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Effects Of Earthworms On Soil Microbial Communities And The Related Mechanisms In Different Habitats

Posted on:2019-05-11Degree:DoctorType:Dissertation
Country:ChinaCandidate:X GongFull Text:PDF
GTID:1360330632454447Subject:Ecology
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With the need for feeding the growing population,the increase of crop yields has resulted a lot of environmental problems in agriculture,such as the decline of soil quality,loss of biodiversity,as well as the damage of ecosystem functionality.Earthworms are known ecosystem engineers which benefit soil ecosystem processes,including other soil biota.Sustainable agriculture based on harmonious relationship between soil and human beings needs to be strengthened,especially in current agroecosystems.Therefore,in order to exploit the full potential of soil biota in sustainable agriculture,knowledge on the functioning of individual species but also interactions between species is mandatory.Such knowledge may be used for engineering soil communities fostering the ecological intensive agriculture.However,there is still knowledge gap on the mechanisms of earthworm effects on soil-microbial communities.Soils are dynamic and heterogenous entities providing diverse habitats for a broad range of biota,which play vital roles in ecosystem services.As ecosystem engineers,earthworms could exert large impacts on soil structure and internal resource cycling,as well as the associated dynamics of other soil biota i.e.,soil microbes.These changes would result in much wider alteration in soil ecosystem functioning.However,related mechanisms are still in vacant.First,we used meta-analysisto investigate the earthworm effects on soil microbial biomass carbon and nitrogen using published data.Then,we explored the earthworm effects on soil microbial communities using soils from an established experimental long-term rice wheat rotation system with two factors i.e.with/without earthworms and two kinds of straw manipulations in 2001.Soil samples were taken from the year of 2014 to 2015.The present study first investigated the microbial communities from a long-term experiment using high throughput sequencing and constructed the microbial networks to illustrate the distinguished responses of prokaryotes and eukaryotes to earthworms.Then we looked into the microbial communities in soil aggregates and found the different pathways,i.e.aggregation and resource quality,that were related to earthworm effects on microbial communities.Last,we surveyed the gut microbial communities of earthworms in light of earthworm evolution.The main results are as follows:1)Meta-analysis results showed that lower earthworm density increased soil microbial biomass carbon(MBC)and nitrogen(MBN)but higher earthworm density decreased MBC and MBN,indicating a favorable density for earthworms in ecological agriculture practices would be 60 ind./m2.Earthworm presence increased soil MBC by 17%significantly(P<0.001),but did not affect MBN,suggesting the exists of differential responses of microbial functional groups to earthworm presence.Meanwhile,earthworm decreased and increased soil MBN when straw was mulched on soil surface and incorporated to soil,respectively.The importance of resource distribution exerted by straw application methods could not be neglected when considering the earthworm effects.2)The abundance of prokaryotes and eukaryotes were all reduced by earthworms,with the reduction of eukaryotes were more significant.However,the ratio of Proteobacteria to Acidobacteria was increased by earthworms,which implied the beneficial effects of earthworms on soil fertility.These results also suggested that the fast-growing microbes,like Proterobacteria are favored by earthworm activities.Earthworms differentially modify soil prokaryotic and eukaryotic communities varying in residue management.When straw was mulched on soil surface,earthworms shifted the keystone species of soil microbial communities from Planctomyces to Proteobacteria,but when straw were incorporated to soil,the situation were inversed.3)Earthworms significantly increased the formation of macro-aggregates(>2 mm),and also have significant effects on microbial communities within soil aggregates.The bacterial communities were mainly separated by soil aggregates,while the fungal communities were more influenced by straw manipulation methods.There were positive relationships between the bacterial communities and soil aggregation,which was increased by earthworms.The relationships between fungal communities and soil aggregation was negative.Meanwhile,earthworms had positive effects on bacterial diversity.These results suggested different roles of soil aggregation and resource allocation in shaping bacterial and fungal communities.Given the fact that responses of bacterial and fungal communities were different in the structure equation models,different pathways of bacterial and fungal community dynamics were influenced by earthworm effects.4)In order to distinguish the contribution of earthworm species to their gut microbiota,we sampled five earthworm species across four provinces in Southwest China(104.1°E to 110.5°E,25.1°N to 28.8°N)to test the hypothesis that earthworm gut microbiota was determined by host phylogeny and geographic distances.The Proteobacteria and Actinobacteria were the most abundant bacteria in the gut of earthworms.The phylogenetic and geographic distance of earthworms both have significant effects on the gut microbial communities,with the effects of geographic distances more significant than phylogenetic distance of the host.The microbial diversity in the gut of earthworms were found to be negatively correlated with the altitude,which was similar to the pattern of above-ground plant communities.Taken together,the relationships between earthworms and soil microbes are much more complex than we have ever seen.The mechanisms of earthworm effects on soil microbial communities could be based on two pathways:indirectly via the change of soil structure and resource quality,which are the habitat and food source of microbes,to the altered microbial internal relationships;and directly via the gut related process,especially under the long-term evolution of earthworms.The conclusion from present study could benefit for our understanding of soil fauna-fauna,fauna-microbe and microbe-microbe interactions,which in turn will providing knowledge on the ecological intensive agriculture.
Keywords/Search Tags:agricultural management, straw application, soil animal, ecological networks, aggregates, ecological restoration
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