Land Use‐Induced Changes in Nutrient Accumulation and Bacterial Diversity Shift Stoichiometry of Soil Enzyme Activity

Soil enzymes are the rate‐limiting steps in the catalytic breakdown of organic matter, governing the process and efficiency of nutrient cycling in soil. Despite their crucial role in agricultural management and climate change mitigation, our understanding of the enzyme‐mediated mechanisms by which soil microorganisms regulate nutrient cycling in agricultural soils remains limited. This study investigated patterns of extracellular enzyme activities related to carbon (C), nitrogen (N), and phosphorus (P) cycling, along with their driving factors, in both agricultural and natural ecosystems. Our results indicated that citrus cultivation significantly reduced soil bacterial community diversity. Compared with natural forest soils, citrus‐planted soils exhibited markedly higher levels of available nitrogen and phosphorus, which correspond with decreased activities of C‐ and P‐acquiring enzymes and increased activity of N‐acquiring enzymes. Regression analyses revealed that the activities of soil C‐ and P‐acquiring enzymes were positively correlated with bacterial diversity, whereas N‐acquiring enzyme activity was negatively associated with bacterial diversity. In contrast, N‐acquiring enzyme activity was positively correlated with the availability of soil N and P, while C‐ and P‐acquiring enzyme activities showed negative correlations. These findings suggested that extracellular enzyme activities are highly responsive to variations in soil nutrient availability and microbial diversity. Enzyme vector analysis further indicated that as soil bacterial diversity decreased, microbial nutrient limitation shifted from phosphorus to nitrogen. This transition is primarily driven by citrus‐induced decline in bacterial diversity, resulting in enhanced microbial nitrogen limitation. The shift in microbial nutrient limitation, influenced by soil pH, available phosphorus, and bacterial diversity, has significant implications for soil fertility management, particularly in enhancing soil enzyme activity to reduce chemical fertilizer use and support climate‐smart agriculture in the face of global environmental challenges.