Variation in Photosynthesis and Stomatal Conductance in an Ozone-Stressed Ponderosa Pine Stand: Light Response
Abstract:The seasonal course (May to October 1977) of gross photosynthesis (from 14CO2 uptake and stomatal conductance) in a stand of ponderosa pine (Pinus ponderosa Laws.) in the San Bernardino National Forest was characterized as a function of light. Nine sapling trees, classified for comparative studies into three chronic injury classes (slight, moderate, severe) had experienced oxidant fumigations from California's South Coast Air Basin for approximately 18 years, since their establishment following fire. The CO2-transfer pathway was partitioned into its stomatal and residual (mesophyll, carboxylation, excitation) resistance components, for conditions of light saturation and 20°C. Light-saturated gross photosynthetic rates and photochemical conversion efficiencies were highest in the current-year needles and decreased with increasing needle age and oxidant injury. Maximum stomatal conductance and stomatal sensitivity to increasing light during stomatal opening followed a trend similar to that of photosynthesis, except for current-year needles, where conductance parameters were highest in the severely injured trees. This higher conductance may contribute to observed differential ozone sensitivity in ponderosa pine. Premature senesence and abscission of the 1-year (severely injured trees) and 2-year (slight to moderate injury) needles occurred at about the time CO2 uptake dropped to 10 percent of the potential for current needles of slightly injured trees without foliar injury symptoms. The ratio of the stomatal CO2 resistance to the total CO2 resistance decreased with increasing oxidant injury and needle age, suggesting that loss of photosynthetic capacity was primarily related to the loss of chloroplast function rather than to increased resistance of CO2 diffusion through the stomata. Forest Sci. 28:257-273.
Document Type: Journal Article
Affiliations: Environmental Scientist, University of California, Lawrence Livermore Laboratory, Livermore, CA 94550
Publication date: 1982-06-01
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- Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
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