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The mean transit time (MTT) is a fundamental property of a groundwater flow system that is strongly related to the ratio of recharge rate to storage volume. However, obtaining samples for estimating the MTT using environmental tracers is problematic as flow‐weighted samples over the full spectrum of transit times are needed. Samples collected from the base flow of a gaining stream in the North Carolina Coastal Plain (West Bear Creek) that were corrected for exchange with the atmosphere yielded environmental tracer concentrations (SF6and CFC‐11) very similar to flow‐weighted values from nine or ten streambed piezometers that directly sampled groundwater during low streamflow. At higher streamflow on the falling limb of the hydrograph, stream tracer concentrations (after correction for gas exchange) were significantly higher than the flow‐weighted mean from piezometers, consistent with dominance of the stream tracer signal by transient influx of surface water and/or younger subsurface water. The apparent MTT derived from SF6in low flow stream water samples was 26 years, suggesting a groundwater recharge rate of about 210 mm/yr, that is consistent with vertical profiles obtained by sampling nested piezometers in the aquifer. When sampled under low flow conditions when streamflow consists of a high component of groundwater discharge, West Bear Creek appears to act as a flow‐weighted integrator of transit times and, streamflow samples can provide fundamental information regarding groundwater recharge rate and MTT. Our study suggests that watershed‐scale evaluation of some groundwater flow systems is possible without utilizing monitoring wells. Stream sampling can yield flow‐weighted mean concentration in groundwater, CgwCgw was obtained from stream water for two age‐dating tracers, SF6and CFC‐11Cgw for SF6, 0.55 fmol/L, suggests a groundwater mean transit time of 30 ± 5 years

Warming open‐field plots using arrays of infrared heaters has proven feasible for conducting experiments to determine the likely effects of global warming on various ecosystems. To date, however, such experiments have been done for only a few degrees (≤3.5°C) of warming, yet climate projections, especially for high latitudes, indicate that future warming may be 10°C or more. Therefore, there is a need to conduct such experiments with more heating, which increases expense. To estimate energy requirements and costs for such temperature free‐air controlled enhancement (T‐FACE) experiments, improved theory was developed whereby: (i) the canopy temperature of an unheated plot is computed using the well‐accepted Monin–Obukhov similarity theory, with some constraints to calculate aerodynamic resistance; (ii) the desired amount of warming is added; and (iii) the energy balance is re‐solved to obtain the additional infrared radiation needed from the heaters to attain the desired temperature of the heated plots. Performance data are presented from T‐FACE experiments with 3‐m‐diameter plots conducted over six wheat (Triticum aestivumL.) crops and for 1‐wk periods over soybean [Glycine max(L.) Merr.] and northern mixed‐grass prairie. The T‐FACE system over wheat provided warming temperatures for day and night that were within 0.1°C of the desired setpoint differences. The measured or predicted energy requirements of the T‐FACE system for raising the wheat canopy temperatures averaged about 7.0 kWh m−2d−1. Predictions of canopy temperatures and infrared heating requirements agreed with measurements most of the time for wheat, soybean, and prairie.

Foraging behavior is an expression of learning, context, and experience arising from integration of sensory information obtained during feeding with postingestive consequences of food ingestion. Although it has been well established that gustatory and olfactory systems of the mouth and nose provide sensory information to the consumer (in the form of flavor), sweet and bitter taste receptors have recently been identified in the intestinal tract of humans and rodents. It remains possible that sensory information generated in the gut could contribute to the learning process. Thus, a series of experiments was conducted to determine if classical associative learning occurs when the conditional stimulus circumvents oronasal presentation via direct delivery to the gut or peritoneal cavity. Mice receiving an intragastric infusion of 5 mMsodium saccharin immediately followed by LiCl administration demonstrated a significant decrease in preference for 5 mMsaccharin in 4 consecutive 23h, 2-bottle preference tests versus water (P= 0.0053). Saccharin was highly preferred in mice receiving intragastric (IG) saccharin only or interperitoneal (i.p.) injection of LiCl only. This reduced preference indicated that mice “tasted” saccharin infused into the gut. However, efforts to replicate with a reduced infusion volume failed to result in decreased preference. To understand if there were alternative pathways for oral detection of infused saccharin, mice received intragastric infusions (5.4 mM) and i.p. injections (10.8 mM) of sodium fluorescein. Fluorescence was observed from the tongues and esophagi of mice infused with volumes of 0.5 mL or more or injected with volumes of 0.25 mL or greater. Interperitoneal injections of 5 mMsaccharin in mice resulted in reduced preference for 5 mMsaccharin presented orally in 2-bottle preference tests (P= 0.0287). Oral delivery of a 500-fold less concentration of saccharin (0.01 mM) during conditioning resulted in a similar preference expression as shown in the initial IG experiment. These results demonstrate that although compounds may be tasted in the mouth absent of oral contact, associative learning is attenuated. Therefore, intestinal taste receptors are unlikely to participate directly in learning and recognition of foods during foraging events.

