analysis between leaf vein density and LMA in emergent (67 species) and floating-leaved plants (28 species). In emergent plants, minor veins significantly negatively correlated with LMA and leaf dry mass (LDM), with or without phylogeny correction, resembling the patterns in terrestrial plants. However, neither major nor minor vein density in emergent plants correlated significantly with LDM, indicating that environmental filtering primarily acted on traits per area rather than on the whole-leaf level. In floating-leaved plants, neither major nor minor vein density showed significant correlations with LMA, reflecting reduced needs for water transport or mechanical support from veins. In contrast, LDM correlated negatively with major and minor vein density, but the correlation weakened after phylogenetic correction, confirming that shared ancestry among closely related species in floating-leaved plants affected the trait-trait correlation. These findings highlight distinct adaptive strategies of trait co-ordination between floating-leaved plants and emergent plants and provide a basis for future research on trait-trait relationships in aquatic plants.

ABSTRACT A primary ecological challenge is to disentangle how abiotic factors affect species richness using measured environmental variables in addition to broad proxies such as elevation. Considering direct ecogeographical gradients, such as climate harshness, it is therefore essential to understand whether these underlying abiotic factors might consistently drive the distribution of different groups of organisms along elevational gradients. To address how elevation shapes species richness patterns, we performed a systematic review and a subsequent meta‐analysis to answer the following questions: (i) Does elevation influence species richness in global freshwater zooplankton and macrophyte communities? (ii) Can climatic harshness, such as temperature and precipitation variability, geography and different freshwater ecosystem types explain relationships between elevation and species richness? (iii) Are these ecogeographical patterns consistent for both organismal groups? Our meta‐analysis included 84 effect sizes spanning 48 countries and both hemispheres from −54.9 S to 84.7 N, with an elevational range up to 4200 m above sea level within six distinct freshwater ecosystems. We found that the relationship between elevation and species richness in zooplankton and macrophyte communities is context‐dependent. These responses varied among different taxonomic groups and broad habitat categories (i.e., flowing vs. standing waters). We found a general negative relationship between zooplankton species richness and elevation. Zooplankton species richness decreased along the elevational gradient, but this pattern was primarily associated with a concomitant decrease in cladoceran species numbers. The negative correlation between elevation and species richness was observed solely in flowing waters for macrophytes. Additionally, we found that negative elevation–richness relationships were more pronounced at high latitudes in the global north for both zooplankton and macrophyte communities. This research challenges the prevailing assumption that elevational diversity gradients are universal, with species richness decreasing with increasing elevation in freshwater ecosystems. We also emphasize that the conventional ecogeographical measures employed in terrestrial studies, such as air temperature, may be insufficient on their own to explain richness patterns in freshwater organisms. These findings underscore the necessity for future freshwater assessments to build on well‐established biogeographical traditions rooted in terrestrial systems while recognizing the unique features of inland waters.

Aim This study aims to evaluate whether the trait-environment relationships known for terrestrial plant height extend to freshwater macrophytes, and to identify the primary environmental factors influencing global height patterns in emergent and fully submerged aquatic plants.Location Global.Time Period Species occurrence records and height measurements compiled from 1931 to 2022.Major Taxa Studied Freshwater plant species.Methods We compiled a global dataset of maximum plant height records for 1735 aquatic plant species, categorised by life form (partially emergent vs. submerged). Using generalised additive models, we tested how plant height varied along latitudinal gradients and how it was related to environmental predictors including temperature, relative inorganic carbon supply, and water depth (indicated by habitat availability). We explicitly analysed whether these relationships differed between the two life forms and validated these patterns using site-scale species and environmental data from northern temperate lakes and streams.Results Species with emergent growth increase in height with warmer temperature. On the contrary, fully submerged species exhibit increased height with higher inorganic carbon availability and colder climates. At the local scale, submerged plant height is positively associated with relative inorganic carbon supply in lakes and streams of the northern temperate zone.Main Conclusions The relationships between environmental variables and plant height differ between emergent to completely submerged life forms, consistent with realm-specific patterns in trait-environment correlations. These differing patterns highlight that trait-environment coupling in freshwater systems may not parallel those in terrestrial ecosystems and suggest that life form mediates species' responses to environmental variation.

