Ectomycorrhizae (EM) are beneficial relationships between tree roots and fungi that increase tree survival and stress tolerance in resource (e.g. nutrient, water) limiting environments. EM abundance is often negatively correlated with increasing nutrient availability (e.g. through fertilization), which may affect long term and health of trees, especially in managed systems where fertilization is commonplace. However, the mechanisms behind this pattern are relatively unknown.
Fertilization impacts metabolic tradeoffs between tree growth and the accumulation of secondary metabolites, which have multiple roles in improving tree health. Over a fertility gradient, secondary metabolism is predicted to respond parabolically, such that rapidly growing trees contain lower concentrations of secondary metabolites and vice versa. We hypothesize that increased nutrient availability affects plant carbon allocation and investment in secondary metabolism in a way that reduces EM colonization. Such information is important because fertilizers are often overused, (ex. urban and nursery settings) which may prove unfavorable to the establishment and survival of trees.
Growth, carbon allocation, carbohydrates, phenolics, lignin, and EM were measured in foliage and roots of fertilized and non-fertilized paper birch (Betula papyrifera Marsh) growing in contrasting soil types (nutrient poor subsoil and nutrient rich topsoil) in a controlled greenhouse environment. Treatment effects on measured variables were determined by using the Generalized linear model function of SPSS v.15, while non-parametric correlations were carried out to determine relatedness of variables.
Results/Conclusions
Overall, levels of foliar phenolics and root-to-shoot ratios decreased with increasing fertility. Root phenolics and lignin decreased upon fertilization of subsoil, but increased in fertilized topsoil. EM abundance was strongly negatively correlated with levels of root phenolics and lignin, suggesting that the host may regulate its EM associations by manipulating general defense responses in complex interactions with resource availability.
