Effects Of Earthworm Activities On Soil Microbial And Micro-Fauna Composition And Function In Agro-Ecosystem

As one of the most important macro-fauna in terrestrial ecosystem, earthworm plays a crucial role in the nutrient cycling through altering soil physicochemical and biological properties. Earthworms directly and indirectly influence soil microorganisms and micro-faunal communities via their burrowing, grazing and casting activities. So far, fewer studies explored the long-term influences of earthworm on soil community structure and function, particularly under the field condition. Therefore, based on a long-term field experiment lasting for 15 years, the changes of soil microbial and micro-faunal community and function influenced by earthworms were evaluated.Earthworms (Metaphire guillelmi) were inoculated in the plots experiment with an upland rice-winter wheat rotation agro-ecosystem with different maize residues amendment method (mulched or incorporated). The influences of earthworms on soil microbial biomass, microbial community composition, protozoan abundance, nematodes abundance and trophic structure and soil enzyme activity were investigated through seasonal sampling regiem. The experimental field plots were laid out in a completely randomized design with five treatments:the control treatment, no maize residues, no earthworm inoculated (ROEO); maize residues mulched on soil, no earthworm inoculated (RmEO); maize residues mulched on soil, earthworm inoculated (RmE1); maize residues incorporated into soil, no earthworm (RiEO); maize residues incorporated into soil, earthworm inoculated (RiE1). The main results were as followed:1) Residue amendment promoted soil nutrient contents. The presence of earthworm increased soil available nutrients (available potassium, available phosphorus, ammonium and nitrate nitrogen), but had no significant influences on the contents of soil total organic carbon, total nitrogen, total phosphorus and pH.2) Regardless of residues mulched or incorporated, the residues promoted microbial biomass contents. At rice heading stage, when maize residues were mulched on soil, the earthworm led to higher microbial biomass carbon (MBC); but in other sampling times, earthworm activity had no significant effects on MBC. Earthworms did not modify the contents of soil microbial biomass nitrogen (MBN). Earthworm activity altered soil microbial community structure. When maize residues were mulched on soil, earthworm enhanced the abundance of total PLFAs and bacterial PLFAs (gram-positive and gram-negative) PLFAs in rice harvest stage. When maize residues were incorporated into soil, earthworms reduced abundance of total PLFAs and bacterial PLFAs (mostly gram-positive) PLFAs in both wheat harvest and rice heading stage. Independent of residues incorporated and mulched, earthworms decreased significantly the fungal PLFAs across almost all sampling time, leading to remarkably reduced fungal to bacterial ratio.3) Residue amendments strongly altered the abundance and community structure of protozoa and nematodes. Flagellate numbers significantly increased in all sampling times in both maize residues incorporated and mulched treatments in the presence of earthworms. When residues incorporated into soil, earthworm significantly increased the amoebae abundance at all sampling times; while notably increased amoebae numbers in wheat and rice heading stage when residues mulched on soil. Earthworm significantly reduced total nematodes numbers at all sampling times, independent of residues incorporated or mulched. Moreover, earthworm altered trophic structure of nematode community. At rice harvest stage, the bacterivorous nematodes significantly decreased due to the presence of earthworm. Earthworm significantly decreased the proportion of fungivorous nematodes at all sampling time following residues amendment. At heading stage of wheat, earthworm reduced the proportion of herbivorous nematodes, but increased it at rice heading and harvest stages.4) Residue amendment and sampling time significantly affected soil enzyme activities. Regardless of sampling times and residues incorporated or mulched, earthworm notably increased the activities of cellulase and β-D-glucosidase. When residue mulched, earthworms significantly enhanced soil invertase activity at the heading stage of wheat and rice; or at the harvest stage of wheat and rice when residue incorporated into soil. At rice and wheat harvest stage, earthworms significantly enhanced the protease activity independent of residues incorporated or mulched. At wheat heading or harvest stage, earthworms increased alkaline phosphatase activity with residues incorporated or mulched. No marked changes for urease activity were detected due to earthworm.In conclusion, the presence of earthworm affected soil microbial and micro-faunal community composition, which led to the changes of soil function. And such effects depended on the way of residues amendment or the sampling time (crop growth stage).