Long-term effects of single potassium fertilization on 137 Cs levels in plants and fungi in a boreal forest ecosystem K. Rosén a, * , M. Vinichuk a, b , I. Nikolova a , K. Johanson a a Department of Soil and Environment, Swedish University of Agricultural Sciences, SLU, P.O. Box 7014, SE-750 07 Uppsala, Sweden b Department of Ecology, Zhytomyr State Technological University, 103 Chernyakhovsky Str., 10005 Zhytomyr, Ukraine article info Article history: Received 13 April 2010 Received in revised form 24 September 2010 Accepted 9 November 2010 Available online 8 December 2010 Keywords: Bilberry Fungi Heather Lingonberry Potassium Radiocaesium abstract We examined the long-term effects of a single application of potassium (K) fertilizer (100 kg K ha 1 ) in 1992 on 137 Cs uptake in a forest ecosystem in central Sweden. 137 Cs activity concentrations were determined in three low-growing perennial shrubs, heather (Calluna vulgaris), lingonberry (Vaccinium vitis-idaea) and bilberry (Vaccinium myrtillus), and in four wild fungal species (Cortinarius semi- sanguineus, Lactarius rufus, Rozites caperata and Suillus variegatus). Uptake of 137 Cs by plants and fungi growing on K-fertilized plots 17 years after application of the K fertilizer was significantly lower than in corresponding species growing in a non-fertilized control area. The 137 Cs activity concentration was 21 e58% lower in fungal sporocarps and 40e61% lower in plants in the K-fertilized area compared with the control. Over the study period, this decrease in 137 Cs activity concentration was more consistent in plants than in fungi, although the effect was statistically significant and strongly pronounced in all species. The effect of K fertilization in reducing 137 Cs activity concentration in fungi and plants decreased over time but was still significant in 2009, 17 years after fertilization. This suggests that application of K fertilizer to forests is an appropriate and effective long-term measure to decrease radiocaesium accumulation in plants and fungi. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Radiocaesium ( 137 Cs) uptake by plants and fungi in boreal forest ecosystems in Scandinavia has been very high post-Chernobyl and only slow decreases in the following 10e15 years in the activity concentrations of 137 Cs in forest plants, fungal sporocarps and game animals have been reported (Johanson and Bergström, 1994; Nelin and Nylèn, 1994; Johanson and Kardell, 1996; Kiefer et al., 1996; Palo et al., 2003). Recent studies have shown that the 137 Cs activity concentration in edible fungi species either did not decrease over the last 20 years (Suillus variegatus) or even significantly increased (Cantharellus spp.) (Mascanzoni, 2009). The combination of high 137 Cs activity concentrations in food products derived from forest ecosystems and the long effective ecological half-life of 137 Cs in forest ecosystems can result in high time-integrated intake of 137 Cs by humans through local non-commercial consumption of berries, fungi, moose and roe deer. 137 Cs uptake by plant species, particularly those belonging to the Ericaceae family such as heather (Calluna vulgaris), has decreased over the past 15e20 years but is still rather high, compared to other vascular species, such as cloudberry (Rubus chamaemorus), bog bean (Menyanthes trifoliate) and cranberry (Vaccinium oxycoccus and Vaccinium microcarpon)(Rosén et al., 2009; Vinichuk et al., 2010a). Lingonberry (Vaccinium vitis-idaea) and bilberry (Vaccinium myrtillus) have been shown to have high uptake of 137 Cs (Johanson and Kardell, 1996) and these species are important feed plants for moose and roe deer. In these forest ecosystems, heather usually has the highest 137 Cs activity concentration, with bilberry and lingon- berry plants typically having less than 30% of the 137 Cs activity concentration found in heather. The 137 Cs levels in fungal species that are less prone to accumulating 137 Cs can be similar to the levels found in bilberry and lingonberry, but most fungal species can have 10e100 times higher levels than the vascular plant species. Potassium (K) fertilization has been shown to decrease soil- plant transfer of 137 Cs in agricultural ecosystems (Rosén, 1996). The effect of K fertilization in reducing 137 Cs uptake by forest plants growing on radionuclide-polluted soils has been studied in a few experiments, e.g. using Scots pine trees (Kaunisto et al., 2002) and the effect seemed to be long-lasting. In studies by Levula et al. (2000), 137 Cs activity concentrations in lingonberries were shown to decrease as a result of ash fertilization and prescribed burning. In * Corresponding author. Tel.: þ46 018 67 14 42; fax: þ46 018 67 28 95. E-mail address: Klas.Rosen@mark.slu.se (K. Rosén). Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad 0265-931X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2010.11.009 Journal of Environmental Radioactivity 102 (2011) 178e184