Phosphate addition intensifies the increase in N2O emission under nitrogen deposition in wet meadows of the Qinghai-Tibet Plateau.

Abstract

Alpine wet meadows are known as N₂O sinks due to nitrogen (N) limitation. However, phosphate addition and N deposition can modulate this limitation, and little is known about their combinative effects on N₂O emission from the Qinghai-Tibet Plateau in wet meadows. This study used natural wet meadow as the control treatment (CK) and conducted experiments with N (CON₂H₄ addition, N15), P (NaH₂PO₄ addition, P15), and their combinations (CON₂H₄ and NaH₂PO₄ addition, N15P15) to investigate how N and P supplementation affected soil N₂O emissions in wet meadow of QTP. Contrary to previous studies on grasslands, the effect of phosphate addition treatment on soil N₂O flux was not detectable during the growing seasons of 2019 and 2020. Over a span of two years, the N addition treatment significantly increased the N₂O flux by 3.45 μg⋅m^-2⋅h^-1 due to increased soil N availability. Noticeably, phosphate addition intensified the effect of N deposition treatment on soil N₂O flux with high significance in the early growth season of 2020. This augmentation can be attributed to the alleviation of limiting factors imposed by plants and microorganisms on soil N and P, fostering the mineralization and decomposition of litter and soil nutrients by microorganisms. Consequently, the results showed that total nitrogen and nitrate nitrogen were the main controls on soil N₂O emission under N and P addition. In addition, redundancy analysis showed that the relative abundance of NirK genes in soil microorganisms (Bradyrhizobium, Devosia, Ochrobactrum, Alcaligenes, Rhizobium) is the main factor affecting N₂O flux and available nitrogen. We project that if nutrient input continues to increase, the main limiting factor of soil will change from N restriction to P restriction due to the unique microbial nitrogen conversion process in the alpine meadow, significantly increasing N₂O emissions. Consequently, the heightened contribution of alpine wet meadows to global warming and ozone depletion hinges on the dynamics of nutrient input regimes, spotlighting the urgent need for informed environmental management strategies.