IMPACT OF GASEOUS AIR-POLLUTION ON LEAF GROWTH OF HYBRID POPLAR

Production of woody biomass in poplars is closely linked to leaf area development. Air pollution may stimulate the premature senescence and loss of poplar leaves, but little work has focused on understanding how pollution alters leaf growth. This report describes two experiments which address this question. When trees were grown in open-top chambers and exposed to ambient pollution, final leaf size was initially reduced compared with that achieved in filtered air. After approximately 8 weeks of exposure leaf growth rate and final leaf size were stimulated in ambient pollution compared with leaves in filtered air and this was associated with senescence and loss of older leaves. A biophysical analysis of leaf cell expansion revealed that the effective turgor for growth of young poplar leaves was large and declined with leaf age, reaching zero as the leaf stopped growing. Cell wall extensibility was also maximal in rapidly growing leaves and declined for older leaves. Exposure of poplars to 50 ppb O3 had no effect on leaf growth or the control of leaf cell expansion.