The Indirect Effect of Drought on Tracheid Diameter in Red Pine

Abstract

Five-year-old Pinus resinosa trees were subjected to artificial drought periods of varying duration during the growing season. A single drought period resulted in a zone of narrow-diameter latewood tracheids and the formation of a false ring, whereas two drought periods produced two false rings. The formation of these false rings could be readily correlated with the decreased needle elongation and auxin synthesis (determined by auxin bioassay) resulting from the drought. The increase in tracheid diameter and the formation of a false ring that normally followed the drought could be prevented by inhibiting renewed needle elongation and, consequently, increased auxin synthesis. Therefore, it was concluded that the influence of drought was directly on the growth of the terminal meristems and only indirectly on tracheid diameter through the intermediate action of auxin.