Effects Of Fertilization On Soil Organic Carbon Stability In Yellow Soil Drylan

Making more organic carbon fixed in the soil can achieve the goal of reducing greenhouse gas emissions.The stability of soil organic carbon determines the retention of soil organic carbon in soil,so it is of great significance to study the stability of soil organic carbon.In order to clarify the effect of fertilization on the stability of organic carbon in yellow soil,four treatments were set up from 2020 to2021: no fertilization(CK),single application of chemical fertilizer(NP),reduced application of chemical fertilizer combined with organic fertilizer [1/2(NPM)] and single application of organic fertilizer(M).The response of soil organic carbon stability to different fertilization treatments was studied from the point of view of soil organic carbon and its components,mineralization and microbial community structure.The main results and conclusions are as follows:(1)The reduction of chemical fertilizer combined with organic fertilizer and single application of chemical fertilizer significantly increased the content of soil organic carbon.The increase of soil organic carbon in 1/2(NPM)treatment was 8.5%,8.8%,7.9% and 9.5%,respectively.Fertilization increased soil active organic carbon components,among which the reduction of chemical fertilizer combined with organic fertilizer treatment was the most significant,which increased oxidizable organic carbon by 19.5%-29.3%.Fertilization significantly increased the content of soluble organic carbon and microbial biomass carbon by 30.9%-97.0% and 16.3%-47.0%,respectively.Fertilization significantly increased soil ROC/SOC,DOC/SOC and MBC/SOC by 12.7%-16.7%,20.0%-100.0% and 14.3%-36.5%,respectively.The results showed that the treatment of reducing chemical fertilizer combined with organic fertilizer had higher utilization efficiency of soil carbon pool and better stability of soil carbon pool,which was more conducive to the accumulation of organic carbon.(2)There was no significant difference in the content of free active organic carbon in fertilization.1 NPM treatment significantly increased the content of physically protected organic carbon and chemically protected organic carbon,which increased by 35.0%-83.3% and 9.9%-18.5%,respectively.Only M treatment significantly increased the content of biochemical protected organic carbon components.Compared with CK treatment,there was no significant difference in the distribution proportion of free active organic carbon and biochemically protected organic carbon among different treatments,only 1/2(NPM)treatment significantly increased the distribution proportion of physical protected organic carbon and chemically protected organic carbon by 70.6% and 18.5%,respectively.The results showed that the reduction of chemical fertilizer combined with organic fertilizer significantly increased the stable components of soil organic carbon and thus improved the stability of soil organic carbon.(3)On the whole,the mineralization rate of soil organic carbon decreased sharply at first,then decreased slightly,and finally tended to be stable.The accumulated mineralization of soil organic carbon increased with the culture time,but its intensity gradually slowed down.The cumulative mineralization of soil organic carbon in M treatment was the highest,followed by NP treatment and 1/2(NPM)treatment,and CK treatment was the lowest.Compared with CK treatment,NP treatment and M treatment significantly increased the cumulative mineralization rate of soil organic carbon.The results showed that fertilization promoted soil organic carbon mineralization,and the mineralization of soil organic carbon tended to be stable from fast to slow,among which the reduction of chemical fertilizer combined with organic fertilizer was the most beneficial to soil carbon sequestration.(4)The reduction of chemical fertilizer combined with organic fertilizer significantly increased the bacterial community richness and fungal community diversity,but had no significant effect on the bacterial community diversity and fungal community richness.Fertilization had no significant effect on the dominant species of bacteria and fungi in soil,but changed the relative abundance of bacteria and fungi.The results of Beta diversity showed that the bacterial communities treated with NP and M belonged to their own class,and the fungal communities treated with CK and1/2(NPM)showed their own class.In addition,the results of Lefse multistage species difference discriminant analysis showed that there were 75 species of bacteria and 45 species of fungi in soil under different fertilization treatments,and M treatment accounted for the most,accounting for 36.0% and 28.9%,respectively.Soil CMROC and CMOC are the main contributors to bacterial community variation,while soil DOC,CMOC,CMROC and ROC are the main factors leading to fungal community variation.The results showed that the reduction of chemical fertilizer combined with organic fertilizer affected the abundance of soil microbial community and reduced the abundance of degradable microbial community through soil organic carbon mineralization,so as to improve the stability of soil organic carbon.To sum up,the reduction of chemical fertilizer combined with organic fertilizer can reduce the decomposition of complex substrates,increase the content of stable components of soil organic carbon and reduce the cumulative mineralization rate of soil organic carbon by changing the abundance of some soil microorganisms.Furthermore,the stability of soil organic carbon and the content of soil organic carbon were improved.