Project description:Numerous studies have shown that the function of earthworms may depend on their ecotype and density, which affects how they impact soil microbial and nematode communities. However, it is unclear how different earthworm species and densities alter the composition of soil microbial and nematode communities and how these modifications impact the soil micro-food web. The structural equation model (SEM) is a more accurate tool for identifying the intricate relationships between various trophic levels in the soil micro-food webs than the widely used bivariate data analysis. In order to ascertain the effects of earthworm species, including epigeic earthworm Eisenia fetida and anecic earthworm Metaphire guillelmi, as well as varying densities on the composition of main microbial groups, soil nematodes and their relationships, a microcosm experiment was conducted in a greenhouse. After nine weeks of observation, compared with the control treatments, Eisenia fetida increased the biomasses of total microorganism and bacteria, whereas Metaphire guillelmi decreased the biomasses of total microorganism, bacteria, and gram-positive bacteria, but showed an increase in AMF biomass. Additionally, both two earthworm species decreased the abundance of total soil nematode, bacterivores, and omnivore-predators, which is in contrast with the control treatments. The SEM results indicated that the addition of Eisenia fetida at different densities had indirect negative effects on the abundance of omnivore-predators, as it significantly increased the content of soil organic carbon, ammonium nitrogen, and nitrate nitrogen. The bottom-up effects were found to be the dominant forces, which promoted bacterial-dominated decomposition channels. The addition of Metaphire guillelmi with different density had direct negative impact on bacterivores and fungivores. Moreover, it had indirect negative effects on omnivore-predators by altering the soil properties. The dominant forces were still the bottom-up effects. Our study suggests that different earthworm species have distinct mechanisms that affect the soil micro-food web in different ways.
Project description:Earthworms enhance plant growth but the precise mechanism by which this occurs is not known. An understanding of the mechanism could potentially support changes in agricultural management reducing fertiliser usage and therefore costs and the carbon footprint of agriculture. We conducted a factorial experiment in which 5 strains of wheat were grown in the presence and absence of earthworms under regular watering and droughted conditions. The different wheat strains all responded in a similar fashion. Plant biomass was greater in the presence of earthworms and under regular watering. The presence of earthworms reduced the impact of drought on plant biomass and also slowed down the rate of drying of the droughted soils. Plant nutrient content (N, P, Si) showed no consistent pattern with treatments but total N, P and Si mirrored plant biomass and decreased in the order earthworm-present watered > earthworm-present droughted > earthworm-absent watered > earthworm-absent droughted. Nutrient availability in the soil, as assessed by chemical extractions showed no consistent pattern with treatments. Differential gene expression of plants was greater between watering treatments than between earthworm treatments. Genes that were differentially expressed between the earthworm treatments predominantly related to plant defences, abiotic stress and control of plant growth though a couple were linked to both nitrogen cycling and stress responses. The soil microbiome of the earthworm-present treatments was more associated with nutrient-rich environments, the promotion of plant growth and the suppression of plant pathogens. Our data suggest that enhanced plant growth was due to changes in the microbiome due to earthworm processing of the soil rather than changes in nutrient availability due to the presence of earthworms.