Photosynthesis and needle elongation response of Pinusstrobus clones to low level sulfur dioxide exposures

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Abstract
Sensitive and tolerant eastern white pine (P. strobus L.) clones were exposed to 5.0 .+-. 0.5 pphm SO2 for 2 h. At the end of the fumigation, the average apparent photosynthetic rate was depressed by 27% in sensitive clones and by 10% in tolerant clones. Regression analysis of rate of reduction in photosynthesis over the 2 h was significant (0.05 level) for both classes, as was the difference (0.01 level) between the levels of the 2 regressions. Differences in final needle lengths of fumigated tolerant and sensitive clones were not significant.