Nitrogen uptake from prey and substrate as affected by prey capture level and plant reproductive status in four carnivorous plant species

Uptake of nitrogen from prey and substrate and partitioning of prey-derived nitrogen were studied in the carnivorous plant species Pinguicula alpina, P. villosa, P. vulgaris and Drosera rotundifolia in a subarctic environment. Efficiency in nitrogen uptake from prey was evaluated by tracing N-15 from N-15-enriched Drosophila flies fed to the plants. The in situ uptake efficiency differed somewhat between species and ranged from 29 to 41% of prey N. This efficiency was not affected by different feeding levels or plant reproductive status (flowering or non-flowering). A test of the amount of N absorbed from prey caught on flower stalks of Pinguicula villosa and P, vulgaris showed that both species took up little of what was available in prey (2.5% or less). The uptake efficiency found in greenhouse grown plants was higher than in plants in situ (40-50% vs. 30-40% respectively). This could probably best be explained by the absence of rain and a higher temperature in the greenhouse. The prey-derived N-15 was traced to reproductive organs and winter buds, Non-flowering individuals allocated 58-97% of the N derived from prey to their winter buds. Flowering individuals allocated 17-43% of the N income from prey to reproduction, while 34-71% were allocated to buds. Root uptake of nitrogen was stimulated by increased prey capture, This increase in uptake of nitrogen from the substrate was larger than the potential direct uptake of nitrogen from captured prey.