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THE EFFECTS OF TRANSIENT REDUCTIONS IN FUNCTIONAL LEAF AREA ON STOMATAL CONDUCTANCE: BRANCH LEVEL EXPERIMENTS ON YOUNG AND OLD TREES
Citation:
Brooks, J R., B. J. Bond, R. Coulombe, J. C. Domec, T. M. Hinckley, N. McDowel, N. Phillips, AND P. J. Schulte. THE EFFECTS OF TRANSIENT REDUCTIONS IN FUNCTIONAL LEAF AREA ON STOMATAL CONDUCTANCE: BRANCH LEVEL EXPERIMENTS ON YOUNG AND OLD TREES. Presented at Ecological Society of America Annual Meeting, Snowbird, UT, August 6-10, 2000.
Description:
As trees age and increase in size, the resistance along the water transport path has been hypothesized to increase and potentially limit the ultimate size a tree can reach. Past research has demonstrated that branches are a source of significant resistance in the transport path. Architecturally, branches on old and young trees are also quite different and could pose different restrictions on the hydraulic pathway. In this study, we altered the amount of leaf area that was transpiring through bagging, and monitored the gas-exchange responses of the remaining functional foliage in young and old Douglas-fir at the Wind River Canopy Crane Research Facility. Reductions in functional leaf area on a branch should increase leaf specific conductance to the remaining functional foliage. However, we found no increases in stomatal conductance in either young or old trees as a result of transient reductions in functional leaf area. The drop in water potential, mid-day stomatal closure and associated photosynthetic decline occurred at the same time and were of the same magnitude on both shaded and unshaded branches. This was true for both young and old trees even though specific conductivity was much lower in old-growth branches. Mid-day water potentials were slightly lower in old trees compared to young, but in both age groups about half the water potential drop along the transport pathway occurred below 1.3 m. These results indicate that conductance within a branch plays a small role in mid-day decline in stomatal conductance and that other parts of the overall pathway maybe more critical.