Natural and human-related drivers affect belowground biomass and nutrients in a Caatinga dry forest

Belowground biomass represents a significant carbon reserve with a crucial role in terms of ecosystem functioning, but very little is known about root systems across tropical dry forests. Here we investigate patterns of root biomass, nutrient concentration/stocks, and the effect of aboveground biomass, chronic anthropogenic disturbance, precipitation, and soil depth as their potential drivers in a Caatinga dry forest, northeastern Brazil. Belowground biomass was obtained by a destructive method from July 2020 to March 2021 across forest stands in three 0.49-m² and 1-m deep trenches per stand. Root biomass ranged from 3.23 Mg ha⁻¹ to 29.6 Mg ha⁻¹, accounting for less than 1/3 of total forest biomass. Belowground biomass greatly varied across forest stands mainly represented by large roots concentrated in the superficial soil layer. In general, nutrient concentrations and stocks did not vary significantly across forest stands regarding both root size class and soil depth, although fine roots support a higher concentration of P than large-sized roots. Finally, chronic disturbance, aboveground biomass, precipitation, and soil depth were important predictors affecting root biomass and nutrients. Our results suggest that a combination of natural and human-related drivers modulate root biomass and nutrients in Caatinga dry forests immersed in human-modified landscapes.