Earthworm Presence Maintains Stable Nematode-based Soil Food Web In Urban Greenland Ecosystems

The urban greenland system is an indispensable part of the urban ecosystem.In the urban greenland ecosystem,the community and structure of soil animals have different performances.With the development of the economy,the degree of human activities is intensified and the scope is expanded.The structure and distribution of small and medium-sized soil animals are disturbed,which in turn weakens the ecosystem service function of urban greenland.Soil nematodes play different nutritional roles in soil food webs,and the soil food webs characterized by soil nematodes can be used as effective indicators of soil fertility and health.Exploring the characteristics of nematode community can not only evaluate the impact of nematodes on the ecosystem,but also understand the health status of the whole ecosystem.As an "ecosystem engineer",the dominant nutritional and non-nutritional processes of earthworms may play an important role in the regulation of free-living nematodes and herbivorous nematodes.Exploring the effect and mechanism of earthworms on nematodes in urban greenland ecosystem is helpful to understand the balance mechanism of soil food web itself and provide a scientific basis for urban greenland ecosystem management.In this study,the relationship between earthworms and nematodes in Kaifeng urban greenland ecosystem was investigated,as well as the influence of ecological geographical features and environmental factors on the characteristics of earthworms and nematodes.And two kinds of soil with more earthworms(soil 1)and less earthworms(soil 2)were inoculated with different numbers of earthworms,including 0(CK),1(1W),2(2W)and 4(4W).Microcosm experiments were carried out to verify the results,and the characteristics of soil nematode in urban green space system and natural ecosystem were compared and analyzed.The changes of total individuals and nutrient levels of soil nematode community,soil physical and chemical properties,survival of earthworms and soil nematode quantity variation coefficient were measured,and vermicompost and mucus were extracted to culture nematodes for a short time.The inactivation rate of nematodes was observed when different concentrations of extracts were added,in order to pave the way for further exploration of the mechanism involved in the effect of earthworms on nematodes.The main results are as follows:(1)In the urban greenland ecosystem,the number of nematodes decreased with the increase of earthworm density,and the responses of bacteria-feeding nematodes and predatory and omnivorous nematodes were more obvious.With the increase of earthworm density,the stronger the inhibitory effect of earthworms on potential explosive nematodes,and the more stable equilibrium state of soil food web characterized by nematodes.(2)The results of indoor culture experiments showed that in the absence of plants,earthworm inoculation could inhibit fungal-feeding nematodes,but had no significant effect on other nutritional groups.In the soil with high earthworm density,in the process of indoor culture,the number of soil nematodes in the culture basin inoculated with earthworms decreased slightly,but the number of nematodes in the culture basin without earthworms also decreased.However,in the soil with low earthworm density,the number of soil nematodes in the culture basin inoculated with earthworms decreased greatly,while the number of nematodes in the culture basin without earthworms changed little,indicating that the soil with high earthworm density could also inhibit nematodes to a certain extent after the removal of earthworms.(3)For earthworm mucus and vermicompost extract,vermicompost extract significantly increased the inactivation rate of nematodes,but mucus had no obvious effect on nematode inactivation,100% concentration of vermicompost extract had higher inactivation rate of nematodes.When earthworms affect nematodes through vermicompost and mucus,the effect of mucus is very low,but the fatality rate of vermicompost to nematodes is high,but it can be shown only after a long time.The above results showed that although the existence of earthworms showed a potential inhibitory effect on nematode communities in the field,and the extract of earthworm feces also had a certain inhibitory effect on nematodes,in indoor microcosm experiments,the existence of earthworms did not significantly reduce the density of nematode communities,while the effect of soil types on nematode communities was very obvious.It can be seen that in the urban greenland ecosystem,the regulation process of earthworms on soil food web characterized by nematodes is much more complex than that simulated by microcosmic soil culture experiments.In the follow-up work,the effects of vegetation and soil characteristics on the regulation of nematodes by earthworms should be further explored.