The hydraulic conductivity of the xylem in conifer needles (Picea abies and Pinus mugo)

摘要

Main resistances of the plant water transport system are situated in leaves. In contrast to angiosperm leaves, knowledge of conifer needle hydraulics and of the partitioning of resistances within needles is poor. A new technique was developed which enabled flow-meter measurements through needles embedded in paraffin and thus quantification of the specific hydraulic conductivity (K_s) of the needle xylem. In Picea abies, xylem K_s of needle and axes as well as in needles of different age were compared. In Pinus mugo, resistance partitioning within needles was estimated by measurements of xylem K_s and leaf conductance (K_leaf, measured via ‘rehydration kinetics’). Mean K_s in P. abies needles was 3.5×10−4 m2 s−1 MPa−1 with a decrease in older needles, and over all similar to K_s of corresponding axes xylem. In needles of P. mugo, K_s was 0.9×10−4 m2 s−1 MPa−1, and 24% of total needle resistance was situated in the xylem. The results indicate species-specific differences in the hydraulic efficiency of conifer needle xylem. The vascular section of the water transport system is a minor but relevant resistance in needles.