THE RESPONSE OF PHOTOSYNTHETIC MODEL PARAMETERS TO TEMPERATURE AND NITROGEN CONCENTRATION IN PINUS-RADIATA DON,D

Responses of photosynthesis (A) to intercellular CO2 concentration (c( i)) in 2-year-old Pinus radiata D. Don seedlings were measured at a ra nge of temperatures in order to parametrize a biophysical model of lea f photosynthesis. Increasing leaf temperature from 8 to 30 degrees C c aused a 4-fold increase in V-cmax, the maximum rate of carboxylation ( 10.7-43.3 mu mol m(-2) s(-1)) and a 3-fold increase in J(max), the max imum electron transport rate (20.5-60.2 mu mol m(-2) s(-1)). The tempe rature optimum for J(max) was lower than that for V-cmax, causing a de cline in the ratio J(max):V-cmax from 2.0 to 1.4 as leaf temperature i ncreased from 8 to 30 degrees C, To determine the response of photosyn thesis to leaf nitrogen concentration, additional measurements were ma de on seedlings grown under four nitrogen treatments, Foliar N concent rations varied between 0.36 and 1.27 mol kg(-1), and there were linear relationships between N concentration and both V-cmax and J(max). Mea surements made throughout the crown of a plantation forest tree, where foliar N concentrations varied from 0.83 mol kg(-1) near the base to 1.54 mol kg(-1) near the lender, yielded similar relationships. These results will be useful in scaling carbon assimilation models from leav es to canopies.