1. An understanding of how biodiversity confers ecosystem stability is crucial in managing ecosystems under major environmental changes. Multiple biodiversity drivers can stabilize ecosystem functions over time. However, we know little about how local environmental conditions can influence these biodiversity drivers, and consequently how they indirectly shape the ecological stability of ecosystems. 2. We hypothesized that environmental factors can have opposite influences (i.e., not necessarily either positive or negative) on the temporal stability of communities in different environmental ranges depending on the biodiversity drivers involved. We tested this novel hypothesis by using data from a 4-year-long field study of submerged macrophyte across a water depth gradient in 8 heterogeneous bays of Erhai lake (with total sample size of 30,071 quadrats), a large lentic system in China. 3. Results indicate that a unimodal pattern of stability in temporal biomass measurements occurred along the water-depth gradient, and that multiple biodiversity drivers (the asynchrony in species dynamics, and the stability of dominant species) generally increased the temporal stability of aquatic primary producers. However, the effect of water depth either increased or decreased the stability of biomass according to the environmental conditions associated with sites along the water depth gradient. 4. Synthesis. These results reveal the influence of local environmental conditions on the biodiversity drivers of stability may help predict the functional consequences of biodiversity change across different scenarios of environmental change.

Sediment properties have a crucial effect on the growth and recovery of aquatic plants in lakes. Addition of various chemical substances has been proposed to reinforce the recovery of plants after a nutrient loading reduction. However, the effects of such sediment amendments on plant growth, especially those from rhizosphere microorganisms, is limited. We added Kaolin clay to sediments in different concentrations to explore its impact on the growth of Vallisneria natans and Ottelia acuminate and the concurrent shift in rhizosphere microorganisms using high-throughput sequencing technology. We found that the addition of low doses (10 % and 20 % in mass ratio) of Kaolin significantly modified sediment conditions (oxidation reduction potential and pH), with implications also for the composition, diversity, and stability of rhizosphere microorganisms. LEfSe analysis revealed that low-dose addition of Kaolin increased the abundances of functional microbial groups that benefit plant nutrient absorption and enhance plant stress resistance, such as Spirillaceae, Rhodocyclaceae, and Burkholderiales. Moreover, low doses of Kaolin significantly promoted the photosynthesis and nutrient absorption of submerged macrophytes, thereby facilitating plant growth. A structural equation model (SEM) indicated that the direct impact of Kaolin on the growth of submerged plants was relatively minor, while the indirect effect through modulation of rhizosphere microorganisms was important. Our study suggests that low doses of Kaolin may be used to promote the growth of submerged macrophytes when lakes with a high organic content in the sediment are recovering after nutrient loading reduction.

Lake Erhai is an important lake on the Yunnan-Guizhou Plateau, which has experienced pollution and treatment in recent years. Since 2017, the high-level protection and management have been carried out in the entire Lake Erhai basin, resulting in spatiotemporal changes in the external pollution and water quality. To analyze the influencing factors of external pollution on the water quality of Lake Erhai, this study conducted monthly water quality monitoring in eight major bays, as well as in the central of the northern, middle, and southern parts of Lake Erhai from 2017 to 2022. The concentrations of total nitrogen, total phosphorus, chlorophyll- a and water transparency were measured in the water column. The eutrophication was evaluated by the trophic level index( TLI). The results showed that: 1) The TLI decreased from the northern area to southern area, in agreement with the higher nutrients input of rivers in the northern part of the lake. 2) During the period from 2017 to 2022, the trophic index decreased significantly in the southern area of Lake Erhai and decreased slightly in the middle area, while increased in the northern area, indicating that the pollution control was more effective in the southern and middle areas than in the northern area. 3) the trophic index was higher in the wet season than in the dry season, and the seasonal variation of TLI was higher in the northern area than in the middle and southern areas. 4) It is important for the control of phosphorus input into the lake, particularly for the northern area of Lake Erhai basin and/or in the flooding season, as well as the phosphorus concentration in the lake water.

