Leaf CNPK concentrations and isotopic signatures

<p>Previous meta-analyses suggested that carnivorous plants – despite access to N, P, and K from prey – have significantly lower leaf concentrations of these nutrients than non-carnivores. Those studies, however, largely compared carnivores in nutrient-poor habitats with non-carnivores in more nutrient-rich sites, so that the differences reported might reflect habitat differences as much as differences in nutrient-capture strategy. Here we examine three carnivorous and 12 non-carnivorous plants in the same nutrient-poor bog to compare their foliar nutrient concentrations, assess their patterns of nutrient limitation using leaf NPK stoichiometry, and estimate %N derived from prey by carnivores using a mixing model for stable N isotopes. We hypothesized that (1) carnivore leaf nutrient concentrations approach or exceed those of non-carnivores in the same nutrient-poor habitat; (2) species in different functional groups show different patterns of stoichiometry and apparent nutrient limitation; and (3) non-carnivores might show evidence of employing other means of nutrient acquisition or conserv­ation to reduce nutrient limitation.</p> <p>At Fallison Bog in northern Wisconsin, carnivorous plants (<em>Drosera rotundifolia, Sarracenia purpurea, Utricularia macrorhiza</em>) showed significantly lower leaf % C and N:P ratio, higher δ¹⁵N, and no difference from non-carnivores in leaf N, P, K, and δ¹³C. Sedges had significantly lower leaf % P, % C, and N:K ratio, and higher K:P ratio than non-sedges restricted to the <em>Sphagnum</em> mat, and may tap peat N via aerenchyma-facilitated peat oxidation (oxipeditrophy). Evergreen erica­ceous shrubs exhibited significantly higher levels of % C and lower values of d¹⁵N than mat non-ericads. <em>Calla palustris</em> – growing in the nutrient-rich moat at the bog's upland edge – had very high values of leaf N, K, δ¹⁵N, and N:P ratio, suggesting that it may obtain nutrients from minero­trophic flows from the adjacent uplands and/or rapidly decay­ing peat. Stoichiometric analyses indicated that most species are N-limited. A mixing model applied to δ¹⁵N values for carnivores, non-carnivores, and insects produced an estimate of 50% of leaf N derived from prey for <em>Utricularia</em>, 42% for <em>Sarracenia</em>, and 41% for <em>Drosera</em>.</p>