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.