Root density distribution and biomass allocation of co-occurring woody plants on contrasting soils in a subtropical savanna parkland

Abstract

Background and aims: Root niche partitioning among trees/shrubs and grasses facilitates their coexistence in savannas, but little is known regarding root distribution patterns of co-occurring woody plants, and how they might differ on contrasting soils. Methods: We quantified root distributions of co-occurring shrubs to 2m on argillic and non-argillic soils. Results: Root biomass in the two shrub communities was 3- to 5- fold greater than that in the grassland community. Prosopis glandulosa, the dominant overstory species was deep-rooted, while the dominant understory shrub, Zanthoxylum fagara, was shallow-rooted (47% vs. 25% of root density at depths >0.4m). Shrubs on argillic soils had less aboveground and greater belowground mass than those on non-argillic soils. Root biomass and density on argillic soils was elevated at shallow (< 0.4m) depths, whereas root density of the same species on non-argillic soils were skewed to depths >0.4m. Root density decreased exponentially with increasing distance from woody patch perimeters. Conclusions: Belowground biomass (carbon) pools increased markedly with grassland-to-shrubland state change. The presence/absence of a restrictive barrier had substantial effects on root distributions and above- vs. belowground biomass allocation. Differences in root distribution patterns of co-occurring woody species would facilitate their co-existence.