Effects Of Earthworm Activities On Turnover Of Soil Oraganic Carbon In Agro-ecosystem

Earthworms are the most important macro-animal in soil and they play an important role on the substance cycling and the energy flow in terrestrial ecosystem.Earthworms affect the mineralization and leaching of soil organic carbon through modifying the structure,aeration,moisture of soil.Earthworms affect the content and composition of soil organic carbon through modifying the nutrition supply and component of soil.Earthworms affect the cycling and turnover of soil oranic carbon through modifying soil microbial structure and activity.Most works of earthworm effects on the soil nutrition cyclying, microbial activity were simplex.The all-around information of earthworm effects on soil organic carbon cycling and turnover are essential,especially take into account the synthesis of knowledge about earthworms and photosynthate,straw residue,organic carbon mineralization,plant growth,microbial community dynamic,soil aggregation.In order to confirm the relation between earthworms and soil organic carbon,a series of experiments were conducted and Metaphire guillelmi was chosen to focus on.The main objectives of these experiments are as follows:(1) Earthworm effects on the renewal of soil oranic carbon in a long-term plot experiment.(2) Earthworm effects on soil labile organic carbon in a long-term plot experiment.(3) Earthworm effects on soil microbial properties under straw application.(4) Earthworm effects on soil aggregation and organic carbon distribution under different straw residue input.(5) Earthoworm effects on soil microbial properties during the renewal of structure-degenerated soil.(6) The mineraliztion dynamics of organic carbon of fresh cast and ageing cast.(7) Earthworm effects on rice photysynthates distribution in plant-soil system.The main results as follows:After six years straw input in plots,soil organic carbon originating from maize straw increased,meanwihile,soil oranic carbon originating from original soil and plant decreased Compared with straw incorporated,straw mulching was more beneficial to the transfer of straw carbon to soil carbon and decreased the proportion of carbon originating from original soil and plant.Earthworm activities increased the content of soil organic carbon originating from straw,and decresed the content of soil organic carbon originating from original soil and plant.Earthworm inoculation showed different effects on diverse soil labile organic carbon under two straw application methods.Straw application method was the major factor on affecting soil organic carbon and labile organic carbon,and earthworms didn't show significant effects on all soil labile organic carbon.The presence of earthworms had significant effects on soil microbial biomass, microbial activity and the microbial ability of carbon source utilization.Microbial biomass increased in the presence of earthworms irrespective of the way of straw application.Soil microbial activity,richness and biodiversity all decreased in the presence of earthworms under straw mulching method,and the reverse was true under straw incorporation method. It was indicated that soil microbial community composition changed significantly under straw application using BIOLOG carbon utilization analysis.The experiment of earthworms and aggregates stability indicated that earthworms affected water-stable aggregates distribution and micro-aggregate dispersion and soil organic carbon distribution differently under different soil substrate and straw residue input. Earthworms decreased the dispersion of micro-aggregate and didn't affect the distribution of water-stable aggregates in silt soil.Meanwhile,earthworms decreased the dispersion of micro-aggregate and increased the percentage of water-stable macro-aggregate and the distribution of soil organic carbon in macro-aggregate in silt clay loam soil.Earthworm inoculation with straw residue input increased soil organic carbon content in the two soils.Earthworms significantly affected soil basil respiration(BR) and qCO₂,both of them increased under earthworm activities,especially under no straw residue input and white clover straw input in silt soil.Differently,earthworms had less effect on soil microbial biomass carbon.The AWCD(average well color development) and substrate richness(S) and biodiversity index(H) all increased with earthworm activities through Biolog test.It was indicated that the composition and structure of soil microbial community changed significantly under earthworm activities through principal component analysis(PCA). Earthworms had interactive effects with soil and straw residue types.The mineralization in fresh cast was more than those in corresponding soil,especially the cast originating form soil with maize residue input.The mineralization of ageing casts was more than those in corresponding soil except that the cast originating from clayed soil with no straw residue input.The mineralization of cast was related to soil texture,soil oranic carbon content,straw residue,and the ageing degree of cast.The ¹⁴C pulse-labelling experiment indicated that rice growth was inhibited by earthworms(Metaphire guillelmi) at early stage,but the inhibition disappeared at later stage. Earthworms significantly increased the ¹⁴C percentages in root at day 15 after tillering stage labelling,but the effect disappeared at harvest.Earthworms(Metaphire guillelmi) significantly increased the ¹⁴C percentages in root at day 15 after heading stage labelling, and increased ¹⁴C percentage in soil at harvest.Earthworms decreased the ratios of microbial biomass ¹⁴C(MB¹⁴C) to total organic ¹⁴C(TO¹⁴C) and increased the ratios of dissolved organic ¹⁴C(DO¹⁴C) to total organic ¹⁴C(TO¹⁴C) at all sampling times.It is suggested that earthworms might alter the transfer of plant photosynthates from the aboveground to the belowground and thus soil active C pool.In general,earthworm activities accelerated the turnover of soil organic carbon,and affected the content of soil labile organic carbon significantly.Earthworms enhanced the soil aggregation and induced the change of soil microbial community.Earthwoms increased the transfer of photosynthate from aboveground to belowground.It is indicated that earthworm inoculation in cropland and degenerate field to maintain and enlarge soil organic carbon pool are of ecological significance.