NUTRIENT DYNAMICS IN CROWN TISSUES OF CORK-OAK (QUERCUS-SUBER L)

The seasonal fluctuation of N, P, K, Ca and Mg in leaves, young stems and fruits of young and mature Quercus suber trees growing at the same site was studied. Nutrient dynamics within the tree appeared to be li nked to phenological events. Leaves maximized their nutrient contents throughout summer whereas stems maintained rather constant values duri ng most of the year. Before the spring growth flush they apparently ac ted as temporary reservoirs for some nutrients, translocated from leav es or other organs, so that such nutrients would be easily invested in the new tissues. A significant investment was made in sink organs lik e flowers and fruits. The tree probably relies not only on leaves but also on other nutrient reservoirs like older branches and roots for an adequate supply to those sinks and to the spring growth. The importan ce of the sampling dates and the basis of expression used for nutrient concentrations has also been emphasized. Nutrient contents and season al trends of the studied trees were similar to those of other evergree n oaks, although somewhat higher values for N, K, and Mg were found. M oreover, soil nutrient contents in the studied ''montado'' were much l ower than in other Iberic oak stands. However the nutrient status and requirements of cork-oak suggest high (or at least adequate:) nutrient availability to the trees. The mechanisms by which this could be achi eved are discussed.