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The use of cryogenic techniques allows collection and storage of large numbers of samples for later processing for biochemical assays. In large field studies it is very difficult to obtain an accurate measure of leaf area as the samples are collected while preserving biological activity. Measurement of leaf area at the time of processing is also difficult because thawing of leaf tissue can cause degradation of leaf biochemical components and processes. The objective of this study was to design a liquid [N.sub.2]--chilled tray that allows cryogenically preserved samples to be sorted and measured without the risk of sample thawing. A stainless steel lid (working surface) was brazed to a stainless steel pan, creating a reservoir that could be filled with liquid [N.sub.2]. The working surface could then be maintained at approximately the temperature of liquid [N.sub.2]. Enzyme activities and polyacrylamide gel separations of ribulose-1,5-bisphosphate carboxylase (Rubisco) and phosphoenol pyruvate carboxylas (PEPCase) of sorghum [Sorghum bicolor (L.) Moench] were used to assess the performance of the tray. Enzyme activity assays and gel separations of Rubisco and PEPCase confirm that biological activity is maintained through use of the multipurpose cryogenic surface (MCS) tray., CRYOGENIC TECHNIQUES are commonly used to preserve leaf tissue for measurements of metabolic processes. To accurately assess treatment effects on biochemical processes, it is necessary to preserve tissues in their [...]

The development and application of cropping system simulation models for cotton production has a long and rich history, beginning in the southeastern U. S. in the 1960s and now expanded to major cotton production regions globally. This paper briefly reviews the history of cotton simulation models, examines applications of the models since the turn of the century, and identifies opportunities for improving models and their use in cotton research and decision support. Cotton models reviewed include those specific to cotton (GOSSYM, Cotton2K, COTCO2, OZCOT, and CROPGRO-Cotton) and generic crop models that have been applied to cotton production (EPIC, WOFOST, SUCROS, GRAMI, CropSyst, and AquaCrop). Model application areas included crop water use and irrigation water management, nitrogen dynamics and fertilizer management, genetics and crop improvement, climatology, global climate change, precision agriculture, model integration with sensor data, economics, and classroom instruction. Generally, the literature demonstrated increased emphasis on cotton model development in the previous century and on cotton model application in the current century. Although efforts to develop cotton models have a 40-year history, no comparisons among cotton models were reported. Such efforts would be advisable as an initial step to evaluate current cotton simulation strategies. Increasingly, cotton simulation models are being applied by nontraditional crop modelers, who are not trained agronomists but wish to use the models for broad economic or life-cycle analyses. Although this trend demonstrates the growing interest in the models and their potential utility for a variety of applications, it necessitates the development of models with appropriate complexity and ease-of-use for a given application, and improved documentation and teaching materials are needed to educate potential model users. Spatial scaling issues are also increasingly prominent, as models originally developed for use at the field scale are being implemented for regional simulations over large geographic areas. Research steadily progresses toward the advanced goal of model integration with variable-rate control systems, which use real-time crop status and environmental information to spatially and temporally optimize applications of crop inputs, while also considering potential environmental impacts, resource limitations, and climate forecasts. Overall, the review demonstrates a languished effort in cotton simulation model development, but the application of existing models in a variety of research areas remains strong and continues to grow. [ABSTRACT FROM AUTHOR]

Summary • The simulation model DEMETER was used here to investigate which mechanisms led to a larger CO2 effect on biomass production and yield of a spring wheat crop under drought compared with unlimited water supply. • Field data of the free-air CO2 enrichment (FACE) wheat experiments in Arizona (1993–94) were used to test the model. The influence of a particular mechanism leading to a higher CO2 effect under drought was investigated by eliminating the influence of the other causes on the simulation results on selected days during the growing seasons. • A larger CO2 effect under drought was caused in the model by the lower potential transpiration rate, higher root biomass and the nonlinear functional dependence of net assimilation rate on leaf internal CO2 concentration. The contribution of the different mechanisms changed in significance during the growing season depending on the degree of soil water limitation. The model successfully described the qualitative and quantitative behaviour of the crop under elevated CO2 . • A well-tested simulation model can be a useful tool in understanding the complex interactions underlying observed ecosystem responses to stress under elevated CO2 . [ABSTRACT FROM AUTHOR]

