Whole-soil warming effects on carbon cycling of an alpine grassland ecosystem on the Tibetan Plateau

The impact of warming on the carbon cycling of terrestrial ecosystems determines the carbon cycle-climate change feedback and the future climate. Specifically, how warming affects the carbon cycling in deep soils (>20 cm) remains uncertain, because most of existing manipulation experiments only warm surface soils (<20 cm). In 2018, we started a Total-soil-warming Experiment in an Alpine Meadow (TEAM). We have maintained year-round warming (+4 oC) of the whole soil profile (0-100 cm) in an alpine meadow on the Tibetan Plateau. We anticipate running the experiment for >10 years. I will present an overview and some of the results of TEAM during the first 5 years (2018-2023), including treatment effects on plant communities, soil and microbial properties, and ecosystem processes.

First, warming did not significantly affect plant richness and diversity, and above- and belowground biomass and productivity, but changed the relative proportion of plant functional groups in aboveground biomass (decrease in legumes and increase in forbs). Second, soil physico-chemical properties (including organic carbon and total nitrogen concentrations) and microbial community characteristics (such as carbon use efficiency, community diversity and composition) throughout the profile were mostly unresponsive to warming, although they changed dramatically (e.g. declined) with depth. Third, warming significantly stimulated soil respiration (and microbial respiration) and soil N₂O emission, but did not significantly change root respiration and soil CH₄ uptake. Lastly, warming promoted plant growth, soil microbial respiration, and soil fauna feeding by 8%, 57%, and 20%, respectively, but caused dissimilar changes in their phenology during the growing season. Overall, although ecosystem carbon stocks were not significantly affected by the whole-soil-warming, some processes and variables of the alpine grassland ecosystem showed significant responses. We will continue to monitor these processes and variables to gain a long-term mechanistic understanding of the response of ecosystem carbon cycling to whole-soil-warming in the alpine grassland.