Distinct responses of soil carbon-degrading enzyme activities to warming in two alpine meadow ecosystems on the Qinghai-Tibet Plateau

Abstract

Soil C-acquiring enzyme activities of alpine and swamp meadows were examined under warming. BG activity increased with warming duration in alpine meadow but not in swamp meadows. Warming tended to decrease POX activity in both alpine and swamp meadows. SOC was negatively correlated with the ratio of oxidase to hydrolase activity in alpine meadows. Soil extracellular enzymes play a central role in regulating soil organic carbon (SOC) dynamics. However, the effects of varying warming magnitudes and duration on permafrost soil carbon-degrading enzyme activities remain poorly understood. Here, we investigated warming effects on three representative carbon-degrading enzymes (β-1,4-glucosidase (BG), peroxidase (PER), phenol oxidase (POX)) in alpine and swamp meadows on the Qinghai-Tibet Plateau. The warming experiments were conducted using Open-top chambers at different warming magnitudes (+2.4 and +4.9 °C) and duration (3 and 6 years) in both meadows. The activity of BG increased with warming duration in alpine meadows regardless of the warming magnitude (69% and 45% for lower and higher warming treatments, respectively), although the effect was significant (p<0.05) only under 6-year warming. In contrast, warming did not significantly (p>0.05) alter BG activity in swamp meadows. Warming decreased POX activity in both alpine (62%) and swamp meadows (81%), but the effect was significant only under 6-year higher warming. Moreover, PER activity was not significantly influenced by warming in either meadow. Dissolved organic carbon and above-ground biomass were the primary factors influencing soil enzyme activities under warming in alpine meadow, while soil water content in swamp meadow. Noticeably, a negative correlation (p<0.05) was observed between SOC and oxidase/hydrolase activity in alpine meadow, suggesting the suppression of oxidase activity may benefit SOC storage under warming. Noticeably, a negative correlation (p<0.05) between SOC and oxidase/hydrolase activity was found in alpine meadow but not in swamp meadow, which was due to the difference in above-ground biomass. These findings highlight the need to consider the time-cumulative warming effects on plant growth and enzyme ratios in carbon models to improve the accuracy of model predicting of soil carbon dynamics in permafrost regions.