AXIAL AND RADIAL WATER-FLOW IN THE TRUNKS OF OAK TREES - A QUANTITATIVE AND QUALITATIVE-ANALYSIS

Axial water flow in the trunks of mature oak trees (Quercus petraea (M att.) Liebl. and Q. robur L.) was studied by four independent techniqu es: water absorption from a cut trunk, sap flowmeters, heat pulse velo city (HPV) and thermoimaging. Estimation of the total water flow with sap flowmeters, HPV and water absorption yielded comparable results. W e concluded from dye colorations, thermograms and axial profiles of sa p flow and heat pulse velocity that, in intact trunks, most of the flo w occurred in the current-year ring, where early-wood vessels in the o utermost ring were still functional. Nevertheless, there was significa nt flow in the older rings of the xylem. Total water flow through the trunk was only slightly reduced when air embolisms were artifically in duced in early-wood vessels, probably because there was little change in hydraulic conductance in the root-leaf sap pathway. Embolization of the current-year vessels reactivated transport in the older rings.