Radiation, soil water content, and temperature effects on carbon cycling in an alpine swamp meadow of the northeastern Qinghai–Tibetan Plateau

[摘要] Predicted intensified climate warming will likely alterthe ecosystem net carbon (C) uptake of the Qinghai–Tibetan Plateau (QTP).Variations in C sink–source responses to climate warming have been linked towater availability; however, the mechanisms by which net C uptake respondsto soil water content in saturated swamp meadow ecosystems remain unclear.To explore how soil moisture and other environmental drivers modulate net Cuptake in the QTP, field measurements were conducted using the eddycovariance technique in 2014, 2015, 2017, and 2018. The alpine swamp meadowpresented in this study was a persistent and strong C sink of CO 2 ( −168.0   ±  62.5 g C m −2  yr −1 , average  ±  standarddeviation) across the entire 4-year study period. A random forestmachine-learning analysis suggested that the diurnal and seasonal variationsof net ecosystem exchange (NEE) and gross primary productivity (GPP) wereregulated by temperature and net radiation. Ecosystem respiration (Re),however, was found mainly regulated by the variability of soil water content(SWC) at different temporal aggregations, followed by temperature, thesecond contributing driver. We further explored how Re is controlled bynearly saturated soil moisture and temperature comparing two differentperiods featuring almost identical temperatures and significant differenceson SWC and vice versa. Our data suggest that, despite the relativelyabundant water supply, periods with a substantial decrease in SWC orincrease in temperature produced higher Re and therefore weakened the C sinkstrength. Our results reveal that nearly saturated soil conditions duringthe growing seasons can help maintain lower ecosystem respiration rates andthus enhance the overall C sequestration capacity in this alpine swampmeadow. We argue that soil respiration and subsequent ecosystem C sinkmagnitude in alpine swamp meadows could likely be affected by future changesin soil hydrological conditions caused by permafrost degradation oraccelerated thawing–freezing cycling due to climate warming.

[学科分类] 大气科学