The decline of submerged plants in shallow lakes is a global concern due to their critical roles in maintaining water quality and ecosystem stability. Propagules of these plants can survive long in sediment, making the propagule bank crucial for restoration. We aimed to determine the long-term dynamics of the aquatic plant community and its propagule bank in Changhu Lake, a typical large shallow lake in the middle and lower reaches of the Yangtze River, China, identify factors influencing plant changes, and propose restoration measures. We combined literature data with in situ investigations on the plant community and propagule bank, and analyzed long-term fluctuations in water quality, land use changes, and water level variations. The study revealed a severe decrease of the aquatic plant community, with coverage plummeting from nearly 100 % in the 1950s to less than 1 % by 2018. The propagule bank has also been nearly depleted, with significant declines in species richness and density from 2008 to 2023. Increased total phosphorus led to eutrophication, and frequent extreme climatic events occurred in recent decades. These stressors caused a shift from a clear-water state to a turbid-water state. Our findings highlight the importance of the propagule bank in restoration strategies. Successful restoration of Changhu Lake requires reducing external nutrient inputs, managing water levels, and supplementing the propagule bank to re-establish a resilient submerged plant community.

Aquatic angiosperms represent an important but underexplored lineage for understanding genome evolution, particularly in species with exceptionally large genomes. Here, we present a chromosome-scale genome assembly of the endangered aquatic monocot Ottelia songmingensis (similar to 10.8 Gb), providing a valuable genomic resource for studying genome gigantism and conservation. Using ONT and Hi-C technologies, we anchored 87.7% of the assembly to 11 pseudochromosomes and predicted 35362 protein-coding genes. Comparative genomics revealed two whole-genome duplication events, including a more recent duplication and an ancestral triplication shared within Alismatidae. Repetitive elements constitute 94.3% of the genome, with long terminal repeat retrotransposons alone accounting for over 90%. A recent burst of LTR activity (similar to 6 Mya) combined with a low solo-to-intact ratio (0.61) suggests inefficient transposon removal as a driver of genome expansion. Whole-genome bisulfite sequencing showed globally high DNA methylation levels (CG similar to 85%, CHG similar to 78%), particularly enriched in transposable element-rich regions, highlighting the role of epigenetic regulation in stabilizing large genomes. Population resequencing further indicated extremely low nucleotide diversity (pi = 5.31 x 10(-4)) and a long-term decline in effective population size since the Middle Pleistocene. Together, these resources provide a genomic foundation for exploring the evolutionary forces underlying genome gigantism and for guiding conservation genomics in endangered aquatic plants.

Plant structures function as integrated modules, reflecting coordinated development and function across traits. In terrestrial plants, stomatal traits that regulate carbon uptake are tightly coordinated with xylem traits supplying water, maintaining trade-offs between photosynthetic demand and hydraulic capacity. In aquatic plants, however, contrasting environments experienced by emergent and floating leaves may alter these coordination patterns. Whether heterophylly modifies fundamental scaling relationships among traits remains unclear. Here, we examined 15 heterophyllous aquatic species that produce both floating and emergent leaves within the same individual, allowing isolated effects from phylogeny. We found that emergent leaves exhibited greater leaf area, total stomatal area, and petiole thickness, indicating increased hydraulic and mechanical investment. Both leaf types followed hypoallometric scaling between leaf and petiole traits, but coordination regimes diverged. Emergent leaves showed tighter scaling between total stomatal area and petiole xylem area, reflecting strengthened coupling between transpirational demand and hydraulic supply. In contrast, floating leaves exhibited steeper scaling between leaf area and petiole transverse area and a more centralized trait network structure. These divergences persisted after accounting for phylogeny. Together, our results showed that heterophyllous plants could maintain core developmental proportionality while reorganizing trait coordination in response to different habitats.

Floating-leaved plants in the shallow littoral zone of wetland ecosystems are a unique life-form group whose responses to environmental change are likely to follow distinctive patterns. This study explored the adaptive strategies of three floating-leaved Nymphoides species—N. peltata, N. hydrophylla, and N. indica—in wetland habitats under varying water depths (0.4 m, 0.8 m, and 1.2 m). We analyzed morphological, hydraulic, and photosynthetic traits to understand how these wetland plants respond to hydrological fluctuations. Although water depth had limited effects on most traits, significant interspecific differences were found. N. indica displayed larger leaf area, thicker petioles, and greater total stomatal area, suggesting enhanced hydraulic capacity. In contrast, N. peltata and N. hydrophylla exhibited higher photosynthetic efficiency through increased chlorophyll content and specific leaf area (SLA). Plant trait network (PTN) analysis indicated tighter trait integration in N. indica, while N. peltata and N. hydrophylla showed higher modularity, implying more flexible adaptation strategies in wetland environments. We also found significant correlations between hydraulic and photosynthetic traits across three Nymphoides species, indicating a consistent functional trait coordination under the distinct trait values. These findings offer important theoretical insights into the adaptive mechanisms of floating-leaved plants in aquatic environments.

