Mycorrhizal networks (MNs) are fungal hyphae that connect the roots of at least two plants, potentially providing a conduit for interplant resource transfer. Interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) is an obligate ectomycorrhizal (EM) tree species that has high potential to form MNs with neighboring trees because of its receptivity to a diverse community of EM fungi. This MN potential is expected to be greatest among conspecific trees. In this thesis, I determined the influence of MNs formed by residual Douglas-fir trees on interplant carbon transfer and survival, growth, physiology, and EM status of neighboring naturally regenerated and planted Douglas-fir seedlings. To do this, I used MN-restricting treatments and isotope gas-labeling techniques on sites harvested with variable tree retention to investigate how varying: i) proximity to conspecific trees affects EM colonization and performance of planted seedlings; ii) ‘donor’ tree size affects seedling establishment and carbon or nitrogen transfer, and; iii) soil disturbance stress affects net carbon transfer between established seedlings. Because I used physical barriers (i.e., mesh bags) to control for the presence and characteristics of the MN, I also verified the effectiveness of different-sized mesh pores at reducing hyphal connections between plants in the greenhouse. In my experiments, I found that MN-mediated colonization was not the dominant mechanism responsible for EM colonization of planted seedlings; other sources of inoculm (e.g., spores, sclerotia, hyphal fragments) were more important. I found that mature trees not only competed for resources with seedlings but offered some facilitative effects at intermediate distances within their rooting zones. My key finding was that access to a MN with residual trees benefited seedling survival and that this corresponded with increased carbon and nitrogen transfer to seedlings. In addition, I found that there was consistently a net gain in carbon by one seedling in a MN and this net transfer increased with relative growth rate of the receiver seedling. These results indicate that MNs can facilitate interplant carbon transfer and be important in regeneration dynamics in dry Douglas-fir forests.

Mycorrhizal networks (MNs) are fungal hyphae that connect the roots of at least two plants, potentially providing a conduit for interplant resource transfer. Interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) is an obligate ectomycorrhizal (EM) tree species that has high potential to form MNs with neighboring trees because of its receptivity to a diverse community of EM fungi. This MN potential is expected to be greatest among conspecific trees. In this thesis, I determined the influence of MNs formed by residual Douglas-fir trees on interplant carbon transfer and survival, growth, physiology, and EM status of neighboring naturally regenerated and planted Douglas-fir seedlings. To do this, I used MN-restricting treatments and isotope gas-labeling techniques on sites harvested with variable tree retention to investigate how varying: i) proximity to conspecific trees affects EM colonization and performance of planted seedlings; ii) ‘donor’ tree size affects seedling establishment and carbon or nitrogen transfer, and; iii) soil disturbance stress affects net carbon transfer between established seedlings. Because I used physical barriers (i.e., mesh bags) to control for the presence and characteristics of the MN, I also verified the effectiveness of different-sized mesh pores at reducing hyphal connections between plants in the greenhouse. In my experiments, I found that MN-mediated colonization was not the dominant mechanism responsible for EM colonization of planted seedlings; other sources of inoculm (e.g., spores, sclerotia, hyphal fragments) were more important. I found that mature trees not only competed for resources with seedlings but offered some facilitative effects at intermediate distances within their rooting zones. My key finding was that access to a MN with residual trees benefited seedling survival and that this corresponded with increased carbon and nitrogen transfer to seedlings. In addition, I found that there was consistently a net gain in carbon by one seedling in a MN and this net transfer increased with relative growth rate of the receiver seedling. These results indicate that MNs can facilitate interplant carbon transfer and be important in regeneration dynamics in dry Douglas-fir forests.

Mycorrhizal networks (MNs) are fungal hyphae that connect the roots of at least two plants, potentially providing a conduit for interplant resource transfer. Interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) is an obligate ectomycorrhizal (EM) tree species that has high potential to form MNs with neighboring trees because of its receptivity to a diverse community of EM fungi. This MN potential is expected to be greatest among conspecific trees. In this thesis, I determined the influence of MNs formed by residual Douglas-fir trees on interplant carbon transfer and survival, growth, physiology, and EM status of neighboring naturally regenerated and planted Douglas-fir seedlings. To do this, I used MN-restricting treatments and isotope gas-labeling techniques on sites harvested with variable tree retention to investigate how varying: i) proximity to conspecific trees affects EM colonization and performance of planted seedlings; ii) ‘donor’ tree size affects seedling establishment and carbon or nitrogen transfer, and; iii) soil disturbance stress affects net carbon transfer between established seedlings. Because I used physical barriers (i.e., mesh bags) to control for the presence and characteristics of the MN, I also verified the effectiveness of different-sized mesh pores at reducing hyphal connections between plants in the greenhouse. In my experiments, I found that MN-mediated colonization was not the dominant mechanism responsible for EM colonization of planted seedlings; other sources of inoculm (e.g., spores, sclerotia, hyphal fragments) were more important. I found that mature trees not only competed for resources with seedlings but offered some facilitative effects at intermediate distances within their rooting zones. My key finding was that access to a MN with residual trees benefited seedling survival and that this corresponded with increased carbon and nitrogen transfer to seedlings. In addition, I found that there was consistently a net gain in carbon by one seedling in a MN and this net transfer increased with relative growth rate of the receiver seedling. These results indicate that MNs can facilitate interplant carbon transfer and be important in regeneration dynamics in dry Douglas-fir forests. / Forestry, Faculty of / Graduate

Saprophytic fungi can be paired with companion crops in interplant systems to increase production efficiency. However, fungal species/strain, substrate, and inoculation rate can affect the growth of companion crops. This project investigated the viability of open-field mushroom production by interplanting three strains of Pleurotus ostreatus (Elm A, Elm B, and 8801) with kale (B. oleracea var. acephala) and forage radish (Raphanus raphanistrub sub. sativus), and measured the effect of interplanting on plant yield over two field seasons. In the field, Elm A showed an increase in plant yield at a low inoculation rate and decrease in plant yield at a high inoculation rate, compared to the untreated. Conversely, 8801 showed a reduction in plant yield at high and low inoculation rates in the field. Elm B at a high rate showed a reduction in plant yield both in the field and greenhouse. Kale was grown in hydroponics with fungal secretions added at a range of concentrations (10, 100, 1,000 and 10,000 ppm). Elm A showed an overall increase in plant yield in hydroponics, and Elm B showed an overall decrease in plant yield, compared to the untreated. Mushroom production was low in field plots and was not a commercially viable option. Pleurotus ostreatus interplanting methods with companion crops need improvement to make this a commercially viable practice.

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