Effects Of Poplar Leaf Litter And Earthworms On Soil Aggregates And Soil Organic Carbon Composition In Poplar Plantations

The soil organic carbon content of most of the plantation ecosystems in China is low,and there is a high risk of land decline due to multi-generation continuous cropping.Earthworms play a very important role in maintaining plantation fertility,especially in accelerating soil organic carbon accumulation and stability.In order to reveal the effects and mechanisms of poplar leaf litter and earthworms on soil organic carbon and nitrogen,as well as on different active organic carbon,this paper takes poplar plantation along the coast of Dongtai as a research object,and uses random block method to set up field fixed experimental plots.A total of 6 different treatments are set,namely control treatment(CK);poplar leaf litter surface application treatment(T1);poplar leaf litter mixed application treatment(T2);earthworm inoculation only treatment(T3);poplar leaf litter surface application And inoculated with earthworm treatment(T4);poplar leaf litter mixed application and inoculated with earthworm treatment(T5).The effects of poplar leaf litter and earthworm on soil organic carbon and nitrogen and different activated organic carbon were analyzed in order to further study artificial the impact of forest management measures on the soil carbon and nitrogen cycles in poplar plantations with providing a theoretical basis.The research indicates:(1)Compared with the control experiment,the application of poplar leaf litter and earthworminoculation increased the soil organic carbon content,and the total organic carbonincreased by about 10.29% ? 26.80%;while the mixed application of litter increased thesoil organic carbon content by about 26.80 %.Compared with surface application of litter,mixed application of litter increased soil organic carbon content by approximately 14.03%,while total nitrogen content increased in all litter application treatments.(2)Except for the blank CK treatment,the remaining aggregates larger than 2mm account forthe highest proportion in the soil,reaching 37.43% ? 49.18%;in different treatments,theproportion of the microaggregates with a particle size of 0.053 ? 0.25 mm in the soil is thelowest,and the distribution interval is between 5.39% and 9.43%.Compared with the CKtreatment,the MWD values of the other treatments have increased,with an increase of7.92% to 27.72%.(3)The organic carbon content in water-stable agglomerates with different particle sizesincreases with the increase in particle size.Comparing the total nitrogen content ofagglomerates with different particle sizes in the same treatment,the content ofagglomerates with a particle size of 0.25 ? 2 mm is higher than other particle sizes,whilethe total nitrogen content of agglomerates with a particle size of <0.053 mm is relativelylowest,and the approximate size order is [0.25 ?2mm agglomerates]> [>2mmagglomerates]> [0.053?0.25 mm agglomerates]> [<0.053 mm agglomerates].(4)Among aggregates with different particle sizes in soil,the C / N ratio of larger aggregatesis higher than that of micro-aggregates.In addition to the CK treatment,the correspondingcontribution rates of the other treatments are in order: [> 2 mm agglomerates]> [0.25 ? 2mm agglomerates]> [<0.053 mm agglomerates]> [0.053 ? 0.25 mm agglomerates].(5)In the treatment of litter surface application(T1),the coarse aggregates with a particlesize > 2 mm contribute up to 61.41% of the total nitrogen in the soil,while in the CKtreatment the contribution rate of the aggregates with the particle size is the lowest,27.95 %.Aggregates with a particle size of > 2mm and 0.25 ? 2mm have an absoluteadvantage in the contribution rate of soil total nitrogen in different treatments,whileaggregates with a particle size of <0.053 mm have a higher contribution rate than thosewith a particle size of 0.053 ? 0.25 mm Aggregates.(6)Inoculation of earthworms increased the contents of DOC,HWEC,MBC,ROC,POC,and LFOC in the soil.Only AEC inoculated with earthworms after applying the leaf litterreduced its content;the mixed application treatment of poplar leaf litter was moreconducive to the increase of soil active organic carbon content than the surface applicationtreatment except AEC and ROC.Under the conditions of litter mixed treatment(T2 andT5),the soil DOC,HWEC,MBC,POC and LFOC content was higher than that of littersurface treatment(T1 and T4).Among them,the HWEC content increased the most,about12.43%;For ROC,surface application treatment is more beneficial to increase soil activeorganic carbon content than mixed application treatment.In summary,the results of the study indicate that: mixed application of poplar leaf litter can increase the content of soil organic carbon more effectively than surface application of litter;inoculation with earthworms can effectively increase the content of organic carbon and total nitrogen in the soil;The application of poplar leaf litter and earthworms in the forest soil improved the stability of aggregates in the soil.Inoculation with earthworms can increase the total nitrogen content in the soil aggregates of poplar plantations,and the mixed application of poplar leaf litter is more effective than the surface application in increasing the total nitrogen content in soil aggregates.Inoculation with earthworms accelerated the humification of soil organic matter in poplar plantations.Earthworm inoculation,surface application of litter and mixed application of litter all increased the contribution rate of organic carbon and total nitrogen of the large aggregates in the soil of poplar plantation,and enhanced the stability of soil organic carbon.