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Volume 2 Number 9:  1 May 1999

Editorial
Where is Truth?: We discuss a few principles about the search for truth in science, especially climate science.

Journal Reviews
Coral Stress in the Florida Keys: A study of a Florida Keys coral suggests a link between coral bleaching and solar irradiance.  It also reveals the ability of corals to recover and adapt to stressful environments.

Ultraviolet Radiation Can Damage the Protective Mucus Coverings of Corals: The authors demonstrated that typical levels of UV radiation can cause damage to the DNA of microbial communities inhabiting the protective mucus coverings of corals, suggesting thereby a "potential role of UVR [ultraviolet radiation] in the global decline of coral reefs."

Intertidal Coral Bleaching: Natural occurrences of a localized and highly directional form of bleaching in intertidal massive corals near Thailand were shown to be due to exposure to high levels of solar irradiance.

Coral Tissue Retraction: Tissue retraction in certain corals may mistakenly be interpreted as coral bleaching events, since both phenomena display visual similarities and may occur under the same environmentally-stressed conditions.

Coral Bleaching and Multiple Symbionts: Keen observations of natural bleaching events in Caribbean corals revealed them to have multiple species of symbionts of differential susceptibility to stress, suggesting that this situation should enable reefs to better withstand the effects of climate change than has been previously been believed.

Multiple Symbionts in Corals: Observations of Caribbean corals reveal them to have multiple species of symbionts stratified by depth, which may provide adaptive measures to such corals to better withstand or recover from the effects of coral bleaching.

Influence of Elevated CO2 on Rubisco Content in Leaves of Wheat: A study of spring wheat plants grown in controlled environment growth chambers demonstrated that acclimation is not a direct negative effect of atmospheric CO2 enrichment but rather an indirect positive consequence of low soil nitrogen that, in the absence of acclimation, limits plant sink development.

Responses of Pasture Species to Elevated CO2 and Water Stress: Intact sections of turf composed of mixed grassland species from New Zealand that were water-stressed exhibited greater CO2-induced plant photosynthetic enhancements and water-use efficiencies than similar sections of turf that were well-watered.  In addition, elevated CO2 allowed plants to maintain less negative (more favorable) leaf water potentials during periods of severe soil moisture deficit.

Interactive Effects of Elevated CO2 and Drought on Cherry Seedling Growth and Water-Use Efficiency: Cherry seedlings grown for two years in open-top chambers at 700 ppm CO2 exhibited greater dry mass and water-use efficiency than seedlings grown at 350 ppm CO2.  In addition, water-stress did not negate the growth promoting effects of CO2 enrichment, and in the case of trunk basal area, the percentage growth stimulation was greatest under water-stressed conditions.

Interactive Effects of Elevated CO2 and Drought on Cherry Seedling Photosynthesis and Water Relations: Cherry seedlings grown for two years in open-top chambers at 700 ppm CO2 exhibited higher rates of photosynthesis and instantaneous transpiration use efficiencies, regardless of soil moisture content, than seedlings grown at 350 ppm CO2.  In addition, even though rubisco activity was significantly reduced in well-watered seedlings, rates of photosynthesis did not acclimate to elevated CO2.

Effects of Elevated CO2 and Water Stress on Red Oak: Red oak seedlings grown for 8 to 11 weeks in controlled environment chambers with 700 ppm atmospheric CO2 displayed photosynthetic rates that were 34 and 69% greater than rates observed in seedlings grown at 400 ppm CO2 under well-watered and water-stressed conditions.  In addition, elevated CO2 decreased stomatal conductance and increased plant water-use efficiency in all seedlings, regardless of soil moisture status.  Thus, elevated CO2 ameliorated the negative effects of water stress on growth, as water-stressed seedlings grown at 700 ppm CO2 had total biomass values that were similar to those of well-watered plants grown at 400 ppm CO2.