Reliance on stored water increases with tree size in three species in the Pacific Northwest

Abstract

In tall old forests, limitations to water transport may limit maximum tree height and reduce photosynthesis and carbon sequestration. We evaluated the degree to which tall trees could potentially compensate for hydraulic limitations to water transport by increased use of water stored in xylem. Using sap flux measurements in three tree species of the Pacific Northwest, we showed that reliance on stored water increases with tree size and estimated that use of stored water increases photosynthesis. For Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), water stored in xylem accounted for 20 to 25% of total daily water use in 60-m trees, whereas stored water comprised 7% of daily water use in 15-m trees. For Oregon white oak (Quercus garryana Dougl. ex Hook.), water stored in xylem accounted for 10 to 23% of total daily water use in 25-m trees, whereas stored water comprised 9 to 13% of daily water use in 10-m trees. For ponderosa pine (Pinus ponderosa Dougl. ex Laws.), water stored in xylem accounted for 4 to 20% of total daily water use in 36-m trees, whereas stored water comprised 2 to 4% of daily water use in 12-m trees. In 60-m Douglas-fir trees, we estimated that use of stored water supported 18% more photosynthesis on a daily basis than would occur if no stored water were used, whereas 15-m Douglas-fir trees gained 10% greater daily photosynthesis from use of stored water. We conclude that water storage plays a significant role in the water and carbon economy of tall trees and old forests.

Maximum height in a conifer is associated with conflicting requirements for xylem design

“…The trunk is the superhighway through which the water moves, but the branches make up the distribution network and typically show more pronounced transpirationinduced fluctuations in xylem tension (5). Transient release of stored water into the transpiration stream resulting from hydraulic capacitance of sapwood is likely to exert a greater damping effect on fluctuations in xylem tension in massive trunks than in more slender branches (27)(28)(29). In addition, lower xylem specific conductivity in branches than trunks (9,15) contributes to steeper axial tension gradients in branches.…”

Comparative hydraulic and anatomic properties in palm trees (Washingtonia robusta) of varying heights: implications for hydraulic limitation to increased height growth

“…Similarly, within-palm cross-correlation analysis indicated a larger petiole-bole time lag in a larger palm (44 min lag in a 28 m tall palm; maximum r 2 = 0.87) than a shorter palm (28 min lag in an 8 m tall palm; maximum r 2 = 0.8). These lags correspond to approximately 16 and 22% of daily water use, respectively, according to procedures and assumptions described in Phillips et al (2003b).…”

Sapwood hydraulic recovery following thinning in lodgepole pine

“…Stored water in stem sapwood likely had little influence on sap flow in the relatively small stems we examined because lags between increasing E o and v s that can be attributed to use of stored water [29,31] were infrequently observed. A rapid increase in Q l associated with increasing E o in the morning (Fig.…”