DISSERTATION RESEARCH: Canopy hydraulic redistribution: Tree water uptake via canopy roots in epiphytic bryophyte mats

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Trees in temperate and tropical rainforests can sprout roots from branches into epiphyte mats that occur in the tree canopy. These mats develop a structure similar to soil through the accumulation of living and dead plants in the canopy. Whether these roots take up significant water and nutrients, however, has not been measured or even confirmed. The nutrient and water resources that are potentially transferred by the roots may offer a considerable benefit to the health and growth of trees. This Doctoral Dissertation Improvement Grant will provide funds to examine the exchange of water and nutrients between epiphytic mats and host trees that grow roots underneath the canopy soil. Temperatures in the Pacific Northwest are likely to continue to rise, and drought to become more severe. Canopy roots and epiphytes may be crucial to maintaining plant biodiversity in critical habitats, and convey an advantage, especially under conditions where trees become heat-stressed. Results from this project will significantly improve the effectiveness of ecological restoration plans. In addition, students including those from underrepresented groups will be involved in this project, gaining valuable experience in scientific research. This project will assess canopy root activity, canopy water redistribution and physiological and ecological roles of adventitious roots. Three approaches will be used to accomplish these objectives: lab, greenhouse and field experiments. (Need to mention the lab experiments) Greenhouse trials are designed to simulate plant water relations (in a simplified system) between epiphytes and host trees via canopy roots using poplar trees (Populus trichocarpa). Preliminary data show that there is water uptake by canopy roots in this poplar system, and suggest potential bi-directional water flow (i.e. up- and downwards sap flow) within the tree. Data also suggest that trees with canopy roots can mitigate drought conditions by taking up water from epiphyte mats. Similar procedures will be applied to confirm that these activities also occur under field conditions in Olympic National Park, WA. There the focus will be on bigleaf maple trees (Acer macrophyllum), which develop canopy roots naturally. Stable isotopes will be used to track water transport from canopy roots to other parts of the tree during different seasons, and to understand the physiological and ecological role of adventitious roots under adverse conditions of water availability.