| The soil type in Jiangxi Province is dominated by red soil,accounting for about 71% of the total land area of the province.This area is a typical representative of red soil erosion in the south.The long-term water and soil conservation and ecological restoration work has promoted the substantial improvement of soil structure and function of eroded land.As the most basic material and functional unit of the soil,soil micro-aggregates play an important role in the supply,transformation and maintenance of soil nutrients.Soil organic carbon is the main cementing agent for the formation of water-stable aggregates.Stability has an important impact.Therefore,studying the effect of external organic carbon input from woodland and grassland on red soil micro-aggregates and their organic carbon during the restoration process of red soil eroded and degraded land is useful for exploring the mechanism of soil micro-aggregate organic carbon fixation and storage,and improving the soil ecological environment.It is of great significance to improve soil fertility and soil productivity,and to achieve sustainable development.This study is based on the long-term positioning test base of subtropical red soil forest restoration in Luoxi Forestry Farm,Taihe County,Ji’an City,Jiangxi Province,selecting Schima superba forest land and natural restoration grassland in the study area as the research objects.The method of combining field positioning experiment and indoor analysis is adopted.The experiment was set in Schima superba forestland to retain litter + retain root + retain mycorrhiza(L+R+M),double litter + retain root + retain mycorrhiza(2L+R+M),remove litter + remove root + retain Mycorrhiza(NL+NR+M),litter removal + root removal + mycorrhiza removal(NL+NR+NM),litter removal + root retention + mycorrhiza retention(NL+R+M),etc.Each treatment is repeated 5 times;3 types of root retention + retention mycorrhiza(R+M),root removal + retention mycorrhiza(NR+M),root removal + removal mycorrhiza(NR+NM)are set in natural restoration grassland Treatment,each treatment is repeated 4 times.All processed undisturbed soil samples were separated into 3 grain-size soil micro-aggregates(0.05-0.2 mm,0.02-0.05 mm,<0.02 mm),and the internal particle composition,total organic carbon,and bound organic carbon(calcium bond,Ironaluminum bonded organic carbon)and other indicators,the results are as follows:(1)The distribution of soil micro-aggregate particles in Schima superba forest land and naturally restored grassland showed similar laws,with the dominant particle size class being <0.02 mm.As the particle size of soil micro-aggregate cement increased,the proportion of the particle components decreased accordingly.In Schima superba forest land,litter doubling reduces the proportion of micro-aggregates with a particle size of <0.02 mm;removing litter reduces the proportion of micro-aggregates with a particle size of <0.02 mm,and increases the proportion of 0.05-0.2 mm in diameter;removing roots It did not lead to a decrease in the proportion of micro-aggregates with a particle size of <0.02 mm;the isolation of mycorrhiza led to a decrease in the proportion of micro-aggregates with a particle size of <0.02 mm,and a slight increase in the proportion of 0.05-0.2 mm.In the natural restoration of grassland,root removal reduces the proportion of microaggregates with a particle size of <0.02 mm;isolated mycorrhiza increases the proportion of microaggregates with a particle size of 0.05-0.2 mm.(2)In terms of total organic carbon(TOC)content of soil micro-aggregates,Schima superba forests have larger particle sizes than naturally restored grasslands,and the dominant particle size of TOC content is <0.02 mm.In Schima superba forest land,the TOC content of soil microaggregates with a particle size of 0.05-0.2 mm increased slightly after the litter was doubled;the TOC content of each particle size of the soil microaggregates decreased to varying degrees after the litter was removed;the root removal increased by <0.02 mm and The TOC content of soil microaggregates under the particle size of 0.05-0.2 mm;the TOC content of soil microaggregates under the particle size of <0.02 mm and 0.05-0.2 mm in the isolation mycorrhizal treatment was less than that of the non-isolation treatment.In the natural restoration of grassland,the TOC content of the soil microaggregates under the treatment of root removal was lower than that of the no removal treatment;the isolation mycorrhizal treatment reduced the TOC content of the soil microaggregates under the particle size of <0.02 mm.(3)The changes of soil micro-aggregate bound organic carbon content in Schima superba forest land and naturally restored grassland show similar patterns,the dominant particle size is <0.02 mm,and the chemically bound organic carbon content of microaggregates increases with the decrease of the micro-aggregate size.In Schima superba woodland,the content of combined organic carbon did not increase significantly after doubling the litter;the removal of litter resulted in a decrease in the content of both combined organic carbon;the removal of roots resulted in a decrease in the content of both combined organic carbon;isolated bacteria Roots caused a slight decrease in the Ca-SOC content of soil micro-aggregates,but the Fe(Al)-SOC content did not change significantly.In naturally restored grasslands,removal of roots resulted in a slight decrease in the content of both bound organic carbon in soil microaggregates;isolation of mycorrhizas resulted in a slight decrease in the content of bound organic carbon in soil microaggregates.(4)The ratio of Fe(Al)-SOC/TOC in soil micro-aggregates of iron-aluminum bonded organic carbon/total organic carbon(Fe(Al)-SOC/TOC)is higher than that of calciumbonded organic carbon/total organic carbon in Schima superba forest land and natural restoration grassland.Ratio(Ca-SOC/TOC).In Schima superba forests,doubling the litter caused the soil micro-aggregates to increase in the ratio of the two combined organic carbon/total organic carbon content in the 0.02-0.05 mm diameter of the soil to varying degrees,<0.02 mm,0.05-0.2 mm diameter Ca-The SOC/TOC ratio and the Fe(Al)-SOC/TOC ratio decreased,and the bound organic carbon/TOC ratio at the particle size of 0.05-0.2 mm was smaller than the other two particle sizes;the removal of litter resulted in the combined organic carbon at the three particle sizes The carbon/TOC ratio decreased to varying degrees,and the bound organic carbon/TOC ratio at a particle size of 0.05-0.2 mm was smaller than the other two particle sizes;removal of roots resulted in an increase in the bound organic carbon/TOC ratio of soil microaggregates;removal of bacteria Roots led to a decrease in the bound organic carbon/TOC ratio of soil microaggregates,and the largest change in the bound organic carbon/TOC ratio of microaggregates with a particle size of <0.02 mm.In the natural restoration of grassland,removal of roots leads to an increase in the ratio of soil microaggregates bound organic carbon/TOC;removal of mycorrhizas leads to a slight decrease in the ratio of soil microaggregates Ca-SOC/TOC,with a particle size of 0.02-0.05 mm microaggregates Ca-The SOC/TOC ratio has the largest change range.The ratio of Fe(Al)-SOC/TOC of the microaggregates in the three particle size ranges all increases in different ranges,and the Fe(Al)--SOC of the microaggregates with a particle size of 0.02-0.05 mm The /TOC ratio changes the most.(5)The order of the contribution rate of different particle sizes to the organic carbon of microaggregates is: <0.02 mm>0.02-0.05 mm>0.05-0.2 mm.In summary,the input of exogenous organic carbon such as litter,root system and mycorrhiza is beneficial to promote the formation and stability of soil micro-aggregates in the process of ecological restoration of eroded and degraded red soil.The research results can provide a further understanding of soil micro-aggregate organic The mechanism of carbon fixation and sequestration provides scientific basis and reference,which is of great theoretical and practical significance for the ecological restoration of soil and water conservation in the severely eroded and degraded red soil area of southern China. |
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