Interspecific carbon transfer in ectomycorrhizal tree species mixtures Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rf55zb04v

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  • The overall goal of this study was to investigate influences of ectomycorrhizae (EM) and interspecific carbon transfer on seedling performance in species mixtures. The objectives were to: (I) determine the potential for EM to link paper birch and Douglas-fir, (ii) quantify gross and net interspecific carbon transfer, and (iii) evaluate effect of transfer on seedling performance. A soil bioassay showed that paper birch and Douglas-fir shared seven EM morphotypes in common over 90% of their root tips, indicating potential for hyphal connections. The number and percent colonization of shared morphotypes were greater when species were grown in dual- than monoculture. Reciprocal labelling of paper birch and Douglas-fir with ¹³CO₂[subscript(gas)] and ¹⁴CO₂[subscript(gas)] in laboratory rootboxes and the field resulted in bi-directional transfer, with net gain by Douglas-fir. In rootboxes, gross and net transfer represented 29% and 4% of total isotope assimilated by both species. Net transfer was three times greater and one-way gross transfer to Douglas-fir 50% greater where interconnecting hyphae were left intact than where severed, but high p-values (p>0.05) leave in question whether hyphal connections facilitated transfer. In the field, gross and net transfer between paper birch and Douglas-fir represented 4% and 2%, respectively, of total isotope assimilated in 1993, and 7% and 6%, respectively, in 1994. Net transfer to Douglas-fir occurred where Douglas-fir grew full sun in 1993, and in all light intensities in 1994. The change in amount transferred and shading effect between years coincided with greater root development and improved seedling vigor in 1994 than 1993. Net and gross transfer were two times greater in 5% than 50% or 100% sun treatments in 1994, suggesting transfer was affected by changes in photosynthate sink strength of Douglas-fir. Isotope transferred to western redcedar represented <1-18% of gross transfer between paper birch and Douglas-fir, indicating most carbon was transferred between EM species via interconnecting hyphae. Douglas-fir seedlings were grown in untrenched and trenched treatments to evaluate the ability of overstory paper birch and Douglas-fir to influence seedling EM inoculation patterns and performance. Greater diversity of EM coincided with higher photosynthesis among seedlings in the untrenched than trenched treatment. The effect on seedling performance was attributed to differences in EM colonization, because trenching had no effect on soil water, soil nutrients, or light availability.
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