Effects Of Different Ecological Types Of Earthworms And Their Interactions On The Distribution Of Exogenous Organic Matter In Soil Aggregates

As a soil ecosystem engineer,earthworms play a very important role in soil ecosystem nutrient cycling and soil carbon dynamic regulation.A large number of studies have shown that earthworms can affect the incorporation and redistribution of organic matter into the soil,and then affect the storage and stability of soil organic carbon.Different ecological types of earthworms may have different effects on the redistribution and transformation of soil organic matter due to their different eating habits and ecological habits.at present,there are few reports on the effects of different ecological groups of earthworms and their interactions on the redistribution of exogenous organic matter in soil aggregates.In this paper,three kinds of earthworms with different ecological types（the epigeic earthworm Eisenia foetida,the epi-endogeic earthworm Amynthas corticis,and the anecic earthworm Pheretima guillemi）were selected as experimental materials.The soil of poplar plantation was used as the experimental object,and ¹³C labeled poplar leaf litter was added to the indoor culture experiment for 120 days.Nine different experimental treatments were set up.Namely,soil control treatment（CK）;litter（T1）;litter+epigeic earthworm（T2）;litter+epi-endogeic earthworm（T3）;litter+aneci earthworm（T4）;litter+epigeic earthworm+epi-endogeic earthworm（T5）;litter+epigeic earthworm+aneci earthworm（T6）;litter+epi-endogeic earthworm+aneci earthworm（T7）.Litter+epigeic earthworm+epi-endogeic earthworm+aneci earthworm（T8）.Combined with ¹³C isotope labeling technique,the effects of three different ecological groups of earthworms and their interaction on soil physicochemical properties,soil organic carbon functional group structure,exogenous organic matter incorporation and distribution in soil aggregates were analyzed.The results showed that:（1）Earthworm inoculation decreased the soil p H value.Under the treatment of different ecotypes of earthworms alone,the effect of the Eisenia foetida on soil p H value was more significant,and the effect of earthworm interaction on soil p H value was more significant than that of single population.Different ecotypes of earthworms had no significant effect on soil ammonium nitrogen content,but earthworm interaction decreased soil ammonium nitrogen content more than earthworms alone,and the effect of earthworm interaction on soil ammonium nitrogen content was dominated by Eisenia foetida and Pheretima guillemi.Different ecological types of earthworms and their interaction had no significant effect on soil nitrate nitrogen and available phosphorus content.（2）Among different ecotypes of earthworms,Pheretima guillemi had a great effect on soil structure,while other earthworm inoculation treatments had no significant effect on the distribution of soil water-stable aggregates.Under the treatment of Pheretima guillemi alone,the content of coarse and fine aggregates was significantly reduced,the content of soil silt-clay aggregates was significantly increased,and the soil MWD was significantly reduced,but the soil structure under the interaction with the Eisenia foetida was improved compared with that under the action of Pheretima guillemi alone.（3）The effect of different earthworms on soil organic carbon content did not reach a significant level,and the decrease of soil organic carbon content under the interaction of earthworms was higher than that of single earthworm population.The effects of different ecological types of earthworms and their interactions on the organic carbon content of soil aggregates were as follows:Compared with only adding litter,among different ecological types of earthworms,the organic carbon content of soil aggregates under the treatment of the Pheretima guillemi was higher than that of Eisenia foetida and Amynthas corticis,which significantly increased the organic carbon contents of coarse aggregates and micro aggregates.Under the treatment of Amynthas corticis,the organic carbon content of soil aggregates with d≤2mm was higher than that of Eisenia foetida,which significantly increased the content of soil micro aggregates carbon.Under the interaction of earthworms,the treatment of inoculating Eisenia foetida increased the organic carbon content of fine aggregates and silt-clay aggregates,while the interaction of Amynthas corticis and Pheretima guillemi earthworms significantly decreased the organic carbon content of soil aggregates.（4）Under different ecotypes of earthworms and their interaction,the functional structure of soil organic carbon was mainly alkoxy carbon and alkyl carbon,and Eisenia foetida had more significant effect on soil alkyl carbon content.William ring earthworm has a more significant effect on the content of soil alkoxy carbon and aromatic carbon.Under the action of Eisenia foetida alone,the soil organic carbon hydrophobicity and A/A-O value increased significantly,while Amynthas corticis and Pheretima guillemi decreased the soil organic carbon hydrophobicity and A/A-O value.Under the interaction of different ecotypes of earthworms,Amynthas corticis and Pheretima guillemi significantly reduced the ratio of soil A/A-O value.（5）Earthworm inoculation significantly promoted the incorporation of exogenous organic matter into soil.under the treatment of different ecotypes of earthworms alone,Eisenia foetida had the lowest effect on the incorporation of exogenous organic matter into soil,and Pheretima guillemi had the most significant promoting effect.Under the interaction of different earthworms,the incorporation of exogenous organic matter into soil was the highest under the interaction of epigeic earthworms and epi-endogeic or anecic earthworms.Under the interaction,the incorporation of exogenous organic matter into soil is more easily affected by the types of earthworms in the deeper active soil layer.（6）The distribution of exogenous organic matter in soil was mainly concentrated in coarse aggregates and fine aggregates.Earthworms of different ecological types and their interaction significantly increased theδ¹³C value of water-stable aggregates with different particle diameters,and significantly increased the distribution of exogenous organic matter in fine aggregates.Under the treatment of different ecological types of earthworms alone,Pheretima guillemi had a more significant effect on the distribution of carbon from litter sources to larger aggregates.Under the interaction of earthworms,epi-endogeic and anecic earthworms obviously accelerated the retention of exogenous organic matter in soil,and the litter source carbon was fixed in the larger aggregates.To sum up,although the inoculation of different ecotypes of earthworms had no significant effect on the content of soil total organic carbon,it significantly promoted the incorporation of exogenous organic matter into the soil and the distribution of exogenous organic matter in soil aggregates.especially in the case of simultaneous inoculation of epigeic earthworms and epi-endogeic or anecic earthworms,and more exogenous organic matter carbon into soil fine aggregates.However,earthworm inoculation promoted the retention of exogenous organic matter in soil,increased the proportion of low alkylated organic carbon in soil,and increased the degree of mineralization of soil organic carbon.Therefore,it is suggested that when inoculating earthworms in the process of forestry production and management,different ecotypes of earthworms should be inoculated according to the demand,and organic wastes should be added at the same time,so as to improve or enhance the potential of earthworms to regulate the dynamics of soil organic carbon in forestry ecosystems.