Spatial Distribution of Roots across Three Dryland Ecosystems and Plant Functional Types

Abstract

Roots play a critical role in carbon storage, carbon cycling, and resource acquisition in dryland ecosystems, yet their distribution and production patterns are poorly understood. We aimed to compare the vertical and horizontal distribution of roots of the dominant plant functional types across 3 dryland ecosystems in the western Great Plains of the United States. We collected consecutive soil cores from directly under plants to 29 cm away from the center of plant individuals (horizontal plane), to a 20-cm depth (vertical plane). Across the 3 ecosystem types, grass root biomass decreased with depth and, for the sagebrush steppe, at a distance beyond 6.5 cm from the center of the plant. At the 10–20 cm depth increment, there was no horizontal pattern in root biomass. Uniformity in root biomass in the 10–20 cm depth and at distances >6.5 cm from the plant center is best explained by the overlap of roots of individual and neighboring plants to maximize belowground resource uptake. There was much lower root biomass in the surface 20 cm adjacent to shrubs than adjacent to grasses in the sagebrush steppe, and while grass root biomass decreased significantly with depth and distance as described above, shrub roots were uniform in both planes. Our study confirms that root distribution in drylands differs among plant functional types, with grasses exploiting surface soils both horizontally and vertically to capitalize on surface resources, and shrubs capitalizing less on those resources.