Response of the fynbos shrubs Protea repens and Erica plukenetii to low levels of nitrogen and phosphorus applications

The responses of five-year-old fynbos shrubs, Protea repens (L.) L. and Erica plukenetii L., to low levels of nitrogen and phosphorus application were examined. Ammonium nitrate (2 g N m − 2 ), superphosphate (0,2 g P m − 2 ) and ammonium nitrate plus superphosphate (2 g N m − 2  + 0,2 g P m − 2 ) were applied in early spring 1982. Erica plukenetii responded to the phosphorus and particularly nitrogen plus phosphorus treatment with increases in height, stem diameter, crown cross-sectional area and biomass by the end of the second growing season. These responses were lower on plots treated with nitrogen than on the control. Vegetative growth of Protea repens on the fertilized plots, particularly those treated with nitrogen and nitrogen plus phosphorus, was lower than on the control. Nitrogen addition increased shoot production in the second year while phosphorus addition increased flower production. Low levels of nutrient application are quite capable of altering morphological characters of fynbos species. Nutrient enrichment by atmospheric inputs might therefore lead to changes in species composition and could result in increased invasion of fynbos areas by alien herbaceous species.