Legumes have a higher root phosphatase activity than other forbs, particularly under low inorganic P and N supply

Recent studies suggest that phosphatase activity in soil under legumes is higher than under other plants, but whether this is due to plant activity, microbe activity, or a response to altered soil N or P is unclear. I addressed two main questions: (i) do legumes have a higher root phosphomonoesterase (PME) activity than non-legumes?, and (ii) does root PME activity of legumes and non-legumes respond differently to variation in P or N supply? In four greenhouse experiments, I compared PME activity of seven leguminous forbs and nine other herb species (mostly forbs), under various supplies of inorganic P or N. Under low P and high N supply, legumes had on average a 50% or 120% higher PME activity than other forbs (expressed per fresh or dry roots). Legumes were similar or more plastic in their response to gradients of P, but less plastic to gradients of N. Root PME activity did not seem to depend on the presence of nodules, nor on growing in species monocultures or mixtures. On average leguminous forbs do have a higher root PME activity than other forbs, particularly under low inorganic P and N supply. Under higher N supply, the difference between leguminous and non-leguminous forbs becomes smaller, and PME activity of grasses may even be higher than that of legumes. The results help explaining why legumes can become abundant in plant communities on P and N-poor soils.