NEEDLE CO2 EXCHANGE, STRUCTURE AND DEFENSE TRAITS IN RELATION TO NEEDLE AGE IN PINUS-HELDREICHII CHRIST - A RELICT OF TERTIARY FLORA

Pinus heldreichii Christ is a long-lived, slow-growing Tertiary relict from the Balkans. In this study we evaluated the physiological charac teristics of eight needle-age classes of P. heldreichii grown at the A rboretum of the Institute of Dendrology in Kornik, Poland. At the end of the growing season, current-year foliage had the highest rates of m ass-based light-saturated net photosynthesis (A(sat) of 33.5 nmol CO2. g(-1).s(-1). A(sat) decreased with needle age, but older needle classe s retained from approximately 62 to 26% of the current needles' rate. The relationship between leaf N and chlorophyll a concentration among all needle-age classes was highly significant (r = 0.96, P = 0.0006). The variation in A(sat) of 1- to 7-year-old needles was linearly relat ed to needle N concentration (r = 0.98, P = 0.0001). Needle dark respi ration rates among these needle age classes ranged from 0.8 to 2.2 nmo l.g(-1).s(-1) and decreased with needle age and nitrogen concentration . Total phenols and glucose concentrations increased linearly with nee dle age. A similar pattern was observed in acid buffering capacity and the pH of tissue homogenates. The water content ranged from 62% for t he current needles to 51% for the 6-year-old needles. Greater investme nt in leaf structural tissue and increased chemical defense is associa ted with higher structural cost of older needles and may reduce their photosynthetic activity. Significant declines in water and nitrogen co ntent with needle age and an increase in content of phenolics is most likely a defense adaptation of P. heldreichii related to the species' long-lived leaves.