NATURAL-ABUNDANCE OF DELTA-N-15 CONFIRMS INSECTIVOROUS HABIT OF RORIDULA-GORGONIAS, DESPITE IT HAVING NO PROTEOLYTIC-ENZYMES

Natural abundance values of plant delta(15)N give an indication as to the source of nitrogen. In particular, carnivorous plants are expected to be relatively enriched due to trophic enrichment of their prey. Va lues of delta(15)N for adult Roridula gorgonias (mean + 3.02 parts per thousand,) are 4-9 parts per thousand greater than co-occurring non-c arnivorous plant species and 5.24 parts per thousand, greater than juv enile R. gorgonias plants. They are also 3.5-4.26 parts per thousand, greater than co-occurring Drosera species which, being sundews, are co nsidered to be carnivorous. These high levels of delta(15)N in adult p lants are best explained as being due to access to trophically enriche d N from insects. As is the case for other carnivorous plants, leaves and stems of R. gorgonias are highly ultraviolet reflective and are th erefore probably attractive to potential insect prey. This is further support for this plant species being insectivorous. (C) 1998 Annals of Botany Company.