The response of photosynthetic model parameters to temperature and nitrogen concentration in Pinus radiata D. Don

Responses of photosynthesis (A) to intercellular CO2 concentration (c(i)) in 2-year-old Pinus radiata D. Don seedlings were measured at a range of temperatures in order to parametrize a biophysical model of leaf photosynthesis. Increasing leaf temperature from 8 to 30 degrees C caused 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 maximum electron transport rate (20.5-60.2 mu mol m(-2) s(-1)). The temperature optimum for J(max) was lower than that for V-cmax, causing a decline in the ratio J(max):V-cmax from 2.0 to 1.4 as leaf temperature increased from 8 to 30 degrees C, To determine the response of photosynthesis to leaf nitrogen concentration, additional measurements were made on seedlings grown under four nitrogen treatments, Foliar N concentrations 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). Measurements 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 leaves to canopies.