How diverse ecosystems remain stable

Eutrophication diminishes bacterioplankton functional dissimilarity and network complexity while enhancing stability: Implications for the management of eutrophic lakes

Eutrophication is a growing environmental concern in lake ecosystems globally, significantly impacting the structures and ecological functions of bacterioplankton communities and posing a substantial threat to the stability of lake ecosystems. However, the patterns of functional dissimilarity, network complexity, and stability within bacterioplankton communities across different trophic states, along with the underlying mechanisms through which eutrophication influences these aspects, are not well-understood. To bridge this knowledge gap, we collected 88 samples from 34 lakes spanning trophic gradients and investigated bacterioplankton communities using network analysis and multiple statistical methods. Our results reveal that eutrophication, progressing from mesotrophic to hyper-eutrophic states, reduces the putative functional dissimilarity of bacterioplankton, particularly affecting the relative proportions of functional groups such as oxygenic photoautotrophy, phototrophy, and photoautotrophy. Network complexity exhibited a unimodal pattern across increasing trophic states, peaking at mesotrophic states and then decreasing towards hyper-eutrophic conditions, while stability exhibited the opposite pattern (U-shaped), indicating a variation in response to trophic state changes. In essence, eutrophication diminishes network complexity but enhances network stability. Collectively, these findings shed light on the ecological impact of eutrophication on bacterioplankton communities and elucidate the potential mechanisms by which eutrophication drives functional dissimilarity, network complexity and stability within bacterioplankton communities. These insights carry significant implications for the ecological management of eutrophic lakes.

Spatiotemporal variations, assembly processes, and co-occurrence patterns of particle-attached and free-living bacteria in a large drinking water reservoir in China

Particle-attached (PA) and free-living (FL) bacterial communities are sensitive to pollutant concentrations and play an essential role in biogeochemical processes and water quality maintenance in aquatic ecosystems. However, the spatiotemporal variations, assembly processes, co-occurrence patterns, and environmental interactions of PA and FL bacteria in drinking water reservoirs remain as yet unexplored. To bridge this gap, we collected samples from 10 sites across four seasons in Lake Tianmu, a large drinking water reservoir in China. Analysis of 16S rRNA gene libraries demonstrated spatiotemporal variations in bacterial diversity and identified differences in bacterial community composition (BCC) between PA and FL lifestyles. Capacity for nitrogen respiration, nitrogen fixation, and nitrate denitrification was enriched in the PA lifestyle, while photosynthesis, methylotrophy, and methanol oxidation were enriched in the FL lifestyle. Deterministic processes, including interspecies interactions and environmental filtration, dominated the assembly of both PA and FL bacterial communities. The influence of environmental filtration on the FL community was stronger than that on the PA community, indicating that bacteria in the FL lifestyle were more sensitive to environmental variation. Co-occurrence patterns and keystone taxa differed between PA and FL lifestyles. The ecological functions of keystone taxa in the PA lifestyle were associated with the supply and recycling of nutrients, while those in FL were associated with the degradation of complex pollutants. PA communities were more stable than FL communities in the face of changing environmental conditions. Nutrients (e.g., TDN and NO₃ ^-) and abiotic and biotic factors (e.g., WT and Chl-a) exerted positive and negative effects, respectively, on the co-occurrence networks of both lifestyles. These results improve our understanding of assembly processes, co-occurrence patterns, and environmental interactions within PA and FL communities in a drinking water reservoir.