Effects of Earthworms on Phosphorus Dynamics – A Review

Belowground biotic interactions are known to influence soil fertility and plant growth by changing the physical environment and the soil nutrient cycles. Among the great diversity of soil biota, earthworms are keystone soil organisms in regulating nutrient cycling through: (i) their own metabolism that leads to high availability of carbon (C) and nitrogen (N) from metabolic wastes such as urine, mucus and tissue, (ii) the dispersal and the stimulation of soil microorganism activity associated with passage through the intestinal tract and (iii) the distribution and the mixing of organic matter and soil mineral particles. While many studies have examined impacts of earthworm on C and N fluxes in soils, less attention has been paid to the impact of earthworms on soil phosphorus (P). This paper reviews the current state of knowledge of the global earthworm’s impact on soil P dynamics in order to evaluate further involvements: i) on plant production and ii) on P transfer by runoff waters at the plot scale. This mini-review aims at considering research issues at several ecological levels, from individual earthworms (P distribution during food assimilation and excretion; gut microbial activities) to earthworm populations and communities (ecological categories and their influence on P dynamics) and, to the full extent, to the ecosystem scale (storage and/or loss of P). Interacting effects with other organisms (plants, microorganisms) are taken into account as well as the role of earthworms on physicochemical parameters (casting and burrowing activities, soil stability). Such a synthesis highlights the necessity to conduct interdisciplinary studies on biological, chemical and physical processes to better understand the effects of earthworms on P cycling at the ecosystem and landscape levels. _____________________________________________________________________________________________________________