Combined application of biochar and N increased temperature sensitivity of soil respiration but still decreased the soil CO2 emissions in moso bamboo plantations.

Biochar addition to soil is increasing worldwide, the effect of combined application of biochar and nitrogen (N) fertilizer on soil respiration is still unknown. Understanding of the interactive effects of biochar and N fertilizer addition on temperature sensitivity of soil respiration and temporal dynamics of soil CO2 emissions in forest ecosystems remains limited. We conducted a full factorial experiment with biochar (B0, B1 and B2 with 0, 5 and 20 t·ha-1, respectively) and N fertilizer addition (N0 and N1 with 0 and 50 kg·ha-1 NH4NO3, respectively) as factors, to study their effects on soil respiration rate, temperature sensitivity (Q10), soil available nutrients, and their relations in moso bamboo plantations in subtropical China from April 2014 to April 2016. We found that, irrespective of biochar addition rate, N fertilization increased Q10 on the one hand, and irrespective of N fertilization rate, lower application rate of biochar resulted in a higher Q10, on the other hand. In spite of increased Q10, combined application of biochar and N decreased soil respiration rate in both growing season and non-growing season, as well as the annual cumulative soil CO2 emissions. Annual cumulative soil CO2 emissions were found to be significantly positively correlated with soil total nitrogen (STN) (p = 0.028) in 0-10 cm soil layer, and with soil ammonium (NH4+) (p = 0.000) and soil microbial biomass carbon (MBC) (p = 0.000) in both 0-10 cm and 10-20 cm soil layer. The present study suggests that the combined application of biochar and N fertilizer can be widely used in subtropical forest ecosystems where soil N is limited, because it increases soil fertility and, at the same time, decreases soil CO2 emissions.