A custom oxygen analyzer in conjunction with an infrared carbon dioxide analyzer and humidity sensors permitted simultaneous measurements of oxygen, carbon dioxide, and water vapor fluxes from the shoots of intact barley plants (Hordeum vulgare L. cv Steptoe). The oxygen analyzer is based on a calciazirconium sensor and can resolve concentration differences to within 2 microliters per liter against the normal background of 210,000 microliters per liter. In wild-type plants receiving ammonium as their sole nitrogen source or in nitrate reductase-deficient mutants, photosynthetic and respiratory fluxes of oxygen equaled those of carbon dioxide. By contrast, wild-type plants exposed to nitrate had unequal oxygen and carbon dioxide fluxes: oxygen evolution at high light exceeded carbon dioxide consumption by 26% and carbon dioxide evolution in the dark exceeded oxygen consumption by 25%. These results indicate that a substantial portion of photosynthetic electron transport or respiration generates reductant for nitrate assimilation rather than for carbon fixation or mitochondrial electron transport.The influence of NO3-assimilation upon photosynthesis and respiration has been the subject of much speculation (9,17,20,25). To provide energy for NO3-assimilation, a portion of the electrons that are usually transferred to CO2 during photosynthesis or to 02 during respiration may be instead transferred to 19 (8, 26). Plant material is exposed to an atmosphere highly enriched with the heavy isotope 180. Changes in the levels of 160 and 180 indicate rates of oxygen production and uptake, respectively. These systems cannot monitor water fluxes and, therefore, cannot estimate intercellular CO2 concentrations. (c) Paramagnetic analyzers can resolve small 02 concentration differences (1 1), but demonstrate a high sensitivity to gas flow rate and vibration ( 16). (d) The signal drift and noise of polarographic 02 sensors require that relatively large (_300 ML L-') 02 depletions be obtained (13,14). (e) Commercial instruments based on ceramic electrolytic cells have had adequate sensitivity and stability only at very low ambient 02 concentrations (_2000 AL L-') (4,15

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The roots of barley plants (Hordeum vulgare L. cv Steptoe) were monitored before and after excision for net uptake of carbon dioxide, oxygen, ammonium, potassium, nitrate, and chloride and for their content of sucrose, glucose, fructose, and malic acid. All fluxes began to attenuate within 2 hours after excision. Net potassium uptake returned to control levels 6 hours after excision, but carbon dioxide, oxygen, ammonium, and nitrate fluxes continued to diminish for the remainder of the observation period. The addition of 0.1 molar glucose or 0.1 molar sucrose to excision medium had no significant effect on these changes in ion and gas fluxes. Net chloride uptake was negligible for all treatments. Sugar and malic acid content of the root declined after excision. Sucrose and glucose levels remained depressed for the entire observation period, whereas fructose and malic acid returned to control levels after 9 hours. These results indicate that excision has profound, adverse effects on root respiration and the absorption of mineral nitrogen.Although excision ofplant tissue often produces severe changes in metabolic processes (23), many studies of nutrient absorption have been based on data obtained from excised roots. Use of excised roots wasjustified in some cases. For example, differences in 86Rb+ influx between excised and intact barley or corn roots became insignificant after 2 to 4 h of washing (11,12,15). Calcium and phosphate absorption also was relatively unaffected by excision (7, 13). In contrast, excised barley roots absorbed less NO3 (1) and excised barley and corn roots developed smaller pH gradients (9, 12) than intact roots. These results suggest that the effects of excision may be ion specific.Our research has compared absorption of NH4' and N03 (2, 3, 5) and determined the influence of different nutrient solutions upon respiration (4) Ion and Gas Fluxes. About 2 weeks after germination, when the third leaf had just emerged and the roots were over 15 cm in length, a plant was transferred to a measurement system. Teflon tape was wrapped around the root about 1 cm below the endosperm. A slotted rubber stopper was placed around the wrapped section of root, and the remaining 12-cm portion of root was placed into a Plexiglas/stainless steel cuvette (3). On top of the cuvette, a bath 3 cm deep was fabricated from putty and filled with nutrient solution or nutrient solution plus 0.1 M sucrose or 0.1 M glucose; the upper 1 cm of root sat in this bath, and the shoot was held erect above it. To permit recovery from any transplant shock, this plant was kept for at least 8 h in the dark and 3 h in the light at 500 ,umol m-2s-' PAR before experimental data were taken. The temperature of the root cuvette was 20Cand that of the shoot was 25°C.Ion-selective electrodes simultaneously and continuously monitored depletion or addition of CO2, NH4', K+, and NO3-, and a miniature polarographic electrode monitored depletion of 02 from a nutrient solution flowing through the root cuvette (3,4). This solution initia...

Different approaches are necessary when Community Based Participatory Research (CBPR) of environmental illness is initiated after an environmental disaster within a community. Often such events are viewed as golden scientific opportunities to do epidemiological studies. However, we believe that in such circumstances, community engagement and empowerment needs to be integrated into the public health service efforts in order for both those and any science to be successful, with special care being taken to address the immediate health needs of the community first rather than the pressing needs to answer important scientific questions. We will demonstrate how we have simultaneously provided valuable public health service, embedded generalizable scientific knowledge, and built a successful foundation for supplemental CBPR through our on-going recovery work after the chlorine gas disaster in Graniteville, South Carolina.

Changes in botanical compositionand productivity of total herbage and 14 categories of annual range plants caused by elemental sulfur fertilization, range site, and precipitation were studied. Total herbage production on the wetter and more fertile swale sites was not affected by sulfur fertilization, but production on adjacent open upland and rocky, brushy upland sites usually increased with added S. Herbage production increased 28% or 1,400 kg/ ha on fertilized open upland sites and 51% or 1,800 kg/ ha on fertilized rocky, brushy uphnd sites during the wettest year sampled. Over the 3 years sampled, the most desirable grass, soft chess, averaged 68,22, and 66% higher production (438,287, and 388 kg/ha increases, respectively) on fertilized versus control range units for swale, open upland, and rocky, brushy upland range sites, respectively. Likewise, the less desirable but important earlyforage species, ripgut brome, increased 164% or 544 kg/ha on swales and 205% or 437 kg/ha on rocky, brushy uplands with fertilization; only a 16% increase or 98 kg/ha occurred on open upland sites. Grass responses were offset by decreased forb production, while the proportion of legumes remained nearly the same. Upland sites benefited from sulfur fertilization by exhibiting both increased clover and other legume production in the wettest year. Filaree was unaffected by sulfur fertilization.Sulfur is recognized as an important macro-nutrient on California's unimproved and improved annual-type rangeland. Martin (1958) noted a sulfur deficiency on sites in 34 of the 58 California counties representing 60 soil series. Conrad (1950) found that The authors are post-graduate researcher and associate professor, Department of Agronomy and Range Science, University of California, Davis 95616, and range scientist (retired), Pacific Southwest Forest and Range Experiment Station, Forestry Sciences Laboratory, Fresno, Calif. 93710. Data were collected by a number of scientists in the U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station, Fresno, Calif. Our data analysis and manuscript preparation were supported under Cooperative Aid Agreement PSW-69.