[Effects of Biochar Addition on Organic Carbon Mineralization and Enzyme Activity in Purple Soils with Different...

This study investigated the effects of biochar addition on soil nutrients, acidification indicators, organic carbon mineralization, and enzyme activities related to the carbon cycle in purple soils with different degrees of acidification developed from the same parent material, providing a scientific basis for the improvement of purple soils with different degrees of acidification and soil carbon management. An indoor incubation experiment was conducted with three acidification treatments: ① severe acidification (AS), ② moderate acidification (AM), and ③ mild acidification (AL). Equal amounts of biochar were added to each treatment, and soil nutrient content, acidification indicators, organic carbon mineralization, and enzyme activities related to the carbon cycle were measured at different time periods. The results showed that: ① After incubation, soil pH, soil organic carbon (SOC), total nitrogen (TN), carbon-to-nitrogen ratio (C/N), and exchangeable base cations increased, while exchangeable acidity decreased. The pH range in the AS, AM, and AL treatments was 4.57-6.19, increasing by 0.09, 0.34, and 0.37 units, respectively, compared to that before biochar addition. ② The carbon mineralization rate [R(CO₂)] and cumulative carbon mineralization [C(CO₂)] were in the order of AL > AM > AS. Particulate organic carbon (POC) was the lowest in moderately acidified purple soil, light fraction organic carbon (LFOC) increased with decreasing acidification degree, and dissolved organic carbon (DOC) and microbial biomass carbon (MBC) were the highest in mildly acidified purple soil. ③ The activities of cellulose bisection hydrolase (CBH), β-glucosidase (GLU), invertase (INV), and the geometric mean of enzyme activities (GM_EA) decreased with increasing acidification degree. ④ C(CO₂) was significantly positively correlated with soil physical and chemical properties (pH, SOC, and TN), enzyme activities (CBH, GLU, INV, and GM_EA), and carbon fractions (DOC and LFOC) (P<0.01) and was significantly positively correlated with AP and C/N (P<0.05). Overall, biochar addition can increase soil nutrient content, raise soil pH, and promote cumulative carbon mineralization in acidic purple soils. The application rate of biochar should be determined based on local conditions for different degrees of acidification in purple soils to improve the quality of cultivated land.