Measurement of the optical properties of leaves under diffuse light.

Measuring leaf light absorptance is central to many areas of plant biology including photosynthesis and energy balance. Absorptance is calculated from measured values of transmittance and reflectance, and most such measurements have used direct beam light. However, photosynthesis and other processes can differ under direct and diffuse light.

A new paradigm in leaf-level photosynthesis: direct and diffuse lights are not equal.

Global-change scenarios suggest a trend of increasing diffuse light due to expected increases in cloud cover. Canopy-level measurements of plant-community photosynthesis under diffuse light show increased productivity attributed to more uniform distribution of light within the forest canopy, yet the effect of the directional quality of light at the leaf level is unknown. Here we show that leaf-level photosynthesis in sun leaves of both C(3) and C(4) plants can be 10-15% higher under direct light compared to equivalent absorbed irradiances of diffuse light.

Ultraviolet radiation and the snow alga Chlamydomonas nivalis (Bauer) Wille.

Aplanospores of Chlamydomonas nivalis are frequently found in high-altitude, persistent snowfields where they are photosynthetically active despite cold temperatures and high levels of visible and ultraviolet (UV) radiation. The goals of this work were to characterize the UV environment of the cells in the snow and to investigate the existence and localization of screening compounds that might prevent UV damage. UV irradiance decreased precipitously in snow, with UV radiation of wavelengths 280-315 nm and UV radiation of wavelengths 315-400 nm dropping to 50% of incident levels in the top 1 and 2 cm, respectively.

Photoacoustic analysis indicates that chloroplast movement does not alter liquid-phase CO2 diffusion in leaves of Alocasia brisbanensis.

Light-mediated chloroplast movements are common in plants. When leaves of Alocasia brisbanensis (F.M.

Surface gas-exchange processes of snow algae.

The red-colored chlorophyte Chlamydomonas nivalis is commonly found in summer snowfields. We used a modified Li-Cor gas-exchange system to investigate surface gas-exchange characteristics of snow colonized by this alga, finding rates of CO(2) uptake up to 0.3 micromol.