The stability of biochar in the environment determines the stability of its environmental effects and is an important aspect to evaluate the environmental and environmental significance of biomass carbon. This paper mainly discusses the three major processes of physical, chemical and biological decomposition that biomass carbon may undergo in the environment and its influencing factors, pointing out physical fragmentation, physical migration, chemical dissolution, chemical oxidation, biocatabolism, And the nature of biochar itself affects the stability of biochar in the environment, and proposes future research directions worthy of attention.

The physical decomposition of biochar in soil mainly includes physical erosion and physical migration, resulting in a certain loss of C. The main action pathways and influencing factors are summarized in Figure 1. Physical erosion is mainly caused by the fragmentation of biomass carbon, which changes from large particles to small particles. In this process, biomass carbon is mainly affected by environmental effects such as grinding, freezing and thawing, expansion and water flow impact, and produces some biomass carbon particles. Physical migration is mainly the movement process of biomass carbon particles in the soil, mainly in the form of lateral migration and longitudinal migration. During the migration process, it is affected by factors such as pyrolysis temperature, pH, ionic strength, and environmental medium composition.

Figure 1 Physical decomposition and migration process of biomass charcoal in the environment
The chemical decomposition of biochar mainly includes dissolution and chemical oxidation. The main action pathways and influencing factors are summarized in Figure 2. Biomass carbon produces a release of soluble biomass carbon and soluble organic carbon through dissolution, and the amount of release is related to the pyrolysis temperature of biomass carbon and the type of biomass. Oxidation promotes the formation of oxygen-containing functional groups on the surface of biomass carbon and increases its reactivity. Its oxidation in the environment is mainly affected by factors such as humidity, exposure time, temperature, soil minerals and organic matter, pyrolysis temperature, and biomass sources.

Fig. 2 Chemical decomposition process and influencing factors of biomass carbon in the environment

The biodegradation process of biochar mainly includes soil bio-utilization, metabolism and catalytic degradation process of enzymes. The action pathways and influencing factors are summarized in Figure 3. Microbial degradation is one of the important pathways for the decomposition of biomass carbon in soils and sediments. At present, the biological metabolism of biomass carbon is mainly measured by the bioavailability of biomass carbon. The biological stability of biomass carbon is affected by both its own nature and environmental conditions. Biomass carbon enhances biostability by interacting with environmental components. At the same time, biomass carbon also has a certain impact on microbial composition and activity, which affects the degradation of biomass charcoal by microorganisms.

Figure 3 Biodegradation process of biomass charcoal in the environment

In view of the above analysis, the following research directions are worthy of attention: (1) release and migration behavior of biomass carbon particles under water flow and its influencing factors, (2) redox activity of biomass carbon itself and its environment The relationship between chemical oxidation, (3) physical, chemical and microbial decomposition of biomass charcoal in the rhizosphere of plants. The systematic and in-depth study of the role of postgraduate material charcoal in the environment is conducive to improving people’s understanding of the process of biochar charging, and thus more comprehensive understanding of the stability of biochar in the environment.