Seasonal distribution of carbohydrates in loblolly pine seedlings

Abstract

Carbohydrates from loblolly pine (Pinus taeda L.) seedlings of a mesic and zeric family were compared under adequate soil moisture conditions and soil moisture stress. Carbohydrate trends in one-year-old seedlings grown with adequate soil moisture were similar to those found previously by other investigators in temperate zone plants. Reducing sugars and starch concentrations were high during the spring, low during the summer, and started a build-up during the fall season. The monthly reducing sugar and starch trends, specifically in the old needles, were different in the two families. Individual pentose and galactose sugar concentrations were coordinated with height and diameter growth. In comparison with seedlings grown under adequate moisture conditions, two-year-old loblolly pines from the xeric family subjected to moisture stress showed high levels of reducing sugars and starch in the needles, stem, and roots at the critical needle moisture level of 70-80 percent. Reducing sugars decreased in the needles, remained relatively constant in the stem and increased in the roots. The reducing sugar levels in the xeric family roots were significantly higher than in the mesic family roots. Individual pentose and galactose sugar concentrations were reduced to less than one percent in all plant parts at the critical needle moisture content.