Shifting patterns in fine root distribution of four xerophytic species across soil structural gradients and years of growth

1. Fine root distribution influences the potential for resource acquisition in soil profiles, which defines how plants interact with local soil environments; however, a deep understanding of how fine root vertical distribution varies with soil structural variations and across plant ages is lacking. 2. We subjected four xerophytic species native to an arid valley of China, Artemisia vestita, Bauhinia brachycarpa, Sophora davidii, and Cotinus szechuanensis, to increasing rock fragment content (RFC) treatments (0%, 25%, 50%, and 75%, v v-1) in an arid environment and measured fine root vertical profiles over four years of growth. 3. Fine root depth and biomass of woody species increased with increasing RFC, but the extent of increase declined with plant age. Increasing RFC also increased the degree of interannual decreases in fine root diameter. The limited supply of soil resources in coarse soils explained the increases in rooting depth and variations in the pattern of fine root profiles across RFC. Fine root depth and biomass of the subshrub species (A. vestita) in soil profiles decreased with the increase in RFC and plant age, showing an opposite pattern from the other three woody species. 4. Within species, the annual increase in fine root biomass varied with RFC, which led to large interannual differences in the patterns of fine root profiles. Capacity of younger or subshrub plants to cope with soil environmental changes were greater than the older or shrub plants. These results provide insights into the limitations of soil resources in dry and rocky environments, and have management implications for degraded agroforest ecosystem.