Canopy Hydraulic Redistribution –Tree Water Uptake via Canopy Roots in Epiphytic Bryophyte Mats

It is known that a wide range of tree species in temperate and tropical rainforests have the ability to sprout adventitious roots from branches into epiphyte mats (soil made by the accumulation of living and dead plants in the canopy); however, water and nutrient uptake via these aerial or canopy roots has not been confirmed or measured. This study will examine the water relations between epiphytic mats and host trees that grow adventitious roots underneath the canopy soil. The activity and effect of canopy roots is largely unknown, but the nutrient and water resources that are potentially transferred by them may offer a considerable benefit to the health and growth of trees. It is expected that temperatures in the Pacific Northwest will rise, and drought will become more severe, increasing heat stress-related tree mortality in the western US. The role of canopy roots and epiphytes may be crucial to plant biodiversity in critical habitats, and likely account for an important but understudied source of water and nutrients in trees, especially under conditions where trees become heat-stressed.

We will assess canopy root activity, canopy water redistribution and ecophysiological roles of adventitious roots. Preliminary data show that there is water uptake by canopy roots in poplar (Populus trichocarpa) and suggest potential bi-directional water flow (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. We will apply similar procedures to confirm activity in the field with bigleaf maple trees (Acer macrophyllum), which develop canopy roots naturally. Using stable isotopes to track water transport from canopy roots to other parts of the tree during different seasons, we will be able to understand the physiological and ecological role of adventitious roots under adverse conditions of water availability.