Moisture Stress and Composition of Xylem Oleoresin in Loblolly Pine

Abstract

Abstract The effect of moisture stress on composition of xylem oleoresin in large loblolly pines was examined in three tests conducted over a 3-year period. Two of the tests were in the lower Gulf Coastal Plain and one in the upper Coastal Plain. Moisture stress was induced by trenching around individual trees and constructing shelters to prevent recharge of soil moisture. Over the 3-year period, moisture stress was induced in 9 trees. Stress decreased the proportion of resin acids relative to monoterpene hydrocarbons in the oleoresin. Most of the change in resin acids was due to decrease in levopimaric + palustric acid, and most of the change in monoterpene hydrocarbons was due to an increase in α- and β-pinene. Trees growing on poorly drained, flat sites showed greater changes than adjacent trees on low mound sites. With stress, the greatest changes occurred in trees which had lost much of their root systems to rootlet pathogens. The changes may influence the susceptibility of trees to attack by bark beetles. Forest Sci. 21:283-290.