Global Ecology and Conservation (Dec 2021)
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 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 < 0.05). The soil pH and dissolved organic C (DOC) concentration were positively correlated with the abundance of those MFGs, suggesting that the decreases in abundance of MFGs were more likely to be driven by changes of soil pH and DOC concentration. In contrast, the abundance of AOB-amoA gene increased linearly with the increasing N rates, which was strongly and positively correlated with soil nitrate-N (NO3–-N) concentration (P < 0.001, r = 0.82). In addition, soil greenhouse gases emissions linked with the abundance of corresponding MFGs. Specifically, the soil CO2 and N2O emissions were strongly and positively correlated with the AOB-amoA gene abundance (P < 0.001, r = 0.78, r = 0.84), and the soil CH4 emissions were significantly correlated with the pmoA (P < 0.01, r = 0.60) and AOA-amoA (P < 0.001, r = 0.72) gene abundance. The above results showed that the AOB-amoA gene had a positive response to increasing N rates, which was different from other genes. Indicating that elevated N deposition may improve the ammonia-oxidation process in alpine steppe soil mediated by AOB communities, and AOB communities may play an important role in donating the soil-atmosphere C and N exchange via CO2 and N2O emissions.
