Microbial Quotients and Stoichiometric Imbalance Reflect Divergent Responses to Wetland Land-Use Conversion

Wetland degradation alters soil nutrient cycling and microbial functioning, yet how microorganisms adjust resource-use strategies after wetland conversion remains poorly understood. This study examined the effects of wetland degradation-induced land-use conversion on soil-microbial quotients (qMBC, qMBN, qMBP) and soil-microbial stoichiometric imbalance (C:Nimb, C:Pimb, N:Pimb) in the A’er Xiang lake marsh wetland, northeastern China. Five sites were compared: native wetland, 5- and 10-year forestland converted from wetland, and 5- and 10-year cropland converted from wetland. The qMBP increased from 11.15% in native wetland to 30.40% in 10-year cropland, while qMBC rose from 5.97% to 9.81%, indicating that microbial P and C quotients were highly sensitive to wetland conversion. C:Nimb increased to 2.93 in 10-year cropland, whereas N:Pimb rose from 4.93 in native wetland to 13.79 and 10.59 in 5-year and 10-year forestland, respectively. Correlation analysis demonstrated that soil, microbial, and enzyme stoichiometry jointly regulated microbial quotients. Specifically, C:Nimb was strongly and negatively correlated with N:Pimb (r = −0.839, p < 0.01), and microbial biomass showed contrasting responses, being positively correlated with C:Nimb but negatively correlated with C:Pimb and N:Pimb. These indicators can guide future land-use decisions by integrating water availability with microbial adaptation in degraded sandy wetland regions.