Effects of Drought and Defoliation on Some Metabolites in Roots of Black Oak Seedlings

Starch levels in roots were lower in defoliated, watered black oak seedlings than in non-defoliated, watered seedlings in two separate experiments. Starch levels in unwatered, non-defoliated seedlings were lower only when drought was severe. Drought and defoliation together resulted in lower starch levels than either one alone. Reducing sugars and several amino acids were higher in unwatered seedlings than in nondefoliated and watered ones, but not in those subjected to less severe droughts. Some increase in averages of reducing sugars and certain amino acids occurred in once- and twice-defoliated, watered plants. Levels of catechin and quercitrin were usually lower in defoliated than in nondefoliated seedlings, regardless of watering, and higher in unwatered seedlings than in watered ones, regardless of defoliation. Addition of fertilizer to the soil had no effect on growth, but in some combinations of drought and defoliation it resulted in lower carbohydrate levels.