Abstract
Tropospheric ozone is a worldwide phenomenon causing injuries to forest trees. Californian ponderosa and Jeffrey pines are well known for their sensitivity to ozone, while other pine species have varied in their susceptibility. Sensitive pine species are known for their chlorotic mottle and tip burn symptoms, caused by ozone air pollution. Epistomatal wax plugs and filamentous waxes around stomata are typical for pine needle surfaces. In this study, we investigated epistomatal and epicuticular needle waxes in eight species of field-grown pines in 1985, 1986 and 2006. The epistomatal wax plugs were present in asymptomatic needles without chlorotic mottle (23% of needles). A lack of wax plugs in needles with chlorotic mottle and tip burn symptoms was common (76% of needles). More abundant existence of mottling associated with stomata without wax plugs in two-year-old needles, compared with one-year-old needles (43% and 33%, respectively), indicated chronic injury development over time.
Highlights
Ozone (O3) injuries in montane coniferous forests in California have been recorded since the1950’s [1] [2]
Experimental results during different seasons revealed O3 sensitivity to vary with exposure time, with the order of species sensitivity being: P. ponderosa, P. jeffreyi, P. coulteri, P. lambertiana
We studied epistomatal wax plugs and injury of epicuticular waxes of needles in several California pine species in situ
Summary
Ozone (O3) injuries in montane coniferous forests in California have been recorded since the1950’s [1] [2]. Diagnostic injuries of oxidant and winter fleck on Western pine needles were first recognized in the 1970’s [3]. The most O3 sensitive Western pines are P. coulteri D. Don (Coulter pine), P. jeffreyi Balf (Jeffrey pine), P. lambertiana Douglas (sugar pine), and P. ponderosa (ponderosa pine) [4]. Experimental results during different seasons revealed O3 sensitivity to vary with exposure time, with the order of species sensitivity being: P. ponderosa, P. jeffreyi, P. coulteri, P. lambertiana. Ozone injuries of the most sensitive pine species were associated with epidermal and hypodermal thickness, while in more tolerant species the injuries were found especially in substomatal mesophyll cells [5]-[7]
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