CHEMICAL-COMPOSITION OF CALLUNA-VULGARIS (ERICACEAE) - DO RESPONSES TO FERTILIZER VARY WITH PHENOLOGICAL STAGE

The effects of ammonium nitrate fertilizer on the content of total nitrogen, acid detergent fiber (ADF), lignin, total phenolics and condensed tannins of current season's shoots of Calluna vulgaris were measured. Fertilizer applications were either (i) prior to flowering or (ii) after flowering. Samples of green shoots were collected from the pre-flowering fertilizer treatment at the onset of flowering (August) and from both treatments at the end of the growth season (November); all showed increased total nitrogen and decreased ADF, consistent with increased growth, as compared with unfertilized controls. Contrary to the predictions of the carbon-nutrient balance hypothesis, levels of total phenolics and condensed tannins did not decline significantly with fertilizer additions. However, fertilizer applied prior to flowering tended to reduce total phenolics and condensed tannins whereas fertilizer applications after flowering tended to increase them. There was a strong seasonal increase in condensed tannins and total phenolics between August and September, at the time of flowering. These results are discussed in relation to Calluna's changing demand for and supply of resources at different phenological stages.