Response of Norway spruce seedlings in relation to chemical properties of forest soils

The response of Norway spruce seedlings to 157 samples of upper soil layers obtained from 66 forest sites with Norway spruce distributed throughout Sw itzerland was examined during a 4 months growth chamber study. The pH value s of the soil samples ranged from 2.95 to 7.41, with 43% of the samples bei ng acidic (pH<4.75) and with high concentrations of exchangeable Al. A comp arison of two soil extraction methods, the NH4Cl-extraction representing th e 'exchangeable' fraction of cations in soils and the NH4-acetate-EDTA-extr action representing the 'extractable' (potentially plant available) fractio n, revealed similar results only for the cation K. With the NH4-acetate-EDT A-extraction, slightly more Al was extracted in nearly all the samples, and distinctly more Ca was extracted from samples with pH>6. Seedlings growing in these soil samples showed clear differences in biomass responses, when soils were arranged in classes according to the pH, the sum of 'exchangeabl e' basic cations (BC), or the BC/Al molar ratio. Reduced biomass was observ ed at pH<4.75, at BC<100 mmol, kg(-1), and at a BC/Al ratio <1. Additionall y, a significant positive relationship occurred between root biomass and BC /Al ratio in soils with a low BC/Al ratio (<10), indicating a potential for the use of the BC/Al ratio of soil extracts to assess the risk of Al stres s. In acidic soils, Ca concentrations in the shouts were reduced but Al con centrations were enhanced. This trend was also apparent when soils were arr anged according the BC/Al ratio. Here, Ca concentrations in the shoots were steadily enhanced from BC/Al <1 to >1000, whereas Al was reduced. The Ca c oncentrations in the shouts were similar to the 'exchangeable' amount of Ca in the soils, whereas for K and Mg an accumulation in the shoots occurred. The Al concentrations in the shoots, on the other hand, indicated a consta nt translocating rate of Al from the roots to the shoots independent of the 'exchangeable' amounts of Al in the soils. (C) 1999 Elsevier Science B.V. All rights reserved.