Impact of nitrogen and phosphorus additions on soil gross N transformations in a temperate desert steppe

Abstract

Nutrient addition has a significant impact on plant growth and nutrient cycling. Yet, the understanding of how the addition of nitrogen (N) or phosphorus (P) significantly affects soil gross N transformations and N availability in temperate desert steppes is still limited. Therefore, a ¹⁵N tracing experiment was conducted to study these processes and their underlying mechanism in a desert steppe soil that had been supplemented with nitrogen and phosphorus for 4 years in northwestern China. Soil N mineralization was increased significantly by P addition. And N and P additions significantly promoted soil autotrophic nitrification, rather than NH₄⁺‐N immobilization. The addition of N promoted dissimilatory NO₃⁻ reduction to NH₄⁺ (DNRA), while that of P inhibited it. Soil NO₃^‐‐N production were greatly increased by N added alone and by that of N and P combined, while net NH₄⁺‐N production was decreased by these treatments. Soil N mineralization was primarily mediated by pH, P content or organic carbon (C), while soil NH₄⁺‐N content regulated autotrophic nitrification, mainly, and this process was mainly controlled by ammonia‐oxidizing bacteria rather than archaea and comammox. And NH₄⁺‐N immobilization was mainly affected by functional microorganisms, the abundance of narG gene and comammox Ntsp‐amoA. In conclusion, gross N transformations in the temperate desert steppe largely depended on soil inorganic N, P contents and related functional microorganisms. Soil acidification plays more key role in N mineralization than other environmental factors or functional microorganisms.

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