Temporal variation in soil respiration and its sensitivity to temperature along a hydrological gradient in an alpine wetland of the Tibetan Plateau

Abstract Wetlands are predicted to experience lowered water tables due to permafrost degradation in the Tibetan Plateau. These changes may affect carbon cycle processes such as soil respiration (Rs). However, the magnitude, patterns and controls of Rs remain poorly understood in alpine wetlands with their distinct hydrological regimes. Here, we conducted a field study on Rs from 2012 to 2014 in three alpine ecosystems on the Tibetan Plateau—fen, wet meadow and meadow—with soil water decreases along hydrological gradients. From 2012 to 2014, the annual Rs was 128.9–193.3 g C m−2yr−1, 281.5–342.9 g C m−2yr−1, and 663.4–709.1 g C m−2yr−1 for the fen, wet meadow, and meadow, respectively. An abrupt increase in CO2 emissions was caused by the spring thawing of the frozen soil in the fen and wet meadow, contributing 20.4–37.6% and 13.2–17.4%, respectively, to the annual Rs. The diurnal variation in the Rs was site specific among the three ecosystems, with one peak at 1300 h in the fen and meadow and two peaks at 1300 h and 1900 h in the wet meadow. The temperature-independent components of the diurnal variation in Rs were generally explained by photosynthetically active radiation in the fen and wet meadow, but not in the meadow. The temperature sensitivity of the Rs (unconfounded Q10) varied significantly among the three ecosystems, with the highest values occurring in the wet meadow, implying that permafrost thaw-induced wetland drying from the fen to the wet meadow could enhance the response of CO2 emissions to climate warming but that further drying from the wet meadow to the meadow probably weakens the effect of warming on the Rs. Our study emphasized the important role of the hydrological regime in regulating the temporal variation in Rs and its response to climate warming.