Nitrogen availability alters the expression of carnivory in the northern pitcher plant, Sarracenia purpurea

Abstract

Atmospheric transport and deposition of nutrients, especially nitrogen, is a global environmental problem with well-documented consequences for ecosystem dynamics. However, monitoring nitrogen deposition is relatively expensive, monitoring stations are widely spaced, and estimates and predicted impacts of nitrogen deposition are currently derived from spatial modeling and interpolation of limited data. Ombrotrophic (''rain-fed'') bogs are nutrient-poor ecosystems that are especially sensitive to increasing nutrient input, and carnivorous plants, which are characteristic of these widespread ecosystem types, may be especially sensitive indicators of N deposition. Botanical carnivory is thought to have evolved in nutrient-poor and well-lit habitats such as bogs because the marginal benefits accruing from carnivory exceed the marginal photosynthetic costs associated with the maintenance of carnivorous organs. However, the production of carnivorous organs can be a phenotypically plastic trait. The northern pitcher plant, Sarracenia purpurea, produces leaves specialized for prey capture and nutrient uptake (pitchers) and leaves that are more efficient at photosynthesis (phyllodia). We hypothesized that relative allocation to these two types of leaves reflects ambient nitrogen availability. We manipulated nutrient availability to plants with leaf enrichment and whole-plot fertilization experiments. Increased nitrogen, but not phosphorus, reduced production of pitchers relative to phyllodia; this result provided empirical support for the cost-benefit model of the evolution of botanical carnivory. Because this phenotypic shift in leaf production occurs in ecological time, our results suggest that S. purpurea could be a reliable and inexpensive biological indicator of nitrogen deposition rates. This suggestion is supported by field observations across a geographic gradient of nitrogen deposition.

Photosynthetic light response in three carnivorous plant species: Drosera rotundifolia, D. capensis and Sarracenia leucophylla

“…bogs. Ellison and Gotelli (2002) showed that by elevating soil nitrogen levels, pitchers of S. purpurea were reduced relative to phyllodia size resulting in an increase in the rate of Mean values (±SD, n = 6) of light-saturated area-based photosynthesis (P Nmax (area) ), light-saturated mass-based photosynthesis (P Nmax(mass) ), dark respiration (R D ), light compensation point (PPFD comp ), convexity factor (k), and apparent photosynthetic quantum yield (α, P N /PPFD at low PPFD). Means followed by different letters indicate significant differences in P Nmax (area) and R D between greenhouse-and field-collected Drosera rotundifolia (Student's t-test, p< 0.05).…”

Nitrogen deposition and prey nitrogen uptake control the nutrition of the carnivorous plant Drosera rotundifolia

“…There is no evidence as yet that D. rotundifolia actually attracts prey (Foot et al 2014); but investment in prey capture (through the production of sticky mucilage) is reduced when root N availability is increased experimentally (Thorén et al 2003), which might be the mechanism here. Such a reduction in investment in prey capture has not been demonstrated in-situ for D. rotundifolia but has been shown for Sarracenia purpurea by Ellison and Gotelli (2002). Changes in other parts of the process should, however, not be discounted; the production of digestive enzymes, for example, also carries a metabolic cost and so the plants might reduce enzyme production, thus reducing rates or efficiency of prey digestion.…”

Evidence for competition between carnivorous plants and spiders

“…Some carnivorous plants, such as pitcher plants (Ellison & Gotelli 2002), bladderworts (Englund & Harms 2003) and different species of sundew (Thorén et al 2003), have been found to reduce their investment in carnivory (e.g. produce fewer traps) in response to increased nutrient levels.…”