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

Abstract

We investigated radial patterns of sap flux density and wood properties in the sapwood of young loblolly pine (Finns 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 (Rs) and sapwood specific gravity (ρr) 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 Rs; rather, an accompanying 9% reduction in ρr 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.

Sensitivity of mean canopy stomatal conductance to vapor pressure deficit in a flooded Taxodium distichum L. forest: hydraulic and non-hydraulic effects

“…Variation among trees in lags between J S and Q o were unrelated to tree size (P>0.05). Furthermore, unlike nearby Pinus taeda, which showed stomatal closure at night thus using water uptake for recharge (Phillips et al 1996), water taken up at night by T. distichum is immediately transpired. This behavior was especially clear on 13 September when nighttime flux, mostly in the outer sapwood, accompanied a nighttime surge in D to 0.6 kPa (Oren et al 1999a).…”

“…J S is calculated from the temperature difference, relative to the maximum difference occurring at times of zero flow. Complete information on sensor installation and flux calculations can be found in Granier (1987) and Phillips et al (1996). J S may be used to estimate G S only after it is converted to a spatially weighted mean flux.…”

“…In five of the trees, a Granier-type sensor was installed in the outer 20 mm of the sapwood. In the other five trees, the modified Granier-Phillips type (Phillips et al 1996) was used. This sensor measures sap flux separately in the outer 20 mm sapwood and the next 20-mm band of xylem (20-40 mm from the cambium), and uses a single unheated reference thermocouple in the sapwood 10-30 mm from the cambium, after verifying that diurnal radial temperature gradients over these depth ranges were insignificant.…”

Species‐specific transpiration responses to intermediate disturbance in a northern hardwood forest

“…Although transpiration accounting for~80% of LE in dry sites is not unheard of [Miller et al, 2010], we acknowledge that our lack of sap flux measurements over depth ranges within the sapwood and radial scaling of sap flux measurements contributed to errors in the sap flux data [Phillips et al, 1996;Schäfer et al, 2000]. Due to the increased number of large red maples and large bigtooth aspen trees in the control plot, these errors were likely greater in the control plot and would reduce the fraction of LE that is accounted for by E C in that plot.…”

“…Sap flux sensor data were processed using a baselining procedure to account for the daily maximum temperature of each sensor and times when the 2 h average VPD was lower than 0.5 kPa in order to account for nocturnal recharge flux [Oishi et al, 2008]. No radial scaling information was available for our plots [Phillips et al, 1996]. We therefore assumed that our sap flux measurements represent an average sap flux density through the entire conductive area.…”