Leaf absorptance of photosynthetically active radiation in relation to chlorophyll meter estimates among woody plant species

The quantum yield of photosystem II, determined by chlorophyll fluorescence and the quantum yield of CO₂ uptake, determined from gas exchange, are two physiologically important measurements in clarifying the response to environmental stress. Both measurements, however, require an accurate assessment of leaf light absorption in the photosynthetically active radiation wavelength range (400-700nm). To date, integrating sphere and field-portable spectroradiometer measurements of leaf reflectance, transmittance, and absorptance are time consuming, costly, and cumbersome. It is therefore desirable to determine if SPAD meter chlorophyll concentration estimates could be used in lieu of an integrating sphere and field-portable spectroradiometer for determining leaf reflectance, transmittance, and absorptance in woody plant species. An integrating sphere and field-portable spectroradiometer were used to measure reflectance, transmittance, and absorptance of leaf samples at 2nm intervals between 400 and 700nm. A paired SPAD 502 hand-held chlorophyll estimate was also determined for each sample. Regression analysis revealed a strong relationship between the SPAD estimate and leaf transmittance and absorptance. The reflectance relationship, although still present, was not as accurate. The study indicates that the SPAD meter could be used to provide a rapid estimate of leaf absorbance and transmittance in the 400-700nm wavelength range in woody plant species.