Impacts Of Earthworm On Soil Structure Formation And Soil Organic Carbon Turnover Under Conservation Tillage

The earthworm plays an important role in soil structure and soil organic matter dynamics.Conservation tillage could increases earthworm abundance due to low disturbance and residue returned.The interaction of earthworms and residue returned on soil pore structure and the turnover of soil organic carbon?SOC?in black soil still need to be future studied.In this study,based on the long-term tillage experiment and the laboratory incubation on the undisturbed soil,our objectives are 1)to study the effects of different tillage practices on species,numbers,and biomass of earthworms;2)to explore the effects of earthworms and residue additions on SOC and its labile fractions,soil pore structure under conventional tillage?CT?and no tillage?NT?.The NT combined with continuous corn and corn-soybean rotation both significantly increased the number of Drawida Japonica Michelsen.The risge tillage with continuous corn significantly increased the number of Bimastus Parvus.Earthworms had no effects on soil CO₂ emissions.Residue returning significantly increased soil CO₂ emissions.NT increased the SOC content in the 0-5 cm layer.Under NT,original residue was decomposed by the earthworms,which resulted in the increase in SOC content.In NT soil,the newly added residue inhibited the decomposition of the original residue,and the SOC released from decomposition of new residue was lower than that released from the original SOC decomposition,and thereby reduced SOC content.In contrast,under NT the effect of stimulating decomposition of orginal residues induced by earthworms was greater than that of inhibiting the decomposition of original residues by newly added residue.After 180-day lab incubation,NT with new residue returned increased the percentage of aggregates and the concentrations of aggregate-associated SOC in>1000?m and 250-1000?m size aggregate.The CT with new residue returned decreased the concentrations of soil aggregate-associated SOC in>1000?m,250-1000?m and 53-250?m size aggregate.In NT soil,either residues or earthworms addition could significantly increase the percentage of 53-250?m aggregate.The addition of earthworms in CT soils also increased the concentration of aggregate-associated SOC in>1000?m size and reduced the concentration of aggregate-associated SOC in<53?m size.The NT increased the mean weight diameter?MWD?of aggregates in the 0-5 cm soil layer.NT soil had the higher number of micro-pores and pore connectivity.The NT with earthworms addition reduced the number of micro-pore,increased the average macro-pore diameter and volume fraction.Earthworms had a potentialeffect to force the soil pore to an ellipsoid and thusdeclinepore connectivity.In CT soils the new added residue increased the MWD and soilpore connectivity but,when earthworms existed,the addition of residue reduced the amount of macro-pore in CT soil.The SEM?Sructural Equation Model?showed that CT increased soil pore anisotropy and macro-pore volume,and then led to the decrease of SOC content,while NT increased MWD and pore connectivity,and thereby resulted in the increase of SOC content.When earthworms were added,CT affected soil aggregate formation,the dynamics of aggregate-associated SOC and soil microbial activity,thus affected the SOC content;NT increased SOC content through increasing soil porosity,pore anisotropy,pore connectivity and MWD.