Under field conditions, vesicles were the most frequently observed mycorrhizal structures in sugar maple, while greenhouse grown seedlings formed more arbuscules. Seasonal fluctuations of vesicular-arbuscular mycorrhizae existed. Mycorrhizal associations formed within 30 days in the greenhouse. Arbuscules were usually formed from hyphal coils and occasionally from linear hyphae spreading from cell to cell. Degenerating arbuscules were not observed. The addition of basic cations increased the number of vesicles formed and decreased the overall infection rates and seedling growth. The uptake of calcium, magnesium, and nitrogen decreased, and potassium uptake increased as fertilization rates increased. Positive correlations existed between the incidence of arbuscules and plant growth and health and between the incidence of arbuscules and the uptake of calcium, magnesium, nitrogen and phosphorus, and with the uptake ratios and these elements with potassium. This suggests that vesicular-arbuscular mycorrhizae may in some way be regulating ionic balance in these seedlings.

Sugar maple trees were fertilized in June 1988 on an individual tree basis in an attempt to improve tree vigour. Fertilizers included K$ sb2$SO$ sb4$, a phosphate and base cations mix, and a commercial organic mix (Maplegro). No effect of fertilization was found on foliar nutrient concentrations and water status of trees during the 1990 growing season. This is possibly the result of dilution in tree biomass, the addition of non limiting nutrients or the experimental design. A positive effect of fertilization on growth was found for one site and, at another, fertilization was found to impair growth. Thus fertilization requirements of declining sugar maple are site specific. Soil Mg was higher around trees fertilized with Maplegro, and trees fertilized with K$ sb2$SO$ sb4$ had low leaf buffering capacities.

Studies were undertaken to determine the effects of fertilizer and liming materials on soil and fine root chemistry and fine root biomass, and on the starch content of larger diameter sugar maple (Acer saccharum Marsh.) roots. Responses in fine root biomass, fine root chemistry, and soil chemistry were observed using root-free ingrowth cores containing an organic based fertilizer (3-4-8 plus dolomitic limestone at a rate of 800 kg/ha), an inorganic fertilizer (0-3-29 plus calcite and dolomite at a rate of 1370 kg/ha), or no fertilizer. The cores were installed in three mature sugar maple stands for one year. Significant differences (p $ leq$ 0.05) in many root and soil chemical properties existed among sites. Greatest treatment response in soil and fine root chemistry occurred at the site with the poorest nutrient status. Fine root biomass decreased due to treatment at one site. No other response in fine root biomass was observed. / Larger diameter roots were sampled at two sites from sugarbush fertilization plots treated with base rich fertilizers. At one site, an acidifying treatment was also applied. Significant differences (p $ leq$ 0.05) in root starch content were observed between the acidifying treatment and the most base enriched treatments several years following fertilization.

Sugar maple foliage litters from fertilized and unfertilized plots on a base-poor site and from a naturally base-rich site were incubated in litterbags of 1 and 3 mm mesh on fertilized and unfertilized plots at the base-poor site. Mass loss of unfertilized litter was slower in fertilized than unfertilized plots, suggesting a negative effect of fertilization on decomposers. Mass loss of fertilized litter was faster than unfertilized litter in the same plots, indicating that changes in litter quality due to fertilization enhanced microbial decomposition. Mass loss was higher in large mesh than in small mesh size bags, suggesting that larger soil fauna played a significant role in litter decomposition. / Potassium appeared to be rapidly leached, whereas Ca and Mg were released at rates more closely related to litter mass loss. Nitrogen was mineralized from N-rich Arboretum litter only; all other litters immobilized N. Release of Ca and Mg was reduced significantly on fertilized plots. Large soil fauna enhanced Ca release, while they delayed N-mineralization in Arboretum litter.

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Two studies were conducted to assess physiological responses of declining sugar maple (Acer saccharum Marsh.) in southern Quebec to wet acidic precipitation and increased soil fertility. Leaves of sugar maple were relatively acidic, had low external neutralization capacity (ENC = 5.1 $ mu$equiv. H$ sp{+} rm g sp{-1}$) and buffering capacity index (BCI = 103 $ mu$equiv. H$ sp{+} rm g sp{-1}$), and higher ENC/BCI compared to three other tree species. Deciduous species showed a higher BCI and a lower ENC in August. Our results suggest that sugar maple may be relatively sensitive to wet acidic deposition and that leaf buffering capacity is related to photosynthesis potential and seasonal change in foliar Ca concentration. Foliar analyses revealed that fertilization with a mixture of K, Ca, and Mg had significant effects on leaf concentrations of K, free amino acids (FAA) and the ratios of N to K, and FAA to N after two growing seasons. Our results suggest that base cation fertilization improved the N and K status of sugar maple and that leaf carbon partitioning appeared to be more dynamic in fertilized trees.

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