Plant functional type and species determine elemental concentrations in boreal mire vegetation

Uptake of radionuclides into plants is a key process in radioecological modelling.  Typically, the uptake is incorporated into these models and in environmental impact assessments using an empirical soil-to-plant transfer factor (CR). The elemental concentration in plants is expected to vary with plant species and plant functional type (PFT), but also with soil concentration and elemental properties. Specifically, elements subject to regulated plant uptake (i.e. essential elements) are expected to be less related to soil concentrations than non-essential elements with no or limited biological function. Environmental conditions may also influence the CR value, and for assessment purposes, differential values are commonly listed for different soil types. In this study, we have addressed the impact of PFT and species as well as environmental factors to the CR of four peatland species (Andromeda polifolia, Vaccinium oxycoccus, Eriophorum vaginatum and Carex rostrata) representing two different PFTs (heathers and sedges).

The results show that while plant species and PFT are the most important factors determining the CR value, environmental factors, such as pH and peat depth, also modify the CR. As expected, plant concentrations of essential elements were only weakly related to soil concentrations, whereas the correlation between soil and plants was stronger for non-essential elements.

Based on our results, we verify that CR values may vary substantially between species and PFTs also in wetland environments.  Further, we suggest that since PFT may have a large impact on the exposure pathway to humans, it would be reasonable to differentiate between PFTs and to account for between-species variation in environmental impact assessment. Since CR varies systematically with several soil properties, CR values could also be adjusted to illustrate effects of expected future changes in the soil environment.