The stable isotopic (C and N) composition of modern plants and lichens from northern Iceland: with ecological and paleoenvironmental implications

Abstract

The stable carbon and nitrogen isotopic composition (δ13C and δ15N) of plants and lichens can indicate a considerable amount of information about the physiology and ecology of an environment. To our knowledge no stable isotope (C and N) data have been generated for plants and lichens from Iceland. These data could subsequently provide a unique perspective of nitrogen and carbon cycling in Iceland and aid in interpretation of data generated from stable isotope analyses of organicmatter preserved in lake sediments. We analyzed plants and lichens around four lakes (Litla-Viðarvatn, Torfadalsvatn, Stífluvatn, Arnarvatn stóra) in northern and interior Iceland. The δ13C values for plants from the sites ranged from –30.9‰to –23.3‰that are typical of plants using C3 photosynthesis. Aquatic plant samples (e.g. Potamogeton sp.) analyzed from the sites had δ13C values (mean=–13.0‰) that were considerably less negative than the terrestrial plants and are typical for submerged freshwater aquaticmacrophytes. The δ15N values from the analyses of plants and lichens showed a surprisingly large range (∼ –12.4‰to +5.5‰), and many of the specimens had δ15N values lower than –6.0‰. A number of competing and testable causalmechanisms for the low δ15N values are proposed and discussed, including plant uptake of atmospheric ammonia and phosphorus limitation.