Biochar increased soil respiration in temperate forests but had no effects in subtropical forests

As a climate change mitigation strategy, biochar application to soil has been demonstrated to increase soil carbon (C) sequestration and reduce greenhouse gas (GHG) emission. Although numerous manipulative studies have been conducted, it is still not fully understood how biochar application affects soil respiration (Rs) and its components (i.e., autotrophic [Ra] and heterotrophic respiration [Rh]) in forest ecosystems, especially in subtropical forests. In this study, we performed a meta-analysis of forest ecosystems and a field experiment with biochar amendments of 0, 10, and 30 t ha⁻¹ in a subtropical forest in Zhejiang, China to examine the effects of biochar application on Rs and its components. Our results showed that biochar application significantly increased Rs by 20.92% at the global scale with an increase of 20.25% in temperate forests and a nonsignificant effect in subtropical forests. Responses of Rs to biochar application varied with experimental methods and soil textures. Similarly, our field experiment showed that biochar amendment did not significantly affect Ra, Rh, and Rs in a subtropical forest in Eastern China. Specifically, the average Rs under biochar amendments of 0, 10, and 30 t ha⁻¹ were 2.37, 2.06 and 2.15 μmol m⁻² s⁻¹, respectively (P > 0.05). Both Rs and Rh were positively correlated with microbial biomass C (MBC) and negatively with dissolved organic C (DOC). Both apparent temperature sensitivity (Q₁₀) of Rh and Rs were significantly higher under biochar treatments than in the control. Our findings indicate the importance of the differential effects of biochar application on Rs in different forest types for C sequestration, which may inform ecosystem and regional models to improve prediction of biochar effects on forest C dynamics and climate-biosphere feedbacks.