Effects of tension wood on water transport and morphology in the evergreen oak Quercus ilex.
Gartner, Barbara *,1, Roy, Jacques2, 1 Oregon State University, Corvallis, OR, 973312 CNRS, Montpellier, France
ABSTRACT- Where xylem has tension wood in it, the wood is providing a specialized mechanical role in addition to providing water transport. 1) We hypothesized that this mechanical support comes at a cost to water transport, and thus that tension wood decreases specific conductivity (ks). 2) We expected plants with much tension wood to maintain similar leaf-specific conductivity (kl) as plants with little tension wood. 3) The similar kl would occur by morphological adjustment, either a decrease in the leaf area/sapwood area ratio, or a shortened stem. We grew seedlings of the diffuse-porous evergreen oak Quercus ilex either upright or at an inclination of 30°, and we rotated the pots weekly by 180°. Contrary to the first hypotheses, there was no significant effect of inclination on ks. Contrary to the second hypothesis, the inclined plants actually had 30% higher leaf-specific conductivity (kl) than the upright ones (P=0.031). Regarding morphology, there was no significant difference in leaf area/sapwood area between the two treatments (P<0.2550), although the variance was enormous. The inclined plants produced significantly less leaf dry mass in the treatment year than did the upright plants (15.7 vs. 18.2 g per plant, p=0.0376). There was no significant difference in the length of primary stem (p= 0.6824), but the inclined plants had significantly less secondary stem, and thus less total stem length than did upright plants (337 vs. 401 cm, respectively, P<0.0435). These morphological differences suggest that there were, indeed, effects of tension wood on the water transport within the stems, as hypothesized. It is possible that there were small but biologically important differences in ks that we did not detect in our direct measurements of ks, It is interesting that the kl was actually higher in the plants with much tension wood: inclined plants apparently were more able to deliver water to leaves at a given tension gradient than were upright plants.
Key words: tension wood, specific conductivity, leaf-specific conductivity, water transport
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