Predation has a significant impact on the complexity and stability of microbial food webs in subalpine lakes

ABSTRACT Microbial food webs are drivers of material circulation and energy flow in lake ecosystems. The structural shifting of microbial food webs has important implications for the function of lake ecosystems. However, we continue to lack a clear understanding of the mechanisms underlying the complexity and stability of microbial food web structures. In this study, we investigated the diversity and structure of protist communities and bacterial communities by using DNA meta-barcoding to reveal the key factors affecting the complexity and stability of microbial food webs in subalpine lakes. Our analysis shows that significant seasonal variations occurred in protist taxonomic and functional communities (e.g., algivores, bacterivores, and phototrophs), which were mainly controlled by hydrological and nutrient parameters such as temperature, pH, and NH 4 + -N. Based on the network approach, the most complex food webs in the summer exhibited the lowest stability. We also found that the trophic interaction between bacterivorous protozoans and bacteria was the main factor significantly having influence on microbial food web complexity and stability ( P < 0.01). Moreover, biotic factors (i.e., bacterivorous protozoan composition) were better predictors of the relative abundance of several bacteria (Proteobacteria and Cyanobacteria) as prey than abiotic factors. Thus, these results suggest that predation is essential for the complexity and stability of the microbial food webs in lake ecosystems. Our findings suggest that understanding these complex interactions of microbial food webs is critical for ecosystem management and for predicting the ecological consequences of future climate changes in aquatic ecosystems. IMPORTANCE As an important part of microbial food webs, protists transfer organic carbon and nutrients to higher trophic levels in aquatic ecosystems. Protist predation often influences the abundance and composition of bacterial communities. However, we still do not understand whether and how predation affects the complexity and stability of microbial food webs. This study assessed the seasonal dynamic characteristics and driving factors of microbial food webs in terms of complexity and stability. Our findings have implications for future surveys to reveal the effects of climate and environmental changes.