Microtopographic Hydrological Coupling Drives Soil–Microbe–Plant Interactions in Floodplains: A Case Study in Poyang Lake of China

Microtopography regulates wetland ecosystem processes through coupled hydrological pathways, but how topographic factors jointly drive soil–microbe–plant networks remains limited. This study integrated high‐resolution topographic surveys, Sentinel‐1 SAR‐derived inundation dynamics, soil–vegetation investigations, and high‐throughput sequencing of soil microbial communities in a representative Poyang Lake floodplain wetland. Results demonstrated that inundation frequency was predicted by both elevation ( E ) and distance‐to‐shore ( x min ), with multiple regression confirming their independent contributions ( R 2 = 0.585, p < 0.001). Variance partitioning analysis (VPA) revealed that x min dominated soil biogeochemical patterns, independently explaining 41.8% of soil organic carbon and 24.0% of phosphate variation, whereas E showed negligible independent contributions. Elevation structured vegetation zonation, with sequential dominance of Carex cinerascens , Artemisia selengensis and Triarrhena lutarioriparia from low to high elevations. Within each zone, plants exhibited adaptive traits including reduced height but increased stem density with rising elevation. For microbial communities, x min emerged as the dominant topographic filter, independently explaining 43.9% of community variation, whereas E contributed only 5.6%, with no detectable shared fraction. These findings demonstrate that floodplain ecosystems operate through differentiated regulatory modules with lateral connectivity governing both biogeochemical processing and microbial community assembly, whereas elevation filtering sensitive vegetation and exerting secondary, indirect effects on microorganisms. This hierarchical framework challenges elevation‐centric wetland paradigms and provides targeted guidance for conservation under hydrological change.