River sediments are primary sinks for microplastics (MPs) while the MPs hazards are of great concern. River depth and anthropogenic activities are reported to influence MPs distribution, but emerging evidence suggests that extreme events and biological interactions also alter MPs fate. Here, we conducted a one-year monitoring program in a river section downstream of a reservoir to investigate the impacts of a flood event caused by increased reservoir discharge and aquatic plants on the MPs characteristics in sediments. A significant increase in MPs abundance was observed in July (post-flood; 551–4174 items/kg) and September (during peak plant proliferation; 4104–4908 items/kg). MPs abundance showed a positive correlation with aquatic plant biomass and density. The Granger causality test suggested that other environmental factors simultaneously influence MPs accumulation. Redundancy analysis further confirmed that current velocity and discharge remained significant factors shaping MPs composition, and the flood was significantly associated with an increase in small-sized MPs. Our findings demonstrated that storm events could induce a short-term increase in MPs abundance and aquatic plant communities can enhance MPs deposition and acting as a biological sieve. Future control and management of MPs pollution can introduce aquatic plants and need to consider the far-reaching impacts of extreme events.

C4 photosynthesis has emerged in various plant lineages as an adaptive response to abiotic stress, as it allows for higher photosynthetic efficiency. C4 photosynthesis has been uncovered in both terrestrial and aquatic plants. However, the extent to which C4 photosynthesis serves as an adaptation to submerged environments in aquatic plants remains elusive. Here, we studied the heterophyllous aquatic plant Nuphar pumila, which has phenotypically distinct leaves, depending on the level of submergence. By applying 13C labeling experiments, submersed leaves of N. pumila were shown to exhibit both C4 and C3 photosynthesis, whereas floating leaves are limited to C3 photosynthesis. Leaf-specific single-cell trajectories of epidermal and bundle sheath cells show that, in contrast to terrestrial C4 plants, CO2 fixation in C4 photosynthesis in submersed leaves primarily occurs in the epidermal cells rather than in the mesophyll cells, allowing the leaves to cope with limited inorganic carbon in water. The combined presence of C3 and C4 photosynthesis, along with tissue-specific adaptations in the heterophyllous aquatic plant N. pumila, demonstrates how C4 photosynthesis in aquatic environments likely evolved as an adaptive trait from C3 photosynthesis.

Previous studies have demonstrated differences between common and rare species in dispersal ability and reproductive strategies, leading to distinct responses to environmental and spatial processes. In this study, we collected data from 111 ponds within a multi-pond system, including environmental variables, land use, connectivity variables, and macrophyte species abundance. We aimed to investigate the influence of hydrological connectivity (watercourse dispersal) and geographical connectivity (overland dispersal) on the macrophyte species turnover in ponds, with a specific focus on common and rare species. Our findings emphasized the common macrophytes served as better indicators of species richness than rare species, suggesting that common species played a more significant role in shaping diversity patterns. Results showed that water flow, weighted by watercourse distance, accounted for 5.12

The coexistence of submerged macrophytes is crucial for maintaining ecosystem health and biodiversity in shallow lake ecosystems. The modern coexistence theory (MCT) has been extensively used to explain species coexistence in grasslands and microbial communities by considering average fitness differences and niche differences at local scales. However, this theory has not yet been applied to investigate the coexistence of submerged macrophytes. In freshwater ecosystems, fish play a vital role in regulating the structure of the submerged macrophytes community. Fish could affect inter/intra specific competition of submerged macrophytes by indirectly changing the water environment or directly acting as herbivores, which might be described as apparent competition. Here, we employed a short-term mesocosm experiment to explore how omnivorous fish (Rhodeus ocellatus) and herbivorous fish (Megalobrama amblycephala) affect the co-existence of rosette-forming macrophytes (Vallisneria denseserrulata) and canopy-forming macrophytes (Myriophyllum spicatum), based on the MCT. We hypothesised that both herbivorous fish and omnivorous fish could influence the co-existence dynamics of these macrophytes through apparent competition, that is two macrophytes interact indirectly through their shared grazer. In the absence of fish or with only omnivorous fish present, V. denseserrulata and M. spicatum couldn't stably coexist, with V. denseserrulata exhibiting stronger growth and clonal reproductive with more ramets, winning the interspecific competition according to the prediction of MCT. However, the herbivorous fish, with preferential grazing, altered their fitness and niche differences between the macrophytes, promoting their coexistence. Our results reveal a case study of apparent competition between submerged macrophytes via fish presence, which provides insightful solutions for maintaining high species diversity of submerged macrophytes in restored shallow lakes.

