response of heather (Calluna vulgaris) to shade and nutrients--predictions of the carbon-nutrient balance hypothesis

Two treatments, shade and a compound fertilizer (N, P, K, Ca, Mg) were applied in the field to heather (Calluna vulgaris) in a factorial design with two levels (presence or absence) of each treatment. Treatments were designed to mimic the changes in shade and soil nutrients occurring with incursion of birch woodland to heather moorland and were continued for two growing seasons. The resulting morphological and chemical changes to Calluna were measured, the latter to test some of the premises of the carbon-nutrient balance hypothesis. Shading resulted in etiolation of shoots, lower shoot densities and almost complete cessation of flowering. Overall lower shoot weights were due solely to reduced flowering. The concentration of total nitrogen increased whereas lignin, total phenolics and condensed tannins, all carbon-based constituents, decreased in the green shoot material with application of shade. Application of fertilizer led to increased flowering per shoot and a greater proportion of flowering shoots. The concentration of total nitrogen in the non-flowering component of the shoots increased whereas that of lignin decreased. Unlike lignin, which is a structural polyphenolic, there was no significant decrease with addition of fertilizer, in total phenolics and condensed tannins. The results are hence not wholly consistent with the decrease in carbon-based secondary metabolites which is predicted by the carbon-nutrient balance hypothesis.