Photosynthetic capacity and carbon allocation patterns in diverse growth forms of Eucalyptus

Eucalytptus species originating in Australian habitats differing in moisture regimes were examined under uniform growth conditions for their photosynthetic characteristics and allocation patterns. Species from the driest environments, the 'mallee' types, had the smallest leaf sizes and the highest leaf specific weights; and forest species, from moist coastal sites, had the largest and thinnest leaves. Photosynthetic rates on a dry weight basis were highly correlated with leaf nitrogen content in all species. Leaf nitrogen content on a dry weight basis varied little between species in nature; however, there were increasing amounts of nitrogen per unit leaf area as the habitat became drier because of the changes in specific leaf weight. This resulted in a greater light-saturated photosynthetic rate per leaf area of arid habitat species, which were presumably more efficient in water use as a consequence. A simple simulation model showed that changes in the allocation ratio to leaf weight reduces total leaf area in the expected direction without affecting total dry matter accumulation.