Stem-growth response of Pinus sylvestris and Picea abies to nitrogen fertilization as related to needle nitrogen concentration
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Responses of stem-volume growth to N application were evaluated in relation to foliar N concentrations. Data from N-fertilization experiments in 28 Pinus sylvestris stands and 21 Picea abies stands were used. Relative stem-growth responses were negatively related to concentrations of N in current-year needles of unfertilized trees. There appeared to be a threshold value of 15–16 mg (g DM)–1 N in current-year needles, above which N-application is unlikely to stimulate growth. However, relations were non-significant between N concentrations in current-year needles and the absolute stem-growth response [dm3 ha–1 (5 years)–1]. The indicated threshold values are discussed in relation to other variables reflecting the N richness of the environment.-->
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