Relationships between Growth of Sitka Spruce (Picea sitchensis), Soil Factors and Mycorrhizal Activity on Basaltic Soils in Western Scotland

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Abstract
A survey was made of soil factors likely to be responsible for checked growth of Sitka spruce on soils derived from basalt in western coastal areas of Scotland. Despite the high organic P contents of these soils, availability of P appears to be the main factor limiting growth; growth indices were significantly correlated with foliar P concentrations and inorganic P levels of the soil. The low availability of soil P appears to be associated with high levels of oxalate-extractable Al (amorphous) in the soils, a strong correlation existing between the latter and the P sorption index of Bache and Williams. CaCl 2 -extractable Al (‘available’) values were also high and although they exhibited no significant correlation with growth there was a negative correlation between growth and foliar Al concentrations. High mycorrhizal counts were associated with tree roots on sites with better growth while beaded roots were mainly associated with poor growth. There is a suggestion that high CaCl 2 -extractable Al in these soils may affect mycorrhizal development, as a strong correlation was found between the occurrence of beaded roots and foliar Al concentration. Factor analysis confirmed that low availability of P in these soils may be ameliorated by mycorrhizal development and that a negative association exists between growth, the occurrence of beaded roots and foliar Al concentration.