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

Abstract

Despite the importance of soil respiration (R_s) in the global carbon (C) cycle, our understanding of the dynamics of R_s and its temperature sensitivity (Q₁₀) over time and across timescales remains to be improved for dryland ecosystems. We measured R_s continuously in a temperate semiarid shrubland in northern China during 2013–2019 to examine seasonal and interannual variations in R_s and Q₁₀. Daily mean R_s ranged from values close to zero in winter to 1–3 µmol CO₂ m⁻² s⁻¹ in summer. Daily mean R_s increased exponentially with soil temperature (T_s) at 10-cm depth in spring and autumn, being greater in autumn at a given T_s, but decoupled from T_s in summer. Summertime R_s 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 R_s 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 R_s−T_s relationships) than for diel Q₁₀ (estimated from diel R_s−T_s relationships over a five-day moving window). Synchronizing the diel oscillations in R_s and T_s enhanced diel Q₁₀ from 1.8 ± 0.4 (mean ± SD) to 2.5 ± 0.6, suggesting the need to consider the diel hysteresis between R_s and T_s for accurate modeling of hourly R_s dynamics. Both seasonal and diel Q₁₀ decreased with increasing T_s, and diel Q₁₀ increased with increasing SWC. Our findings demonstrate that hydrothermal controls on R_s and Q₁₀ vary across seasons and timescales, and highlight the role of seasonal hydrothermal drivers in regulating long-term ecosystem C balance.