Hydrothermal drivers of seasonal and interannual dynamics of soil respiration and its temperature sensitivity in a temperate semiarid shrubland

Despite the importance of soil respiration (Rs) in the global carbon (C) cycle, our understanding of the dynamics of Rs and its temperature sensitivity (Q10) over time and across timescales remains to be improved for dryland ecosystems. We measured Rs continuously in a temperate semiarid shrubland in northern China during 2013-2019 to examine seasonal and interannual variations in Rs and Q10. Daily mean Rs ranged from values close to zero in winter to 1-3 mu mol CO2 m-2 s-1 in summer. Daily mean Rs increased exponentially with soil temperature (Ts) at 10-cm depth in spring and autumn, being greater in autumn at a given Ts, but decoupled from Ts in summer. Summertime Rs increased with soil water content (SWC) at 10-cm depth up to about 0.16 m3 m-3, beyond which it levelled off or decreased. Annual Rs ranged from 231.8 to 334.9 g C m-2 yr-1 and increased with summer rainfall amount. Estimates of Q10 were generally lower in spring than in autumn, and this difference was more obvious for seasonal Q10 (estimated from seasonal Rs-Ts relationships) than for diel Q10 (estimated from diel Rs-Ts relationships over a five-day moving window). Synchronizing the diel oscillations in Rs and Ts enhanced diel Q10 from 1.8 +/- 0.4 (mean +/- SD) to 2.5 +/- 0.6, suggesting the need to consider the diel hysteresis between Rs and Ts for accurate modeling of hourly Rs dynamics. Both seasonal and diel Q10 decreased with increasing Ts, and diel Q10 increased with increasing SWC. Our findings demonstrate that hydrothermal controls on Rs and Q10 vary across seasons and timescales, and highlight the role of seasonal hydrothermal drivers in regulating long-term ecosystem C balance.