Mechanisms of phosphorus activation in charosphere and non-charosphere: The priming effect of biochar

Abstract

Biochar is widely used in soil to increase the soil phosphorus content, but a special ecological zone called the “charosphere” zone is formed where biochar comes into contact with soil. The physical and chemical properties of charosphere soil are different from those of the original soil and the biochar itself, leading to uncertainty regarding the effect of charosphere soil on the phosphorus cycle. Hence, we designed a barrier device to separate biochar from soil and analyzed the impact of biochar diffusion on soil nutrient content and microbial activity. Then, the variation characteristics of the community structure of phoD-harboring bacteria and fungi in the carbonosphere (group B) and non-carbonosphere (group C) were explored. Finally, the key factors and potential driving mechanisms of soil phosphorus activation were explored. The results show that biochar improved soil microbial activity and stimulated the soil nutrient recycling, resulting in a 67.28 % greater percentage of the labile P fraction in group B than in group C. The alpha diversity and nutrient transfer efficiency of the phoD-harboring bacterial community in group B were greater than those in group C, while the phoD-harboring bacterial co-occurrence network of group C was more complex. Moreover, the synergy between the co-occurrence networks of the soil fungal community was stronger than that of the bacterial community. Biochar stimulates microbial activation of phosphorus by increasing the DOC content and pH in the charosphere, and the phoD-harboring bacterial community dominates soil phosphorus activation. These findings offer a new perspective on how biochar regulates soil phosphorus cycling, providing crucial information to guide the application of biochar in agroecosystems.