Changing Photosynthetic Capacity during Leaf Ontogeny in Juvenile and Mature Metrosideros polymorpha Trees

Net CO2 uptake at light saturation (Pmax) was measured (both area and weight basis) for leaves of four categories based on leaf age and branch position in juvenile and mature trees of Metrosideros polymorpha, a tropical, dicot evergreen species. Conductance, weight /area, and Nand P concentrations were also measured. In both juvenile and mature trees, Pmax was higher in terminal leaves 6-14 months old than in younger or older leaves. Low Pmax of leaves less than 6 months old was related to factors of immaturity, including low weight /area and low N concentration. Low Pmax of older and subterminal leaves was correlated with low N concentration related to withdrawal during leaf aging. This correlation was stronger in mature than in juvenile trees. Pmax was significantly lower, and nitrogen concentration and specific leaf weight were higher, in the sample of mature trees than in the juvenile tree sample (Pmax 5.89 and 4.99 molm- 2 S- 1 in juvenile and mature trees, respectively)