Roots-Enhanced Preferential Flows in Deciduous and Coniferous Forest Soils Revealed by Dual-Tracer Experiments

Macropores formed by roots are crucial channels for preferential flows in forest soils that are largely responsible for water percolation and solute leaching. Using dual-tracer experiments (Brilliant Blue FCF and bromide [Br]), this study investigated the preferential flows of water and solutes in a deciduous forest dominated by Bl. and a coniferous forest mainly planted with (L.) Franco. Dye-stained patterns and concentrations of Brilliant Blue and Br were obtained in vertical soil profiles (0-30 cm), whereas stained and unstained roots were collected and analyzed in horizontal soil profiles to a 30-cm soil depth. Brilliant Blue and Br were mainly accumulated in the 0- to 20-cm soil depth, which had greater total root length density than the 20- to 30-cm soil depth ( < 0.05). Only part of the roots facilitated the preferential flows, with finer roots (i.e., diameter <1 mm) contributing the most. More intriguingly, the coniferous forest soil had a greater degree of preferential flows and greater tracer concentrations at deeper soil depth than the deciduous forest soil, suggesting the importance of tree species and forest composition on water and solute transport in forest ecosystems.