Seasonal timing of extreme drought regulates N2O fluxes in a semiarid grassland

Authors: LI, L.F. - Chinese Academy Of Sciences; HAO, Y.B. - Chinese Academy Of Sciences; WANG, W.J. - University Of Queensland; Biederman, Joel; ZHENG, Z. - Chinese Academy Of Sciences; ZHANG, Z. - Chinese Academy Of Sciences; WANG, Y. - Chinese Academy Of Sciences; SONG, X. - Chinese Academy Of Sciences; CUI, X. - Chinese Academy Of Sciences; XU, Z. - University Of Queensland

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2023
Publication Date: 5/30/2023
Citation: Li, L., Hao, Y., Wang, W., Biederman, J.A., Zheng, Z., Zhang, Z., Wang, Y., Song, X., Cui, X., Xu, Z. 2023. Seasonal timing of extreme drought regulates N2O fluxes in a semiarid grassland. Geoderma. 436. Article 116530. https://doi.org/10.1016/j.geoderma.2023.116530.
DOI: https://doi.org/10.1016/j.geoderma.2023.116530

Interpretive Summary: Agroecosystems are important sources of nitrous oxide (N2O) a key greenhouse gas which is more than 250 times as potent as the more well-studied carbon dioxide (CO2). We lack information about how drought in different parts of the year affects N2O fluxes. Here we conducted a 3-year field experiment with drought artificially imposed at different times of the growing season in a semiarid grassland. We found that early-season drought could have variable impacts on N2O emissions, but mid-growing season drought consistently suppressed N2O flux. Late-season drought had little effect. These results suggest that the timing of seasonal rainfall, not just the amount, regulates the balance of greenhouse gas emissions from grassland agroecosystems.

Technical Abstract: Terrestrial ecosystems are important sources of nitrous oxide (N2O), a powerful greenhouse gas which can be strongly impacted by increasing droughts in association with climate change. However, detailed information on whether and how drought timing regulates N2O fluxes is still lacking. Here, we conducted a 3-year field experiment on a semiarid grassland in which extreme drought was imposed in either early-, mid-, or late-growing seasons repeatedly from 2014 to 2016. We found that early drought affected N2O emission with high interannual variability (increased, decreased and unchanged N2O emission in 2014, 2015, and 2016, respectively), coincident with changes in inorganic nitrogen (SIN), dissolve organic carbon (DOC), microbial biomass carbon (MBC), and soil functional genes (bacterial amoA, nirK, nirS, and nosZ). However, middle drought consistently suppressed N2O emissions due to simultaneous decreases in MBC, DOC and the abundances of archaeal amoA, nirK, and narG genes, causing the largest reduction in N2O emissions across the three years. In contrast, late drought had little effect on N2O fluxes, even though DOC and SIN decreased and the abundance of nirK, nirS, and nosZ increased. As a result, soil organic C and mineral N availability and functional gene abundances were not always robust factors for predicting N2O emissions under droughts across all treatments, except for abundance of AOA and nosZ. Our results highlight the vital role of seasonal timing in regulating the response of N2O emissions to extreme droughts.