Soil microbial biomass C:N:P stoichiometry is driven more by climate, soil properties and plant traits than by N enrichment in a desert steppe

The impacts of increased ecosystem nitrogen (N) inputs on soil microbial biomass C:N:P stoichiometry have been extensively explored. However, the stoichiometric homeostasis and driving mechanisms of microbial C:N:P stoichiometry following N enrichment remain elusive in dryland ecosystems, especially in moderately alkaline desert steppes. Here, we employed a five-year (2015–2019) N enrichment experiment to examine the changes in microbial C:N:P stoichiometry and the strength of stoichiometric homeostasis in a moderately alkaline desert steppe in northwest China. Climate factors, plant traits, and soil properties were analyzed to determine the critical factors influencing microbial C:N:P stoichiometry. The results showed that microbial C:N:P stoichiometry changed little under low doses of N input (<10 g m−2 yr−1), and only microbial biomass C increased significantly by 35.89%-51.26% at 1.25 and 2.50 g m−2 yr−1. In contrast, a high N enrichment rate (20 g m−2 yr−1) significantly enhanced the microbial biomass N (average 61.88%) and N:P (44.55%) but decreased the microbial biomass C:N (37.25%). However, microbial biomass P and C:P showed no significant changes under N enrichment. Significant interannual differences were observed in microbial C:N:P stoichiometry, whereas the effects of the interaction of N enrichment and year were not significant (except for microbial biomass C and C:P). With increasing N enrichment, microbes basically maintained strong elemental homeostasis. Moreover, we found that climate factors (explaining about 16% of the variation), soil properties (13%) and plant traits (4%) played critical roles in shaping microbial C:N:P stoichiometry. N enrichment represented only ∼ 3% of the variation and thus had a weaker effect on microbial C:N:P stoichiometry. Altogether, our findings suggest that soil microbial C:N:P stoichiometry is more likely driven by climate factors, soil properties, and plant traits than by N enrichment in dryland ecosystems.