Tree proximity,soil pathways and common mycorrhizal networks: their influence on the utilization of redistributed water by understory seedlings |
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Authors: | Amanda L Schoonmaker François P Teste Suzanne W Simard Robert D Guy |
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Institution: | (1) Department of Renewable Resources, University of Alberta, Edmonton, AB, Canada, T6G 2H1;(2) Department of Forest Sciences, University of British Columbia, Vancouver, BC, Canada, V6T 1Z4 |
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Abstract: | Hydraulic redistribution (HR) is a process by which water moves through plant roots from moist to dry soils. An experiment
was conducted to quantify the influence of common mycorrhizal networks (CMNs) and proximity to mature HR-source trees on the
water relations of surrounding seedlings. Douglas-fir (Pseudotsuga menziesii var glauca (Mirb.) Franco) seedlings were planted at four distances (0.5, 1, 2.5, and 5 m) from six mature Douglas-fir trees, either
directly into soil (soil plus CMN pathway) or inside 0.5 μm mesh bags (soil-only pathway). Deuterated water was used to irrigate
soil beside mature trees in order to identify different HR water pathways to surrounding seedlings. This was followed by measurements
of seedling deuterium enrichment, seedling water potential, soil water potential, gravimetric soil water content, and tree root density surrounding the seedlings. There was no significantly detectable difference
in the quantity of HR water transferred to seedlings having access to soil and CMN pathways or soil-only pathways of water
movement. Water from the irrigation plot contributed up to 1.4% of the water of Douglas-fir seedlings. Based on the assumption
that the only pathway through which seedlings could access irrigation water was through the mature trees, we estimate that
as much as 21.6% of the seedling water was supplied by the nearby tree. Seedling water potential was not significantly affected
either by proximity to mature trees or pathway, suggesting HR may have compensated for increasing tree competitive effects
with proximity. It is also possible that the lack of difference was due to a relatively moist summer. Our results suggest
that residual mature trees are potentially important for hydraulic redistribution to regenerating seedlings in harvested dry
interior Douglas-fir forests. |
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Keywords: | Hydraulic redistribution Deuterium labeling Douglas-fir Facilitation Competition |
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