Tropospheric ozone (O3) is a federally regulated air pollutant long-known to be a phytotoxic source of oxidative stress in plants. Effects of O3 on individual plants range from oxidative injury and reduction of photosynthesis to loss of stomatal control to reductions in growth. These effects cascade up to alter populations, communities, and ecosystems. And yet, a comprehensive list of ozone sensitive plant species in the United States is lacking.
We asked: Which plant species in the United States (native and introduced) are O3 sensitive? For each species, at what O3 exposure levels do which effects appear? Are there rare or culturally important species that are O3 sensitive?
We started with a published global-scale literature database of peer-reviewed studies, published since 1980, that assessed the effects of controlled O3 exposure on plant species, including reductions in biomass, changes in gas exchange measures, visible foliar injury and decreased fecundity. Then, we added other published references that met these selection criteria. We determined species presence and native/introduced status in the United States using the USDA PLANTS database. Population status (rare, threatened, or endangered) was determined using the IUCN redlist. Cultural and economic importance were assessed using several sources including the USDA PLANTS database, the Native American Ethnobotany database, and several US Forest Service publications.
Results/Conclusions
Currently, our database consists of 710 vascular plant species (which represents 0.1% of vascular plants)evaluated in controlled experiments for O3 sensitivity and published in peer-reviewed studies. Of these, 259 species have populations native to the United States (determined by USDA), and 193 of these native species display some O3 sensitivity (growth reduction, foliar injury, yield reduction, or stomatal response). Another 310 species are introduced in the United States, with 258 of these exhibiting O3 sensitivity. Three of the sensitive native species are critically endangered: American ash, green ash, and giant sequoia. Seventeen ozone-sensitive native tree species are considered culturally significant by multiple sources; these include a number of dogwoods, willows, and oaks along with elderberry, sweetgum, speckled alder and cottonwood. This database addresses a critical shortage in the assessment of ecological effects of O3 in the United States and provides guidance for future work.