Nitrogen enrichment affects soil enzymatic stoichiometry via soil acidification in arid and hot land

Abstract Soil enzymatic stoichiometry reflects the patterns of soil microbial resource allocation for the acquisition of nutrients from different forms of soil organic matter. Nitrogen enrichment derived from human activities greatly affects soil biological properties and chemical properties. However, the mechanism for changing soil enzymatic stoichiometry due to nitrogen enrichment remains unclear. We established a factorial field experiment in an arid-hot valley to investigate the effects of nitrogen addition and plant species on the enzymatic stoichiometries for leucine aminopeptidase (LAP), acid phosphatase (AP), β-1,4-glucosidase (BG) and β-N-acetyl glucosaminidase (NAG). We found that nitrogen addition consistently reduced LAP activities but elevated AP activities beneath different grass species. Plant species had no effects on soil enzymatic stoichiometries although it significantly influenced the absolute values of soil enzyme activities. Nitrogen addition increased ln(BG):ln(LAP), but decreased ln(BG):ln(AP), ln(LAP):ln(NAG) and ln(LAP):ln(AP). Furthermore, by using structure equation modelling analyses, we found that the effects of N addition on enzymatic stoichiometries were mediated by soil acidification and microbial community structures. Our findings highlight that soil acidification alters microbial community structures and the patterns of microbial resource allocation for nutrient acquisition, both of which in turn play important roles in shaping soil enzymatic stoichiometry under the scenario of nitrogen enrichment.