ISHS Acta Horticulturae 817: I International Symposium on Horticulture in Europe
IMPACTS OF TROPOSPHERIC OZONE ON GROWTH AND PHOTOSYNTHESIS OF LETTUCE |
| Authors: | Eleni Goumenaki, Jeremy Barnes |
| Keywords: | CO2 assimilation, productivity, stomatal conductance, foliar injury, carbon allocation |
| Abstract:
Ozone is a common gaseous pollutant in many regions of the world, and ambient hourly mean concentrations commonly reach, or exceed, the recognized threshold for crop damage in the most sensitive plants (40 nmol mol-1) during the spring and summer in many parts of Central and Southern Europe. Areas suffering the highest ozone concentrations tend to be remote from major sources of emissions, so the pollutant most frequently attains phytotoxic levels in rural, pristine and peri-urban situations. Lettuce (Lactuca sativa L.) is a crop seen as ‘sensitive’ to ozone and is of particular economic significance in Southern Europe. In this study, Lactuca sativa L. cvs. ‘Paris Island’ and ‘Grenada’ were exposed in controlled environment chambers to either charcoal/Purafil®-filtered air (CFA) or CFA plus environmentally-relevant levels of ozone. ‘Sensitivity’ to ozone was gauged in terms of visible foliar injury and effects on relative growth rate, biomass accumulation, stomatal conductance and capacity for carbon dioxide assimilation. Cultivar ‘Paris Island’ developed chlorotic mottling and small necrotic lesions after two weeks’ exposure to ozone. It showed a reduced rate of growth within 24 days of exposure to 100 nmol mol-1 ozone, whilst effects on growth and biomass accumulation were not statistically significant in cv. ‘Grenada’ until plants had been exposed for 40 days. Both genotypes appeared ‘sensitive’ to ozone; exposure resulting in a 25% depression in shoot weight (i.e., productivity of the crop). Leaf gas exchange appeared particularly sensitive to ozone, exposure to both 75 and 100 nmol mol-1 resulting in partial stomatal closure over the course of the diel cycle in both genotypes and a significant decline in net carbon dioxide assimilation rate measured under ‘growth conditions’. | |
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