Possible future increases in atmospheric temperature may threaten wheat (Triticum aestivumL.) production and food security. The purpose of this research is to determine the response of wheat growth to supplemental heating and to seasonal air temperature from an unusually wide range of planting dates. A field study was conducted at Maricopa, AZ, where wheat was planted from September to May over a 2‐yr period for a total of 12 planting dates. Supplemental heating was provided for 6 of the 12 planting dates using infrared heaters placed above the crop which increased canopy temperature by 1.3°C during the day and 2.7°C during the night. Grain yield declined 42 g m−2(6.9%) per 1°C increase in seasonal temperature above 16.3°C. Supplemental heating had no effect on grain yield for plantings in winter (Dec./Jan.) since temperatures were near optimum (14.9°C). However, in spring (Mar.) plantings where temperature (22.2°C) was above optimum, supplemental heating decreased grain yield from 510 to 368 g m−2. Supplemental heating had the greatest effect in the early fall plantings (Sept./Oct.) when temperature was slightly below optimum (13.8°C) and mid‐season frost limited the yield of unheated plots to only 3 g m−2whereas yield of heated plots was 435 g m−2. Thus, possible future increases in temperature may decrease wheat yield for late plantings and shift optimum planting windows to earlier dates in areas of the world similar to the desert southwest of the United States.

To determine the likely effects of global warming on field‐grown wheat (Triticum aestivumL.), a “Hot Serial Cereal” experiment was conducted—so‐called “Cereal” because wheat was the crop, “Serial” because the wheat was planted about every 6 wk for 2 yr, and “Hot” because infrared heaters were deployed on six of the planting dates in a temperature free‐air controlled enhancement (T‐FACE) system, which warmed the canopies of the Heated plots. During the experiment, measurements of canopy reflectance were made two to five times per week from which values of normalized difference vegetation index (NDVI) were calculated. As expected, curves of NDVI from the Heated plots vs. time and vs. growing degree days (GDD) computed from air temperatures generally were ahead of those from Reference plots. However, when plotted against GDD computed from canopy temperatures the curves coalesced, which gives confidence that the infrared‐heater treatment simulates natural warming and will produce plant responses not unlike those expected with future global warming. Biomass and grain yields were correlated with the areas under the NDVI vs. GDD curves for the air‐temperature‐based GDDs, but high variability prevented such a correlation to be detected using canopy‐temperature‐based GDD. Large differences existed between the total amounts of air or canopy temperature‐based GDDs required for wheat to mature in our irrigated fields in an arid region. This implies that GDD based on air temperatures should be regarded only as a local guide to plant development rates, whereas those based on canopy temperatures would be more universal.

Climate warming may raise wheat (Triticum aestivumL.) yields in cooler climates and lower them in warmer climates. To understand these contrasting effects, infrared heating lamps were used to warm irrigated spring wheat by 1.5°C (day) and 3.0°C (night) above unheated controls during different times of the year at Maricopa, AZ. Changes in wheat growth with warming were used to test hypotheses for temperature effects on crop growth in the process model ecosys. Infrared heating substantially raised phytomass growth and grain yield under lower air temperature (Ta) following plantings from September through December. The same heating, however, lowered growth and yield under higher Tafollowing plantings from January through March. Gains in wheat yield of as much as 200 g C m−2with heating under lower Tawere attributed in the model to more rapid CO2fixation and to reduced chilling effects on seed set. These gains were only partially offset by losses from shortened wheat growth periods. Losses in wheat yield of as much as 100 g C m−2with heating under higher Tawere attributed in the model to adverse effects of heating on crop water status and on CO2fixation vs. respiration, to greater heat stress effects on seed set, and to shortened crop growth periods. Model hypotheses thus explained contrasting effects of heating on wheat yields under different Tafound in the field experiment as well as in many earlier studies. Well‐constrained tests of these hypotheses are vital for models used to project climate change impacts on agricultural ecosystems.

Changes in temperature, CO2, and precipitation under the scenarios of climate change for the next 30 yr present a challenge to crop production. This review focuses on the impact of temperature, CO2,and ozone on agronomic crops and the implications for crop production. Understanding these implications for agricultural crops is critical for developing cropping systems resilient to stresses induced by climate change. There is variation among crops in their response to CO2, temperature, and precipitation changes and, with the regional differences in predicted climate, a situation is created in which the responses will be further complicated. For example, the temperature effects on soybean [Glycine max(L.) Merr.] could potentially cause yield reductions of 2.4% in the South but an increase of 1.7% in the Midwest. The frequency of years when temperatures exceed thresholds for damage during critical growth stages is likely to increase for some crops and regions. The increase in CO2contributes significantly to enhanced plant growth and improved water use efficiency (WUE); however, there may be a downscaling of these positive impacts due to higher temperatures plants will experience during their growth cycle. A challenge is to understand the interactions of the changing climatic parameters because of the interactions among temperature, CO2, and precipitation on plant growth and development and also on the biotic stresses of weeds, insects, and diseases. Agronomists will have to consider the variations in temperature and precipitation as part of the production system if they are to ensure the food security required by an ever increasing population.

