The ecophysiological significance of insectivory as well as nitrogen and phosphorus availability to sundew nutrient cycling, growth, and success
The impact of nutrient addition on growth and nutrient accumulation in insectivorous plants was studied in field populations and greenhouse plantings. Drosera rotundifolia was studied in the field, and D. binata var. multifida and D. capensis were studied in long-established plantings in the greenhouse. In each case, experiments were performed by enclosing insects and/or adding phosphorus and/or nitrogen to the soil.
None of the species significantly benefitted from insect capture nutritionally or energetically in nutrient-poor or rich soils. Added nutrients to the soil or by foliar insect feeding decreased phosphorus retention in hibernacula by 50% (D. rotundifolia). Nutrient additions reduced D. rotundifolia vegetative growth in both N and P addition treatments. In addition, reproductive output (inflorescences) decreased flowering by 98% when N was added to the soil. Nutrient addition to soil increased nutrient concentration significantly in D. rotundifolia (N and P), and to a greater extent in D. capensis (N and P) and D. binata (P), and increased growth in D. capensis (N and P).
In natural settings, insectivory was not found to be a significant source of nutrients for the species of Drosera studied. Larger subtropical species such as D. capensis and D. binata var. multifida is found in relatively richer (nutrient) soil than cool temperate species (D. rotundifolia) and are better able to utilize available nutrients in a substrate by high absorption rates and luxury consumption.