SEASONAL-VARIATION IN NUTRIENT CONCENTRATION IN LEAVES AND BRANCHES OF QUERCUS-PYRENAICA

Seasonal variation in nutrient concentration in leaves and branches of Quercus pyrenaica was studied in natural Q. pyrenaica forest in the S ierra de Gata (Salamanca Province, Spain). Two permanent plots were es tablished at the two extremes of a rainfall gradient in this area: ann ual mean precipitation from 720 mm at Fuenteguinaldo (granite bedrock) to 1580 mm at Navasfrias (schists and graywackes). Leaf and branch sa mples were collected every three weeks during the growing season from May to October, at three height levels of the tree canopy. Seasonal ch anges and internal nutrient dynamics were investigated for N, Ca, Mg, K, Na, Mn, Fe and P during a two-year period. The concentrations of al l nutrients varied among the seasons; these variations were related to nutrient mobility and the annual physiological cycle. Nutrient concen trations decrease in the case of K and P, while the sparse mobile nutr ients Ca, Mg, Mn and Fe gradually accumulated during each growing seas on. In Navasfrias a considerable resorption of P from senescing leaves was detected. Different patterns were found for the other nutrients s tudied (Na and N).