Effects Of Rice Residue And Its Biochar Addition On The Mineralization Of Soil Organic Carbon

A 13C tracing study was carried out to assess the effects of biochar,rice straw and their mixed addition on soil labile carbon and soil microbial community structure and soil CO2 emission flux which can provide scientific insight on reasonable use of biomass resource and efficient management of soil carbon sequestration.The main results showed that the mineralization rate of soil organic carbon of rice straw addition and biochar plus rice straw addition were significantly higher than biochar alone amendment and control soil(CK)during the whole incubation period.The mineralization rate of soil organic carbon had no significant difference between biochar alone amendment soil and CK at the earlier stage of incubation(3～21 day);whereas at the later stage of incubation(42～112 day),the mineralization rate of soil organic carbon of biochar alone amendment was obvious decreased than CK.Compared to CK,the accumulation amount of soil CO2-C was increased by 332%and 321%under mixture of biochar and rice straw addition and rice straw alone amendment respectively,while the accumulation amount of soil CO2-C was reduced by 18%under biochar alone amendment.During the whole incubation period,compared to CK,the mineralization amount of native soil organic carbon was reduced by 27%with biochar alone amendment,while the mineralization amount of native soil organic carbon was increased at the earlier stage of incubation(1～28 day),and was significantly decreased at the later stage of incubation(28～112 day)with rice straw alone addition.After incubation,the decomposition rate of biochar was 1.1%and rice straw was 51%.Compared to CK,the mineralization amount of native soil organic carbon was increased by 18.1%with mixture of biochar plus rice straw.Rice straw addition had no significant effect on the decomposition rate of biochar,and biochar slightly decreased the decomposition rate of rice straw.Compared to control soil(CK,pH 5.44),soil pH was increased by 8%under biochar alone addition(p<0.01),and soil pH had no significant change under mixture of biochar plus rice straw addition,whereas soil pH was decreased by 13%under rice straw alone addition(p<0.01).Furthermore,exogenous carbon input obvious increased the content of soil total nitrogen(TN),soil total organic carbon(TOC)and C/N ratio.Compared to CK,there was no significant difference in DOC content for soil with biochar amendment alone,while the contents of DOC with rice straw alone and mixture of biochar plus rice straw addition were improved by 25%and 31%,respectively.The content of DOC derived from biochar and rice straw was 0.16%-0.2%and 16%-17%,respectively,indicating that the decomposition of soil native DOC was depressed by biochar addition.Besides,the content of microbial biomass carbon(MBC)in soil with biochar addition was lower than in CK,meanwhile the content of MBC with rice straw and mixture of biochar plus rice straw addition was 1.56 and 1.46 times greater than CK(133.50 mg·kg-1)respectively,suggesting that soil microbial activity was impressed by biochar addition while stimulated by rice straw application.In comparison to CK,the gross of phospholipids fatty acids(PLFAs)was reduced by 17%with biochar amendment,and the corresponding value was significantly increased by 146%和 118%with mixture of biochar plus rice straw or rice straw addition,respectively.Biochar,rice straw addition alone as well as biochar plus rice strawamendment significantly increased the abundance of soil fungus and fungus/bacteria ratio,but soil bacteria abundance and the Gram-positive bacteria(G+)/Gram-negative bacteria(G-)ratio decreased obviously.Meanwhile,the abundance of actinomycete was significantly stimulated by 12%and 13%respectively with biochar addition and with mixture of biochar plus rice straw amendment(p<0.05).On the contrary,the abundance of actinomycete was remarkably decreased by 26%with rice straw addition alone(p<0.01).