Photoacoustic spectroscopy was used to monitor acid damage to photosynthesis by measuring photosynthetic O2 evolution in leaves from com and sugar maple plantlets. For 2 months the seedlings were treated with simulated acid rain either by spraying the leaves or by watering the soil at different pH levels. The results indicated a decline of photosynthetic oxygen evolution as the pH of the foliar application of simulated acid rain decreased. The reduced photosynthetic activity was sometimes followed by depigmentation (below pH 3.5). For plantlets treated by watering the soil with an acid mixture, the results showed an increase in the growth rate at higher acidity levels without effect on the photosynthetic activity. All corn seedlings from seeds that germinated in media of different pH levels showed the same photosynthetic activity regardless of the pH, as measured by photoacoustic spectroscopy, but the growth rate was higher at lower pH values than at higher pH values. These results clearly indicate the importance of acid damage to photosynthesis at the foliar level, and the ability of photoacoustic spectroscopy to assess forest decline in its early stages. Key words: photoacoustic spectroscopy, photosynthesis, corn, maple, acid rain, oxygen evolution.
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