Methane uptake responses to extreme droughts regulated by seasonal timing and plant composition

Authors: ZHENG, Z. - University Of Chinese Academy Of Sciences; WEN, F.Q. - University Of Chinese Academy Of Sciences; Biederman, Joel; TUDI, M. - Chinese Academy Of Sciences; LV, M. - University Of Chinese Academy Of Sciences; XU, S.R. - Chinese Academy Of Sciences; CUI, X.Y. - University Of Chinese Academy Of Sciences; WANG, Y.F. - University Of Chinese Academy Of Sciences; HAO, Y. - University Of Chinese Academy Of Sciences; LI, L. - Fujian Agriculture And Forest University

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2024
Publication Date: 1/13/2024
Citation: Zheng, Z., Wen, F., Biederman, J.A., Tudi, M., Lv, M., Xu, S., Cui, X., Wang, Y., Hao, Y., Li, L. 2024. Methane uptake responses to extreme droughts regulated by seasonal timing and plant composition. Catena. 237. Article 107822. https://doi.org/10.1016/j.catena.2024.107822.
DOI: https://doi.org/10.1016/j.catena.2024.107822

Interpretive Summary: Long seasonal droughts (consecutive days without rain) are becoming increasingly common. Drought is thought to change the uptake of methane, a potent greenhouse gas, by ecosystems, potentially affecting future climate change. Here we conducted an experiment in which we imposed a 50-day drought at different stages of the summer growing season on a grassland in Inner Mongolia, with different parts of the experiment containing grasses, shrubs, or their mixture. We found that drought increased ecosystem methane uptake regardless of plant composition or seasonal timing. The main mechanism for increased methane uptake was soil moisture reduction, which increased the ease of atmospheric methane entering the soil to encounter methane-consuming microbes. These results suggest that climate-change induced droughts in grasslands may actually slow climate change in terms of atmospheric methane concentrations.

Technical Abstract: Atmospheric concentrations of methane (CH4) have increased over the last century, contributing to global warming. Corresponding increases in extreme drought are likely to alter biological CH4 uptake in terrestrial ecosystems, representing a climate change feedback. To examine how drought seasonal timing and plant community composition regulated CH4 uptake response to extreme-duration droughts, experimental droughts were imposed in early, middle, or late growing season in three different communities (two graminoids, two shrubs and their mixture) in a semiarid grassland. Droughts increased CH4 uptake, but the effect size and pathways varied with seasonal timing. Early-season drought had the least positive effects on CH4 uptake compared to the ambient control, because it excluded the least precipitation and SWC at this climatologically drier part of the growing season. Early and middle drought increased CH4 uptake through pomA abundance and high diffusivity resulting from reduced soil moisture, while late drought increased CH4 uptake only by reducing SWC. In addition, soil NH4+-N content had significant negative impact on CH4 uptake under late drought. Plant composition did not affect CH4 uptake but regulated CH4 uptake in response to droughts. Early and middle drought had larger positive effects on CH4 uptake in shrub communities than in other two communities, in coincidence with larger reductions in SWC and larger increase in pomA abundance, respectively. In contrast, late drought had consistent effects on CH4 uptake across three communities. Our results suggested that magnitude and pathways of extreme drought effects on CH4 uptake are strongly co-regulated by seasonal timing and plant composition.