Stable isotopes indicate nitrogen sources in Pinguicula vulgaris across contrasting habitat types in sub-arctic Sweden

Background/Question/Methods

Like most carnivorous plant species, Pinguicula vulgaris (common butterwort) obtains nitrogen from both soil pools and insect prey. Prior studies have estimated percent prey-derived nitrogen (%PDN) for the entire plant, but it may be expected that %PDN varies between plant parts. By measuring stable isotopic ratios in the soil, plants, and naturally captured prey, this study estimated %PDN in both foliage and roots. Plants, soil and insects were collected in sub-arctic Sweden across two habitat types: dry heath and moist sphagnum. Insect samples were homogenized for each site, and all samples were cleaned, dried, and measured for δ¹⁵N in an isotope ratio mass spectrometer. 

Results/Conclusions

Roots showed consistent %PDN in both habitat types, whereas foliage in moist sphagnum sites had significantly greater %PDN than foliage in dry heath sites. Amount of captured prey did not differ significantly between habitat types. These results provide the framework for a rough model of the differential distribution of prey- and soil-derived nitrogen in P. vulgaris, where root nitrogen is split approximately evenly between the two sources, and foliar nitrogen varies by site, possibly dependent on the accessibility of nitrogen in the soil pool.