Ammonia nitrogen and dissolved organic carbon regulate soil microbial gene abundances and enzyme activities in wetlands under different vegetation types

Soil microorganisms are important bioactive components of wetland ecosystems. Their abundances and enzyme activities directly influence biogeochemical cycle processes and are strongly associated with vegetation type. Our study aims to investigate the changes in microbial gene abundances and enzyme activities in Sanjiang Plain wetlands under different vegetation types, namely, Carex lasiocarpa, Deyeuxia purpurea, Glyceria acutiflora subsp. japonica, Oryza sativa, and Phragmites australis. Our results demonstrated that soil microbial gene abundances and enzyme activities were greatly affected by changes in vegetation type and soil chemical properties. The abundances of the carbon fixation gene (cbbL) and activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) in topsoil and subsoil were higher in C. lasiocarpa and D. purpurea wetlands than in other wetlands. This result indicated that the C. lasiocarpa and D. purpurea wetlands have stronger carbon fixation capacity than other wetlands. The highest nifH, nirK, and nirS gene abundances in subsoil were found in the D. purpurea wetland, indicating that soil microorganisms in subsoil under D. purpurea have stronger nitrogen fixation capacity and denitrification potential compared with those in subsoils under other vegetation types. The significantly higher nifH, nirK, and nirS gene abundances in topsoil than in subsoil in the C. lasiocarpa and G. acutiflora wetlands illustrated that topsoil has higher nitrogen fixation and denitrification capacity than subsoil. Redundancy analysis revealed that the cumulative interpretation rates of ammonia-N and dissolved organic carbon (DOC) for soil microbial gene abundances and enzyme activities were 73.1 % and 85.4 %, respectively, showing that ammonia-N and DOC are crucial drivers inducing alterations in soil microbial gene abundances and enzyme activities. Overall, our research clarified the mechanism underlying the linkage among plants, soil, and microorganisms in wetlands and improved the theoretical basis for predicting the effect of wetland vegetation changes on microbial function under the influence of future climate change and human activities.