Drosera rotundifolia growth and nutrition in a natural population with special reference to the significance of insectivory

Abstract

The impact of nutrient addition on growth and nutrient accumulation in Drosera rotundifolia was studied in a field population. Experiments were performed by exclosing insects and (or) adding phosphorus and (or) nitrogen to soil. Drosera rotundifolia did not significantly benefit from insect capture nutritionally or energetically in native or nutritionally enhanced soils. Added nutrients to the soil or supplemental foliar insect feeding decreased phosphorus retention in hibernacula by 50%. Nutrient additions reduced D. rotundifolia vegetative growth in both N and P addition treatments. In addition, allocation to reproduction (inflorescences) decreased by 98% when N was added to the soil. Phosphorus retention in hibernacula was especially high in plots in which no nutrients were added via the soil or by insect applications. Although not statistically significant, flower stalk density and floral biomass were greater where insects were available to plants. The data from this study indicate that insectivory has little impact on growth of field grown D. rotundifolia. This species is adapted to low nutrient availability and nutrient enhancement reduces growth. Indices of nutrient retention suggest that phosphorus is conserved more than nitrogen and therefore may be an important limiting nutrient. Key words: insectivory, nitrogen, phosphorus, sundew.