Neighbourhood-dependent root distributions and the consequences on root separation in arid ecosystems

1. Inter-specific root separation is an important example of spatial niche differentiation that drives species coexistence in many ecosystems. Particularly under water-stressed conditions, it is believed to be an inevitable outcome of species interactions. However, evidence for and against this idea has been found. So far, studies aiming at reconciling the debate mainly focus on abiotic determinants. It remains unclear if and to what extent root separation depends on the type and growth form of interacting plants. 2. We conducted a detailed field study in three adjacently located (with pairwise distances < 500 m) arid patchy communities where a common tussock grass species Achnatherum splendens grew in association with either a tree (Elaeagnus angustifolia), a shrub (Nitraria tangutorum) or a perennial forb species (Sophora alopecuroides). In each community, roots and soils were sampled along the soil layers from five depths (0-10, 10-30, 30-60, 60-100 and 100-150 cm) in the patches ...