IntroductionWater depth (WD) and snail abundance (SA) are two key factors affecting the growth of submersed aquatic plants in freshwater lake ecosystems. Changes in WD and SA drive changes in nutrients and other primary producers that may have direct or indirect effects on submersed plant growth, but which factor dominates the impact of both on aquatic plants has not been fully studied.MethodsTo investigate the dominant factors that influence aquatic plant growth in plateau lakes, a one-year field study was conducted to study the growth of three dominant submersed macrophyte (i.e., Vallisneria natans, Potamogeton maackianus, and Potamogeton lucens) in Erhai Lake.ResultsThe results show that, the biomass of the three dominant plants, P.maackianus, is the highest, followed by P.lucens, and V.natans is the lowest. Meanwhile, periphyton and snails attached to P.maackianus are also the highest. Furthermore, WD had a positive effect on the biomass of two submersed macrophyte species of canopy-type P.maackianus and P.lucens, while it had a negative effect on rosette-type V.natans. Snail directly inhibited periphyton attached on V.natans and thereby increasing the biomass of aquatic plants, but the effect of snails on the biomass of the other two aquatic plants is not through inhibition of periphyton attached to their plants.DiscussionThe dominant factors affecting the biomass of submersed macrophyte in Erhai Lake were determined, as well as the direct and indirect mechanisms of WD and snails on the biomass of dominant submersed macrophyte. Understanding the mechanisms that dominate aquatic plant change will have implications for lake management and restoration.

Investigations of water flow movements affected by vegetation is a research hotspot in vegetation ecological restoration. The theory and equations of the flow velocity distribution under the influence of rigid vegetation are relatively mature. This study proposes a new drag force equation that varies with the vegetation bending angle and a new analytical solution of the velocity profile. Comparisons between the model calculation and experimental data, results showed that this new proposed model produced accurate simulations for flow through flexible vegetation for various deflections. In addition, this analytical model was verified to be applicable to rigid vegetation without a bending angle. Moreover, the features of the parameters adopted in this analytical equation are discussed, and the empirical equation for these parameters are presented. This study further improves the research in the field of environmental fluid mechanics and can serve as a theoretical underpinning for the ecological restoration of river courses. A new drag force equation of flexible vegetation is proposed based on the bending angle This new drag force equation of bending vegetation can recover to the traditional equation when applied to erect rigid vegetation New analytical solutions of velocity profiles for flexible and rigid vegetation are established

The preservation of biodiversity is crucial for sustaining ecosystem functioning, and recently the ongoing loss of biodiversity in lake ecosystems due to human activities has raised significant concerns. This study aimed to assess the impact of human activities on the biodiversity of aquatic plants through long-term empirical evidence. By comparing species composition and genetic diversity of submerged macrophyte within last decade, this research focused on the long-term changes of submerged macrophyte biodiversity resulting from human disturbances and restoration efforts. Three plateau lakes - Lake Erhai, Lake Fuxianhu, and Lake Jianhu - were selected as study sites, exhibiting varying biodiversity alterations in response to different levels of human disturbance and restoration activities. The oligotrophic Lake Fuxianhu demonstrated a stable level of both biodiversity levels, and the eutrophic Lake Jianhu exhibited a significant reduction in species diversity and genetic diversity. Meanwhile, the strong restoration measures in Lake Erhai between the 2010s and the 2020s effectively safeguard species diversity and alleviate declines in genetic diversity due to eutrophication during the last decade. We also found that improper use of alien species and the transplantation of clones of aquatic plant may pose ecological risks to biodiversity. Given the importance of aquatic plant re-establishment for the long-term recovery of plateau lakes, conservation strategies could prioritize large-scale propagation of aquatic plant materials through local seed banks.