The positive impact of elevated atmospheric CO2concentration on crop biomass production suggests more carbon inputs to soil. Further study on the effect of elevated CO2on soil carbon and nitrogen dynamics is key to understanding the potential for long‐term carbon storage in soil. Soil samples (0‐ to 5‐, 5‐ to 10‐, and 10‐ to 20‐cm depths) were collected after 2 yr of grain sorghum [Sorghum bicolor(L.) Moench.] production under two atmospheric CO2levels: (370 [ambient] and 550 μL L−1[free‐air CO2enrichment; FACE]) and two water treatments (ample water and limited water) on a Trix clay loam (fine, loamy, mixed [calcareous], hyperthermic Typic Torrifluvents) at Maricopa, AZ. In addition to assessing treatment effects on soil organic C and total N, potential C and N mineralization and C turnover were determined in a 60‐d laboratory incubation study. After 2 yr of FACE, soil C and N were significantly increased at all soil depths. Water regime had no effect on these measures. Increased total N in the soil was associated with reduced N mineralization under FACE. Results indicated that potential C turnover was reduced under water deficit conditions at the top soil depth. Carbon turnover was not affected under FACE, implying that the observed increase in soil C with elevated CO2may be stable relative to ambient CO2conditions. Results suggest that, over the short‐term, a small increase in soil C storage could occur under elevated atmospheric CO2conditions in sorghum production systems with differing water regimes.

The purpose of this article is to explore the relevance of Plato's Sophistin the context of coaching. The Sophistdialogue focuses upon the role of the philosopher as a therapist of the soul rather than simply a conveyer or wholesaler of knowledge. This article provides a rationale for the coach to be more than a technical conveyer of skill in which the athlete is perceived to be machine-like (i.e., homo mechanicus) in order to take on a more holistic role in the life of the athlete. Through the application of the noble sophist to the Ecological Task Analysis theory (ETA), we demonstrate how the fundamental perception of the role of the coach may be expanded and redefined to become more of a “midwife” for the birth of personal and moral development.

Atmospheric CO2concentration (Ca) continues to rise. An imperative exists, therefore, to elucidate the interactive effects of elevated Caand drought on plant water relations of wheat (Triticum aestivumL.). A spring wheat (cv. Yecora Rojo) crop was exposed to ambient (Control: 370 μmol mol−1) and free‐air CO2enrichment (FACE: ambient + 180 μmol mol−1) under ample (Wet), and reduced (Dry), water supplies (100 and 50% replacement of evapotranspiration, respectively) over a 2‐yr study. Our objective was to characterize and quantify the responses of 26 edaphic, gas exchange, water relations, carbohydrate pool dynamics, growth, and development parameters to rising Caand drought. Increasing Caminimized the deleterious effects of soil–water depletion by increasing drought avoidance (i.e., lower stomatal conductance and transpiration rate, and growth and development of a more robust root system) and drought tolerance (i.e., enhanced osmoregulation and adaptation of tissue) mechanisms, resulting in a 30% reduction in water stress–induced midafternoon depressions in net assimilation rate. An elevated Ca–based increase in daily and seasonal carbon gain resulted in a positive feedback between source capacity (shoots) and sink demand (roots). Devoid of a concomitant rise in global temperature resulting from the rise in Ca, improved water relations for a herbaceous, cool‐season, annual, C3cereal monocot grass (i.e., wheat) are anticipated in a future high‐CO2world. These findings are applicable to other graminaceous species of a similar function‐type as wheat common to temperate zone grassland prairies and savannas, especially under dryland conditions.

Increasing atmospheric CO2concentrations are expected to increase plant production and demand for N and other nutrients. The objectives of this investigation were to characterize and quantify the temporal trends in soil mineral N and aboveground biomass N during the growing season of wheat (Triticum aestivumL.) with adequate N, ambient and elevated CO2, and two levels of water stress. The free‐air CO2enrichment (FACE) technique was used to enrich the air from 370 to 550 μmol mol−1CO2. Spring wheat was planted in late December of 1992 and 1993 and harvested at the end of May. Each main plot (CO2level) was split into two irrigation treatments to replace 100 and 50% of the potential evapotranspiration. Soil and plant samples were taken for N analysis six times each year. Elevated CO2lowered soil mineral N concentrations in the top 0.3 m of soil as much as 40% and increased aboveground biomass N by as much as 16% compared with the ambient treatment. Before anthesis, irrigation level had little effect on either soil mineral N or aboveground biomass N, but at harvest in 1992–1993 and at dough stage in 1993–1994 deficit‐irrigated plots had higher soil mineral N (p< 0.05) and lower aboveground biomass N than plots that received adequate irrigation. There was little variation in the concentrations of N in the aboveground biomass among treatments within a sampling date. The data suggest elevated CO2may lead to rapid N uptake, which could result in increased early vegetative growth.

