Effect of soil base saturation and endomycorrhization on growth and nutrient status of sugar maple seedlings

Nutrient imbalances of declining sugar maple (Acer saccharum Marsh.) stands in southeastern Quebec have been associated partly with high soil exchangeable acidity and low base saturation. A greenhouse experiment was set up to determine how growth and nutrient status of sugar maple seedlings can be influenced by soil acidification and the presence of an endomycorrhizal fungus. The experiment consisted of five levels of soil base saturation (from 12 to 50%) and two levels of soil inoculation by an endomycorrhizal fungus (inoculated and control) in a complete factorial arrangement. Sugar maple seedlings were grown for 3 mo in the treated soil substrates. Seedling shoot elongation rate, growth [dry matter (DM) mass, stem diameter, and total leaf area], and K, Ca and Mg concentrations in foliage and roots decreased with soil acidification, with base saturation used as an indicator of the soil-acidification status. Foliar K and Ca levels reached values below critical thresholds when soil base saturation was reduced to 12%. Under the experimental conditions, seedling growth was not significantly affected by endomycorrhization, except for root DM mass, which was reduced by 24% compared with the control treatment. For mycorrhizal seedlings, foliar Al concentration increased linearly from 113 mg kg(-1) to 210 mg kg(-1) with the reduction of soil base saturation from 50% to 12%, while, for non-mycorrhizal seedlings, foliar Al concentration remained at a high level (195 mg kg(-1)) independently of the soil acidification level. Sugar maple seedling growth was not related to accumulation of Al in foliage. The results of this experiment support the hypothesis that a causal relationship exists between the level of soil base saturation and the growth decrease and associated nutrient disorders observed in declining sugar maple stands in Quebec.