ABSTRACT Soil extracellular enzymes and microbial functional genes play essential roles in regulating carbon (C), nitrogen (N), and phosphorus (P) cycling by mediating nutrient transformations and maintaining soil biochemical balance. However, how functional genes modulate enzyme stoichiometry in response to microbial nutrient demands under drought conditions remains poorly understood. In this study, we integrated metagenomic sequencing with extracellular enzyme activity (EEA) analysis to explore how microbial C‐, N‐, and P‐cycling genes and extracellular enzyme stoichiometry (EES)‐specifically the vector length (an indicator of microbial C limitation) and angle (an indicator of microbial N vs. P limitation)‐respond across an aridity gradient in the rhizosphere and bulk soils of Caragana microphylla plantations. Our results demonstrate that microbial communities in both rhizosphere and bulk soils experience C and N limitations under arid conditions. In the rhizosphere, increasing aridity intensified microbial C limitation but alleviated N limitation, likely due to reduced root exudation and enhanced nitrogen fixation by C. microphylla . In bulk soils, microbial nutrient limitations exhibited threshold‐type responses to aridity: N limitation intensified under low aridity but was alleviated beyond a critical threshold (aridity index: AI < 0.24), while C limitation emerged only under higher aridity levels (AI < 0.285). These dynamics likely reflect buffered organic inputs and enhanced microbial nitrogen turnover, emphasizing the nonlinear and context‐dependent nature of nutrient constraints in dryland ecosystems. Partial least squares path modeling (PLS‐PM) revealed that N‐cycling enzymes were the primary predictors of microbial nutrient limitation in both compartments. However, C‐cycling enzymes exerted a stronger influence in the rhizosphere, while C‐ and N‐related functional genes played a greater role in bulk soils, reflecting compartment‐specific microbial strategies under drought stress. This study advances understanding of C‐N‐P cycling and microbial C‐N limitations in C. microphylla plantations, offering new insights into land degradation mechanisms and a scientific basis for vegetation and soil management in arid regions.
Dong et al. (2025) studied this question.