Linking roots, preferential flow, and soil moisture redistribution in deciduous and coniferous forest soils

Purpose Soil moisture (i.e., the changes in the gravimetric soil water content) redistribution is closely linked with root distribution and preferential flow in soils. This study aimed at exploring the soil water content distribution in the presence of root-enhanced preferential flow in deciduous (Quercus variabilis BI.) and coniferous forests (Platycladus orientalis (L.)). Methods Dual-tracer experiments (Brilliant Blue FCF and Bromide [Br-]) were conducted in both forests under large (40 mm) and extreme (70 mm) rainfall amount. The distribution of soil water contents was investigated in vertical soil profiles after dual-tracer experiments. Additionally, the correlations among soil water contents, root traits (diameter <= 5 mm), and preferential flow features (preferential flow paths and root-solute interaction) were analyzed. Results Abundant root-induced soil moisture accumulation was found in the upper soil layer (0-20 cm), which was more apparent in deciduous forest than in coniferous forest. Preferential flow strongly influenced the variation distribution of soil water content. The greater degree of preferential flows was, the higher soil water content was. In both forests, the effect of root traits on soil water distribution was more evident under large rainfall amount as compared to extreme rainfall amount. In addition, positive significant correlation between root-solute interaction and soil water content was found at both sites. Conclusions These results indicated that tree species with different roots distribution patterns enhance different degree of preferential flow, and have varied impacts on the soil moisture redistribution in forest soils. The effects of root traits on soil moisture are more apparent under lower rainfall amount.