Earthworms enhance soil phosphorus cycling but plant responses differ among earthworm ecological categories: a meta-analysis

Earthworms are integral to soil processes and influence plant growth and phosphorus (P) nutrition. We investigated the role of earthworms in the P cycle by synthesizing data from 181 studies, of which 22 % were field observations and 78 % were from pot or mesocosm experiments. Earthworms increase the concentration of soil Olsen P and microbial P, phosphatase activity, and plant biomass. Deep-dwelling epi -anecic and anecic earthworms are more effective than other ecological groups at increasing the soil available P, although surface-dwelling earthworms (epigeic and endogeic) contribute more effectively to plant P uptake. The increase of plant biomass by earthworms decreases with increasing organic matter content, but Olsen P concentration and plant P uptake show the opposite trend. Moreover, the impact of endogeic earthworms on P is sensitive to soil organic matter content. The positive effects of earthworms on P cycling are more pronounced under acidic and alkaline conditions than under neutral conditions (6.5–7.5). Finally, the increased available P concentration due to earthworms directly stimulates microbial P uptake, while all three main ecological categories of earthworms indirectly stimulate root growth and increase plant P uptake. Overall, earthworms can effectively promote P cycling in ecosystems, with a more significant effect in nutrient-poor soils.