Nitrogen addition altered the microbial functional potentials of carbon and nitrogen transformation in alpine steppe soils on the Tibetan Plateau

Abstract The microbial-mediated functional potentials of soil can be reflected by the abundance of corresponding microbial functional genes (MFGs). Few studies have simultaneously examined the responses of multiple key MFGs involving soil carbon (C) and nitrogen (N) transformation to N deposition, particularly under multiple application levels. In this study, we treated the alpine soil from the Tibetan Plateau with N fertilization at six addition rates. Absolute quantitative analysis (qPCR) was used to detect the abundance of MFGs related to soil C process: carbon dioxide (CO2) fixation(cbbL), methane (CH4) oxidation (pmoA) and production (mcrA), and soil N process: ammonia oxidation (AOA-amoA: archaea amoA, AOB-amoA: bacterial amoA), hydroxylamine oxidation (hao), nitrate, nitrite, nitric oxide and nitrous oxide (N2O) reduction (narG/napA, nirS/nirK, norB, and nosZ). The abundance of MFGs involved in both the soil C and N transformation processes were reduced as N rates increased (except AOB-amoA gene). Specifically, the abundance of the mcrA, AOA-amoA, nirK, norB, and nosZ genes were decreased non-linearly (U-shape) with the increasing N rates (P