Long-term artificial drainage altered the product stoichiometry of denitrification in alpine peatland soil of Qinghai-Tibet Plateau

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Peatlands, which play a vital role in the global storage of carbon (C) and nitrogen (N), have been artificially drained worldwide over the last few decades. However, the effects of long-term artificial drainage on the soil N cycle and subsequent potent greenhouse gas emissions in peatland soils are not fully understood. In this study, we investigated the effect of drainage on soil properties, aboveground and belowground community compositions, and the N cycle-related functional gene abundances in the world's largest alpine peatland (Zoige Peatland, Qinghai-Tibet Plateau), which has been artificially drained for the past 50 years. We further examined the different responses of soil-borne CO2, N2O, and N2 emissions to three successive “hot moment” events (rewetting, nitrogen deposition, and an oxic-to-anoxic transition) between the drained and natural alpine peatlands using a robotized continuous flow system under an He/O2 atmosphere. A markedly lower CO2 flux (34%) was observed in drained peatlands compared to natural peatlands, likely associated with the increased soil bulk density, plant species diversity, and microbial diversity in the former. The N2O emissions in the drained peatland were 45% lower than those in the natural peatland under oxic conditions, with the 15N-N2O site-preference (SP) value indicating a higher denitrification contribution in the drained peatland (57%) than in the natural peatland (42%). In contrast, under anoxic conditions, higher N2O emissions (52%), lower denitrification rates (20%), lower denitrification functional gene abundances (nirK: 34%; nirS: 19%; nosZ: 24%), and lower N2 emissions (36%) were observed in drained peatlands than in natural alpine peatlands. Molecular analyses further suggested that the different responses of N2O emissions might be driven by the reshaping of microbial communities, which are strongly affected by changes in the soil physicochemical properties. Our results indicate that drainage is unfavorable in terms of greenhouse gases (GHGs) emissions in peatlands and that rewetting the Zoige alpine peatlands should be considered as a smart option from a climatic perspective in the future.