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Structural injury underlying mottling in ponderosa pine needles exposed to ambient ozone concentrations in the San Bernardino Mountains near Los Angeles, CaliforniaAuthor(s): Pierre Vollenweider; Mark E. Fenn; Terry Menard; Madeleine Gunthardt-Goerg; Andrzej Bytnerowicz
Source: Trees 27:895-911
Publication Series: Scientific Journal (JRNL)
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DescriptionFor several decades, southern California experienced the worst ozone pollution ever reported. Peak ozone concentrations have, however, declined steadily since 1980. In this study, the structural injuries underlying ozone symptoms in needles of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) collected in summer 2006 from one of the most polluted sites in the San Bernardino Mountains were investigated using serial sections examined by light and electron microscopy. Ozone-specific light-green diffuse mottling was observed in the currentyear needles, whereas older foliage showed brownish mottling similar to winter fleck injury. Especially, within the outer layers of mesophyll, many markers of oxidative stress, typical for ozone, were observed in both apoplast and symplast. Altogether within cells of mottles, these markers were indicative of hypersensitive-like response, whereas degenerative structural changes were diagnosed in the surrounding mesophyll. Evidence of drought stress and frost injury to older needles was also detected. Hence, mottling injury appeared to be primarily caused by ozone stress, however, other environmental stressors also determined the symptom morphology and distribution, especially within the older foliage.
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CitationVollenweider, Pierre; Fenn, Mark E.; Menard, Terry; Gunthardt-Goerg, Madeleine; Bytnerowicz , Andrzej. 2013. Structural injury underlying mottling in ponderosa pine needles exposed to ambient ozone concentrations in the San Bernardino Mountains near Los Angeles, California. Trees 27:895-911. Published online Feb. 9, 2013; DOI 10.1007/s00468-013-0843-7.Springer-Verlag Berlin Heidelberg
KeywordsPonderosa pine, Los Angeles basin, Ozone visible injury, Microscopic diagnosis, Needle histochemistry, Mesophyll ultrastructure
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