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


Adrian Walcroft. Fax: +64 78384324; e-mail: asw@waikato.acanz


Responses of photosynthesis (A) to intercellular CO2 concentration (ci) 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 Vcmax, the maximum rate of carboxylation (10.7–43.3 μol m−2 s−1 and a 3-fold increase in Jmax, the maximum electron transport rate (20.5–60.2 μmol m −2 s−1). The temperature optimum for Jmax was lower than that for Vcmax, causing a decline in the ratio Jmax:Vcmax 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 Vcmax and Jmax. 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.