Photosynthesis, carbon allocation, and nitrogen fixation in red alder (Alnus rubra Bong.) seedlings: Effects of nodulation, carbon-dioxide enrichment, and substrate nitrogen

Research reported in the three sections of this dissertation addresses the problem of the effect of potentially high carbon costs of nitrogen fixation by alder-Frankia symbioses on host plant biomass productivity.;Effects of root nodulation and nitrogen fixation on plant biomass productivity and allocation patterns were evaluted by growing inoculated and uninoculated red alder seedlings in atmospheres containing ambient (350 ;Effect of nodulation, CO;The potential problem of ethylene and acetylene adsorption and solubility in growth medium at two moisture levels when using the acetylene reduction assay for determining biological nitrogen fixation was first studied. These processes effectively sequestered significant amounts of both gases from the head space of assay chambers, with greatest decreases occurring in ethylene (because of its initial presence in very low concentration) in dry substrate due to adsorption. Sequestering of gases in substrate maintained at field capacity was minimal. Therefore, use of static acetylene reduction assays is still useful and valid if control pots (without plants) containing the same growth medium as pots with plants are included in assays, and if substrate moisture status is uniform across all treatments and near field capacity when the assay commences.