Biochar addition increases subsurface soil microbial biomass but has limited effects on soil CO2 emissions in subtropical moso bamboo plantations.

Biochar addition affects soil conditions and soil microorganisms, and it may reduce soil CO 2 emissions. However, knowledge on how biochar addition induces the changes in soil microbial communities with soil depth and time and affects soil respiration is limited in forest ecosystems. We investigated the effects of biochar addition on soil respiration rate and its sensitivity to soil temperature and microbial community composition in moso bamboo (Phyllostachys eduis) plantations in subtropical China for two years. We set up four treatments of biochar addition onto the soil surface of the plantations with the level of 0 (control, CK), 5 (low biochar, LB), 10 (medium biochar, MB), or 20 t biochar ha−1 (high biochar, HB) in April 2014. Biochar addition significantly improved soil moisture at 5 cm soil depth but did not affect soil temperature. Microbial biomass increased significantly with biochar addition at 10–20 cm soil depth but showed no response in the 0–10 cm depth soil layer. Compared to CK, biochar addition significantly affected the mean soil respiration rate during the two–year experiment, but the difference between CK and biochar treatments decreased both with time following biochar addition and with increasing biochar dosage. Annual cumulative soil respiration was significantly and positively correlated with the biomass of total PLFAs, gram-negative bacteria, bacteria, and arbuscular mycorrhizal fungi (P < 0.05) at 0–10 cm soil depth but not at 10–20 cm. Overall, only LB significant decreased the total CO 2 emissions. Our results suggest that lower dosage additions of biochar have a positive effect in reducing total CO 2 emissions and promote soil organic carbon sequestration in bamboo forests in subtropical China. • Low biochar addition seems to be the best dosage to decrease soil respiration rate. • Biochar addition significantly increased microbial biomass in subsurface soil layer. • Increased subsurface microbial biomass has limited effect on reducing soil CO 2 efflux. • Annual cumulative CO 2 efflux was consistent with total PLFAs biomass in surface soil. [ABSTRACT FROM AUTHOR]