Plant communitymediated methane uptake in response to increasing nitrogen addition level in a saline-alkaline grassland by rhizospheric effects

Methane (CH4) uptake in dryland ecosystems is a pathway in mitigating atmospheric CH4 concentrations. A number of studies have demonstrated that nitrogen availability is a key regulator of the CH4 oxidation process. However, how plants mediate soil CH4 oxidation in response to N addition, particularly in saline-alkaline grasslands in the vast regions of the northern China, has received little attention. We conducted a 3-yr (2017-2019) in-situ experiment with eight N addition levels to examine the effect of N on soil CH4 oxidation, and to explore the linkages between the N-induced changes of plant community and the seasonal dynamics of CH4 in a saline-alkaline grassland. We found that the saline-alkaline grassland was a weak CH4 sink displaying nonlinear CH4 uptake levels in response to N additions, possibly due to the nonlinear changes in the abundance of key functional genes (pmoA) that were responsible for CH4 oxidation. The changes in plant productivity and diversity that were induced by N additions explained 21 % of the variations in CH4 uptake. The N-induced increase in productivity indirectly enhanced CH4 uptake at N addition rates of <10 g m(-2) yr(-1), while the decrease in biodiversity indirectly inhibited CH4 uptake when N addition exceeded 10 g m(-2) yr(-1). The N-induced changes in the plant community can affect CH4 uptake, mainly through the rhizospheric effects of plants. In conclusion, our findings underscore the importance of rhizosphere when assessing the CH4 uptake in saline-alkaline grassland ecosystems.