Soil carbon-degrading enzyme activities were more sensitive to warming in the alpine meadow than swamp meadow

The continuously increasing temperature is expected to accelerate soil organic carbon (SOC) decomposition and release additional CO₂ into the atmosphere by stimulating microbial activity. However, there remains significant uncertainty regarding the response of microbial activity to warming, which hinders accurate predictions of the SOC-climate feedback. Extracellular enzymes produced by soil microbes are the primary agents of SOC decomposition. Investigating soil carbon-degrading enzymes has improved our understanding of the physiological mechanisms underlying the SOC response to warming. This study demonstrates that the activities of soil extracellular enzymes were significantly altered in the alpine meadow, but not significantly in the swamp meadow, which coincided with the SOC content of these grasslands. The observed disparities can be attributed to variations in enzyme types, as well as the unique physicochemical and microbiological properties of each meadow type. The researchers' findings were published on March, 2025, in Soil Ecology Letters.

An in-situ warming experiment, involving the manipulation of both warming magnitude and duration, was conducted in alpine and swamp meadows simultaneously in a representative permafrost zone of the Tibetan Plateau by Ruiying Chang's team at the Institute of Mountain Hazards and Environment, Chinese Academy of Sciences. They measured the activities of three typical soil carbon-degrading enzymes (β-1, 4-glucosidase (BG), peroxidase (PER), phenol oxidase (POX)) after 3 and 6 years of warming at magnitudes of +2.4 and +4.9°C above the ambient temperature, respectively.

In this study, they found that the duration of warming plays a varying role in regulating the responses of enzyme activities and SOC storage in different types of alpine grasslands. A time-cumulative effect of warming on carbon-degrading enzyme activities was observed in the alpine meadow. After six years of warming, BG activity was significantly increased, while POX activity and the ratio of oxidase to hydrolase activities were decreased. These changes coincided with an increase in SOC content in the grassland. In contrast, neither the warming intensity nor the duration had a consistent impact on soil enzyme activities or SOC content in the swamp meadow. The primary factors influencing soil enzyme activities under warming in the alpine meadow were dissolved organic carbon and above-ground biomass, while soil water content was the main factor influencing enzyme activities in the swamp meadow. The variation in above-ground biomass, soil physicochemical, and microbiological properties can account for the discrepancies (a negative correlation (p < 0.05) between SOC and oxidase/hydrolase activity was found in the alpine meadow but not in the swamp meadow) between the two meadows. This indicates that carbon input and enzyme characteristics jointly determine how SOC responds to warming in alpine grasslands.

The study investigated the responses of SOC and soil carbon-degrading enzyme activities to different warming magnitudes and durations and revealed the enzymatic mechanisms underlying SOC responses. Furthermore, they emphasized the need to consider the time-cumulative effects of warming on plant growth and enzyme ratios in carbon models to improve the accuracy of model predictions for soil carbon dynamics in permafrost regions.

DOI: 10.1007/s42832-024-0291-x