Convergence in temperature sensitivity of soil respiration: Evidence from the Tibetan alpine grasslands

Abstract Recent studies proposed a convergence in the temperature sensitivity (Q 10 ) of soil respiration (R s ) after eliminating confounding effects using novel approaches such as Singular Spectrum Analysis (SSA) or the mixed-effects model (MEM) method. However, SSA has only been applied to eddy covariance data for estimating the Q 10 with air temperature, which may result in underestimations in responses of below-ground carbon cycling processes to climate warming in coupled climate-carbon models; MEM remains untested for its suitability in single-site studies. To examine the unconfounded Q 10 of R s , these two novel methods were combined with directly measured R s for 6 years in two Tibetan alpine ecosystems. The results showed that, 1) confounded Q 10 of R s estimated from seasonal R s -temperature relationship positively correlated with the seasonality of R s , and 2) estimates of unconfounded Q 10 of R s using SSA (mean = 2.4, 95% confidence interval (CI): 2.1–2.7) and MEM (mean = 3.2, 95% CI: 2.3–4.2) were consistent with the theoretical subcellular-level Q 10 (≈2.4). These results support the convergence in the Q 10 of R s and imply a conserved R s -temperature relationship. These findings indicate that the seasonality of R s has to be eliminated from estimating the Q 10 of R s , otherwise the estimates should be questionable. They also indicate that seasonal Q 10 and its responses to warming should not be directly used in carbon-climate models as they contain confounding effects.