SULFUR NUTRITION OF TREES - A COMPARISON OF SPRUCE (PICEA-ABIES L) AND BEECH (FAGUS-SYLVATICA L)

Sulfur nutrition of herbaceous plants is characterized by sulfate upta ke and xylem loading of sulfate in the roots, assimilatory sulfate red uction in the leaves, and a cycling pool of both, sulfate and glutathi one, the main long distance transport form of reduced sulfur. Also in spruce and beech sulfate aquisition by the roots, sulfate transport to , and assimilatory sulfate reduction in the leaves are important proce sses required to fulfil the tree's needs for sulfur in growth and deve lopment. However, sulfate reduction for protein synthesis may take pla ce in roots of beech as well as in roots and stems of spruce trees. In addition, storage of reduced sulfur and its mobilization is required in spruce and beech to support the early growth of the new flush. In s pruce reduced sulfur in the form of glutathione is stored in the older needles during winter and is transported in phloem and xylem in acrop etal direction to the new needle generation in spring. In beech glutat hione exported from the leaves is removed from the phloem during basip etal transport; its sulfur seems to be stored as protein in the stem a nd apparently undergoes mobilization in spring during bud break. As a consequence, high amounts of cysteine are transported to the developin g leaves in the xylem.