Elevated concentrations of atmospheric CO2(Ca) are believed to raise sorghum [Sorghum bicolor(L.) Moench] productivity by improving water relations. In ecosys, water relations are simulated by solving for the canopy water potential (ψC) at which water uptake from a model of soil–root–canopy water transfer equilibrates with transpiration from the canopy energy balance. Simulated water relations were tested with ψC, water uptake, and energy exchange measured under ambient (363 μmol mol−1) and elevated (566 μmol mol−1) Caand high vs. low irrigation in a free air CO2enrichment experiment during 1998 and 1999. Model results, corroborated by field measurements, showed that elevated Caraised ψCand lowered latent heat fluxes under high irrigation and delayed water stress under low irrigation. Changes in ψCmodeled under ambient vs. elevated Cavaried diurnally, with lower ψCcausing earlier midafternoon stomatal closure under ambient Ca. Modeled changes in sorghum water status caused elevated Cato raise seasonal water efficiency under high and low irrigation by 20 and 26% (vs. 20 and 13% measured) in 1998 and by 9 and 27% (vs. 6 and 26% measured) in 1999. Ecosyswas used to generate an irrigation response function for sorghum yield, which indicated that yields would rise by ≈13% for a range of irrigation rates if air temperatures were to rise by 3°C and Caby 50%. Current high sorghum yields could be achieved with ≈120 mm or ≈20% less irrigation water if these rises in temperature and Cawere to occur.

We demonstrate here that large area periodic arrays of well-aligned carbon nanotubes can be fabricated inexpensively on Ni dots made by the process of self-assembly nanosphere lithography. These periodic arrays appear colorful due to their efficient reflection and diffraction of visible light. In addition, due to their honeycomb lattice structure, these arrays can act as photonic band gap crystals in the visible frequency range. In this report, we present the initial exploration of the optical properties of such arrays. Here we show that these potential 2D photonic band gap crystal arrays might find very important applications in optoelectronics.

Chiseling is now more frequently used for primary tillage in the drylands of eastern Oregon and Washington. Improved measures of chiseling effects on soil water relations are needed to evaluate water intake and infiltration benefits, especially as related to depth of chiseling. Hydraulic conductivity (K)and soil water desorption characteristic (SWDC) were field measured in the 120‐cm soil profile of a Walla Walla (mesic typic Haploxeroll) silt loam before and after chiseling 43‐cm deep. The test Walla Walla soil is layered. Cation exchange capacity, exchangeable Ca2+, clay content, and organic matter all changed at the 30‐cm depth; dry bulk density decreased with depth above 45 cm and was constant below 45 cm; Kwas 10 to 1,000‐fold lower in depths above 30 cm; water contents in the SWDC (−50 to −200 mbar range) were lower in upper 30‐cm layer. Chiseling affected both the SWDC and Kin the upper 30 cm, especially at 10 and 20‐cm depths, but had no influence on these measurements at 40 cm. Both water potential at constant water content in the SWDC and Kwere increased especially in the −50 to −300 mbar range. Failure of chiseling to improve water relations in the mild duripan extending from 30 to 45 cm suggests the need for addition of plant residue or chemical amendments into the chisel slots. Water contents and hydraulic heads during drainage showed that chiseling could reduce evaporation by reducing water content and diffusivity. Overall soil profile hydraulic resistances showed relative average Kup to 15 times greater as a result of chiseling 43 cm deep, but nearly similar accelerated internal drainages were projected for simulated chiseling to 25‐cm depth vs. chiseling to 43 cm.

The Philip and DeVries theory and the “isothermal” theory were used to predict diurnal soil water fluxes near the soil surface. The predicted values were compared with those obtained by measurements of soil‐water content, soil temperature, and evaporation. Previously measured soil‐water diffusivities were used in the theoretical calculations. The thermal vapor diffusivities were calculated using both the “simple” and the “complete” theory of Philip and DeVries. Comparison of measured and calculated fluxes indicated that the theory of Philip and DeVries predicts the measured values better at intermediate water contents, but the “isothermal” theory predicts values better at high and very low water contents.

Six major drying experiments were conducted on a smooth, bare field of Avondale clay loam at Phoenix, Arizona, during all seasons of the year. Intensive measurements of evaporation, soil‐water contents, soil temperatures, soil heat flux, albedo, and net radiation allowed us to delineate the three classical stages of soil drying. The first stage was characterized by potential evaporation. The second stage was characterized by drying of the soil surface, resulting in a significantly reduced evaporation rate. This stage continued until the volumetric water content at the soil surface reached a value of about 0.06, the predicted starting point for stage three for this soil—based on the assumption that physical adsorption takes place in the first two molecular layers of water surrounding the soil particles. Simple albedo measurements often predicted the transition points between the different stages.

