Simulated warming enhances the responses of microbial N transformations to reactive N input in a Tibetan alpine meadow
Yi Zhang, Nan Zhang, Jingjing Yin, Yexin Zhao, Fei Yang, Zhongquan Jiang, Jinjin Tao, Xuebin Yan, Yunpeng Qiu, Hui Guo, Shuijin Hu
Abstract
Alpine ecosystems worldwide are characterized with high soil organic carbon (C) and low mineral nitrogen (N). Climate warming has been predicted to stimulate microbial decomposition and N mineralization in these systems. However, experimental results are highly variable, and the underlying mechanisms remain unclear. We examined the effects of warming, N input, and their combination on soil N pools and N-cycling microbes in a field manipulation experiment. Special attention was directed to the ammonia-oxidizing bacteria and archaea, and their mediated N-cycling processes (transformation rates and N2O emissions) in the third plant growing season after the treatments were initiated. Nitrogen input (12 g m−2 y−1) alone significantly increased soil mineral N pools and plant N uptake, and stimulated the growth of AOB and N2O emissions in the late growing season. While warming (by 1.4 °C air temperature) alone did not have significant effects on most parameters, it amplified the effects of N input on soil N concentrations and AOB abundance, eliciting a chain reaction that increased nitrification potential (+83%), soil NO3−-N (+200%), and N2O emissions (+412%) across the whole season. Also, N input reduced AOB diversity but increased the dominance of genus Nitrosospira within the AOB community, corresponding to the increased N2O emissions. These results showed that a small temperature increase in soil may significantly enhance N losses through NO3− leaching and N2O emissions when mineral N becomes available. These findings suggest that interactions among global change factors may predominantly affect ammonia-oxidizing microbes and their mediated N-cycling processes in alpine ecosystems under future climate change scenarios.