Severe freezing increases soil respiration during the thawing period: A meta-analysis

It is unclear how changes in soil freeze-thaw processes initiated by climate change might alter soil respiration. Using meta-analysis, we quantified the thawing effect on soil respiration under different freezing intensities and explored possible relationships among effect sizes with environmental factors. Our results showed that the overall mean thawing effect size was 18.84% and was highly variable among different ecosystems. Mild soil freezing (>=-5 degrees C) did not produce a significant thawing effect, while severe soil freezing (<-5 degrees C) consistently increased soil respiration during the subsequent thawing period across a diverse range of terrestrial ecosystems. Thawing effect sizes were significantly positively correlated with soil pH and freezing duration, but negatively correlated with soil C/N ratios, suggesting that soil respiration during thawing periods are stimulated more by freeze-thawing events under conditions of higher soil pH, longer freezing periods or lower soil C/N ratios. Consequently, this study reveals the important role of antecedent soil freezing temperatures in triggering the thawing effect and furthers our understanding of climatic interactions with soil carbon dynamics. Highlights Meta-analysis was conducted to quantify the effect of thawing on soil respiration. Mild soil freezing (>=-5 degrees C) did not produce a significant thawing effect. The threshold freezing temperature that triggers the thawing effect was around -5 degrees C. Thawing effect size was regulated by soil C/N ratio, soil pH, and freezing duration.