Document: NAT-3-32-12

Hydraulic capacitance and resistance as a function of tree size.

PHILLIPS, N.* ¹, B.J.BOND ¹, T.HINCKLEY ², N.MCDOWELL ¹, M.G.RYAN ³ and A.SCHAUER ¹

Oregon State University, Corvallis, OR USA ¹
University of Washington, Seattle, WA USA ²
USDA Forest Service, Ft. Collins, CO USA ³

Abstract:
Water stored in a tree's conducting system may compensate for the large hydraulic resistance to water flow in tall trees. If so, as trees grow larger, we would predict that an increasing percentage of daily water use is derived from stored water (capacitance). To test the hypothesis that larger trees rely more on stored water than small trees, we measured capacitive water use as a percent of total daily water flux in 15 m and 60 m tall individuals of Douglas-fir in and near the Wind River Canopy Crane Research Facility. On clear, warm days with moderate soil moisture availability, water use derived from capacitance was 11 percent (1.7 kg) of total daily water use (15.8 kg) in 15 m trees, and 21 percent (89.7 kg) of total daily water use (426 kg) in a 60 m tree. These results are consistent with those found in tropical tree species, where stored water use ranged from 9 to 15% with increasing tree size. A simulation model of diel water uptake and loss from trees demonstrates that (1) the amount of water use derived from storage may differ substantially depending upon the location of capacitive stores along a resistance pathway (from 4 to 14% as a fixed capacitor is placed across 63 to 38% of the bole, respectively), and (2) that the same diurnal lag between water loss and uptake can result from different combinations of hydraulic resistance and capacitance. Since the same time lag is obtained if resistance and capacitance vary inversely, plants may have very different evolutionary adaptations that result in the same dynamical vascular behavior.

Keywords: hydraulic capacitance, hydraulic resistance

This abstract is being presented at: 4:45 PM in session:
Oral Session #34: Water Relations in Trees.