Water movement in the stem xylem in relation to xylem specific conductivity in four hardwood species Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ws859h57s

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  • In deciduous species, water exits stems mainly through leaf traces attached to the outer growth ring and yet we know that water ascends throughout the entire cross-section of the sapwood. There is an increasing amount of information on sap flow and sapwood hydraulic properties from separate studies, but little information exists on how flow and hydraulics vary radially along the sapwood within a tree. In this study, we determined axial sap flux (3) and axial specific conductivity (ks) at five different radial locations within the sapwood, spedfically at 1.2, 2.0, 3.5, 5.0 and 7.0 cm inward from the cambium, and used these values to estimate the tension gradient in the water column at those radial positions. Four hardwood species growing in the Pacific Northwest were used for this study: Acer macrophyllum Pursh (bigleaf maple, n=8), Alnus rubra Bong. (red alder, n=8), Populus trichocarpa Torr. & Gray x Populus deltoides Bartr. ex Marsh. (cottonwood, n=4) and Arbutus menziesii Pursh (Pacific madrone, n=7). Field and laboratory study were performed during 2003 and 2004, and values were pooled for these two years. Sap flux decreased from the outer to the inner part of the sapwood in all species. Arbutus, followed by Acer, showed the highest differences within all analyzed depths. Alnus had a slight declining sap flux profile along the first three depths, with a marked decline from 10.3 g m2 s1 to 5.7 g m2 s1 in the two inner positions. Populus showed the highest sap flux values, averaging 32.1 g m2 s1 in the two outer depths and these values fluctuated as 23.7 g m2 s', 26.3 g m2 s1 and 23.9 g m 2 1, along the radius. Specific conductivity showed a similar radial pattern in Alnus, Populus and Arbutus, declining from the outer sapwood inward. Of these species, Alnus had the most uniform profile, decreasing, on average, by l2% at each depth. In Arbutus and Populus, k had quite high variance, and exhibited the lowest values in the inner depths. In contrast, Acer k5 fluctuated from the outer to the inner sapwood. In general, there was a relationship between J and k5 measured at the same locations for Alnus, Arbutus, and Populus. Arbutus had the most significant linear relationship between J and k at all analyzed depths, with r2= 0.93, followed by Alnus and Populus (r2= 0.79). Acer showed a fluctuating pattern, with a random J/k relationship by depth (r2 < 0.001). Axial tension gradient appeared to be constant across the sapwood radius in Alnus and Arbutus, but it was non-uniform in the inner positions in Acer and Populus. Gradients remained constant in Acer at the first two depths then declined toward the 3.5 cm position, where the highest tension values occurred at the 5.0 cm position. There was a marked increase in tension gradient toward the inner depths in Populus. The observed Jand k5 patterns along the sapwood also demonstrated the resistance to water flux in the radial direction. This demonstrates, in the studied species, the existence of different resistances to water flux in the radial direction. This tension gradient along the sapwood demonstrates the presence of measurable resistance to water flow in the radial direction. This resistance may also affect wood utilization and processing, especially when dealing with drying and treating wood. This study also showed the importance of accurately estimating J along the entire sapwood in order to estimate whole-tree water use.
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