Fine root hydraulic conductivity relates to root functional traits in four coniferous species

Tree fine roots (<2 mm in diameter) are the primary organs for water acquisition from soil, yet how root traits contribute to water uptake under field conditions is not well established. In this study, we quantified the relationship between root water uptake and root functional traits in natural coniferous forests. In cool-temperate coniferous forests, we directly measured in situ hydraulic conductivity (Lp; m 3 m −2 s −1 MPa −1 ) of fine root using a pressure chamber method. We also examined the relationship between the Lp of the intact root segments and root traits, such as morphological traits, including root diameter and tissue density, and chemical traits, such as root N content, particularly at the interspecific level. The Lp of fine root segments differed significantly among species. Fine root Lp was positively correlated with root tissue density and negatively correlated with root diameter and N content across species, suggesting it is related to actual water movement within trees. Our results show that the Lp of fine root systems in the forest field reflects and originates from both water resistance in transportation and absorption, especially a water transport rather than an absorption function. We highlight that the linkage between in situ Lp and the fine root system traits enable understanding of the complex functional balance characterizing the overall hydraulic uptake and transport capacity of water resources from the soil through exploitative root foraging.