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UBC Theses and Dissertations

The role of ectomycorrhizal networks in plant-to-plant facilitation across climatic moisture gradients Bingham, Marcus Alan


Common ectomycorrhizal (EM) networks are expected to facilitate conifer regeneration under abiotic stress, such as drought exacerbated by climate change. This study examined effects of climate, CO₂ concentration ([CO₂]), and EM networks on Douglas-fir seedling establishment. My objectives were (1) to determine the effects of regional climate (represented by a drought index) on EM network facilitation of Douglas-fir seedling establishment; (2) to separate genotypic effects from climatic effects; (3) to compare the importance of EM networks to 3-year-old outplanted nursery seedlings versus 1st year seedlings germinated in the field; (4) to parse the competitive from facilitative effects of residual Douglas-fir trees on small seedlings; and (5) to determine the interaction between soil water and [CO₂], in their effects on EM network-facilitated seedling establishment and C-transfer between different sized Douglas-fir seedlings. Survival was maximized when seedlings were able to form an EM network in the absence of root competition, both in growth chambers and in the field for the medium moisture provenance. When drought conditions were greatest, growth of these same seedlings increased when they could form an EM network with nearby trees in the absence of root competition, but it was reduced when they were unable to form a network. Overall, survival was greatest for these seedlings relative to those from the wet or dry provenances, but decreased with summer heat:moisture index more rapidly. I found no evidence of C transfer between seedlings through growth chamber ¹³CO₂ labeling, but D₂O labeling and natural abundance H₂¹⁸O measurements are suggestive of increasing water transfer from donor to receiver seedlings as receiver water deficiency increased.

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