VARIABILITY IN LEAF OPTICAL-PROPERTIES AMONG 26 SPECIES FROM A BROAD RANGE OF HABITATS

Leaves from 26 species with growth forms from annual herbs to trees we re collected from open, intermediate. and shaded understory habitats i n Mississippi and Kansas, USA. Leaf optical properties including refle ctance, transmittance, and absorptance in visible and near infrared (M R) wavelengths were measured along with leaf thickness and specific le af mass (SLM). These leaf properties and internal light scattering hav e been reported to vary with light availability in studies that have f ocused on a limited number of species. Our objective was to determine whether these patterns in leaf optics and light availability were cons istent when a greater number of species were evaluated. Leaf thickness and SLM varied by tenfold among species sampled. but within-habitat v ariance was high. Although there was a strong trend toward thicker lea ves in open habitats, only SLM was significantly,greater in open vs. u nderstory habitats. in contrast, leaf optical properties were striking ly similar among habitats. Reflectance and reflectance/transmittance i n the NIR were used to estimate internal light scattering and there we re strong relationships (r(2) > 0.65) between these optical properties and leaf thickness. We concluded that leaf thickness, which did not v ary consistently among habitats, was the best predictor of NIR reflect ance and internal light scattering. However, because carbon allocation to leaves was lower in understory species (low SLM) yet gross optical properties were similar among all habitats, the energy investment by shade leaves required to achieve optical equivalence with sun leaves w as lower. Differences in leaf longevity and growth form within a habit at may help explain the lack of consistent patterns in leaf optics as the number of species sampled increases.