from the declines in net ammonification and nitrification rates (Fig. 1 and Fig. S3). Acid addition did not change the content of soil organic carbon or total soil nitrogen (Fig. S3). Total soil CO2 efflux and its sources (microbial and root respiration) were substantially changed by acid addition (Fig. 2), although there was significant difference between months (Fig. 2a–c). Total soil respiration and soil microbial respiration declined with increasing acid addition rate for each month (Fig. 2a–b). In contrast, root respiration increased with acid addition for each month (Fig. 2c). After averaging the total soil CO2 efflux and its sources of three months into one, we also found that the total soil respiration and soil microbial respiration decreased with acid addition while root respiration increased with acid addition (Fig. 2d–f)