As an emerging contaminant, silver nanoparticles (AgNPs) show significant toxicity to the photosynthesis of aquatic plants. However, photosynthesis is a complex process, and it remains unclear which specific steps are critical targets for AgNP toxicity. Here, Spirodela polyrhiza, was used to investigate the effects of AgNPs on various steps of the photosynthetic process. Results showed that AgNPs significantly induced Ag accumulation in chloroplasts and this Ag co-occurrence with the S element further altered the chloroplast morphology and structure. Then, this accumulated Ag significantly decreased the photosynthetic pigments content, reduced the light absorption and conversion, blocked the electron transportation, and inhibited the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (NADP-GAPDH) to suppress the Calvin cycle. Furthermore, evidence showed that Rubisco was sensitive to Ag+, while NADP-GAPDH was more sensitive to nanoparticles themselves. Based on the effective concentration at 50 % (EC50) value and the structural equation modeling, the inhibition of the dark reactions, particularly the inhibition of NADP-GAPDH activity, was the key trigger in the AgNPs toxicity to photosynthesis in S. polyrhiza. Given the key role of aquatic plants, the inhibition of their photosynthesis potentially disrupts primary productivity and energy flow in aquatic ecosystems, and threatens food web stability.

HCO3- use is the most widespread CO2-concentrating mechanism (CCM) in aquatic plants, but the trade-offs between the costs and benefits of this process are unclear. This issue was addressed in the submerged freshwater plant Ottelia alismoides by measuring photosynthesis rates at different inorganic carbon concentrations with and without the addition of HCO3- inhibitors under pH 6.5, 7.5 and 8.5 (high CO2, medium CO2 and low CO2). We showed that depending on CO2 concentrations, O. alismoides uses HCO3- through extracellular carbonic anhydrase, H+-ATPase and anion exchange protein. HCO3- contributed more to photosynthesis as CO2 decreased, and significantly decreased carbon loss by reducing photorespiration. Based on a model building using photosynthesis, photorespiration and dark respiration, in 2 mM total inorganic carbon, under CO2 < 28 μM, the carbon conservation from HCO3- use reducing photorespiration, far exceeded the carbon investment by HCO3- use. When CO2 > 28 μM, although HCO3- use seemed not to be a cost-effective process, it still supported a part of photosynthesis. However, even under higher CO2 concentrations, HCO3- use reduced photorespiration, which improved nitrogen utilization efficiency in leaves, showing lower N content, higher C:N and lower activities of nitrogen assimilation-related enzymes in leaves, including nitrate reductase, glutamine synthetase, glutamate synthase and glutamate dehydrogenase. Our data suggest that CO2 concentration and nitrogen utilization efficiency determine the trade-offs between carbon costs and benefits during HCO3- use.

Pollination is a key process that allows plants to complete their sexual life-cycle and although many different vectors can transport pollen grains from the male organ (anther) to the female organ (stigma), there is a high risk of failure. A perennial wetland plant Monochoria elata (Pontederiaceae) has mirror-image flowers with a large stamen that is of a similar length to the stigma and five small stamens that are half the length. After the flowers close, the perianth twists helically, either clockwise (right-handed flowers as viewed from the plant) or anticlockwise (left-handed flowers). This results in the anthers of the large stamen coming into contact with the stigma, resulting in pollination without the aid of any pollinating vector. This pollination mechanism represents an autonomous delayed self-pollination that safeguards reproductive success when normal pollinator insects are scarce and demonstrates that enantiostyly can allow self-pollination as well as cross-pollination.

Myriophyllum spicatum, a semi-aquatic plant, can develop heterophylly by forming both submerged and aerial leaves to adapt to water level variations in its habitat. The aerial leaves exhibit shorter and fewer lobes, but thicker cuticle and developed stomata than submerged leaves. The heterophylly exhibited by M. spicatum could be controlled by hormones including abscisic acid, indole-3-acetic acid, and Jasmonic acid, as their levels were consistently higher in aerial leaves than in submerged leaves. Genes responsible for the formation of cuticle and stomata exhibited elevated expression in the aerial leaves, offering a molecular explanation for their structural adaptations to terrestrial environment. Moreover, aerial leaves exhibited greater resistance to intense light, while submerged leaves demonstrated a pronounced capacity of utilizing HCO3- for photosynthesis. Differential gene expression patterns pertaining to photosynthesis, carotenoid production, and HCO3- utilization elucidated the molecular mechanisms driving M. spicatum's photosynthetic adaptations to aquatic and terrestrial environment. In conclusion, the ability of M. spicatum to withstand changing water levels can be linked to its adaptable phenotype and the genetic characteristics inherited from its terrestrial ancestors, both of which are governed by hormonal regulation. These features may allow M. spicatum to outcompete other macrophytes that are more sensitive to water level fluctuations in their growing surroundings.