Understorey fine root mass and morphology in the litter and upper soil layers of three Chinese subtropical forests

To quantitatively assess how fine root biomass and necromass of understorey species vary in the litter and upper mineral soil layers. The method combines in situ sampling of the litter layer with sequential coring during the root growth stage in three Chinese subtropical forests: coniferous forest, coniferous and broad-leaved mixed forest, and evergreen broad-leaved forest. Approximately 67-74 % of the total fine root mass occurred in the layer of decomposing litter (L2) and that of the top 7.5 cm of the soil (M1). Layer L2 was the preferential horizon for fine root growth, and the thickness of this horizon strongly affected the vertical fine root pattern. In addition, the fine root mass was positively correlated with total N concentration in layers L2 and M1. For all three forest types, most fine roots had diameters < 1 mm and clear decreasing trends in specific (mass-based) root length and tip number were observed from the litter layer to the soil and the N concentration of live roots also decreased with depth. Understorey roots show a soil exploitation pattern through which absorptive fine roots are arranged to maximize nutrient acquisition from the litter and upper soil layers and to avoid belowground competition with trees, especially in species-rich forests.