Changes in loblolly pine root growth potential from September to April

Loblolly pine (Pinustaeda L.) 1 + 0 seedlings were periodically hand lifted from a Virginia nursery to determine how root growth potential (RGP) varied between September and April. Several seedling characteristics, RGP, and shoot phenology were recorded for each lift date in 1983-1984 and 1984-1985. An attempt was made to relate RGP variation to changes in the nursery environment and to shoot phenology. Root growth potential variation was consistent between years and was more closely related to shoot phenological changes than to short-term environmental changes. During the development of dormancy, RGP was low, RGP increased when shoot activity resumed during the RGP tests (late winter, early spring), and declined as active shoot elongation began in the nursery. When RGP was low, elongation of existing lateral roots primarily contributed to the new root systems, but as seedling metabolism increased in the late winter, new root initiation also contributed to new root systems. Absolute differences in RGP between years may be related to the fibrosity of seedling root systems.