Anatomical variation in juvenile Eucalyptus leaves accounts for differences in specific leaf area and CO2 assimilation rates

Abstract

Specific leaf area (SLA) is an important leaf attribute representing the compromise between the capture of light and CO2, and the limitations imposed by leaf structure, herbivore resistance and the mitigation of water loss. We examined three Eucalyptus species to determine whether variation in CO2 assimilation rate is related to SLA and leaf anatomy. Seedlings were grown in a naturally illuminated glasshouse with adequate water and nutrients. Light saturated rates of photosynthesis and the response of assimilation to intercellular CO2 concentration were measured on the youngest fully expanded leaf. Mesophyll characteristics were measured from 1µm thick sections of the interveinal leaf lamina. Significant interspecies variation in SLA was observed corresponding to clear trends in anatomy and photosynthesis. Low SLA leaves were thicker having increased thickness of palisade mesophyll due to a greater number of palisade layers. E. occidentalis, E. camaldulensis and E. grandis had 3.7, 2.0 and 1.0 layers of palisade cells which corresponded to an SLA of 14.8, 17.6 and 21.8 m2 kg-1 respectively. High investment in this photosynthetic tissue increased leaf nitrogen, chlorophyll and photosynthetic capacity per leaf area. The leaf morphology affected how the leaves used these resources. Thick leaves of E. occidentalis had lowest nitrogen use efficiency and highest instantaneous water use efficiency in contrast to the thin leaves of E. grandis. Differences in leaf structure of these species appear to reflect the environments to which they have adapted and the most limiting resource.