Plant responses to elevational gradients of O ₃ exposures in Virginia

Abstract

In Shenandoah National Park, 03 monitoring data were characterized and attempts were made to relate 03 concentration levels to visible foliar injury observed for five plant species surveyed. Foliar injury for three species increased with elevation. The 24-h monthly mean 03 concentrations tended to increase with elevation; however, the number of elevated hourly occurrences did not. Although the frequency of high hourly 03 concentrations did not consistently increase with elevation, 03 exposures in the park may have been high enough to provoke an effect that may have been enhanced by vegetation sensitivities that differed as a function of altitude.

Ozone inhibits guard cell K + channels implicated in stomatal opening

“…Because the generation of O 3 in photochemical smog depends on high solar irradiation (34), O 3 inhibition of stomatal opening could significantly retard stomatal reopening in the afternoon after this mid-day depression and consequently reduce crop yield. Third, the presence of nighttime O 3 has been documented in rural locations due to long distant transport from urban sources (34) and at high elevation sites, including sites of ecological importance such as Shenandoah National Park in Virginia (38,39). Although it has been reported that there can be an adverse impact on biomass accumulation when O 3 exposure of plants occurs exclusively in the dark (39,40), this impact was previously explained by the modest stomatal conductance that could be detected under darkness and the concomitant O 3 uptake that would be expected.…”

“…Third, the presence of nighttime O 3 has been documented in rural locations due to long distant transport from urban sources (34) and at high elevation sites, including sites of ecological importance such as Shenandoah National Park in Virginia (38,39). Although it has been reported that there can be an adverse impact on biomass accumulation when O 3 exposure of plants occurs exclusively in the dark (39,40), this impact was previously explained by the modest stomatal conductance that could be detected under darkness and the concomitant O 3 uptake that would be expected. Our results suggest that inability of closed stomata to open completely after a dark exposure could be of equal or greater importance in reducing plant productivity.…”

A 13-Week Comparison of Passive and Continuous Ozone Monitors at Forested Sites in North-Central Pennsylvania

“…However, symptoms of wilt in the upper and lower crowns of the black cherry during the mid-morning hours suggested extreme moisture stress occurred at this site for most of the dry summer months. 2,3,5,6 A slight but consistent overestimation of O 3 concentrations was evident with the Ogawa passive system in comparison with the TECO analyzers, but a 2-to 4-ppb difference is not considered to be biologically relevant. These results continue to add to our knowledge of the efficacy of passive samplers in determining O 3 exposures in remote forested and natural areas.…”

“…Rural sites tend to have higher long-term O 3 exposures as polluted air masses are transported downwind of urban/industrial centers and the photochemical generation system continues to develop with little scavenging of O 3 precursors. [2][3][4][5][6] The long-range transport of tropospheric O 3 air pollution into IMPLICATIONS A major benefit of this research has been the determination of the ambient season-long O 3 exposure concentrations at air quality monitoring stations at forested sites in central Pennsylvania using real-time and passive O 3 monitoring methodologies. The use of passive O 3 monitoring devices was tested under rigorous forest conditions, and results were found to be verifiable using real-time O 3 monitors with quality assurance of the methods.…”

“…7,13 Within regional areas, topography has been demonstrated to play a significant role in determining O 3 exposures, with higher O 3 exposures occurring at higher elevation sites. 3,6,[14][15][16][17] As we continue to have iterative discussions regarding the need for developing a longer-term and perhaps cumulative secondary O 3 standard, there is an oftenrepeated statement of the need to better characterize ambient O 3 exposures occurring at more remote and natural forested settings. 18,19 The use of real-time O 3 monitors at such remote areas is often cost-prohibitive due to the inaccessibility of such sites for frequent visits, power supply, and security requirements.…”