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 aggregates, 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·ha-1, respectively), while the nitrogen (N) fertilizer rates were N1/2 (300 kg·ha-1) and N (600 kg·ha-1). The field test showed that the C2N treatment increased the aggregate contents of the > 2 mm and 0.25–2 mm fractions by 56.59 and 23.41 %, respectively. The mean weight diameter increased by 41.53 %, while the geometric mean diameter increased by 21.62 %. The organic carbon content of large aggregates shows a greater increase, with an average of 28.14 %. The phospholipid fatty acids analysis revealed that bacteria (B) were the most prevalent organisms in the soil, followed by fungi (F). The C3N treatment increased the F / B ratio by 36.46 %, whereas the C3 treatment increased the gram-positive (Gm+)/gram-negative (Gm−) ratio by 19.67 %. We concluded that the response of Mollisols to biochar is primarily determined by the interplay of aggregates, organic carbon, and microorganisms. Based on the sequestration of SOC and the sustainability and stability of the ecosystem, we selected the optimal ratio for biochar and N fertilizer application and provide a scientific basis for the sustainable utilization of Mollisols resources.