Radial patterns of xylem sap flow in non-, diffuse- and ring-porous tree species

We investigated radial patterns of sap flux density and wood properties in the sapwood of young loblolly pine (Pinus taeda L.), mature white oak (Quercus alba L.) and sweetgum (Liquidambar styraciflua L.), which represent three major classes of wood anatomy: non-porous (coniferous), ring-porous and diffuse-porous, Radial measurements of xylem sap flux density were made in sections of xylem extending to 20 mm and 20-40 mm from the cambium, These measurements were compared with measurements of the relative water content (R(s)) and sapwood specific gravity (rho(f)) of corresponding radial sections, In both hardwood species, sap flow differences were rarely significant between the two depth intervals, In pine, a 59% reduction in daily sap flux density from outer to inner sapwood was found, This could not be accounted for by a 3% drop in R(s); rather, an accompanying 9% reduction in rho(f) indicated a transition between the depth intervals from mature to juvenile sapwood, and is the probable cause of the lower flux rate in the inner xylem of pine.