- 1We examined biomass and root proliferation responses of Abutilon theophrasti Medic. to the density of high nutrient patches and the patch–background contrast. Contrast in nutrient content between a patch and the background soil, as well as patch density, are important features of heterogeneous soil environments that have received little research attention.
- 2Plants were grown in pots with no, one or two organic nutrient patches, and the equivalent nutrition of no, one or two patches in the background soil in a factorial design. Plant performance (root and shoot biomass) and root proliferation (root length inside and outside high-nutrient patches) were measured.
- 3Root and shoot biomass increased with increasing nutrient heterogeneity, and root biomass declined with increased background soil nutrient availability. Patch–background contrast did not alter root or shoot biomass, nor allocation to roots. Biomass responses appeared to be driven by heterogeneity, as plants with access to the same total nutrients were larger when nutrients were concentrated in patches. The root proliferation response was not affected by either the density of patches or the degree of contrast.
- 4A conceptual model is presented describing how a plant's overall nutrient status could respond to changes in the patch–background contrast. The model predicts that nutrient-sufficient plants should not respond to patches, but nutrient-limited plants should proliferate roots proportionally to the contrast. The proliferation response should saturate when the total nutrients in both patch and background are no longer limiting.