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Harvard Forest Symposium Abstract 2018

  • Title: Intervessel connections across growth rings in xylem of four northern hardwood trees
  • Primary Author: Jay Wason (Yale University)
  • Additional Authors: Craig Brodersen (Yale School of Forestry & Environmental Studies); Brett Huggett (Bates College)
  • Abstract:

    Angiosperm trees transport water in wood through a network of interconnected conduits called xylem vessels. The properties of the xylem-vessel network determine water transport efficiency and resistance to air-embolism spread during drought. In most trees, water transport is restricted to the current-year growth ring, however, additional transport in older growth-rings could increase the xylem-vessel network, thus increasing hydraulic efficiency but also may expose the new xylem to air-embolisms in old growth-rings. Knowledge is limited regarding the extent of cross-ring intervessel connections in northeastern trees and the potential impact on measurements of water transport and drought resistance. We studied the existence of intervessel connections across growth rings in two diffuse-porous and two ring-porous trees from the eastern United States. Dye-staining and X-ray microcomputed tomography (microCT) was used to detect xylem-network connectivity from current-year to older growth-rings, and hydraulic conductivity measurements were used to test the impact on water transport. Acer rubrum had cross-ring intervessel connections, whereas Fagus grandifolia, Fraxinus americana, and Quercus rubra did not. For species without cross-ring connections, including multiple growth-rings in measurements of hydraulic conductivity resulted in inflated maximum conductivity (Fraxinus americana, Q. rubra) or native conductivity (Fagus grandifolia) related to vessel diameter. However, including multiple growth-rings did not impact hydraulic measurements for A. rubrum. Of these four species, A. rubrum is the only species exhibiting vulnerability segmentation from roots-to-shoots, perhaps to protect xylem networks that will be functional for several years, whereas the other species rely on xylem formed in the current year. The presence of cross-ring intervessel connections, therefore, is an important trait that can help explain aspects of whole-tree water transport and should be carefully considered when conducting plant hydraulic studies.

  • Research Category: Physiological Ecology, Population Dynamics, and Species Interactions