Key role of macrophyte-dominated habitats over cyanobacteria-dominated habitats in stability of microbial sulfur cycling in freshwater lakes.

Despite extensive studies on sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) in marine and deep stratified ecosystems, their spatiotemporal dynamics and ecological roles in shallow freshwater lakes remain poorly understood, especially with habitat shifts driven by eutrophication and climate change. Here, we monitored seasonal changes in sediment and porewater chemical parameters, and applied high-throughput sequencing and co-occurrence network analysis to compare SRB and SOB communities in surface sediments from cyanobacteria-dominated (ZSB) and macrophyte-dominated (XKB) habitats of Lake Taihu across four seasons. In ZSB, seasonal variations in acid volatile sulfide (AVS), dissolved sulfide (∑HS), and Fe(II) were the primary drivers of sulfur bacterial communities. In contrast, SRB in XKB were mainly influenced by total nitrogen (TN) and total phosphorus (TP), while SOB were regulated by spatial heterogeneity, with AVS as the key driver. Spore-forming SRB such as Desulfotomaculum were distinctly enriched in ZSB, indicating an adaptive strategy to environmental fluctuations. Notably, Cupriavidus, a genus rarely linked to sulfur oxidation, was the dominant SOB genus in both habitats. Co-occurrence network analysis showed that dominant genera in ZSB acted as network hubs, indicating greater vulnerability to environmental changes in cyanobacteria-dominated habitats. Conversely, XKB displayed evenly distributed interaction networks without dominant network hubs, enhancing resilience to environmental fluctuations. These findings provide new insight into how macrophyte-dominated habitats enhance the resilience of shallow freshwater lakes to algal bloom expansion via stabilized sulfur cycling. Hydrological and hydrodynamic factors should be considered in future to better elucidate sulfur cycling in freshwater lakes.