Foliar response of black cherry (Prunus serotina) clones to ambient ozone exposure in central Pennsylvania

During late summer of 1996 and 1997 we examined ozone-induced foliar injury in a plantation of 111 black cherry trees (ramets) comprising 15 clones or iginating from wild ortets growing in the Allegheny National Forest, Pennsy lvania, and the Monongahela National Forest, West Virginia. The experimenta l plantation was a clonal seed orchard in Centre County, Pennsylvania, star ted in 1971 using ortet buds grafted onto seedling rootstocks of mixed orig in. Clones differed significantly in severity of foliar injury symptoms (F= 31.83, p < 0.001). One clone (R-12) had significantly more foliar injury wi th > 50% leaf area affected than other clones during both years. In contras t, clone R-14, which is from the same area in northcentral Pennsylvania as R-12, exhibited significantly less injury (LAA < 6%). Although ambient O-3 concentrations were similar in both years, foliar injury was significantly greater (15.7%) in 1996 than in 1997 (9.9%). This is probably explained by lower stomatal conductance in 1997 caused by drier and hotter weather patte rns in June and July of that year. Despite very different weather patterns and overall levels of injury in 1996 and 1997, mean clonal injury was signi ficantly correlated between both years of assessment (r = 0.92, p < 0.001). Within tree crowns, foliage in lower and inner crown positions was signifi cantly more injured than foliage in upper and exterior crown positions. The re was no evidence of geographically based population differences in sensit ivity to foliar O-3 injury. On the contrary, results demonstrate that wild genotypes of proximal geographic origin may differ greatly in sensitivity. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.