Linking Soil Ecological Stoichiometry of Nutrients and Microbial Enzyme Activity to Bulk and Aggregate‐Associated Organic Carbon in Karst Rocky Desertification

Abstract

Soil microbial nutrient limitation plays a crucial role in nutrient cycling and soil organic carbon (SOC) accumulation, especially in degraded ecosystems. Karst rocky desertification (KRD) represents severe soil degradation in southwest China, yet its effects on SOC, as well as the underlying microbial mechanisms, remain understudied. Here, we investigated soil nutrients, ecoenzymatic stoichiometry, microbial resource limitation, as well as bulk SOC and aggregate‐associated organic carbon (OC) in four areas of southwest China with varying degrees of rocky desertification: intense rocky desertification (IRD), moderate rocky desertification (MRD), light rocky desertification (LRD), and nonrocky desertification (NRD). The results showed that (1) while early‐stage KRD increased SOC concentrations, this effect weakened with further intensification across soil layers; (2) in contrast to topsoil, microaggregates had significantly higher OC concentrations than large macroaggregates in the subsoil, particularly in LRD and IRD areas, which highlights that KRD's impact on SOC stabilization is influenced by soil depth; (3) vector analysis revealed that soil microbes in NRD areas are primarily N‐limited, whereas those in KRD areas are P‐limited, with the latter becoming more pronounced at both soil depths as KRD intensity increased; (4) the random forest model indicated that microbial nutrient limitations had a greater impact on microaggregate‐associated OC than on large macroaggregates. This is likely due to the higher nutrient‐rich organic matter in microaggregates, making them more attractive to microorganisms, particularly in nutrient‐deficient KRD‐affected ecosystems. This study provides new insights into the accumulation and contribution of aggregate‐associated OC to the SOC pool, highlighting the critical roles of microbial nutrient limitations, enzyme activities, and vector characteristics in regulating SOC dynamics in KRD‐affected ecosystems. Understanding these interactions offers essential knowledge for enhancing SOC sequestration and developing effective soil carbon management strategies in degraded karst environments.