Macrophytes with different growth forms exhibit diverse functional traits and ecological functions. In natural sub-deep lakes, there are often large differences in water quality between nearshore areas with macrophytes and open water areas. However, it remains unclear whether this phenomenon can be attributed to differences in plant growth forms. Therefore, we conducted continuous monitoring for four years, both before and after the implementation of an ecological restoration project, to explore whether the change in plant growth forms caused differences in water quality between the nearshore and open water areas. The results showed that implementing ecological restoration projects proved highly effective in improving the local environment, including water physicochemical properties and biological components, in the implementation area. First, the ecological restoration project greatly altered the plant community structure in the nearshore area before and after restoration. After restoration, there was a significant increase in the biomass and distribution area of noncanopy-forming plants (including erect and rosette-forming plants), while the opposite effect was observed for canopy-forming plants. Second, the transition of macrophyte community growth forms enhanced the stability of both macrophyte communities and water physicochemical parameters. Furthermore, the reduction in canopy-forming plants facilitated a more efficient water body exchange, resulting in greater homogeneity in water quality between the nearshore and open water areas. Overall, the presence of canopy-forming plants can hinder water body exchange due to large canopy formations on the water surface. In light of these findings, it is recommended that ecological restoration projects in natural lakes should consider the functional group composition of macrophytes.

The effect of biodiversity on ecosystem productivity has been a controversial issue in ecological research. The species richness–productivity relationship is highly variable in natural ecosystems, with a positive relationship being one of the most commonly observed relationships. Previous regional studies from terrestrial ecosystems have demonstrated that environmental gradients can regulate the species richness–productivity relationship. However, how this relationship varies in freshwater ecosystems across spatial environment gradients remains unclear. In this study, we propose that the species richness–productivity relationship can be modulated by the water depth. Here, we surveyed the submerged macrophyte community structure by establishing 24 transects and 642 quadrats in Erhai Lake, Yunnan Plateau, China. Our findings highlight that the species richness–productivity relationship gradually changed from slightly positive to strongly positive as the environment became more light-limited with the increasing water depth, supporting the stress-gradient hypothesis. The results from this study provide new insights into the biodiversity–ecosystem functioning relationships and in managing lake macrophyte communities and productivity.

Submerged macrophytes can improve water quality and buffer the effects of external nutrient loading, which helps to maintain a clear-water state in shallow lakes. We constructed 12 large enclosures with contrasting coverages (treatments) of submerged macrophytes (SMC) to elucidate their buffering capacity and resilience to nutrient pulses. We found that aquatic ecosystems with high SMC had higher buffering capacity and resilience, vice versa, i. e, the enclosures with high SMC quickly buffered the nutrient pulse and rebounded to clear-water state after a short stay in turbid-water state dominated by algae, while the treatments with low SMC could not fully buffer the pulse and rebound to clear-water state, and they slowly entered the transitional state after staying in turbid-water state. This means that the enclosures with high SMC had a better water quality than those with low SMC, i.e., the levels of nutrients and Chl-a were lower in the treatments with high plant coverage. In addition, plant coverage had a significantly positive buffering effect against nitrogen and phosphorus pulses, i.e., the nutrient concentrations in the treatments with high SMC took shorter time to return to the pre-pulse level. Overall, our results evidenced that the higher that the SMCs is, the better is the water quality and buffering capacity against nutrient pulses, i.e. the more stable is the clear-water state. However, low SMC may not be able to resist the impact of such strong nutrient pulse. Our results provide reference and guidance for water pollution control and water ecological restoration.

Positive feedback is key to producing alternative stable states and largely determines ecological resilience in response to external perturbations. Understanding the positive feedback mechanisms in macrophyte-dominated lakes is crucial for resilience-based management and restoration. Based on the field investigation of submerged macrophyte communities in 35 lakes in China, we found that morphological complexity (MC) and morphological plasticity (MP) are correlated with the stoichiometric homeostasis of phosphorus (HP ) and are related to ecosystem structure, functioning, and stability. We also found that the positive feedback strength of lakes dominated by macrophytes is biomass- and diversity-dependent. Eutrophication can decrease the community biomass by decreasing community MC, MP, and HP and the species diversity through low-light availability, ultimately decreasing the positive feedback strength and resilience of clear water states. We argue that functional traits and species diversity should be considered to build more resilient ecosystems in future changing environment scenarios.