In an experiment designed to determine the likely consequences of the steadily rising carbon dioxide (CO2) concentration of Earth's atmosphere for the foliage temperature, water use, and yield of cotton (Gossypium hirsutumL. var. Deltapine‐61) plants, cotton was grown out‐of‐doors at Phoenix, AZ, in open‐top, clear‐polyethylene‐wall, CO2‐enrichment chambers for three summers under mean daylight CO2concentrations of 340, 500 and 640 μmol CO2mol−1air on an Avondale clay loam soil [fine‐loamy, mixed (calcareous), hyperthermic Anthropic Torrifluvent]. Infrared thermometer measurements of the cotton foliage temperature (TF) indicated that a 330 to 660 μmol CO2mol−1air doubling of the atmospheric CO2content results in a midday TF, increase of 1.1 °C for well‐watered cotton at Phoenix in the summer. This temperature increase was predicted to produce a 9% reduction in per‐unit‐leaf‐area plant transpiration rate and an 84% increase in crop biomass production, which compared favorably with the measured crop biomass increase of 82% for such a doubling of the air's CO2content. These findings, together with similar findings for a second plant species—water hyacinth [Eichhornia crassipes(Mart.) Solms]—allowed us to develop a technique for assessing the effects of a 330 μmol CO2mol−1air CO2concentration increase on the percentage yield increase (Y) of a crop via infrared thermometry by means of the equation Y = 7.6% × (IJ)−1, where IJ represents the Idso‐Jackson plant water stress index. If this equation holds up under further scrutiny, it could provide a rapid and efficient means for assessing the yield response of crops to atmospheric CO2enrichment.

The rates of leakage of CO2from plant assimilation chambers must be known in order to correct measurements of net photosynthesis and respiration for this unwanted but omnipresent source of error. Similarly, in order to precisely calculate heating or cooling requirements for plant growth structures, air leakage or “infiltration” must be known. The objective of this paper is to derive theoretically exact equations for calculating such leakage rates from measurements of CO2concentration [CO2]. The needed equations were derived from the solution of a basic differential CO2balance equation. The procedure presumes the determination will be done when plant CO2exchange is steady, a condition most nearly satisfied by respiration near the end of the night. The equation had two unknowns, respiration and leakage rate. From measurements before and after a CO2perturbation, it was possible to derive sets of two equations with two unknowns, which were then solved for the respiration and leakage rates. In contrast to prior work, the new equations are theoretically exact, and they can account for changes in ambient [CO2] during the measurement periods and also for differing rates of CO2injection before and after the perturbation. Moreover, these theoretically exact equations are no more complex than the prior approximate equations for a couple of practical cases. Calculations for three specific cases showed the approximation used in the prior equations introduced errors of 0.8, 5.5, and 1.6%. Thus, using these equations derived in this paper should permit more accurate calculations of leakage rate and ultimately, therefore, more accurate determinations of gas exchange rates from plants in assimilation chambers as well as of the heating or cooling requirements of the chambers themselves.

The natural variability of agronomic data often masks underlying true curves. A relatively new Fourier transform data smoothing technique, when tested on several sets of noisy agronomic data, gave very satisfactory reductions of this variability. The data were smoothed by computing the Fourier transform, setting high frequency noise components of the resulting variance spectrum to zero, and then computing the inverse Fourier transform. The key to the technique's success lies in the fact that the data were dominated by relatively low frequencies of variation which could be separated from the higher frequency noise. This simple, lucid interpretation of the filtering action makes Fourier transform smoothing even more attractive than other methods whose filtering action is not so intuitively obvious. The technique was superior to two other methods in extracting a true curve from noisy artificial data.

Prior experiments with cotton (Gossypium hirsutumL.) and water hyacinth [Eichhornia crassipes(Mart.) Solms] demonstrated that porometer chamber conditions may significantly perturb the measurement of leaf stomatal conductance. Thus, this study was conducted to determine if net photosynthesis rate measurements of water hyacinth and cotton leaves were similarly perturbed by leaf chamber conditions and, if so, to devise a method to correct for the instrument‐induced error. Several net photosynthesis rate and concurrent canopy environmental data sets for these two plant species were analyzed at Phoenix, AZ within the context of the non‐water‐stressed baseline paradigm, which relates foliage‐to‐air temperature difference to air vapor pressure deficit. It was found that leaf chamber measurements of net photosynthesis rate were subject to the same type of measurement error as that associated with porometer measurements of leaf stomatal conductance. For plants transpiring at potential rates, photosynthesis rates can be corrected by using ancillary data obtained by the leaf chamber system. However, the proper adjustment of net photosynthesis rates of water‐stressed plants measured with leaf chambers required free‐air foliage and air temperatures, as well as the free‐air humidity. It was demonstrated that concurrent infrared radiation thermometry, as well as simultaneous measurements of air wet‐ and dry‐bulb temperatures, are required to correctly evaluate, by leaf chamber techniques, the net photosynthesis rates of plants that are experiencing any degree of stomatal closure due to some aspect of their normal environment.

