The effect of nitrogen input on methane uptake in a wet and a dry year from a temperate desert steppe

Abstract

Methane is the second most important greenhouse gas, and soils in arid region can oxidise large amounts of atmospheric methane, thereby contributing to mitigating climate warming. Elevating input of atmospheric nitrogen (N) and precipitation change significantly affect the strength of methane sink (uptake from the atmosphere), but this is still unclear in the desert steppe. Therefore, a field simulation N input (Nip) control experiment with a wet year (2019) and a dry year (2021) was done to elucidate the impact of Nip on methane sink in a typical desert steppe of Eurasia. The result showed that this desert steppe was a net sink of atmospheric methane with annaul uptake rate of 3.88 kg CH4 ha−1. And found that methane uptake was much lower in a wet year (33.9 ± 1.6 μg C m−2 h−1, 2019) than that in a dry year (46.9 ± 3.1 μg C m−2 h−1, 2021), which was mainly mediated by soil water-filled pore space. The effect of Nip on methane uptake was varied, both promoting (0.4 % – 1317%) and inhibiting (0.5% – 270.5%). And the inconsistent response of methane uptake was observed to Nip in a wet and a dry year: the methane uptake was decreased significantly with the increase of Nip rate in a wet year (p < 0.05); however, Nip did not significantly affect methane uptake overall in a dry year (p > 0.05). This may attribute to the inhibitory effect of Nip on methane uptake depended on soil moisture (p < 0.01). The abundance ratio of pmoA to mcrA gene was identified as the most significant influencing factors of methane uptake rather than soil inorganic N (NH4+-N or NO3−-N) content. Furthermore, soil moisture had an important indirect effect on methane uptake, mainly through influncing the abundance ratio of pmoA to mcrA gene. Overall, we suggest that the role of soil water-filled pore space and the abundance ratio of pmoA to mcrA gene should be considered when developing biochemical models of methane uptake in arid areas.