Mowing and topography effects on microorganisms and nitrogen transformation processes responsible for nitrous oxide emissions in semi-arid grassland of Inner Mongolia

Abstract

Few studies have been done to investigate the impact of mowing on N2O emissions and the abundance of functional microbial genes, especially in sloping landscapes. This study aims to explore the impact of mowing on key N2O-producing processes under different topographical conditions in a semi-arid grassland. Soil samples were collected from a semiarid grassland ecosystem in Xilingol region, Inner Mongolia, where long-term management practices including non-mowing and mowing in flat and sloping blocks were conducted. We then determined (1) soil moisture, total carbon (TC) and nitrogen (TN), and mineral N (NH4 +-N and NO3 −-N) content; (2) the potential N2O emission from nitrification (NN2O) and from denitrification (DN2O) and potential N2 emission (DN2); and (3) the gene abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), the narG (nitrate reductase) gene, and nosZ (nitrous oxide reductase) gene. Soil moisture and potential N2O emission from nitrification and denitrification were significantly lower in sloping than in flat conditions, whereas the TC, TN, NH4 +-N, NO3 −-N content, gene abundance of AOA, AOB, narG, and nosZ showed no difference between flat and sloping conditions. Mowing significantly decreased the gene abundance of AOA, AOB, narG in both flat and sloping areas, and significantly decreased potential N2O emissions, especially in sloping areas. The potential N2O emission was significantly lower on sloping than flat grassland. Mowing significantly decreased the potential N2O emissions, especially on sloping grassland. Our results suggest that topographical conditions should be incorporated into methods for estimating N2O emission and land management practices in semiarid grassland.