Introduction Macrophytes are essential for maintaining the health of shallow lake ecosystems, however, the driving and responsive relationship between ecological factors (such as seasonal changes and nutrition, etc.) and plant communities is not yet clear. Methods In this study, we conducted seasonal surveys of macrophyte community composition in lakes with different nutrient states, aiming to understand the incidence relation between macrophyte community diversity, seasonal changes and environmental factors. Results According to the classification criteria of comprehensive nutritional index, there were significant differences in the trophic status of the three lakes. Among them, the Xihu Lake has reached mild eutrophication with a TLI value of 56.33, both Cibi Lake and Haixihai Lake are mesotrophic with TLI value of 36.03 and 33.48, respectively. The results of diversity analysis showed a significant negative correlation between α-diversity (include Species richness, Shannon-Wiener index, Simpson index and Pielou index) and lake nutrient status. Among them, Xihu Lake showed the lowest α-diversity in all seasons, Haixihai Lake exhibited the middle α-diversity, Cibi Lake indicated the highest α-diversity. Non-metric multidimensional ordination showed that there were obvious spatial structures differences among the macrophyte communities in the three lakes. Macrophyte community composition in the three lakes was more similar in summer and autumn, but there was a wider gap in spring and winter. The redundancy analysis indicated distinct differences between diversity index and ecological factors, the eigenvalues of Axis 1 and Axis 2 being, respectively, 36.13% and 8.15%. Environmental factors could explain 44.8% of the total variation in macrophyte communities structure. Among these, nitrogen, phosphorus, water transparency and water temperature contributed 50.2%, 3.5%, 3.8% and 27.5%, respectively. Conclusions In summary, the community structure of macrophytes in plateau shallow lakes is co-regulated by seasons and nutrients.

Understanding the link between biodiversity and ecosystem functioning is imperative for ecosystem-based management. The role of multitrophic diversity in sustaining multifunctionality remains unclear, especially in highly diverse aquatic ecosystems. We performed a species-addition experiment consisting of one, two, three, and five species in simulated multitrophic ecosystems to evaluate biodiversity and ecosystem functioning relationships within and across trophic levels. Our results showed that there are positive species richness–productivity relationships within and across trophic levels. We found significant negative correlations between species richness and the cumulative variation of total phosphorus, and between species richness and ecosystem multifunctionality across trophic levels. Also, we found that the relationships between ecosystem multifunctionality and species richness within and across the trophic levels are mediated by a combination of environmental factors, including water temperature, dissolved oxygen, pH, irradiance, and time, rather than by species richness. Our results imply that species richness–ecosystem functioning relationships vary for different ecological functions; the individual ecosystem functions selected and the way multifunctionality calculated are critical when examining links between biodiversity and ecosystem multifunctionality. Our study highlights that multitrophic richness, such as for consumers, is crucial for driving ecosystem multifunctionality. Furthermore, our study implies that management practices for restoring the diversity of aquatic macrophytes in wetlands should consider not only macrophyte richness but also different functional groups and life-forms.

1. Reduced light availability induced by eutrophication has dramatically affected the growth of submerged macrophytes and caused their rapid decline globally in lakes. Functional traits have usually been used to predict ecological processes and explain plant adaptation. Trait networks, which are constructed from a series of nodes (traits) and edges (trait-trait correlations), can reveal complex relationships among traits. Plant traits belonging to different organs are considered relevant for overall plant performance. Therefore, variation in trait network topology at the whole plant level can better reflect plant adaptation and response to environments than traditional methods, but the mechanisms underlying the decline of plants from a trait network perspective are not well understood.2. In this study, based on a 1-year manipulation experiment for Potamogeton maackianus cultured with four levels of light intensity, we constructed trait networks from 20 traits belonging to different organs.3. Our results showed that trait network connectivity decreases in harsh environments, probably due to increased trait modules responding independently to stress. Network connectivity was positively related to the plant relative growth rate (RGR), as high trait connectivity and coordination should be beneficial for plants to acquire and transport resources efficiently across the whole plant. Additionally, we found that specific stem length, leaf: root mass ratios and leaf total non-structural carbohydrates were hub traits with high connectivity. Hub traits expressed high phenotypic plasticity, had close links with plant growth and consistently held their higher importance within the network across light gradients or seasons.4. We found that low phenotypic integration in stressful environments may constrain plant growth, which can provide important implications for understanding plant adaptation strategies to low-light stress and even predicting community dynamics in the context of global environmental change.

