Effect Of Different Regeneration Methods On Soil Microbial Residue Carbon And Lignin In Subtropical Forests

The forest soil carbon pool accounts for about 73%of the terrestrial soil carbon pool,which far exceeds the sum of the atmospheric and vegetation carbon pools.A small change in the soil organic carbon composition will change the concentration of carbon dioxide in the atmosphere,thus having a profound impact on global warming.However,for a long time,there is a lack of effective methods for separation of plant and microbial-derived carbon from soil organic carbon.There is not deep enough to understand soil organic carbon components.In recent decades,along with the construction of southern commercial forest bases and comprehensive mountain development,large-scale natural evergreen broad-leaved forests have been converted into plantations and secondary forests after clear cutting and mountain refining.Different forest regeneration methods have brought different degrees of impact on forest ecosystem diversity,nutrient cycling,productivity,soil carbon storage,etc.However,the effects of soil microbial residues carbon and lignin under different regeneration methods are still unclear.To this end,this study relies on Research Station of Forest Ecosystem and Global Change,Chenda,Sanming,Fujian,chooses Castanopsis carlesii natural forest,and broad-leaved forest transformed from natural forest?Castanopsis carlesii secondary forest SF,Castanopsis carlesii assisted regeneration forest AR?and coniferous forests?Pinus massoniana lamb PM,Cunninghamia Lanceolata plantation CF?were studied.In April 2017,0-10 cm and 10-20 cm soil samples were collected.Characterization of soil microbial residue carbon and plant lignin components use two molecular markers,amino sugar and lignin phenol,respectively.Meanwhile,amino sugar and lignin phenol combined with the changes of litter,fine roots,microbial biomass carbon and soil physical and chemical properties,which aims to explore the effects and mechanisms of different forest regeneration methods on soil organic carbon composition from the perspective of plant and microbial source carbon.Results indicate:?1?After the natural forest was converted into other forests by different regeneration methods,the total amount of amino sugar?TAS?and various amino sugars?glucosamine Glu N,galactose Gal N and muramic acid Mur A?in the 0-10 cm soil layer showed a downward trend,among which the natural forest was significantly higher than the secondary forest,and the secondary forest was significantly higher than Castanopsis carlesii assisted regeneration forest,Pinus massoniana lamb and Cunninghamia Lanceolata plantation.And the soil change trend of 10-20 cm soil layer was consistent with 0-10 cm.In addition,all kinds of soil amino sugar were positively correlated with MBC?litter and fine root biomass,indicating that natural forests and secondary forests are more conducive to the accumulation of soil organic carbon,and forest regeneration affected soil microbial processes by changing litter input,and reduced soil microbial residual carbon content,which was not conducive to soil organic carbon accumulation.After the natural forest was converted into other forests by different regeneration methods,the ratio of glucosamine to muramic acid?Glu N/Mur A?in 0-10 cm soil layer showed a downward trend,among which natural forest?14.72?and secondary forest?15.33?were significantly higher than Castanopsis carlesii assisted regeneration forest?11.36?,Pinus massoniana lamb?12.61?and Cunninghamia Lanceolata plantation?11.21?.It indicated that the contribution of fungal residue carbon to soil organic carbon in natural and secondary forests was significantly higher than Castanopsis carlesii assisted regeneration forest,Pinus massoniana lamb and Cunninghamia Lanceolata plantation.?2?After the natural forest was converted into other forests by different regeneration methods,the total amount of lignin?VSC?and various lignin phenolic monomers?S-type syringyl phenols,V-type vanillyl phenols and C-type cinnamyl phenols?showed a significant decrease.The total amount of lignin natural forest is significantly higher than that of secondary forest,and the secondary forest is significantly higher than Castanopsis carlesii assisted regeneration forest,Pinus massoniana lamb and Cunninghamia Lanceolata plantation.And the soil change trend of 10-20 cm soil layer is consistent with0-10 cm.All kinds of lignin phenols were significantly positively correlated with MBC?litter and fine root biomass,indicating that natural forests and secondary forests are more conducive to the accumulation of soil organic carbon,and forest regeneration changed litter and fine root input,decreased soil lignin content,and was not conducive to organic carbon accumulation.In 0-10 cm soil layer,the S/V values of natural forest,secondary forest and Castanopsis carlesii assisted regeneration forest were 0.39,0.57 and 0.5,respectively,which were significantly higher than that of Cunninghamia Lanceolata plantation?0.09?and Pinus massoniana lamb?0.11?.In the 0-10 cm soil layer,the C/V values of natural forest,secondary forest and Castanopsis carlesii assisted regeneration forest were also significantly higher than that of Cunninghamia Lanceolata plantation and Pinus massoniana lamb.It indicated that the vegetation type changes the source of soil lignin,and the angiosperm-derived lignin has been completely replaced by gymnosperm,which further indicated that soil organic carbon accumulation is a dynamic process.In the 0-10 cm soil layer,the acid/aldehyde ratio?Ad/Al?_V values of the V-type monomers of natural forest,secondary forest and Castanopsis carlesii assisted regeneration forest which were significantly higher than that of Cunninghamia Lanceolata plantation and Pinus massoniana lamb.The acid/aldehyde ratio?Ad/Al?_S value of the S-type monomer in the natural forest was also significantly higher than that of the secondary forest,Castanopsis carlesii assisted regeneration forest,Cunninghamia Lanceolata plantation and Pinus massoniana lamb,indicating that the decomposition rate of lignin was faster in natural forests.?3?After the natural forest was converted into other forests by different regeneration methods,the ratio of fungal carbon and bacterial carbon to soil organic carbon increased.The ratio of fungal carbon to soil organic carbon was 16.93%²9.58%.The ratio of bacterial carbon to soil organic carbon was 8.89%²0.25%.The contribution of soil microbial residue carbon and lignin to soil organic carbon were NF<SF<AR<CF<PM.The ratio of soil microbial residue carbon to soil organic carbon fluctuated in the range of31.98%⁴5.2%,the ratio of total lignin to soil organic carbon was 7.72 mg.g^-116.32mg.g^-1.After the forest regeneration,The contribution of soil microbial residues carbon and lignin to soil organic carbon was generally increasing.It indicated that the rate of soil active organic carbon decreased after forest regeneration was higher than that of soil microbial residues carbon and lignin,and the stability of lignin was high,which was beneficial to maintain the stability of soil organic carbon.?4?SOC,DOC,Clay and pH have an effect on soil amino sugar,which is the main driving factor for amino sugar change in soil.Moreover,SOC,DOC and Clay are positively correlated with soil amino sugar,indicating that substrate supply has a significant effect on microbial activity,which is beneficial to the accumulation of amino sugar in soil.Adsorption of clay is beneficial to improve the physical protection of amino sugars in soil.while pH is negatively correlated with soil amino sugar content,which is mainly because soil pH affects microbial biomass and activity,which in turn affects the contribution of soil amino sugar to soil organic carbon.?5?SOC,Mineral N,pH,Moisture,C/N and TN have effects on soil lignin and are the main driving factors for soil lignin changes.SOC,Mineral N,C/N and TN are positively correlated with soil lignin,indicating that substrate supply has a significant effect on microbial activity,allowing microbes to secrete more enzymes,thereby increasing lignin degradation in the soil.Soil pH and Moisture affect the living environment of microorganisms,which in turn affects microbial community structure and microbial activity,thus affecting the degree of degradation of lignin by microorganisms.