Open‐top chamber use for exposing plants to various levels of CO2and pollutant gases is increasing in field studies. In making a C balance of cotton [Gossypium hirsutum(L.) ‘Deltapine‐61’] for such a system, soil CO2fluxes were observed to be significantly greater outside than inside the chamber. To find the cause, CO2concentration was measured in the soil profile from 5‐ to 60‐cm depths of an Avondale clay loam [fine‐loamy, mixed (calcareous), hyperthermic Typic Torrifluvent]. The soil CO2contents at the various depths sampled outside the chamber were higher than those inside the chamber. The differences in concentration were observable within 2 wk after the blower used to pass ambient of CO2‐enriched air through the chamber was turned on. The largest differences were present approximately 16 wk after the system had been in operation. Approximately 30 d was required for the soil CO2levels inside and outside the chamber to become similar after the blower was turned off. Soil water content was not a factor causing this difference because it was nearly equal at both sites. Pressure differentials inside the growth chamber resulting from the blower operation could lead to a decrease in soil CO2concentration and fluxes measured using the closed chamber technique.

The predicted positive impact of elevated atmospheric carbon dioxide (CO2) concentration on crop biomass production suggests that more C will reach the soil. An aspect of soil C sequestration that requires further study is the effect of elevated CO2on C and N dynamics; this relationship is the key to understanding potential long‐term C storage in soil. Soil samples (0–5, 5–10, and 10–20 cm increments) were collected after 2 yr of wheat (Triticum aestirumL.) production under two CO2levels [370 (ambient) and 550 µL L−1(free‐air CO2enrichment)(FACE)] and two water treatments [100% of ET replaced (wet) and 50% of ET replaced (dry)] on a Trix clay loam [fine, loamy, mixed (calcareous), hyperthermic Typic Torrifluvents] at Maricopa, AZ. Organic C, total N, potential C and N mineralization, and C turnover were determined during a 60‐d incubation study. Organic C content increased at all three soil depths under FACE and the total N content increased at the 5 to 10 and 10 to 20 cm depths. In general, increased N mineralization under dry conditions corresponded well with patterns of higher C mineralization and turnover. Nitrogen mineralization was unaffected by CO2treatment, indicating that factors other than N may limit C mineralization and turnover. Soil respiration and C turnover patterns were not affected by CO2treatment level at the 0 to 5 cm depth; however, these measures were lower under FACE at the lower depths. Soil respiration and C turnover at the 10 to 20 cm depth were increased by water stress under ambient CO2; these measures under both water levels for FACE were similar to the ambient CO2/wet treatment, suggesting that more C storage in wheat cropping systems is likely under elevated CO2regardless of water treatment.

The increasing atmospheric CO2 concentration probably will have significant direct effects on vegetation whether predicted changes in climate occur or not. Averaging over many prior greenhouse and growth chamber studies, plant growth and yield have typically increased more than 30% with a doubling of CO2 concentration. Such a doubling also causes stomatal conductance to decrease about 37%, which typically increases leaf temperatures more than 1 °C, and which may decrease evapotranspiration, although increases in leaf area counteract the latter effect. Interactions between CO2 and climate variables also appear important. In one study the growth increase from near-doubled CO2 ranged from minus 60% at 12 °C to 0% at 19 °C to plus 130% at 34 °C, suggesting that if the climate warms, the average growth response to doubled CO2 could be consistently higher than the 30% mentioned above. Even when growing in nutrient-poor soil, the growth response to elevated CO2 has been large, in contrast to nutrient solution studies which showed little response. Several studies have suggested that under water-stress, the CO2 growth stimulation is as large or large than under wellwatered conditions. Therefore, the direct CO2 effect will compensate somewhat, if not completely, for a hotter drier climate. And if any climate change is small, then plant growth and crop yields will probably be significantly higher in the future high-CO2 world.

