RELATIONSHIPS BETWEEN SOLUBLE SUGAR CONCENTRATIONS IN ROOTS AND ECOSYSTEM STRESS FOR FIRST-YEAR SUGAR MAPLE SEEDLINGS

Accumulation of reducing sugars (i.e., glucose and fructose) in plant roots has been consistently correlated with forest dieback and decline and, therefore, has potential as a biological indicator of ecosystem stress. In this study, the relationships between acidic deposition and ''natural'' (temperature, mycorrhizae, and nutrition) factors with fi rst-year sugar maple seedling root sugar concentrations and growth wer e assessed in two sugar maple dominated forests in Michigan. Seedlings at the southern site (Wellston) had greater root growth, phosphorus, total sugar, and sucrose concentrations in roots, but lower reducing s ugar concentration in roots. In addition, percent root length colonize d by vesicular-arbuscular mycorrhizal fungi was less than that found f or seedlings growing at the northern site (Alberta). Throughfall depos ition of nitrate, sulfate, and hydrogen ions was not significantly cor related with seedling total or reducing sugar concentration. Total sug ar concentration in seedling roots was positively correlated with air and soil temperatures at the southern site, but not at the northern si te. Seedling tissue phosphorus concentration was correlated with total sugars at both sites, with sucrose at the southern site, and reducing sugars at the northern site. Mycorrhizal colonization rates at the Al berta site were positively correlated with reducing sugar concentratio n in seedling roots and negatively correlated with sucrose concentrati on. The results suggest that differences in seedling root sugar concen trations in these two forests are related to seedling root growth and are most likely due to ecological variables, such as available soil ph osphorus, temperature, and growing season length through some complex interaction with mycorrhizae rather than acidic deposition stress.