The Effects of Biochar Derived from Feedstock with Different Si and Al Concentration on Soil N2O and CO2 Emissions.

Desilicification and allitization is important characteristic of acidic soil. While decrease in soil silicon (Si) may generate Si limitation, the increase of aluminum (Al) will aggravate soil acidification. Biochar has been used in acid soil improvement, which could mitigate nitrous oxide (N2O) emissions and alter soil Si and Al concentration. However, the effect of biochar with different Si and Al concentration on greenhouse gas emissions remains unclear. We evaluated the effects of biochar derived from feedstock with different Si (moso bamboo leaves, BL; rice straw, RS) and Al (Camellia oleifera fruit shell, CFS; C. oleifera leaves, CL) concentration on greenhouse gas emissions and soil acidification. Microbial functional gene abundance associated with N2O emissions were measured to further explore the response of microbiological community. The results showed that BL, RS, CFS and CL significantly increased soil pH (by 19.2%, 16.7%, 18.7% and 24.9%, respectively), decreased soil exchangeable acid and exchangeable Al content, and reduced N2O emission rate of soil with nitrogen (N) (by 14.2%, 27.3%, 25.6% and 38.7%, respectively), which correlated with increase in soil nosZ abundance. BL, RS, CFS and CL increased soil nirK (by 325.6%, 66.7%, 155.8%, and 253.2%, respectively) and nosZ (by 198.6%, 174.1%, 72.2%, and 152.0%, respectively) abundance with N. Structural equation model showed that Si input via biochar application directly reduced N2O emissions, and soil acid-extractable Si is inversely proportional to N2O emission rate. In addition, Si input reduced carbon dioxide (CO2) emissions via indirect effects. Al input via biochar addition indirectly affected N2O and CO2 emissions through mainly indirect effects on other soil factors. In intensive management and production activities, Si-rich biochar can be considered instead of sole addition as fertilizer, which will be beneficial to the sustainable development of agricultural and forestry production in acid soil areas, and mitigation of global change.