Effects of nitrogen and phosphorus additions in shaping C:N:P stoichiometry of plants, soil and microbes in a semi-shrub desert ecosystem

Global atmospheric nitrogen (N) and phosphorus (P) deposition significantly affects the C-N-P stoichiometric characteristics of plant, soil and microbe. However, how plant-soil-microbe interactions in semi-shrub desert ecosystems respond to N and P additions remains unclear. This study established four N addition treatments, four P addition treatments, and one control (CK) in a semi-shrub desert on the northern slope of the Kunlun Mountains to evaluate the responses of C:N:P stoichiometry of plants, soil microbial biomass and extracellular enzymes. Both N and P addition alleviated P limitation in the leaves of Reaumuria soongorica and Sympegma regelii. The N:P ratio in all plant organs remained in an absolute steady state. In topsoil, High-dose N addition (N4) significantly reduced soil organic C by 12.15% and total N by 16%, while increasing available N by 155.68%. Microbial biomass C, N and P exhibited a unimodal response along increasing N and P gradients. Low-dose N addition (N1) significantly reduced microbial N Limitation by 23.3% in topsoil and 68.4% in subsoil, but microbes remained N-limited. N addition enhanced the influence of plant nutrients on extracellular enzyme vector length and angle, whereas P addition strengthened the impact of soil and microbes. Short-term N and P additions altered plant nutrient utilization strategies, promoting the stable coexistence of two dominant semi-shrubs within the same ecological niche, but did not alleviate microbial N limitation. In addition, extracellular enzyme vector characteristics exhibited markedly different response mechanisms to N and P additions.