Summary • Stable-carbon isotopic tracers were enlisted in 1996 and 1997 wheat (Triticum aestivum ) free-air CO2 enrichment (FACE) experiments to detect entry of new C into soil organic carbon (SOC) pools. Any enhanced soil inputs might mitigate rising atmospheric CO2 . • The CO2 used to enrich FACE plots (to ambient +190 µmol mol-1 ) resulted in 13 C-depleted wheat relative to ambient plants and the native SOC. To trace new C in control plots C4 -plant-derived exotic soils were placed into subplots in high-N FACE and control treatments, and a 13 CO2 gas tracer was pulsed to subplots in high-N control replicates. • Under high-N, isotopic mass balance showed 6% (P = 0.003) and 5% (P = 0.04) new C in 0–15-cm and 15–30-cm FACE SOC, respectively, after 2 yr. Results from the C4 -soil subplots were ambiguous, but the 13 CO2 tracer induced a SOC δ13 C increase (P = 0.08) at 15–30 cm in control-high N consistent with 6% new C. • We infer c. 3% year-1 (30–40 g C m-2 yr-1 ) SOC turnover in surface soils at high-N under both ambient and elevated CO2 . The 13 CO2 -tracer result, however, is less reliable because of lower significance, fewer replicates and heterogeneous isotopic distribution within plants. [ABSTRACT FROM AUTHOR]

Summary • The likely consequences of future high levels of atmospheric CO2 concentration on wheat (Triticum aestivum L.) grain nutritional and baking quality were determined. • Two free-air CO2 enrichment (FACE; 550 mmol mol-1 ) experiments were conducted at ample (Wet) and limiting (Dry) levels of irrigation, and a further two experiments at ample (High-N) and limiting (Low-N) nitrogen concentrations. Harvested grain samples were subjected to a battery of nutritional and bread-making quality tests. • The Dry treatment improved grain quality slightly (protein +2%; bread loaf volume +3%). By contrast, Low-N decreased quality drastically (protein -36%; loaf volume -26%). At ample water and N, FACE decreased quality slightly (protein -5%; loaf volume -2%) in the irrigation experiments and there was no change in the nitrogen experiments. At Low-N, FACE tended to make the deleterious effects of Low-N worse (protein -33% and -39%, at ambient CO2 and FACE, respectively; loaf volume -22% and -29% at ambient CO2 and FACE, respectively). • The data suggest that future elevated CO2 concentrations will exacerbate the deleterious effects of low soil nitrogen on grain quality, but with ample nitrogen fertilizer, the effects will be minor. [ABSTRACT FROM AUTHOR]

Summary • Sorghum bicolor was exposed to free-air CO2 enrichment (FACE) and drought at the Maricopa Agricultural Center, AZ, USA, in summer 1998. We predicted that bundle sheath leakiness (Φ) would be insensitive to FACE under well-irrigated (wet) conditions, but would be lower in FACE compared with control-CO2 treatments when irrigation was withheld (dry). • Leaf and air δ13 C values and leaf p i /p a from gas exchange were measured to estimate carbon isotope discrimination (Δ) and F. Midday leaf water potential (Ψ) and photosynthetic rate were simultaneously measured to evaluate the influence of plant water status on Φ and the association between Φ and carbon gain. • Irrigation treatments affected Ψ, p i /p a , Δ and Φ in control CO2 and FACE rings. Differences in leaf Δ between wet- and dry-treatment plots resulted from changes in Φ and to stomatal influences on p i /p a . FACE had very little effect on Ψ, Δ and Φ in wet-treatment plots. However, Φ and Δ in dry plots were higher in control than in FACE rings. • FACE ameliorated the effects of drought on bundle sheath leakiness and Δ by reducing transpiration, prolonging soil water availability and enhancing plant water status. Direct effects of CO2 enrichment on C4 photosynthetic metabolism in Sorghum apparently are minimal and indirect effects depend on soil water supply. [ABSTRACT FROM AUTHOR]

Summary • Atmospheric CO2 concentration is expected to increase by 50% near the middle of this century. The effects the free air CO2 enrichment (FACE) is presented here on growth and development of field-grown grain sorghum (Sorghum bicolor ) at ample (wet) and limiting (dry) levels of irrigation water at Maricopa, AZ, USA. • Daytime CO2 mole fractions were 561 and 368 µmol mol-1 for the FACE and control treatments, respectively. Irrigation plus precipitation averaged 1132 mm for the wet plots and 396 mm in the dry plots. • During the growing season, FACE increased biomass accumulation in the dry plots but the effects in the wet plots were inconsistent. At final harvest, FACE increased total yield from 999 to 1151 g m-2 in the dry plots and had no effect in the wet plots. • If atmospheric CO2 continues to increase, total sorghum yield is likely to be higher in the future in areas where water is limited. [ABSTRACT FROM AUTHOR]