Surface soil‐heat fluxes were determined for 6 days in a field of Avondale loam using the null‐alignment method, the combination method, and four variations of the temperature gradient method with thermal conductivities computed from the DeVries' theory for particular reference depths. For all methods, calorimetry was used to obtain the surface flux from the flux determined for the reference depth. There was 10% or less difference between the null‐alignment, combination, and temperature gradient methods for a 20‐cm reference depth. However, the difference with respect to the null‐alignment method increased to 35% for a 5‐cm reference depth when DeVries' theory was closely followed. This difference was reduced to 3% when a modified air shape factor was used in the computations and all vapor movement was ignored. We concluded that the temperature gradient method with conductivities computed from DeVries' theory could be reliably used with a 20‐cm reference depth, but that a “calibration” of the theory for a particular soil should be obtained before the method is used with a 5‐cm reference depth. When properly used, the temperature gradient method with computed conductivities has the advantage that reliable estimates of surface soil‐heat flux can be obtained without requiring heat flux plates like the usual combination method nor many computations like the null‐alignment method.

Soil‐heat fluxes calculated using DeVries' theory (1958, 1963) were compared with those experimentally determined in a field of Avondale loam at Phoenix, Ariz., on 6 days representing different seasons of the year. A fair agreement between measured and computed fluxes was obtained only after modifying the air shape factor curve and ignoring heat transfer due to water vapor movement. The omission of the latter implied that heat transfer by pure conduction was most important and that thermal and isothermal vapor fluxes exactly cancelled during the day and were insignificant at night. “Measured” thermal conductivities were also determined from the ratio of the measured heat fluxes to the corresponding temperature gradient for those times when it was unlikely that isothermal vapor movement was significant. The lack of a temperature dependence in these data, as well as the flux comparisons, strongly indicate that the theory overestimated thermal vapor movement. These data plus others in the literature indicate that an individual “calibration” of the theory for a particular soil is required before reliable predications of soil‐heat flux can be obtained.

The CO2concentration of the atmosphere is increasing and is expected to double sometime near the middle of the next century. To determine the effects of such a CO2increase on cotton (Gossypium hirsutumL.) growth and productivity, a series of experiments from 1983 through 1987 were conducted with open‐top CO2‐enriched field chambers at ample as well as limiting levels of water and N at Phoenix, AZ. Comparisons with open‐field plots showed that there was a significant chamber effect, amounting to a 30% average increase in growth inside, but under dry conditions in 1985, the situation was reversed. No significant effects of CO2on harvest index, root‐shoot ratio, or lint percentage were found, so the primary effect of elevated CO2was to produce plants that were larger. Comparing the results of 500 and 650 µmol mol−1CO2treatments, the increments of growth from ambient (about 350 µmol mol −1) to 500 µmol mol−1were not significantly different from increments from 500 to 650 µmol mol−1. No statistically significant interactions were detected between CO2level and either irrigation or nitrogen level, even when these variables were sufficiently low enough to limit growth. However, under well‐maintained water stress conditions, the growth response to CO2tended to he somewhat larger than under normal irrigation levels. Averaging over all the data available from these experiments, seed cotton yield (lint plus seed) and above‐ground biomass were increased by 60 and 63%, respectively, by CO2enrichmen to 650 µmol mo1−1.

The probable effect of the increasing global atmospheric CO2concentration on agricultural yields was evaluated. More than 430 observations of the yield of 37 species grown with CO2enrichment were extracted from more than 70 reports published during the past 64 years. Most of the studies were performed in greenhouses or growth chambers. Open fields might respond less than greenhouses or growth chambers to increased CO2because nutrient levels in general world‐wide agriculture are lower than those in the indoor studies, or open fields might respond more because light levels are generally higher outside. The data also were dominated by high value crops, but results should be applicable to the three‐fourths of the world agriculture represented by the C3crops and possibly to the remaining C4crops as well. Keeping these limitations of the data in mind, the analysis showed that yields probably will increase by 33% (with a 99.9% confidence interval from 24 to 43%) with a doubling of atmospheric CO2concentration.

Summary: Atmospheric CO2 enrichment tends to induce partial stomatal closure in most higher plants. This phenomenon reduces per-unit-leaf-area plant transpirational water loss rates, which in turn leads to higher plant temperatures. Working in the field with water hyacinths maintained in open-top, clear-plastic wall, CO2 -enrichment chambers at Phoenix, Arizona, we have quantified this relationship for a plant species which has been shown previously to react like most land plants in this regard. Our results indicate that in some parts of the world this non-greenhouse mechanism for surface temperature change may play an important role in determining future climate. Under sunlit and well-watered conditions conducive to active growth, for instance, we found water hyacinth foliage temperatures to increase by 2.7 K in response to a 300 to 600 ppm doubling of the atmospheric CO2 concentration.

Agronomic data frequently requires smoothing in order to obtain a reliable functional relationship for interpolating, predicting, or determining the rate of change of one variable with respect to another. To test whether cubic spline functions could provide satisfactory smoothing, the necessary equations were derived, computer programs written, and several sets of soil temperature and water content data were smoothed. Cubic spline smoothing displayed the following, advantages: 1) Because spline functions are defined piecewise, they can represent any variable arbitrarily well over wide ranges of the other. 2) The data can be obtained at unequal intervals, so high sampling rates can be used where changes are rapid and low rates where they are slow. 3) Additionally, the gradients derived from cubic spline functions are smoothly joined parabolas, not the abruptly joined straightline segments characteristic of parabolic spline smoothing.

