Phosphorus is an essential nutrient for life, but it binds strongly to soil particles. This research focusses on the contribution of earthworms to increase phosphorus availability to plants.

The decline in reserves of rock phosphate, the source of Phosphorus (P) fertilizer, is one of the most serious threats to global food security. Phosphorus is a key nutrient for plants, but very difficult to access by plant roots as P-fertilizer quickly precipitates, adsorbs to soil mineral particles, or is incorporated in organic matter. In the past, large amounts of P fertilizer have therefore been applied to many soils, resulting in a large pool of relatively inaccessible "legacy P". This pool can in theory supply plant growth for decennia. Recent research of our group has shown that earthworm activity can temporarily make this P available, resulting in transient "hot-spots" of plant available P. However, mechanisms are still unclear. We propose to study these pathways through which earthworms make P available, as well as the effect of different earthworm communities. Our main hypothesis is that plant uptake of soil legacy P can be increased by stimulating earthworm functional diversity. We will test this hypothesis using an innovative combination of approaches from soil ecology (trait-based analysis) and -chemistry (surface complexation modeling). We will (i) identify and quantify key traits of earthworms that determine P availability; (ii) determine and model the pathways through which single earthworm species affect P availability; (iii) model the effect of earthworm communities on P availability; and (iv) validate our findings in field experiments. Ultimately, our results will help to better understand the limitations to plant P uptake, and to adapt our agroecosystems to a future with less phosphorus.