Effects of different biomass amendments on soil organic carbon characteristics in alpine desertification grassland of Northwest Sichuan

The special geographical environment, climatic conditions, and excessive artificial grazing in the alpine grassland of northwestern Sichuan have caused grassland desertification. To examine the effects of different biomass amendments on the soil organic carbon composition and respiration characteristics in alpine desertification grassland, we adopted a randomized block test design method and two factors field trials for setting biomass amendments and their application rates. The biomass amendments used were three kinds of straw (JG), slag (JZ), and biochar (SWT). The application rates were 6 t·hm^-2 (JG1, JZ1, SWT1) and 18 t·hm^-2 (JG3, JZ3, SWT3). We used blank treatment (CK) as a control to examine the effects of the different amendments on the total organic carbon, the activated organic carbon, and the respiratory characteristics in desertified soil. The findings demonstrated that:1) application of the biomass amendments significantly increased the contents of soil organic carbon (TOC), microbial biomass carbon (MBC), and easily oxidized organic carbon (EOC), which became more obvious as the amounts of amendments were increased. Compared with CK, the organic carbon in the 0-10 cm soil layer increased averagely by 60.66%, 39.22%, and 34.99% with JG, JZ and SWT treatments, respectively; the soil MBC content was expressed as JZ > JG > SWT in the 0-10 cm soil layer, and the difference among treatments were significant. EOC content was the highest in JG treatment; in the 0-10 cm and 10-20 cm soil layers, it was increased averagely by 108.82% and 79.26%, respectively, compared with CK. 2) Under different biomass amendments, EOC/TOC revealed that JG > JZ > SWT > CK, MBC/TOC revealed that JZ > JG > SWT > CK, and the differences among treatments were significant. 3) The application of different amendments increased the soil respiration rate significantly in proportion to the increased application rate of the amendment. Compared with CK, the soil respiration rates of JG1, JZ1, and SWT1 treatments increased by 103.42%, 86.31%, and 18.83%, respectively. The soil respiration rates were significantly higher under JZ and JG treatments compared with SWT and CK treatments. Correlation analysis revealed significant positive correlation of the soil respiration rate with soil water (P < 0.05), and significant positive correlations with organic carbon, MBC, and EOC (P < 0.01). 4) The application of different biomass amendments significantly increased soil respiration, soil microbial respiration, and net ecosystem productivity (NEP), both of which showed strong carbon sink potential. Under JG treatment, the NEP value was significantly higher than that under JZ and SWT treatments, by 56.45% and 122.12%, respectively, and there were significant differences among treatments. These findings suggested that the straw improver had higher carbon sink strength. This study can provide a basis for the development of scientific and effective soil carbon regulation and management measures for improving alpine grassland desertification soil in the northwestern Sichuan Basin in China.