Short-term acid damage to photosynthesis in corn and sugar maple leaves assessed by photoacoustic spectroscopy

Abstract

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.

The Use and Characteristics of the Photoacoustic Method in the Study of Photosynthesis

“…The resulting alternating electrical current from the microphone is analyzed by a lock-in amplifier (LlA), which selects signals at exactly the same frequency as . that of the light modulation, rejecting irrelevant signals and random noise (10, 83,89). Measurements refer to the fu ndamental mode (in a Fourier series representation) of all the periodic signals.…”

Effects of acid watering of the soil on the photosynthetic activity, growth, and foliar pigments of sugar maple saplings

“…This apparent discrepancy should be discussed at the whole-plant-physiology level. In a former paper [5], an enhanced growth rate has been observed for sugar maple and corn plants sprayed with low pH acid rain associated with decreased photosynthetic O 2 evolution. These results have been explained on the basis of increased supply of nutritive elements like S and N in the acid rain to the foliage.…”

“…We observed a decrease in photosynthetic activity as assessed by the photoacoustic methodology, whereas growth was stimulated at higher acidity levels [5]. In this paper, we present the effects of varying the pH of soil watering on the photosynthetic activity, the growth rate and on the pigment content of sugar maple leaves.…”

“…Fluorescence methods have been developed for that purpose [7]. Quite recently, photoacoustic spectroscopy (PAS) came to be used as noninvasive monitoring method of photosynthetic activity in intact leaves by measuring heat emission, photochemical energy storage and the consequent O 2 evolution [5,8,9].…”

“…For photosynthetically active leaves, O 2 evolution also contributes to the photoacoustic (PA) signal. As the diffusion rate of O 2 is much lower than that of heat ( Figure 2A), it has become possible [5,10] to single out the O2 evolution and photothermal components in the sine and cosine channels of a lock-in amplifier at modulation frequencies generally lower than 200 Hz ( Figure 2B). The amplitude of O 2 evolution is calculated using the formula [5]:…”