Photosynthetic parameters in seedlings of Eucalyptus grandis as affected by rate of nitrogen supply

Seedlings of Eucalyptus grandis were grown at five different rates of nitrogen supply. Once steady-state growth rates were established, a detailed set of CO2 and water vapour exchange measurements were made to investigate the effects of leaf nitrogen content (N), as determined by nitrogen supply rate, on leaf structural, photosynthetic, respiratory and stomatal properties. Gas exchange data were used to parametrize the Farquhar-von Caemmerer photosynthesis model. Leaf mass per area (LMA) was negatively correlated to N. A positive correlation was observed between both day (R-d) and night respiration (R-n) and N when they were expressed on a leaf mass basis, but no correlation was found on a leaf area basis. An R-d/R-n ratio of 0.59 indicated a significant inhibition of dark respiration by light. The maximum net CO2 assimilation rate at ambient CO2 concentration (A(max)), the maximum rate of potential electron transport (J(max)) and the maximum rate of carboxylation (V-cmax) significantly increased with N, particularly when expressed on a mass basis. Although the maximum stomatal conductance to CO2 (g(scmax)) was positively correlated with A(max), there was no relationship between gscmax and N. Leaf N content influenced the allocation of nitrogen to photosynthetic processes, resulting in a decrease of the J(max)/V-cmax ratio with increasing N. It was concluded that leaf nitrogen concentration is a major determinant of photosynthetic capacity in Eucalyptus grandis seedlings and, to a lesser extent, of leaf respiration and nitrogen partitioning among photosynthetic processes, but not of stomatal conductance.