Photosynthetic capacity, integrated over the lifetime of a leaf, is predicted to be independent of leaf longevity in some tree species

The relationships between leaf longevity and the average photosynthetic capacity of the different leaf age-classes present in the crown were studied in several tree species to understand the effects of the differences in leaf longevity on the final C budget of the leaves. Photosynthetic capacity per unit leaf mass (A/mass) was measured in leaves of all age classes present in the crown. Demographic analyses were conducted to establish the age structure of the leaf populations. With these data we estimated the average A/mass of the whole leaf population, weighted by the mass of leaves present in each age class. A/mass decreased in all the evergreen species as the leaves aged. As a result, the assimilation rates averaged over all leaf age classes in species with greater leaf longevity were much lower than assimilation rates of young foliage, and the average rate of assimilation decreased with the increase in leaf life span of the different species. The reduction in the average assimilation rates with the increase in leaf life span was proportional to the increase in leaf longevity. With these results it may be predicted that CO2 assimilation integrated over the lifetime of the leaf should be independent of leaf longevity.