© 1998 Heron Publishing—Victoria, Canada
Variability of the photosynthetic characteristics of mature needles within the crown of a 25-year-old Pinus pinaster
Annabel Porté (1) and Denis Loustau (1)
1. INRA Pierroton, Station de Recherches Forestières, Laboratoire d'Ecophysiologie et de Nutrition, BP 45, 33611 Gazinet Cedex,
France / Received March 5, 1997
Summary
Photosynthetic characteristics of 1- and 2-year-old needles were determined in excised shoots of maritime pine (Pinus pinaster Ait.) with an open gas exchange system. We used the nonlinear least mean squares method to derive values for quantum yield
of electron transport (α), maximum carboxylation velocity (Vcmax), and maximum electron transport rate (Jmax), from photosynthetic response curves to light and CO2. Crown height had no significant effect on any of the parameters; however, Vcmax and Jmax, as well as α were 43, 26 and 35% higher, respectively, in 1-year-old needles than in 2-year-old needles. The main effect
of irradiance on needles was a small decline in leaf concentrations of nitrogen and phosphorus from the top to the bottom
of the canopy. Only Jmax demonstrated a linear relationship with both nitrogen content (R2 = 0.42) and irradiance at the shoot level. Because needle age accounted for most of the variability in photosynthesis, we
incorporated needle age into the photosynthesis model of Farquhar et al. (1980). The modified model underestimated the daily
assimilation rate of 1-year-old needles in the field, especially when assimilation rates were high.
Keywords:
maritime pine, model, needle age, nitrogen, phosphorus, photosynthesis.
