Impacts Of Earthworm Ecotypes On Soil Community Structure And Function

As a soil ecosystem engineer,earthworm plays an important role in the structure and function of soil ecosystem.The effects of earthworm on microbial and micro-faunal community structure depend on numerous factors,among which the difference of earthworm ecotypes is the key factor.But there is a knowledge gap on the roles of earthworm ecotypes,associated with earthrom preferred habitat and food resource,in soil community and funcitoning.Based on the soils collected at the fourth year since the field experiment set-up in 2009,the impacts of two distinct earthworm ecotypes including endogeic Metaphire guillelmi and epigeic Eisenia foetida on soil physicochemical properties and community structure,under two ways of manure application(surface mulch and incorporation into the soil)were investigated.Our results demonstrated that:(1)Under the condition of manure surface mulch,earthworm increased soil water-stable aggregate stability in either tomato season or spinach season.Under the condition of manure incorporation into the soil,E.foetida did not have affect soil aggregate stability,while M.guillelmi did.(2)Earthworm ecotypes significantly influenced soil mineral nitrogen,available phosphorus,microbial biomass carbon,microbial biomass nitrogen,and had significant interactive effect with manure application methods.It was worth mentioning that available phosphorus increased more in the presence of E.foetida and M.guillelmi when the manure applied on soil surface and incorpored into soil,respectively.Regardless of the way of manure application,E.foetida and M.guillelmi significantly increased microbial biomass C and N.The effect of E.foetida on microbial biomass C was stronger than M.guillelmi.By contrast,the effect of M.guillelmi on microbial biomass N was stronger than E.foetida.(3)Both earthworm ecotype and manure application way significantly affected nematode number and trophic structure in tomato and spinach season.Earthworms could significantly decrease total nematode abundance,increased the percentage of fungivores and decreased the herbivores.(4)Earthworm changed soil microbial community.Under the condition of manure applying at soil surface,earthworm decreased the biomass of mycorrhizal fungi and protozoa.When manure were incorporated into soil,earthworms increased Gram-negative biomass,particularly M.guillelmi significantly increased the biomass of mycorrhizal fungi biomass and actinobacteria.(5)Except for E.foetida under the condition of manure being incorporated into soil,earthworm significantly affeted bacterial community structure.In tomato season,only M.guillelmi significantly chang bacterial community structure regardless of manure application way.In spinach season,both M.guillelmi and E.foetida significantly modified bacterial community structure.In addition to field experiment,a microcosm experiment with complete 2 × 2 × 2 design with three earthworm ecotypes(epigeic Eisenia foetida,epi-endogeic Amynthw cortices and endogeic Metaphire guillelmi)were conducted to explore the impacts on soil physiochemical properties,community structure and functions.Results showed:(1)The interactive effect of endogeic earthworm,epigeic earthworm and epi-endogeic earthworm only affected soil available phosphorus at 26 d sampling,but endogeic earthworm significantly increased soil available phosphorus at 26 d sampling and 56 d sampling.Either epigeic earthworm or epi-endogeic earthworm did not have significant effect on soil available phosphorus,but epigeic earthworm × epi-endogeic earthworm significantly increased it at 26 d sampling and 56 d sampling.Single inoculation of endogeic earthworm,epigeic earthworm or epi-endogeic earthworm all significantly increased soil nitrate nitrogen compared with the treatment without earthworms,and double interactive effects of endogeic earthworm and epigeic earthworm,endogeic earthworm and epi-endogeic earthworm,epigeic earthworm and epi-endogeic earthworm,and triple interactive effect of endogeic earthworm,epigeic earthworm and epi-endogeic earthworm could all significantly promote soil nitrate nitrogen at 26 d sampling and 56 d sampling.(2)Soil basal respiration and substrate-induced respiration were significantly affected by three earthworm ecotypes and their interactive effects.Especially,when only epigeic earthworm were inoculated,basal respiration and substrate-induced respiration was significantly lower than other treatments.The enzyme activities related to soil carbon,nitrogen and phosphorus cycle were significantly affected by earthworm ecotypes and their interactive effects.Endogeic × epi-endogeic treatment had the highest activities of four different C-related cycle enzymes and leucine aminopeptidase activity related to N cycling.Endogeic earthwormxepigeic earthworm and endogeic earthworm×epi-endogeic earthworm these two treatments showed highest N-related enzyme acetyl-β-D-glucosidase activity and P-related enzyme phosphatase activity.(3)The 28 d results showed that,only epigeic earthworm treatment and interacting with two other species significantly increased total contents of phospholipid fatty acids.Three different ecotype earthworms significantly affected arbuscular mycorrhizal fungi,but their interactive effect was not significant.The ecotypes of earthworm and their interactions on bacterial PLFAs,anaerobic bacteria,actinomycetes,protozoa was not significant at 28 d,but was significant at 56 d.The principle component analysis showed that,at 28d,microbial community structure from epigeic and epigeic earthworm × endogeic earthworm treatment was significantly different with other treatments.At 56 d,earthworms significanatly shifted microbial community structure compared with no earthworms.(4)At 28 d sampling,all treatments inculated with earthworms significantly changed bacterial community composition compared with the treatment without earthworm.Except for only epigeic earthworm treatment,other treatments all significantly affected fungal microbiological community structure,compared with the treatment without earthworms.At 56d sampling,only epi-endogeic or endogeic earthworm and endogeic earthworm ×epi-endogeic earthworm significantly shifted bacterial composition.However,compared with the treatment without earthworms,only epigeic earthworm treatment did not changed fungal community composition.Field experiment and microcosm experiment confirmed that earthworm ecotypes significantly affected soil properties including soil community structure and functions.