The response of plants to rising global CO2concentration is of critical research interest but one neglected aspect is its effect on roots. Root morphological changes in cotton [Gossypium hirsutum(L.) ‘Delta Pine 77’] were examined in a 2‐yr field study. The test crop was grown under two water regimes (wet, 100% of evapotranspiration [ET] replaced and dry, 75% [1990] and 67% [1991] of ET replaced) and two atmospheric CO2concentrations (ambient = 370 µmol mol−1and free‐air CO2enrichment [FACE] = 550 µmol mol−1). A FACE technique that allows for CO2exposure under field conditions with minimal alteration of plant microclimate was used. Excavated root systems were partitioned into taproot and lateral roots at two growth phases (vegetative and reproductive). Vertical root‐pulling resistance was determined at the second sampling; this measure was higher because of CO2enrichment but was unaffected by water stress. Water stress affected root variables only at the second sampling; water stress reduced taproot variables more than lateral variables. The larger diameter taproots seen at all sample dates under FACE exhibited large increases in dry weight and volume. FACE often increased lateral root number and lateral dry weights were higher at all sample dates. The development of more robust taproot systems in CO2‐enriched environments may allow for greater carbohydrate storage for utilization during periods such as boll filling and to ensure root growth for continued exploration of the soil profile to meet nutrient and water demands during peak demand periods.

C3bi receptors (CR3) on human polymorphonuclear leukocytes (PMN) bind ligand-coated particles and promote their ingestion. The binding activity of CR3 is not constitutive but is transiently enabled by phorbol esters (Wright, S. D., and B. D. Meyer, 1986, J. Immunol. 136:1759-1764). Our observations indicate that the capacity of CR3 to bind ligand is tightly correlated with the degree of ligand-independent aggregation of the receptor in the plane of the membrane. Fixed PMN were labeled with anti-CR3 monoclonal antibodies and streptavidin colloidal gold before viewing in the electron microscope either en face or in thin section. On unstimulated PMN, gold particles marking CR3 were dispersed randomly. Stimulation of PMN for 25 min with phorbol myristate acetate (PMA) dramatically enhances binding of C3bi-coated particles, and the CR3 on such stimulated cells was observed in clusters containing more than six gold particles. CR3 was not aggregated over coated pits. After 50 min in PMA, the binding activity of CR3 falls, and the distribution of CR3 was again observed to be disperse. If a hydrophilic phorbol ester was washed away after a 20-min stimulation, binding activity remains elevated for at least 50 min, and CR3 remained aggregated. Thus, clustering of CR3 was temporally correlated with its ability to bind ligand and initiate phagocytosis. Unlike CR3, Fc receptors and HLA did not exhibit changes in their aggregation state in response to PMA. Treating PMN with formyl-methionyl-leucyl-phenylalanine, which enhances expression of CR3 but not its function, did not lead to aggregation of CR3. These observations suggest that a clustered configuration is a precondition necessary for binding ligand and signaling phagocytosis.

The loss of water vapor through 0.5‐, 1‐, and 2‐cm depths of water repellent mulches was measured under field conditions with lysimeters. Concurrent measurements were made of wind velocities, air vapor pressures, and temperatures at the soil‐mulch interfaces. Mulches used included 0.5‐, 1‐, and 2‐mm glass beads and 1‐mm glass bead aggregates. By assuming that the relative humidity of the soil air at the soil‐mulch interface was essentially 100%, effective diffusion coefficients for field conditions were calculated. The average effective diffusion coefficient for afternoon periods was 1.26 times greater than the molecular diffusion coefficient. An error analysis revealed that the value could have been as low as 0.90 or as high as 1.63, but these values would have been realized only if the effects of several possible systematic errors were completely additive. Little correlattion was found between wind velocity and effective diffusion coefficient. However, the generally low range in wind velocities observed and the smoothing required for the reduction of the lysimeter data may have prevented detection of such a correlation.

The effects of air turbulence upon the exchange of gases between a soil and the atmosphere were investigated using a specially designed vapor exchange meter. The device measured the rate of evaporation of liquid heptane from a porous stainless steel plate buried in a porous medium. Natural air turbulence as indicated by both mean windspeed and root mean square air pressure fluctuations significantly affected the heptane evaporation rates in straw and coarse gravel, but had a decreased effect in media of smaller pore size. In silt loam, the regression coefficient for evaporation rate on windspeed was 20% of its value for straw. Increasing depth from 1 to 8 cm in coarse sand caused a 91% decrease. Although the heptane flux values are quite scattered, the data indicate that air turbulence can significantly increase the transport of water vapor through coarse mulches or through very shallow depths of soil, but that soil aeration is mostly a diffusive process.