Air pollution injury to coastal sage scrub in the Santa Monica Mountains, Southern California
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A field survey observed 26 types of foliar damage symptoms on seven species of coastal sage scrub in the Santa Monica Mountains National Recreation Area near Los Angeles, California. Of these, 6 symptoms were likely related to herbivory. Forty percent of visual injury symptoms in the field matched symptoms observed on these species exposed for 10 weeks to controlled fumigation with 0.1, 0.2 and 0.4 ppm of O3 and 0.05, 0.2 and 0.5 PPM of SO2 or combinations of these. Based on a comparison of field and chamber symptoms, it appeared that both 03 and SO2 were responsible for field injury symptoms, with 03 being the more frequent cause. Symptoms also appeared to be produced at lower concentrations in the field than in chambers. Using the foliar damage symptom present in greatest intensity on a 3-point scale, species were generally found to exhibit increased intensity of this symptom on sites estimated to experience higher levels of 03, SO2 and NO2. Pollution levels at sites were estimated from seven surrounding air quality monitoring stations. One- or two-month-old leaves exhibit sufficient intensity of symptom damage that not all observed injury can be attributed to senescence. Brachyblast leaves of Salvia mellifera exhibited more severe damage symptoms than dolichoblasts, confirming fumigation chamber results; for three other seasonally dimorphic species, brachyblasts were not more sensitive. Fasciated stems were found both in fumigation chambers and in the field on Artemisia californica, Lotus scoparius and Eriogonum fasciculatum, but sample sizes were not sufficient to distinguish among alternative potential causes of this phenomenon.
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