Species and intra-specific competition affect growth in greenhouse more than mycorrhizal colonization on Quercus rubra and Acer rubrum seedlings

AimsDistributions of mycorrhizal guilds correlate with differences in soil nutrient availability and tend to predominate ecosystems where plant growth and development are limited by either soil phosphorus (AM, arbuscular mycorrhiza) or nitrogen (EM, ectomycorrhiza) (Read, 1991). In an effort to characterize functional trait differences, we designed a common garden greenhouse experiment to measure growth and colonization responses between two tree seedling species (Acer rubrum and Quercus rubra) that associate with the two major mycorrhizal guilds. MethodsIn a fully factorial, 12-week greenhouse common garden experiment, seedlings were treated to three levels of nitrogen and phosphorus availability, and grown under inter- and intra-species competition. Change in heights and stem diameters were tracked and mycorrhizal colonization was quantified by percent of total and morphology. ResultsRelative growth rates were higher for Acer rubrum seedlings across treatments and intra-species competition had a strong negative effect on height and stem diameter, especially for Quercus rubra. Both species were highly colonized (>50%) by typically endomycorrhizal forms (arbuscules and vesicles) but varied in the distribution of morphological forms present in cells. ConclusionsThis study highlights the plasticity of tree seedling symbiosis during early developmental stages and challenges the strict static categorization of plant species associations with particular mycorrhizal guilds.