Carnivorous sundews (Drosera rotundifolia) are more carnivorous in high‐light bog microhabitats that are not also nutrient‐rich

Abstract

Abstract Carnivorous plants adapt to variations in nutrient availability and shade by altering investment in carnivory in response to different environmental conditions. It is not clear, however, how carnivorous plants might alter investment in carnivory in relation to habitat heterogeneity at small scales. We hypothesised that the carnivorous plant Drosera rotundifolia would alter investment in carnivory and the amount of plant nitrogen (N) derived from prey in response to differences in shade and nutrients between hummock and hollow microforms on patterned peatlands. We investigated D. rotundifolia growing on three peatlands in Northern Europe: Scotland, Sweden, and Finland where we expect microhabitat variability to differ between peatlands due to differences in the ratio of precipitation to evapotranspiration. We measured differences in the density of sticky leaf tentacles (investment in carnivory) and the proportion of plant N that was prey‐derived (%Ndfp) for plants growing on hummocks and hollows at each peatland. At the Finland site P:ET ratio was lowest (1.86), and root N availability was similar for hollows and hummocks. Here, tentacle density and %Ndfp were ~50% higher for plants on hollows than on the more shaded hummocks. At the Scotland site P:ET was highest (5.40), root N availability was lower for hummocks than for hollows, and hummocks were more shaded. Here, there was little difference in tentacle density and %Ndfp between plants growing on hummocks and hollows. The Sweden site was intermediate in terms of P:ET ratio (2.63), habitat heterogeneity, and carnivory. Our results are consistent with the predictions of an evolutionary cost–benefit model for plant carnivory in which the marginal benefits of carnivory decrease with increasing root nutrient availability and decreasing light. This model predicted carnivorous plant phenotypic variability at small scales in response to different extents of habitat heterogeneity at our three study sites. Our study demonstrates the capacity for a carnivorous plant species to vary investment in carnivory, adjusting the proportion of prey‐derived N, in response to small‐scale habitat heterogeneity. We suggest that as well as an adaptation to low‐nutrient conditions, carnivory may also provide a means for plants to adapt to and persist in heterogeneous habitats. Read the free Plain Language Summary for this article on the Journal blog.