Contrasting Prokaryotic and Eukaryotic Responses to a Simulated Heatwave: Community Assembly and Co-Occurrence Network Reorganization in Lake Taihu Mesocosms

Climate-driven heatwaves can rapidly reorganize freshwater microbial communities, yet whether prokaryotic and eukaryotic communities respond similarly across disturbance and recovery remains unclear. We simulated a + 8 °C, 10-day heatwave in Lake Taihu mesocosms and tracked prokaryotic and eukaryotic communities over a 28-day experiment. By integrating high-throughput sequencing, phylogenetic community-assembly analysis, and co-occurrence networks, we evaluated diversity, composition, inferred assembly processes, and graph-theoretic structural robustness. Prokaryotic alpha diversity showed stronger treatment-associated changes during recovery, whereas eukaryotic alpha diversity showed no comparable decline but community composition remained displaced from the pre-heatwave state. Cyanobacteria increased from 8% to 47% during recovery, coinciding with a decline in zooplankton and thus remaining consistent with, but not demonstrating, weakened top-down control. Community-assembly responses were domain specific: prokaryotes showed a pronounced redistribution toward the null-model category classified as dispersal limitation, whereas eukaryotic βNTI shifted toward more positive values against an already high background contribution of this category. Heatwave-associated co-occurrence networks contained more nodes and edges. Under simulated random node removal, normalized natural connectivity declined more rapidly for the prokaryotic heatwave network, whereas eukaryotic robustness trajectories were broadly similar between treatments. These results reveal contrasting short-term responses and recovery dynamics of prokaryotic and eukaryotic communities to an extreme thermal event without implying unmeasured life-history or evolutionary mechanisms.