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

Responses of photosynthesis ( A ) to intercellular CO 2 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°C caused a 4‐fold increase in V cmax , the maximum rate of carboxylation (10.7–43.3 μol m −2 s −1 and a 3‐fold increase in J max , the maximum electron transport rate (20.5–60.2 μmol 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°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 leader, yielded similar relationships. These results will be useful in scaling carbon assimilation models from leaves to canopies.