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Clarifying the effects of biodiversity on ecosystem stability in the context of global environmental change is crucial for maintaining ecosystem functions and services. Asynchronous changes between trophic levels over time (i.e. trophic community asynchrony) are expected to increase trophic mismatch and alter trophic interactions, which may consequently alter ecosystem stability. However, previous studies have often highlighted the stabilising mechanism of population asynchrony within a single trophic level, while rarely examining the mechanism of trophic community asynchrony between consumers and their food resources.In this study, we analysed the effects of population asynchrony within and between trophic levels on community stability under the disturbances of climate warming, fishery decline and de‐eutrophication, based on an 18‐year monthly monitoring dataset of 137 phytoplankton and 91 zooplankton in a subtropical lake.Our results showed that species diversity promoted community stability mainly by increasing population asynchrony both for phytoplankton and zooplankton. Trophic community asynchrony had a significant negative effect on zooplankton community stability rather than that of phytoplankton, which supports the match‐mismatch hypothesis that trophic mismatch has negative effects on consumers. Furthermore, the results of the structural equation models showed that warming and top‐down effects may simultaneously alter community stability through population dynamics processes within and between trophic levels, whereas nutrients act on community stability mainly through the processes within trophic levels. Moreover, we found that rising water temperature decreased trophic community asynchrony, which may challenge the prevailing idea that climate warming increases the trophic mismatch between primary producers and consumers.Overall, our study provides the first evidence that population and trophic community asynchrony have contrasting effects on consumer community stability, which offers a valuable insight for addressing global environmental change. [ABSTRACT FROM AUTHOR]

Eutrophication has been observed to decrease the ecological resilience of macrophyte‐dominated freshwater ecosystems, thereby resulting in more vulnerability to external perturbations and easily tipping into an algae‐dominated state. The stress‐gradient hypothesis (SGH) posits that plants exhibit positive plant–plant interaction (facilitation) in response to stress, potentially buffering the detrimental impacts of eutrophication. However, few studies attempted to link plant density with species‐species interactions and ecological resilience in the context of eutrophic stress.Here, we investigated how the density of neighbour plant species (Potamogeton lucens) affects the change rate of nutrients or Chl a (chlorophyll‐a) and target plant species (Potamogeton maackianus) along a gradient of nutrient levels (oligotrophic, mesotrophic, eutrophic) via a 42 days mesocosm experiment. Our objective was to corroborate: (1) species interactions may shift from competition to facilitation with the increased eutrophic stress. (2) High plant density is indispensable to generate facilitation and thereby augment ecological resilience under high eutrophic stress.Results showed that eutrophic scenarios significantly augmented chlorophyll‐a concentration and inhibited plant height, number of branches and leaves, showing that submerged macrophytes in eutrophic states are exposed to stressful conditions. However, the increasing density of neighbouring vegetation reduced nutrient and Chl a concentrations and enhanced the performance of Potamogeton maackianus in eutrophic conditions, but not in mesotrophic and oligotrophic conditions. Our results indicated that density‐dependent facilitation is more prevalent in eutrophic circumstances, and species interactions are likely transformed from competition to facilitation with increasing nutrient concentrations.Our research demonstrated that plant density could alter the relationship between facilitation and competition; high plant density is indispensable for the operation of the stress‐gradient hypothesis. Density‐dependent facilitation under severe conditions could mitigate the adverse influence of eutrophication. With freshwater ecosystems progressively subjected to eutrophication, harnessing the density‐dependent facilitation of submerged macrophytes in resilience‐driven management is crucial to inhibiting the transition to an algae‐dominated turbid state, which further broadens our understanding of the theory of alternative stable states in shallow lakes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Freshwater lakes across the world have undergone dramatic changes in biological components and water quality over the past several decades. Previous studies focused on potential drivers mainly on nutrient enrichment in the catchment. However, the relative importance of climate change and the top‐down cascade effects of fish stocking on water quality is not fully understood. Here, by compiling 155 lakes data with four periods of field investigation in subtropical lakes in China, we found no significant changes in water total nitrogen and total phosphorus in the past two decades. However, the phytoplankton abundance increased significantly, and the water clarity declined by 44.1%. We further found that carp stocking and climate change are potentially more important than nutrients driving water quality change, which is also evidenced in two lakes (Lake Donghu and Qiandao) with long‐term monitoring histories. Specifically, carp stocking can decrease the water clarity directly by stirring up sediment and indirectly by trophic cascade along the food web. For climatic factors, mean annual temperature (MAT) has a positive effect on phytoplankton abundance, while mean annual precipitation has a negative one, with climates overall having little effect on water clarity. In addition, nutrient enrichment and climate change also have strong interactions with carp stocking, which may enhance the top‐down effects on water quality. Our findings highlight that either MAT or carp stocking may become an overwhelming driver of water clarity decline, which provides new insights into the conservation strategy for water quality management in the subtropical lakes in China. [ABSTRACT FROM AUTHOR]