Wheat earthworm-plant-microbiota interactions. Wheat earthworm-plant-microbiota interactions

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. Overall design: Five wheat accession (Accession identifiers 1190336=YoGI_178, 1190451=YoGI_203, 1190779=YoGI_287) from the AE Watkins collection and Shamrock (YoGI_349) from the Gediflux collection (both supplied by the John Innes Centre), and commercially available Skyfall (RAGT) were used to examine the role that the presence/absence of the endogeic earthworm Allolobophora chlorotica have under regular watering or drought conditions. Two plants per accession were grown in soil collected from BSSE field, Leeds experimental farm, following a factorial experiment. The soil used for the experiment was a silt loam with pH of 7.69 ± 0.01 and organic matter content of 3.20 ± 0.06% and it was hand sorted to remove earthworms, large stones and roots. The experiment was carried out in a glasshouse at 20°C±5°C daytime and 16°C±5°C night-time. Plants were germinated on wet tissue paper for 6 days before moving them to the soil. Two seedlings were used for each pot. The plants were watered for the first 38 days and after this time point, the drought pots were no longer watered. Samples were collected on day 53 from the beginning of the experiment. Earthworms were collected from Warren paddock, a pasture field at Leeds experimental farm and three were added to each pot.