Fluoride-induced enhancement and inhibition of photosynthesis in four taxa of Pinus



Pinus elliottii Englem. var. elliottii (PEE) and three varities of Pinus caribaea Morelet [var. caribaea Barr, et Golf. (PCC), var. bahamensis Barr. et Golf. (PCB) and var. hondurensis Bafr. et Golf (PCH)] were grown for a total of 125 days under gaseous hydrogen fluoride at 0.0, 1.2, 1.8.and 4.3 μg F m−3. Apparent photosynthesis was measured on 10–12 plants in each taxon and treatment during the last 10 days of the experiment, using needles free from visible injury that had matured before (old) or during the experiment (young). Rates of apparent photosynthesis were significantly greater in young needles of PCB and PCH exposed to 1.2 than to 4.3 μg F m−3, and in old needles of PCH exposed to 1.2 than to 0.0, 1.8 and 4.3 μg F m−3. Chlorophyll concentrations in old needles were consistently lower than those in young needles, but varied less with changes in ambient fluoride concentration, differences in photosynthetic rates of PCB, PCC and PCH corresponded generally with differences in concentrations of chlorophylls a, b and (a+b). Ambient fluoride concentrations less than about 1 μg F m3 appear unlikely to have deleterious short-term effects on chlorophyll concentrations and photosynthesis in these taxa.