Aquatic plants in lakeshore zone play an important role in maintaining the health of lake ecosystem.In order to understand the current status of aquatic plants in the lakeshore zone of Lake Erhai,this study investigated the aquatic plants quarterly in the lakeshore zone from 2020 to 2021.The results showed that there were 206 species of aquatic plants belonging to 56 families and 156 genera in the lakeshore zone of Lake Erhai,including 149 species of hygrophytes,24 species of emergent plants,21 species of submerged plants,7 species of floating plants and 5 species of floating leaf plants.Among all these species,Cynodon dactylon,Zizania latifolia,Vallisneria natans and Trapa bispinosa,etc.were common species,Lonicera japonica,Elymus dahuricus,etc.were occasional species.From the distribution of floristic regions,the species in the lakeshore zone of Lake Erhai were mainly world distribution（83 species） and tropical distribution（55 species）,accounting for 40.28% and 26.71% of the total species,respectively.In terms of plant communities,there were 18 main plant community types in the lakeshore zone of Lake Erhai,including 4 types of hyophytes communities,3 types of emergent plant communities,9 types of submerged plant communities and 2 types of floating leaf plant communities.Among all the communities,the main dominant communities were Cynodon dactylon communities,Zizania latifolia communities,Vallisneria natans communities and Trapa bispinosa communities.Compared with previous investigations,it was concluded that the diversity of aquatic plants in the lakeshore zone of Lake Erhai had been significantly improved in recent years.However,there are some problems such as the small area of lakeshore zone and the single of emergent plant community.Therefore,the construction of lakeshore zone should be further strengthened to improve the habitats and increase species diversity.

Flow velocity profile in the vegetal mixing layer was investigated using data collected in the present experiments and those reported in the literature, which indicates that the inflection point of the velocity profile does not coincide with the middle position of the vegetal mixing layer. Aiming to solve this problem, the hyperbolic tangent formula that is applicable to the plane mixing layer is modified by revising the inflection point and applying different characteristic scales in the free flow and penetration regions. For the problem of predicting flow velocity on top of vegetation, we constructed a new calculation method for flow velocity on top of vegetation based on correlation analysis. The proposed formula yields significant improvements in representing measured velocity profiles in the vegetated open channel flows. In comparison with previous ones, the modified formula performs better in exhibiting the similarity of measured velocity profiles over a wide range of flow and vegetation conditions. The research results provide technical support for the high precision calculation of the vegetated mixing layer.

Decreased underwater light availability is one of the most important environmental factors leading to the decline in submersed macrophytes in lakes. However, previous studies mostly focused on a relatively short time scale and lack data on the continuous monitoring of plant life history traits under different light conditions. The present experiment studied the growth, morphology and C/N metabolism of a representative submersed macrophyte, Vallisneria natans, in response to various light regimes (2.8%, 7.1%, 17.1%, and 39.5% ambient light intensity) over a period of 12 months. The results showed that the total biomass and ramet number increased with increased light intensity; in contrast, individual biomass, leaf number and maximum leaf length decreased with increased light intensity. The C/N metabolism indices of V. natans indicated that leaves were the most sensitive to light availability, stems were moderately sensitive, and roots were the least sensitive. V. natans grown in an extremely low-light environment exhibited decreased soluble carbohydrate (SC) and starch and increased free amino acid (FAA) and total nitrogen (TN) levels. The increasing function of the ramet number under different light regimes was fitted. The obtained maximum environmental capacity of the ramet number (K) and the days that the ramet number reached K/2 in each treatment are useful for lake V. natans restoration and seedling cultivation in similar limited-resource environments. Harvesting partial ramets properly and maintaining the ramet number near K/2 could ensure the maximum increase rate of the population to satisfy the demand of V. natans seedlings for lake restoration. The results obtained in this study can be used for lake water level management to achieve specific purposes during submerged macrophyte recovery, such as plant height elongation or plant population quantity expansion.

