Document: MIC-3-35-11

Whole tree conductance and leaf gas exchange in Eucalyptus saligna trees of different heights.

BARNARD, H.R.* ¹ and M.G.RYAN ²

Colorado State University, Fort Collins, CO 80521 USA ¹
USDA Forest Service, Fort Collins, CO 80526 USA ²

Abstract:
We tested the hypotheses that 1) whole tree conductance is lower in tall (about 25m) compared to short (about 7m) trees, and 2) that decreased conductance limits photosynthesis in tall trees. We measured whole tree sapflow, leaf level gas exchange and leaf water potential in tall and short trees in a fast-growing Eucalyptus saligna plantation on the island of Hawaii throughout the summer in 1999. Sapflow per unit sapwood area averaged 45% lower in tall trees compared to short trees; however, the average sapwood area to leaf area ratio was 50% greater in tall trees compared to short trees so tree height did not affect sapflow per unit leaf area. Leaf water potential in the tall trees averaged 0.7 MPa more negative than the short trees throughout the day. In this study, the negative effect of increased path length of water flow in tall trees was compensated for by the adjustment in the sapwood area to leaf area ratio and the ability of tall trees to maintain high rates of conductance at more negative water potentials.

Keywords: whole-tree conductance, hydraulic conductance, Eucalyptus plantations

This abstract is being presented at: 1:45 PM in session:
Oral Session #50: Plant Gas Exchange.