Impacts of Chronic SO₂, O₃, and SO₂+O₃ Exposures on Photosynthesis of Pinus strobus Clones¹

Abstract

Abstract Grafts of sensitive and tolerant eastern white pine ( Pinus strobus L.) clones were exposed to extended (week‐long) low levels (5 pphm) of sulfur dioxide (S 2 O), ozone (O 3 ), and their combination in order to observe effects on photosynthesis. Consistent but statistically non‐significant increases in photosynthesis over the week were noted in all tolerant clones and in all but one sensitive clone when fumigated with SO 2 or SO 2 +O 3 . Likewise, O 3 consistently depressed photosynthesis in both tolerant and sensitive clones. There were significant differences in response between tolerant and sensitive clones fumigated with O 3 , and in the response of tolerant clones fumigated with O 3 versus those in SO 2 +O 3 .