article id 492,
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                        Research article
                    
        
                                    
                                    
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                            Leaves of bilberry (V. myrtillus), bog bilberry (V. uliginosum) and  downy birch (B. pubescens) were collected five times during a growing  season from 18 plots in a drainage area, and needles of Scots pine  (Pinus sylvestris L.) once during the following winter from the same  plots at Parkano, southern Finland. The aim was to study the potassium  nutrition of the test plants and relationships between the foliar  potassium concentrations of Scots pine and of the test plants. The  estimation of the potassium nutrition of test plants was based on the  accumulation of putrescine in foliage. Apart from single observations,  elevated putrescine concentrations were found when the potassium  concentrations were < 5 mg g–1 in bilberry, < 4 mg g–1 in bog  bilberry and < 6 mg g–1 in downy birch, and the highest  concentrations below the potassium levels of 3.0–3.5 mg g–1. At the  concentrations of 2–3 mg g–1 the accumulation increased pronouncedly in  bog bilberry but less in downy birch and only slightly in bilberry. The  foliar potassium concentrations in test plants correlated closely with  the concentrations in pine needles. The concentrations of all species in  August were quite stable at the levels of the severe and slight  potassium deficiency of pine (3.5 and 4.5 mg g–1 respectively)  indicating that August would be suitable for collecting foliage. The  concentrations in bog bilberry were very close to the concentrations in  pine at the severe and those in bilberry at the slight deficiency level  of pine. All test plants could be used for predicting the potassium  nutrition of Scots pine, but additional research is needed for the  practical application of the method.
                        
                
                                            - 
                            Kaunisto,
                            Finnish Forest Research Institute, Parkano Research Station, Kaironiementie 54, FIN-39700 Parkano, Finland
                                                        E-mail:
                                                            seppo.kaunisto@metla.fi
                                                                                        
                                                     
                                            - 
                            Sarjala,
                            Finnish Forest Research Institute, Parkano Research Station, Kaironiementie 54, FIN-39700 Parkano, Finland
                                                        E-mail:
                                                            ts@nn.fi