MODERATE WATER-STRESS ALTERS CARBOHYDRATE CONTENT AND COLD TOLERANCE OF RED SPRUCE FOLIAGE

Red spruce (Picea rubens Sarg.) has been tested for response to many environmental stresses and found to be relatively tolerant. An explanation for this tolerance is its maintenance of high levels of carbohydrate reserves, mainly soluble sugars and starch, which change with alterations in photosynthetic capacity, rate of growth and degree of cold tolerance through the year. Red spruce saplings responded to moderate water stress in early September by depleting foliar starch and maintaining foliar soluble sugars. Foliar carbohydrate contents of water-stressed trees were restored to control levels within 1 week of rewatering. During and immediately after the water-stress period, foliage of water-stressed trees was more cold tolerant than foliage of well-watered trees as measured by relative electrolyte leakage. Two months after termination of the water-stress treatment, starch content of fine roots and cold tolerance of foliage of well-watered trees were significantly higher than those of water-stressed trees. Before the trees became fully cold tolerant, differences between treatments in the degree of foliar cold tolerance were positively associated with differences in soluble sugar content. As trees became more cold tolerant, soluble sugar contents were not related to the degree of cold tolerance. These results suggest that species with substantial reserves withstand periods of reduced carbon fixation by utilizing reserves for maintenance; however, lowered reserves could result in increased susceptibility to subsequent stresses.