Mechanisms of microbial coexistence in a patchy ecosystem: Differences in ecological niche overlap and species fitness between rhythmic and non-rhythmic species.

Resource patchiness caused by external events breaks the continuity and homogeneity of resource distribution in the original ecosystem. For local organisms, this leads to drastic changes in the availability of resources, breaks down the co-existence of species, and reshuffles the local ecosystem. West Lake is a freshwater lake with resource patchiness caused by multiple exogenous disturbances that has strong environmental heterogeneity that prevents clear observation of seasonal changes in the microbial communities. Despite this, the emergence of rhythmic species in response to irregular changes in the environment has been helpful for observing microbial communities dynamics in patchy ecosystems. We investigated the ecological mechanisms of seasonal changes in microbial communities in West Lake by screening rhythmic species based on the ecological niche and modern coexistence theories. The results showed that rhythmic species were the dominant factors in microbial community changes and the effects of most environmental factors on the microbial community were indirectly realised through the rhythmic species. Random forest analyses showed that seasonal changes in the microbial community were similarly predicted by the rhythmic species. In addition, we incorporated species interactions and community phylogenetic patterns into stepwise multiple regression analyses, the results of which indicate that ecological niches and species fitness may drive the coexistence of these subcommunities. Thus, this study extends our understanding of seasonal changes in microbial communities and provides new ways for observing seasonal changes in microbial communities, especially in ecosystems with resource patches. Our study also show that combining community phylogenies with co-occurrence networks based on ecological niches and modern coexistence theory can further help us understand the ecological mechanisms of interspecies coexistence.

Environmental heterogeneity associated with boat activity shapes bacteria and microeukaryotic communities with discrepant response patterns.

With the development of global tourism, tourist boats, a significant form of anthropogenic disturbance, are having an increasingly serious impact on the structure and function of aquatic ecosystems. In this study, the effects of different intensities of tourist boat activities on the microbial communities of West lake, were investigated by high-throughput sequencing. The results showed significant differences in the composition of bacterioplankton and microeukaryotic communities between the high-intensity boat activity (HIBA) area and low-intensity boat activity (LIBA) area. Variation partitioning analysis showed that environmental factors contributed the most to microbial community variation, and the effect of boat activities on microbial communities mainly occurred through coupling with environmental factors. The contribution of boat activity to microbial community changes occupies the second place, the first being environmental factors. Co-occurrence network analyses showed that microbial communities in the HIBA area had more nodes and edges, higher connectivity and lower modularity than in the LIBA area, suggesting a more complex and stable network. Networks of associations between potential keystone taxa and environmental factors reveal the way in which boat activity affects microbial communities. The bacterial community responded strongly to environmental factors associated with boat activities, whereas the microeukaryotic community was more likely to be regulated by interspecific interactions. This also suggests that when faced with disturbances from the boat activity, microeukaryotes might exert a stronger direct resistance effect compared to bacterioplankton. These findings imply that bacterioplankton and microeukaryotes demonstrate distinct response patterns in the presence of disturbance caused by boat activity. Our research expand our understanding of the effects of boat activities on aquatic ecosystems and provide further insights into the assessment of anthropogenic disturbances in aquatic ecosystems.

High heterogeneity of bacterioplankton community shaped by spatially structured environmental factors in West Lake, a typical urban lake in eastern China.

Elucidating the bacterioplankton spatial distribution patterns and its determinants is a central topic in ecological research. However, research on the distribution patterns of bacterioplankton community composition (BCC) within a small-sized, highly dynamic freshwater lake remains unclear. In this study, we collected surface water samples from West Lake to investigate the spatiotemporal variation of BCC by 16S rRNA gene high-throughput sequencing. Clear spatial heterogeneity in BCC was identified both in summer and winter. The relatively high abundant taxa exhibited greater correlations with environmental factors and other abundant species in summer than in winter. Variation partitioning analysis was used to unravel the relative importance of environmental factors and spatial processes and further explore the underlying mechanism of BCC successions. Our results showed the predominant shared effect of environmental and spatial factors on BCC in summer (68.41%) and winter (57.37%), indicating that spatially structured environmental factors were the key determinants of structuring BCC spatial heterogeneity in West Lake in the two seasons. Furthermore, environmental factors alone explained a higher proportion of the variation in summer whereas spatial factors explained a higher proportion in winter. These divergences may be related to seasonal environmental changes and anthropogenic disturbances. Our study provided knowledge on BCC spatial heterogeneity in small freshwater habitats and their underlying determinants in different seasons.