Effect Of Biochar On Soil Organic Carbon Fractions And Microbial Community Structure In Ningxia Irrigation Region

As a new environmental functional material,biochar has a promising prospect in soil carbon sequestration.There are few studies on the effect of biochar on soil organic carbon and soil microbial community structure in Ningxia Irrigation Region.In this study,we investigated the effect of consecutive biochar application for 3 years on soil organic carbon in Ningxia Irrigation Region.At the same time,we determined the soil microbial community structure by phospholipid fatty acid(PLFA)method,and analyzed its mechanism of action from the perspective of microorganism.Four biochar levels were set up under no nitrogen application and local nitrogen application.Soil samples were collected during the rice harvest in 2015 and during the rice growth period in 2016.Soil total organic carbon(TOC),microbial biomass carbon MBC),dissolved organic carbon(DOC),labile organic carbon(LOC),particulate organic carbon(POC)and soil PLFA.The main findings are as follows:(1)The active organic carbon content in the 2016 rice growth period showed obvious seasonal fluctuation.The seasonal variation of soil MBC(seasonal variation coefficient 44.1%-53.5%)was the highest,and DOC(seasonal variation coefficient 42.0%-44.1%)was the second,and the seasonal variation of LOC(seasonal variation coefficient 16.7%-24.2%)was the smallest.Biochar treatment had no significant effect on the seasonal variation coefficient of soil MBC and DOC(P>0.05),but increased the seasonal variation coefficient(P<0.05)of soil LOC.(2)Application of biochar significantly increased the surface(0-20 cm)soil organic carbon storage,soil TOC,LOC and POC content(P<0.05),decreased the content of soil MBC(P<0.05),and the content of DOC did not had significant difference between biochar treatments and the blank control.Adding biochar had no significant effect on soil TOC and LOC content under 20 cm(P>0.05).(3)Application of biochar increased soil carbon pool management index(CPMI),significantly increased the proportion of POC in total organic carbon,reduced the proportion of DOC and MBC in total organic carbon(P<0.05).(4)The content of gram negative bacteria,bacteria,fungi and total PLFA was significantly decreased by adding biochar.The ratio of fungi to bacteria PLFA was increased under conventional nitrogen(N300).There was a significant negative correlation between bacterial,fungal PLFA and TOC(P>0.05),which was significantly positively correlated with DOC(P<0.05);bacterial PLFA was positively correlated with MBC(P<0.05).(5)Application of biochar significantly increased the content of available potassium,available phosphorus and organic matter,but had no significant effect on soil total nitrogen,total phosphorus and hydrolysable nitrogen in soil.Addition of biochar increased rice yield,but the increase was not significant.This study shows that application of biochar can improve the surface(0-20 cm)soil organic carbon storage,soil TOC,LOC and POC content,is advantageous to soil carbon sequestration,while exogenous biochar improved the soil nutrient,has certain promoting effect on rice yield in the Yellow River Irrigation Region of Ningxia;Application of biochar changed the structure of microbial community and decreased the number and diversity of microorganisms.The effect of biochar on soil organic carbon and microbial is a complex and lengthy process.It is necessary to carry out long-term positioning test for observation.