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Rates and durations of individual phases of wheat (Triticum aestivum L.) apical development are among the most important factors that determine yield components. Because atmospheric [CO.sub.2] has been increasing steadily, it is important to evaluate the effects of elevated [CO.sub.2] on wheat development. This study was conducted to determine rates and durations of leaf, spikelet, and floret primordium initiation in a Free-Air Carbon Dioxide Enrichment (FACE) system. Spring wheat (cv. Yecora Roja) was planted at the University of Arizona Maricopa Agricultural Center. The two [CO.sub.2] concentrations were 550 (elevated) and 370 (ambient) µmol [mol.sup.-1] [CO.sub.2]. Individual plant samples were collected every 3 to 4 d. We dissected the main stem (MS), coleoptile tiller (T0), primary tillers (T1, T2, and T3) and secondary tillers (T00, T01, T02, T10, T11, and T12) and counted primordia. Apex primordium data were fitted to a four-piece linear-spline segmented regression model with the SAS proc NLIN. No influence of elevated [CO.sub.2] (550 µmol [mol.sup.-1]) on leaf primordium initiation of MS was detected. Nevertheless, [CO.sub.2] enrichment significantly increased rates of spikelet primordimn initiation of MS, T1, T2, T10, and T11, and diminished the durations of spikelet development phase of MS, T1, T2, T3, T10, and T11. Within the floret phase, [CO.sub.2] enrichment significantly increased rates of floret primordium initiation of MS, T0, T1, T2, and T3, and diminished the time to the completion of floret primordium initiation of MS, T0, T1, T3, and T11. The information from this study will be utilized to predict wheat apical development and grain production in the elevated atmospheric [CO.sub.2] environments of the future., Wheat apical development consists of three distinct phases: leaf primordium, spikelet primordium, and floret primordium initiation. The transition from initiation of leaf to spikelet, and hence to floret primordia is [...]

Abstract: Atmospheric CO2 concentration (C a) is rising, predicted to cause global warming, and alter precipitation patterns. During 1994, spring barley (Hordeum vulgare L. cv. Alexis) was grown in a strip-split-plot experimental design to determine the effects that the main plot C a treatments [A: Ambient at 370μmol (CO2) mol−1; E: Enriched with free-air CO2 enrichment (FACE) at ∼550μmol (CO2) mol−1] had on several gas exchange properties of fully expanded sunlit primary leaves. The interacting strip-split-plot irrigation treatments were Dry or Wet [50% (D) or 100% (W) replacement of potential evapotranspiration] at ample nitrogen (261kg N ha−1) and phosphorous (29kg P ha−1) fertility. Elevated C a facilitated drought avoidance by reducing stomatal conductance (g s) by 34% that conserved water and enabled stomata to remain open for a longer period into a drought. This resulted in a 28% reduction in drought-induced midafternoon depression in net assimilation rate (A). Elevated C a increased A by 37% under Dry and 23% under Wet. Any reduction in A under Wet conditions occurred because of nonstomatal limitations, whereas under Dry it occurred because of stomatal limitations. Elevated C a increased the diurnal integral of A (A′) that resulted in an increase in the seasonal-long integral of A′ (A″) for barley leaves by 12% (P =0.14) under both Dry and Wet – 650, 730, 905 and 1020±65g (C) m−2 y−1 for AD, ED, AW and EW treatments, respectively. Elevated C a increased season-long average dry weight (DWS; crown, shoots) by 14% (P =0.02), whereas deficit irrigation reduced DWS by 7% (P =0.06), although these values may have been affected by a short but severe pea aphid [Acyrthosiphon pisum (Harris)] infestation. Hence, an elevated-C a-based improvement in gas exchange properties enhanced growth of a barley crop. [Copyright &y& Elsevier]

Absenteeism and its related costs are increasing, yet the causes and consequences are poorly understood. Theories about absenteeism have stemmed primarily from research conducted on blue- collar and clerical workers in the private sector. Very little is known about the absenteeism of public sector managers and professional employees. This study reports research on 644 managers and pro fessionals of a large western U.S. city. Actual sick-time usage was matched against personal, job and attitudinal characteristics of each employee to explore statistical relationships. There are rela tionships between sick-time use and age, sex, race, education, marital status, time with the city and job level of employees. The only hypothesized variables with no relationship were the distance an employee must travel to work and number of children. Furthermore, employees generally felt that rewards work better than penalties. These data may aid managers in establishing policies for coping with this phenomenon. [ABSTRACT FROM PUBLISHER]

A free-air CO2 enrichment (FACE) experiment was conducted at Maricopa, Arizona, on wheat from December 1992 through May 1993. The FACE apparatus maintained the CO2 concentration, [CO2], at 550 µmol mol-1 across four replicate 25-m-diameter circular plots under natural conditions in an open field. Four matching Control plots at ambient [CO2] (about 370 micro;mol mol-1) were also installed in the field. In addition to the two levels of [CO2], there were ample (Wet) and limiting (Dry) levels of water supplied through a subsurface drip irrigation system in a strip, split-plot design. Measurements were made of net radiation, Rn; soil heat flux, G0; soil temperature; foliage or surface temperature; air dry and wet bulb temperatures; and wind speed. Sensible heat flux, H, was calculated from the wind and temperature measurements. Latent heat flux, γET, and evapotranspiration, ET, were determined as the residual in the energy balance. The FACE treatment reduced daily total Rn by an average 4%. Daily FACE sensible heat flux, H, was higher in the FACE plots. Daily latent heat flux, γET, and evapotranspiration, ET, were consistently lower in the FACE plots than in the Control plots for most of the growing season, about 8% on the average. Net canopy photosynthesis was stimulated by an average 19 and 44% in the Wet and Dry plots, respectively, by elevated [CO2] for most of the growing season. No significant acclimation or down regulation was observed. There was little above-ground growth response to elevated [CO2] early in the season when temperatures were cool. Then, as temperatures warmed into spring, the FACE plants grew about 20% more than the Control plants at ambient [CO2], as shown by above-ground biomass accumulation. Root biomass accumulation was also stimulated about 20%. In May the FACE plants matured and senesced about a week earlier than the Controls in the Wet plots. The FACE plants averaged 0.6°C warmer than the Controls from February through April in the well-watered plots, and we speculate that this temperature rise contributed to the earlier maturity. Because of the acceleration of senescence, there was a shortening of the duration of grain filling, and consequently, there was a narrowing of the final biomass and yield differences. The 20% mid-season growth advantage of FACE shrunk to about an 8% yield advantage in the Wet plots, while the yield differences between FACE and Control remained at about 20% in the Dry plots. [ABSTRACT FROM AUTHOR]