Adaptations to low light and water depth stresses are crucial for the survival of submerged macrophytes. To determine the phenotypic responses of Vallisneria natans to such stresses, we combined a field investigation, a light control experiment and an in situ response experiment to evaluate adaptive variations in fresh weight and morphological and physiological characteristics. In the field investigation and the light control experiment, water depth and light intensity were the main environmental factors affecting the fresh weight and morphological characteristics of V. natans. Fresh weight and leaf length were the most significant responding variables, and they were positively correlated with water depth and negatively correlated with underwater light intensity, although the root length and leaf number exhibited no variation. The leaf length elongated more rapidly at sites with intermediate water depth and low light intensity, and the allometric slopes were steeper. Furthermore, the in situ response experiment results showed a unimodal distribution of the chlorophyll-a concentrations of V. natans along with increasing water depths (from 0.5 m to 8.5 m). The turning point of the chlorophyll-a concentration occurred at 5.5 m, which is almost the maximum water depth at which V. natans occurs in Lake Erhai. Overall, our results evidenced that light availability is an important driving factor that controls the status of V. natans by affecting not only its morphology and physiology but also its biomass allocation and ramet production. An alternative resource allocation pattern of V. natans could be a shift between light acquisition and clonal reproduction.

为探究并优化浮萍人工培养技术,研究以广布种紫萍(Spirodela polyrrhiza)和青萍(Lemna minor)为主要研究对象,探索两种浮萍植物在不同营养水平的Hoagland和Hunter培养液中的鲜重、叶状体数的生长变化状况.结果表明:(1)紫萍和青萍鲜重在Hoagland培养液的不同营养水平下先增加后减少,而在Hunter营养液中呈持续增长趋势;两种浮萍的鲜重最大相对增长率(RGR)分别为0.11和0.18,鲜重受浮萍品种和培养基类型及其不同营养水平影响显著(P＜0.05),以青萍在Hunter原液培养基下的无性繁殖产生的生物量最高.(2)紫萍和青萍叶状体数在Hoagland培养液的不同营养水平下先增加后减少,而同鲜重一样在Hunter营养液中呈不断增长趋势;两种浮萍的叶状体最大相对增长率分别为0.14和0.19,叶状体生长的RGR变化同样受浮萍品种和培养基类型及营养水平影响显著(P＜0.05),以青萍在Hunter原液的营养环境下收获的叶状体数最高.(3)两种浮萍在Hoagland和Hunter营养液的不同营养水平下鲜重/叶状体比呈下降趋势,表明两种浮萍在适应不同营养时优先繁殖子代叶状体,以扩大种的适合度.研究认为Hunter原液可作为广布种青萍的最优培养条件,可实现短时间内收获较大浮萍鲜生物量和叶状体数,为进一步资源化利用提供原材料.

Algal dominance between phytoplankton and epiphyton plays an essential role in predicting shallow lake shifts between clear-water and turbid-water states. However, compared to resources competition, studies on algal life-form shifts between phytoplankton and epiphyton have traditionally received less interest, as few studies have focused on algal communities in both habitats concurrently. We conducted a 4 × 3 factorial design microcosm experiment to explore the mutual feedback relationship between phytoplankton and epiphyton. The initial algal life-form (epiphytic algae and phytoplanktonic algae alone or together) and nutrients enrichment (ambient, enrichment with N and P alone or together) were manipulated. After 28 days of incubation, the results suggested that the nutrient effects on the phytoplankton and epiphyton communities differed among the three different initial algal life-forms. A significant competitive advantage of phytoplankton was found even in treatments containing only epiphytic algae as the initial algal community. The contribution of nutrient enrichment to phytoplankton abundance (13%) was similar to that of epiphyton abundance (11%). In the mutual influence between two algal communities, epiphyton was likely to be a beneficiary as the phytoplankton community contributed 15% of the variance in epiphyton abundance. In addition, significant algal life-form shifts between phytoplankton and epiphyton only occurred in treatments containing one algal life-form, but not in treatments containing both algal life-forms at the beginning of the experiment. Our results emphasized the competitive advantage of phytoplankton in utilizing nutrient resources in the water column of shallow lakes. Moreover, we demonstrated that algal life-form shift was an adaptive behavior closely correlated with environmental variation. These results will provide broader insights to explore algal succession between phytoplankton and epiphyton in shallow lakes. To better understand the mutual influence mechanism between two algal life-forms under different nutrient conditions, research on multiple short time-scales based on algal migration is needed in the future.