黄土丘陵区典型人工植被土壤非共生固氮特征及其调控因子OA

Nitrogen is a key limiting nutrient for plant growth in arid and semi-arid regions.Asymbiotic nitrogen fix-ation(ANF)in the soil is a critical pathway for exogenous nitrogen input in the loess hilly region.However,both the characteristics and regulatory mechanisms of soil ANF under different types of artificial vegetation remain un-clear,which limits the accurate assessments of regional nitrogen cycle.We collected soil samples from artificial for-ests(Robinia pseudoacacia),shrubs(Caragana korshinskii),grasslands,and farmlands in the loess hilly region,measured ANF rates,and investigated the regulatory roles of soil physicochemical properties,microbial biomass,and extracellular enzyme activities.The results showed that:(1)Compared with farmland,vegetation restoration significantly increased soil nutrient content and microbial extracellular enzyme activities.Organic carbon and total nitrogen in surface soil(0-10 cm)in restored vegetation sites were up to 3.1 and 2.2 times those of farmland,re-spectively,with significant differences among vegetation types and soil layers.(2)The ANF rates across different vegetation types ranged from 1.60 to 2.91 kg N·hm-2·a-1.Surface soils in shrublands had the highest rate(2.70±0.16 kg N·hm-2·a-1),being 49.88％higher than that in farmlands.The ANF rates increased with soil depth.(3)Vegetation type primarily regulated ANF by altering soil physicochemical properties,which in turn in-fluenced extracellular enzyme activities and nutrient acquisition by soil diazotrophs,ultimately determining ANF rates.This study helps improve our understanding of how vegetation restoration affects soil nitrogen cycling in arid and semi-arid ecosystems and provides insights for guiding regional restoration and nitrogen budget evaluation.