Search

The Intergovernmental Panel of Climate Change (IPCC) has concluded that the greenhouse gases carbon dioxide (CO2) and tropospheric ozone (O3) are increasing concomitantly globally. Little is known about the effect of these interacting gases on growth, survival, and productivity of forest ecosystems. In this study we assess the effects of three successive years of exposure to combinations of elevated CO2 and O3 on growth responses in afive trembling aspen (Populus tremuloides) clonal mixture in a regenerating stand. The experiment is located in Rhinelander, Wisconsin, USA (45 deg. N 89 deg. W) and employs free air carbon dioxide and ozone enrichment (FACE) technology. The aspen stand was exposed to a factorial combination of four treatments consisting of elevated CO2 (560 ppm), elevated O3 (episodic exposure-90 Mu1 1-1 hour-1), a combination of elevated CO2 and O3, and ambient control in 30 m treatment rings with three replications. Our overall results showed that our three growth parameters including height, diameter and volume were increased byelevated CO2, decreased by elevated O3, and were not significantly different from the ambient control under elevated CO2+O3. However, there were significant clonal differences in the responses; all five clones exhibited increased growth with elevated CO2, one clone showed an increase withelevated O3, and two clones showed an increase over the control with elevated CO2+O3, two clones showed a decrease, and one was not significantly different from the control.Notably, there was a significant increase in current terminal shoot dieback with elevated CO2 during the 1999/2000 dormant season. Dieback was especially prominent in two of the five clones, and was attributed to those clones growing longer into the autumnal season wh [ABSTRACT FROM AUTHOR]

To determine whether elevated CO2 reduces or exacerbates the detrimental effects of O3 on aspen (Populus tremuloides Michx.), aspen clones 216 and 271 (O3 tolerant), and 259(O3 sensitive) were exposed to ambient levels of CO2 and O3 or elevated levels of CO2, O3, or CO2+O3 in the FACTS II (Aspen FACE)experiment, and physiological and molecular responses were measured and compared. Clone 259, the most O3-sensitive clone, showed the greatest amount of visible foliar symptoms as well as significant decreases in chlorophyll, carotenoid, starch, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) concentrations and transcription levels for the Rubisco small subunit. Generally, the constitutive (basic) transcript levels for phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) and the average antioxidant activities were lower for the ozone sensitive clone 259 as compared to the more tolerant 216 and 271 clones. A significant decrease in chlorophyll a, band total (a+b) concentrations in CO2, O3, andCO2+O3 plants was observed for all clones. Carotenoid concentrations were also significantly lower in all clones; however, CHS transcript levels were not significantly affected, suggesting a possible degradation of carotenoid pigments in O3-stressed plants. Antioxidant activities and PAL and 1-aminocyclopropane-1-carboxylic acid (ACC)-oxidase transcript levels showed a general increase in all O3 treated clones, while remaining low in CO2 and CO2+O3 plants (although not all differences were significant). Our results suggest that the ascorbate-glutathione and phenylpropanoid pathways were activated under ozone stress and suppressed during exposure to elevated CO2.Although CO2+O3 treatment resulted in a slightreduc [ABSTRACT FROM AUTHOR]

We compared the value of using a digital signal processing unit for gamma-ray spectroscopy with that of an analog one for in situ measurements of gamma-rays generated by inelastic neutron scattering reactions with soil elements. A large cylindrical NaI(Tl) scintillation detector, 15.24 cm high by 15.24 cm diameter was used to measure carbon (C) and oxygen (O). The performance of the systems was assessed as a function of input count rate (ICR) by monitoring the peak areas of the C, 4.43 MeV, and O, 6.13 MeV, gamma-rays. In separate experiments, the digital and the analog systems were also compared using an intense 10.3 mCi 137Cs source to vary the ICR, and the 1.17 MeV peak area of 60Co was used as the reference. [Copyright &y& Elsevier]