THE RESPONSE OF BLACK CHERRY AND HYBRID POPLAR TO OZONE UNDER VARYING ENVIRONMETAL CONDITIONS

Open Access
- Author:
- Orendovici, Teodora
- Graduate Program:
- Ecology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 27, 2005
- Committee Members:
- Donald Durwood Davis, Committee Chair/Co-Chair
John Moore Skelly, Committee Chair/Co-Chair
Dennis R Decoteau, Committee Member
Dennis Lamb, Committee Member
Stephen Rathbun, Committee Member - Keywords:
- ozone
passive samplers
stomatal conductance
ozone uptake/flux
ozne induced injury - Abstract:
- Ozone concentrations were monitored from the end of May to the beginning of September for 3 consecutive years (2002-2004) in remote, forested areas of north-central Pennsylvania using Ogawa Passive ozone monitors. Ambient ozone concentrations were measured on a weekly basis at 20 monitoring sites to explore spatial and temporal patterns of ozone distribution. Passive samplers were sited at low-to-high elevations with three high-elevation sites being co-located with real-time ozone analyzers; resulting data were used for cross-correlation and for synthetically generating hourly frequency distributions of ambient ozone. The efficiency of passive samplers was highly dependent upon climatic factors; i.e. temperature, wind speed and relative humidity. Ambient ozone concentrations were greater in years with greater temperatures and lower relative humidity. During all three monitoring seasons, ambient ozone levels were positively correlated to elevation. Ozone concentrations were greater in 2002 and moderate to low in 2003 and 2004. In addition, spatial models of ozone distribution revealed that the central part of north-central Pennsylvania exhibits lower ozone concentrations than the surrounding areas. A linear model was developed to estimate the influence of local environmental conditions on stomatal conductance of two ozone sensitive tree species. One year-old seedlings of black cherry (R-12) (Prunus serotina) and ramets of hybrid poplar clone NE388 (Populus maximiwizii x trichocarpa) were established in the early spring of the 2003 within open plots at the 20 ozone monitoring locations. Gas exchange measurements were performed at 12 sites (6 sites at high elevation and 6 sites at low elevation), under field conditions, on seedlings and cuttings of the two tree species. The measurements were performed three times a day, under favorable weather conditions (clear sky) during 2003 and 2004 study seasons. Gas exchange data from the 12 sites were used to empirically model stomatal conductance and to model and map ozone flux for the two tree species throughout the study area. Throughout both seasons variances were observed in measured stomatal conductance (gs) and photosynthetic rates (Pn) on a daily basis. The most significant environmental factors explaining stomatal variance were: tree species, air temperature, elevation, and measurement time. The most significant factors in limiting gs were vapor pressure deficit (Vpdl) and air temperature. Stomatal conductance rates were higher for hybrid poplar than for black cherry during both years. Stomatal conductance rates were greater at noon and in the early afternoon at high-elevated sites during 2003. During 2004 gs rates were higher at low-elevation sites. Photosynthetic rates were greater at high-elevation sites in the morning and at noon during both study seasons. Apparently greater air temperature at the low-elevation sites inhibited gs in 2003, reducing ozone uptake. Also lower than normal air temperatures at the high elevation sites might have inhibited gs rates in 2004. Since environmental factors explained less than 30% of the variation in stomatal conductance Vpdl and Pn were used to increase the accuracy of the gs model. The influences of ozone on foliar symptoms and relative growth parameters of the two ozone-sensitive species were also investigated. One main objective was to determine whether foliar injury expressed by genetically stable ozone-sensitive plants can provide quantitative information about ozone exposures. Visible ozone-induced foliar injury was assessed weekly. Above-ground relative growth was measured at the end of the experiment as relative height (H) and basal diameter (D). During both years of investigation ambient ozone and environmental conditions were conducive to development of typical ozone-induced visible symptoms on both tree species. Percentage of total leaf area affected (expressed as percent injury %INJ) was positively correlated with cumulative ozone exposures. Foliar injury was better correlated with a flux-based approach than for an exposure-based approach. The best correlations in terms of exposure-based approach were obtained when the SUM40 (ozone over the threshold of 40 ppb) ozone exposure index was used. More severe foliar injuries were observed on plants growing on plots located at higher elevation sites. The onset of foliar injury for both tree species was first observed at sites located at higher elevation during both years. The year-to year inconsistent plant response to ozone exposures was likely due to the strong influence of environmental factors and possible to the plant defense mechanisms. We found that more study is required before making quantitative estimations of ozone exposures based on plant foliar injury.