Biochar promotes soil aggregate stability and associated organic carbon sequestration and regulates microbial community structures in Mollisols from northeast China

Abstract. Since the 1950s, heavy plowing of Mollisols, combined with a lack of organic matter intake, has resulted in severe soil degradation in northeast China. The use of biochar in combination with fertilizer is a sustainable method of improving soil quality. In this paper, we conducted field experiments to explore the response of the stability mechanism of the soil aggregate, the dynamic properties of organic carbon, and changes in the microbial community structure to biochar. The biochar input levels were C1, C2, and C3 (9.8, 19.6, and 29.4 Mg C ha−1, respectively), while the nitrogen (N) fertilizer rates were N1/2 (300 kg N ha−1) and N (600 kg N ha−1). Results indicated that biochar combined with N fertilizer effectively increases soil carbon storage and aggregates stability (P<0.05). And C2N treatment increased the aggregate contents of the >2 mm and 0.25–2 mm fractions by 56.59 % and 23.41 %, respectively. The phospholipid fatty acid (PLFA) analysis revealed that microbial community structure was effectively improved with biochar combined with N fertilizer application (P<0.05). The F/B ratio increased by 25.22 % and the gram-positive (Gm+) to gram-negative (Gm−) ratio by 4.65 % under the C2N1/2 treatment. This study concluded that the response of Mollisols to biochar is primarily determined by the interplay of aggregate, organic carbon, and microorganisms. Therefore, the use of biochar combined with N fertilizer might mitigate soil degradation of Mollisols under an optimal application ratio, but the underlying mechanism still requires further exploration. This study will provide a scientific basis for the conservation and sustainable utilization of Mollisols resources.