Long-term biochar application influences soil microbial community and its potential roles in semiarid farmland

Biochar addition to soil can change soil physicochemical properties, resulting in a shift of the soil microbial community. However, it is uncertain how long-term biochar application affects the soil microbial community and diversity in drylands. To determine the underlying mechanism, a 3.5-year spring maize (Zea mays L.) field experiment with biochar applications was conducted to elucidate the effect of biochar on soil microbial abundance and community composition as well as its potential applications in drylands of the Loess Plateau in Northwest China. Soil samples from a 0-20 cm depth for four biochar treatments, including 0 (CO, as the control), 10 (C10), 30 (C30) and 50 (C50) t ha(-1), were examined using phospholipid fatty acid (PLFA) analysis. It was found that the proportion of arbuscular mycorrhizal fungi (AMF) and the ratio of AMF/saprotrophic fungi (SF) correlated with the biochar levels, for example, the C30 treatment significantly decreased the absolute SF but increased the ratio of AMF/SF. Especially, both the AMF/SF and Fungi/Bacteria ratios were significantly increased in the C50 treatment, suggesting that high amounts of biochar could increase fungal rather than bacterial diversity. In addition, soil organic C (SOC) (P < 0.01), KMnO4-oxidizable C (KMnO4-C) (P < 0.01), and the C management index (CMI) (P < 0.01) were confirmed to play significant roles in shaping the soil microbial community composition. SOC and total N were significantly increased by biochar application, and total P was increased in the C30 treatment. However, compared with the CO treatment, the C50 treatment significantly decreased KMnO4-C and the CMI, suggesting the proper level of biochar addition to soil should be considered for the improvement of soil organic materials. Accordingly, biochar application at 30 t ha(-1), which was connected with a decreased absolute SF and an increased AMF/SF ratio, could be a choice for improving soil quality and nutrient availability in semiarid farmland.