Contribution And Influencing Factors Of Soil Organic Matter Derived From Microorganism During The Restoration Process Of Pinus Massoniana Forest

Soil organic matter restoration is an important part of ecological restoration of red soil erosion degraded land in South China.Microbial derived organic carbon is the main component of persistent organic carbon pool,which plays an important role in building soil stability and health system.Therefore,it is of great significance to explore the contribution of organic carbon from microbial sources to SOC and its influencing factors.In this study,we selected Hetian Town,Changting County,Fujian Province as the research object.By comparing the distribution and contribution of amino sugar content and microbial organic carbon content of different restoration years(Y0,Y17 and Y35)and different treatment measures of Dicranopteris dichotoma(in 2014,three treatments were set up: CK,NRD and RD),we preliminarily discussed the mechanism and main influencing factors of microbial organic matter restoration in eroded degraded red soil.The results are as follows:(1)Compared with Y0,the contents of glucosamine(GluN),total amino sugar(TAS),fungal residual carbon(FRC)and microbial residual carbon(MRC)of Y17 and Y35 were 91.00% ? 147.78% and 82.25% ? 129.56% higher than Y0(P<0.05),and were59.81% ? 62.04% and 62.57% ? 64.75% lower than those of secondary forest(P<0.01).Mannosamine(ManN),muramic acid(MurA)and bacterial residue carbon(BRC)had no significant effect in the three communities,and there was no significant difference between Y17 and Y35 in fungi,bacteria and total residual carbon.In different treatments of D.dichotoma,the microbial residue in the covered area was significantly higher than that in the bare area under the forest(P<0.05);the removal of D.dichotoma reduced the accumulation of microbial residue in the soil of P.massoniana forest,but had no significant effect on the accumulation of BRC.The total amount of microbial residues decreased with the increase of soil depth(P<0.05).Vegetation restoration can significantly increase GluN/MurA and GluN/GalN ratios,but then remains stable.It indicated that the accumulation of fungal residues was dominant.There was no significant difference in the contribution of recovery years to MRC/SOC and FRC/SOC(P>0.05).The contribution of MRC,FRC and BRC to SOC was 18.84%,12.49% and6.35% respectively.Analysis of variance showed that recovery period,treatments and soil layer had a main effect on microbial residue and its contribution to SOC,but the interaction of the three had no significant effect.(2)The correlation analysis showed that the annual average total litter and total C,N and P returns had significant positive correlation with total microbial and fungal residues,and had significant negative correlation with BRC/SOC and MRC/SOC,but had no significant correlation with bacterial residues.This shows that litter and its nutrient return mainly affect the total microbial residue by affecting fungi.The linear regression analysis showed that the monthly root biomass was significantly correlated with TAS,FRC and MRC(P<0.01),but not with BRC.This means that the effects of the underground roots and the aboveground litter on the carbon content of the microbial residues are similar.(3)The content of MBC and MBN was significantly increased by vegetation restoration(P<0.05).There was a positive correlation between MBC and MBN monthly mean,transfer and circulation with amino sugar and microbial residual carbon(P<0.05).Soil AP enzyme activity had significant positive correlations with total microbial and fungal residues(P<0.05),and soil ?G enzyme activity had significant positive correlations with bacterial residues and contribution of total microbial residues(P<0.05).This indicates that the accumulation of soil microbial organic carbon is closely related to the acquisition of soil P and active organic carbon.The diversity index of soil fungi and bacteria was closely related to microbial residues,and the community structure and abundance had a significant effect on the carbon content of microbial residues(P<0.05).Among them,soil fungi and bacteria,mycorrhizal fungi related to nitrogen cycle and phosphorus acquisition were significantly correlated with soil amino sugar and microbial residue carbon(P<0.05).This indicates that the accumulation of soil microbial residues is closely related to the acquisition of soil mineral nutrients and mycorrhizal cooperation.(4)Soil fungal and bacterial residue accumulation affected by soil environmental factors is quite different.Fungal residues are affected by more soil physical and chemical properties,while bacterial residues are only affected by pH,MBP,AP,etc.SEM analysis showed that the average litter C return during the recovery process of P.massoniana forest was affected by microbial biomass and soluble organic carbon,which accounted for 84% of the change of microbial residual carbon.Therefore,the restoration of Pinus massoniana forest in the eroded and degraded land significantly promoted the total microbial and fungal residues in the soil of P.massoniana forest in the erosion and degradation area.Among them,the understory vegetation Dicranopteris dichotoma has an important role in the accumulation of soil microbial residues.Soil microbial residues are affected by soil physical and chemical properties,litter nutrient return,biomass turnover,soil enzyme activity,microbial diversity and community structure.To understand the contribution and influencing factors of soil organic matter derived from microorganism is helpful to guide the soil management and forest management of P.massoniana forest in the erosion and degradation area.