Variation in the physiological processes of eastern white pine (Pinus strobus L.) differing in sensitivity to ozone, sulfur dioxide, and nitrogen dioxide

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Virginia Polytechnic Institute and State University


Ten clones of eastern white pine (Pinus strobus L.) representing three different pollutant sensitivity classes (i.e. sensitive, intermediate, and tolerant) were exposed to ozone, sulfur dioxide, and nitrogen dioxide singly, and in. combinations at various concentrations. Visible symptom expression, needle length, and needle dry weight of current year needles were determined weekly during long-term pollutant exposures. One clone of each sensitive class was selected to study the effects of long-term exposures with ozone, sulfur dioxide, or nitrogen dioxide on photosynthesis, transpiration, and dark respiration.

Genetically controlled plant responses to pollutant exposures were found in all clones with various degrees of repeatability. A general plant sensitivity to all of the pollutants was not observed in test clones. Foliar symptom expression was only categorically differentiated among sensitivity classes but was not distinguishable in clonal response within the same class. At the end of long-term exposures, needle length was not significantly different among pollutant treatments. Good agreement was found among white pine gas exchange rates, needle dry weight, and chlorophyll content with respect to clonal sensitivity. Sensitive clone exhibited the greatest reduction in net photosynthesis due to ozone and sulfur dioxide exposures followed by intermediate and tolerant clones. Early stimulation of dark respiration was induced by ozone and sulfur dioxide exposures in sensitive clone followed by a dramatic: decrease at late stages of long-term experiment. Nitrogen dioxide at test concentrations did not.significantly reduce net photosynthesis, transpiration, and dark respiration rates. There was a correlation between clonal needle dry weight, chlorophyll content, and degree of its pollutant injury. Different modes of injury actions by different pollutants are proposed based upon presented data.

Results support the concept that the ranking of plant sensitivity to pollutants could be varied with plant response chosen as indexing criterion. Presented data suggest that the adverse effects of pollutant exposures on white pine growth are primary due to inhibition of net photosynthesis, less chlorophyll content, and high respiration rate. Visible injury and needle length are concluded to be less superior than net photosynthesis, transpiration, dark respiration, chlorophyll content, and. needle dry weight measurement in providing reliable indexing. parameter for white pine pollution sensitivity prediction.