Warming and grazing interact to affect root dynamics in an alpine meadow

Aims: Root dynamics plays a fundamental role in determining carbon allocation and other main ecological processes in grasslands. Understanding the responses of root activities to ongoing warming in grazed alpine meadows enable us to predict the potential changes in the carbon budget and ecosystem functions in alpine regions. Methods: We conducted a controlled 4-year field experiment with warming and grazing in an alpine meadow on the Qinghai-Tibetan Plateau. Our objective was to explore the responses of root standing crop, production, mortality and turnover rate to warming and grazing using minirhizotrons. Results: Warming only significantly inhibited root mortality while grazing promoted all the four root metrics, which were also significantly influenced by the interaction of warming and grazing. Warming oppositely affected the four metrics under grazing versus non-grazing conditions. It significantly reduced root mean standing crop, annual production and mortality without grazing, but significantly stimulated only mean standing crop under grazing. Grazing had significantly negative and positive effects on mean standing crop in the no warming and warming plots. It promoted annual root production and mortality regardless of warming, whereas the effects were significant only under warming condition. Moreover, grazing significantly increased turnover rate in no warming plots but slightly decreased it in warming plots. Conclusions: These findings highlight the non-additive interactions on the alpine meadow root dynamics between warming and grazing. Therefore, grazing regimes should be considered to better model the ecosystem feedback to global warming and to improve the prediction of future ecosystem functions.