ABSTRACTThe mid-day responses of wheat ear CO2 and water vapour exchange to full-season CO2 enrichment were investigated using a Free-Air CO2 Enrichment (FACE) apparatus. Spring wheat [Triticum aestivum (L). cv. Yecora Rojo] was grown in two experiments under ambient and elevated atmospheric CO2 (Ca) concentrations (approximately 370 μmol mol-1 and 550 μmol mol-1, respectively) combined first with two irrigation (Irr) schemes (Wet: 100% and Dry: 50% replacement of evapotranspiration) and then with two levels of nitrogen (N) fertilization (High: 350, Low: 70 kg ha-1 N). Blowers were used for Ca enrichment. Ambient Ca plots were exposed to blower induced winds as well the Ca × N but not in the Ca × Irr experiment. The net photosynthesis for the ears was increased by 58% and stomatal conductance (gs) was decreased by 26% due to elevated Ca under ample water and N supply when blowers were applied to both Ca treatments. The use of blowers in the Ca-enriched plots only during the Ca × Irr experiment (blower effect) and Low N supply restricted the enhancement of net photosynthesis of the ear due to higher Ca. In the latter case, the increase of net photosynthesis of the ear amounted to 26%. The decrease in gs caused by higher Ca was not affected by the blower effect and N treatment. The mid-day enhancement of net photosynthesis due to elevated Ca was higher for ears than for flag leaves and this effect was most pronounced under ample water and N supply. The contribution of ears to grain filling is therefore likely to increase in higher Ca environments in the future. In the comparison between Wet and Dry, the higher Ca did not alter the response of net photosynthesis of the ear and gs to Irr. However, Ca enrichment increased the drought tolerance of net photosynthesis of the glume and delayed the increase of the awn portion of net photosynthesis of the ear during drought. Therefore, the role of awns for maintaining high net photosynthesis of the ear under drought may decrease when Ca increases. [ABSTRACT FROM AUTHOR]

AbstractSpring wheat [Triticum aestivum (L). cv. Yecora Rojo] was grown from December 1992 to May 1993 under two atmospheric CO2 concentrations, 550 μmol mol–1 for high-CO2 plots, and 370 μmol mol–1 for control plots, using a Free-Air CO2 Enrichment (FACE) apparatus. In addition to the two levels of atmospheric CO2, there were ample and limiting levels of water supply through a subsurface trip irrigation system in a strip, split-plot design. In order to examine the temporal and spatial root distribution, root cores were extracted at six growth stages during the season at in-row and inter-row positions using a soil core device (86 mm ID, 1.0 m length). Such information would help determine whether and to what extent root morphology is changed by alteration of two important factors, atmospheric CO2 and soil water, in this agricultural ecosystem. Wheat root growth increased under elevated CO2 conditions during all observed developmental stages. A maximum of 37% increase in total root dry mass in the FACE vs. Control plots was observed during the period of stem elongation. Greater root growth rates were calculated due to CO2 enhancement until anthesis. During the early vegetative growth, root dry mass of the inter-row space was significantly higher for FACE than for Control treatments suggesting that elevated CO2 promoted the production of first-order lateral roots per main axis. Then, during the reproductive period of growth, more branching of lateral roots in the FACE treatment occurred due to water stress. Significant higher root dry mass was measured in the inter-row space of the FACE plots where soil water supply was limiting. These sequential responses in root growth and morphology to elevated CO2 and reduced soil water supports the hypothesis that plants grown in a high-CO2 environment may better compensate soil-water-stress conditions. [ABSTRACT FROM AUTHOR]

In order to determine the likely effects of the increasing atmospheric CO2 concentration on future evapotranspiration, ET, plots of field-grown wheat were exposed to concentrations of 550 µmol/mol CO2 (or 200 µmol/mol above current ambient levels of about 360 µmol/mol) using a free-air CO2 enrichment (FACE) facility. Data were collected for four growing seasons at ample water and fertilizer (high N) and for two seasons when soil nitrogen was limited (low N). Measurements were made of net radiation, R n; soil heat flux; air and soil temperatures; canopy temperature, T s; and wind speed. Sensible heat flux was calculated from the wind and temperature measurements. ET, that is, latent heat flux, was determined as a residual in the energy balance. The FACE treatment increased daytime T s about 0.6° and 1.1°C at high and low N, respectively. Daily total R n was reduced by 1.3% at both levels of N. Daily ET was consistently lower in the FACE plots, by about 6.7% and 19.5% for high and low N, respectively. [ABSTRACT FROM AUTHOR]