Root morphological responses to population density vary with soil conditions and growth stages

How plants cope with increases in population density via root plasticity is not well documented, although abiotic environments and plant ontogeny may have important roles in determining root response to density. To investigate how plant root plasticity in response to density varies with soil conditions and growth stages, we conducted a field experiment with an annual herbaceous species (Abutilon theophrasti). Plants were grown at low, medium and high densities (13.4, 36.0 and 121.0 plants ▪ m-2, respectively), under fertile and infertile soil conditions and a series of root traits were measured after 30, 50 and 70 d. Root allocation increased, decreased or canalized in response to density, depending on soil conditions and stages of plant growth, indicating the complex effects of population density, including both competitive and facilitative effects. Root allocation was promoted by neighbor roots at early stages and in abundant resource availability, due to low to moderate belowground i...