Soil hydraulic function: Earthworm-plant root interactions

Relatively little is known about life in the soil, particularly the interactions between its components (such as plant roots, macrofauna and micro-organisms). Many of these interactions drive soil processes that give rise to ecosystem services supporting human wellbeing. Most of the valuable ecosystem services are driven by soil organisms, and earthworms are the key representatives. Earthworm activity underpins a number of soil properties that directly influence soil hydrological functioning and food production. However, the influence of different earthworm ecotypes and plant roots they interact with is largely unknown. This research project examines these effects through laboratory and field experiments.

The data show that the interaction between earthworms and plant roots can significantly increase soil physico-hydraulic properties. However, laboratory experiments indicated that there are species / ecotype effects. The vertical burrowing earthworm Lumbricus terrestris increased soil water flow, but in conditions where their burrows are not connected to drainage systems, plant roots had a greater effect. The lateral burrowing earthworm Allolobophora chlorotica had a greater impact on soil hydraulic properties than L. terrestris. The presence of A. chlorotica in soils resulted in the greatest and most rapid increase in soil water flow through macropores > 3 mm diameter as a result of their interaction with plant roots. In the field experiment, the conversion of arable soil to ley caused a significant improvement to soil properties; the presence of earthworms in the ley was responsible for a significant proportion of these improvements. However, the magnitude of earthworm impacts is significantly controlled by seasonal climate variations. Furthermore, the presence of earthworms significantly increased plant biomass.

These results show that the interaction between earthworms and plant roots can lead to increased soil drainage and also soil water retention which could help mitigate the impacts of increasing extreme weather events such as floods and droughts, thereby helping to maintain ecosystem services that are derived from soils.