Duoji Wu

Microbial necromass carbon (MNC) is the dominant contributor to soil organic carbon (SOC). However, the contribution of MNC in different soil compartments to SOC sequestration has not been comprehensively studied, especially under the organic fertilizers input. To address this gap, we conducted a rice root box experiment by adding organic fertilizer (straw and straw biochar) and chemical fertilizer alone to red loamy paddy soil, respectively. We found that although SOC accumulation was stimulated by both biochar and straw in the rhizosphere, more substantial SOC was sequestered in the rhizosphere due to biochar addition (increased by 25.82% compared to straw addition). Additionally, the input of organic fertilizers resulted in varying degrees of MNC retention in the different soil compartments. Compared with that in bulk soil, fungal necromass carbon (FNC) content was reduced by 1.37% and 7.06%, and bacterial necromass carbon (BNC) content was reduced by 5.53% and 9.49% in the rhizosphere and hyphosphere, respectively, following straw addition. Conversely, the addition of biochar leads to a significant increase of FNC (increased by 2.92%) and BNC (increased by 2.00%) in the rhizosphere compared with bulk soil. However, straw addition also significantly enhanced SOC thermal stability within the rhizosphere and hyphosphere soils. Based on partial least squares path modeling, we found that SOC thermal stability was significantly and positively influenced by FNC, which was strongly associated with carbon degradation gene abundance. These results emphasize the critical role of soil compartments in SOC sequestration under organic fertilizer application and underscore the importance of FNC in enhancing SOC stability in the rhizosphere.

Background and Aims Silicon (Si) -accumulating plants alleviate the problem of low soil Si availability due to high weathering by absorbing labile Si from phytoliths in the soil. However, the efficient release of Si from Si-rich plant residues has not been well studied. Methods Rice husk and bamboo leaves were prepared and transformed into rice husk biochar (RHB), bamboo leaf biochar (BLB) and their alkali-modified biochar (ARHB, ABLB), which were then applied to highly weathered soils (high-available Si soil (HASi) and low-available Si soil (LASi)). Explore efficient Si release pathways and evaluate their potentials as efficient Si fertilizers. Results The first-order model demonstrated that the biochar Si pools were divided into rapidly-released Si pool C1 and slowly-released Si pool C2, and that alkali-modified biochar had higher Si solubilization capacity. A soil incubation experiment showed that available Si of the soils treated with alkali-modified biochar were significantly increased compared to those treated with original biochar, and this effect was more significant in LASi. In a rice growth pot experiment, biochar addition increased the grain, straw, and root Si concentration in LASi, with the effect being independent of amount added. However, for HASi, Si-rich biochar had no effect on straw Si concentration. Conclusions The alkaline pre-treatment of Si-rich biomass can improve its Si release efficiency, leading to increased labile Si content in the soil and improved soil Si availability. Therefore, alkali-modified Si-rich biochar can better sustain Si availability in soils characterized by high weathering and severe desilication.