Effect And Mechanisms Of PH On Soil Carbon Sequeatration Of Biochar

Biochar application in soil has been proposed as a promising method for carbon sequestration,along with the co-benefits of mitigating global warming,improving soil fertility, increasing crop yields and enhancing the sorption for pollutants. Observed effects of biochar on CO₂ are often conflicting. As one of the most important character,soil pH plays a crucial part on the physico-chemical and microbial reaction,thus to change the sequeatration potential of biochar. Yet little information is available for the effect and mechanism of soil pH on carbon sequestration of biochar. Therefore, after determining the CO₂ emission of soil after biochar addition, we studied effects of soil pH on the release of inorganic carbonates, degradation of biochar, the stability of SOC and microbial communities, trying to find the mechanism of soil pH on carbon sequestration of biochar, thus to provide the theoretical basis for the eatimation of carbon sequestration potential of biochar. The main original conclusions of this work are as follows:（1） Soil pH can affect the degradation of biochar through changing the dissolution of inorganic carbonates,composition of surface group and release of organic matter. When soil pH is lower, inorganic carbonates prefered to form CO₂,furthermore, C-O and OH increased on the biochar surface. CO₂ emission was accelerated in acidic soils, but was reduced in alkaline soils after biochar addition.The main reason for the acceleration is higher degradation of biochar.（2） Soil pH is the most important parameter on affecting themicrobial communities and CO₂ emission. Soil pH was possitively related with the ratio of gram-negative and gram-positive bacteria （G-/G+）, and negativly related with the ratio of fungi and bacteria （F/B）. In acidic soils, biochar can decreased the substrate limitation by increasing soil pH and bioavailability of SOC,thus to increase the growth of eutrophic bacteria and the enission of CO₂. While in alkaline soil, biochar slightly increased the growth of oligotrophic bacteria and reduced the CO₂ emission.（3） The degradation and the priming effect of SOC by biochar are negatively related with G-/G+. When the G-/G+ is lower, the microorganism tend to utilize the aromatic substance and increase the degradation of biochar. Through agriculture processes, soils with higher G-/G+ tend to have more nutritients （such as soil with excessive use of fertilizers or straw application）, which would lead to higher carbon sequestration potential. To those soils with lower pH or organic carbon, we can add straw or lime to increase their carbon sequeatration through biochar application.