Phosphate addition intensifies the increase in NO emission under nitrogen deposition in wet meadows of the Qinghai-Tibet Plateau.

Alpine wet meadows are known as NO 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 NO 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 (CONH addition, N15), P (NaHPO addition, P15), and their combinations (CONH and NaHPO addition, N15P15) to investigate how N and P supplementation affected soil NO emissions in wet meadow of QTP. Contrary to previous studies on grasslands, the effect of phosphate addition treatment on soil NO 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 NO flux by 3.45 μg⋅m⋅h due to increased soil N availability. Noticeably, phosphate addition intensified the effect of N deposition treatment on soil NO 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 NO emission under N and P addition. In addition, redundancy analysis showed that the relative abundance of genes in soil microorganisms (, , , , ) is the main factor affecting NO 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 NO 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.