John Nagy

Design and application of a free-air carbon dioxide enrichment facility

Growth chambers and other enclosures used in plant physiology and growth studies tend to introduce chamber effects that alter the microclimate around the plants compared with the natural environment. A free-air (chamberless) carbon dioxide enrichment (FACE) system has been developed by Brookhaven National Laboratory (BNL) to provide controlled fumigation conditions while minimizing the potential to impose a discernible chamber effect. This system is capable of exposing large numbers of field-grown plants to elevated levels of atmospheric carbon dioxide (CO2) from seedling emergence until physiologic maturity. A FACE User Facility was established at the Maricopa Agricultural Center, University of Arizona, for continuous enrichment of CO2 at a set point of 550 μmol mol−1 during daylight hours throughout the cotton crop growing seasons of 1989–1991. The facility consisted of four circular BNL FACE arrays and associated equipment placed in a commercial cotton plantation. FACE array diameters of 23, 25, and 27 m were tested. The FACE facility included the ability to operate the experimental plots under two watering regimes using an automated, sub-surface irrigation system. CO2 was stored in a 48 000 kg receiver and vaporized with a heat exchanger that used water at ambient temperature as the energy source. The 1 min average CO2 concentration was held to within ±20% of the set point more than 98% of the time that the arrays were operating during all three seasons. In 1991, the long term average CO2 concentration measured at 63 points throughout the volume of a 20 m diameter experimental plot (ground to canopy top) centered within a 25 m diameter FACE array was 568 μmol mol−1. All of the FACE arrays operated for more than 99% of the planned experimental period in 1991. These 3 years of operation have demonstrated that the BNL FACE technology can be used as a basis for a large scale facility devoted to studying the fate of carbon in the terrestrial environment.

Growth and yield of cotton in response to a free-air carbon dioxide enrichment (FACE) environment

To quantify the growth and yield responses to CO2 enrichment in an open field setting, freeair CO2 enrichment (FACE) technology was used to expose a cotton (Gossypium hirsutum L.) crop to 550 γmol mol−2 CO2 throughout the growing seasons of 1989, 1990 and 1991 in fields near Maricopa, Arizona. In 1990 and 1991 a water stress treatment was also imposed. Response data for all years were consistent, and the data for 1991 were the least compromised by unusual weather or equipment failures. In that season the biomass was increased 37% by the 48% increase in CO2 concentration. Harvestable yield was increased 43%. The increase in biomass and yield was attributed to increased early leaf area, more profuse flowering and a longer period of fruit retention. The FACE treatment increased water-use efficiency (WUE) to the same amount in the well-irrigated plots as in the water-stressed plots. The increase in WUE was due to the increase in biomass production rather than a reduction of consumptive use.

Next generation of elevated [CO2] experiments with crops: A critical investment for feeding the future world

A rising global population and demand for protein-rich diets are increasing pressure to maximize agricultural productivity. Rising atmospheric [CO(2)] is altering global temperature and precipitation patterns, which challenges agricultural productivity. While rising [CO(2)] provides a unique opportunity to increase the productivity of C(3) crops, average yield stimulation observed to date is well below potential gains. Thus, there is room for improving productivity. However, only a fraction of available germplasm of crops has been tested for CO(2) responsiveness. Yield is a complex phenotypic trait determined by the interactions of a genotype with the environment. Selection of promising genotypes and characterization of response mechanisms will only be effective if crop improvement and systems biology approaches are closely linked to production environments, that is, on the farm within major growing regions. Free air CO(2) enrichment (FACE) experiments can provide the platform upon which to conduct genetic screening and elucidate the inheritance and mechanisms that underlie genotypic differences in productivity under elevated [CO(2)]. We propose a new generation of large-scale, low-cost per unit area FACE experiments to identify the most CO(2)-responsive genotypes and provide starting lines for future breeding programmes. This is necessary if we are to realize the potential for yield gains in the future.

Free air carbon dioxide enrichment: development, progress, results

Credible predictions of climate change depend in part on predictions of future CO2 concentrations in the atmosphere. Terrestrial plants are a large sink for atmospheric CO2 and the sink rate is influenced by the atmospheric CO2 concentration. Reliable field experiments are needed to evaluate how terrestrial plants will adjust to increasing CO2 and thereby influence the rate of change of atmospheric CO2. Brookhaven National Laboratory (BNL) has developed a unique Free-Air CO2 Enrichment (FACE) system for a cooperative research program sponsored by the U.S. Department of Energy and U.S. Department of Agriculture, currently operating as the FACE User Facility at the Maricopa Agricultural Center (MAC) of the University of Arizona. The BNL FACE system is a tool for studying the effects of CO2 enrichment on vegetation and natural ecosystems, and the exchange of carbon between the biosphere and the atmosphere, in open-air settings without any containment. The FACE system provides stable control of CO2 at 550 ppm ± 10%, based on 1-min averages, over 90% of the time. In 1990, this level of control was achieved over an area as large as 380 m2, at an annual operating cost of

Effects of free-air CO2 enrichment on energy balance and evapotranspiration of cotton

668 m−2. During two field seasons of enrichment with cotton (Gossypium hirsutum) as the test plant, enrichment to 550 ppm CO2 resulted in significant increases in photosynthesis and biomass of leaves, stems and roots, reduced evapotranspiration, and changes in root morphology. In addition, soil respiration increased and evapotranspiration decreased.

Carbon isotope dynamics of free-air CO2-enriched cotton and soils

Abstract The effects of free-air CO2 enrichment (FACE) at 550 μmol mol−1 on the energy balance and evapotranspiration, ET, of cotton (Gossypium hirsutum L.) were investigated. Latent heat flux, λET was calculated as the residual in an energy balance approach from determinations of net radiation, Rn minus surface soil heat flux, G0, minus sensible heat flux, H. Rn was directly measured. G0 was determined from measurements with soil heat flux plates at 10 mm depth, corrected for temperature changes in the soil above. H was determined from measurements of air temperature with aspirated psychrometers, of foliage temperature with IR thermometers, and of wind speed with cup anemometers. Under ambient CO2 (control) conditions (about 370 μmol mol−1), the λET from the energy balance approach agreed fairly well with values from several other methods, including the Bowen ratio method, lending credence to the technique. However, the results had an uncertainty of the order of 20% associated with the Rn measurements. Therefore, an apparent increase in ET of about 13% in the FACE plots was judged insignificant. The conclusion that any effects of CO2 enrichment to 550 μmol mol−1 on the ET of cotton were too small to be detected was consistent with the results of other investigators who determined ET in the same experiment using stem flow gauges and the soil water balance.

Cotton evapotranspiration under field conditions with CO2 enrichment and variable soil moisture regimes

A role for soils as global carbon sink or source under increasing atmospheric CO2 concentrations has been speculative. Free-air carbon dioxide enrichment (FACE) experiments with cotton, conducted from 1989 to 1991 at the Maricopa Agricultural Center in Arizona, maintained circular plots at 550 μmol mol−1 CO2 with tank CO2 while adjacent ambient control plots averaged about 370 μmol mol−1 CO2. This provided an exceptional test for entry of carbon into soils because the petrochemically derived tank CO2 used to enrich the air above the FACE plots was depleted in both radiocarbon (14C content was 0% modern carbon (pmC)) and 13C (δ13C≈ −36‰) relative to background air, thus serving as a potent isotopic tracer. Flask air samples, and plant and soil samples were collected in conjunction with the 1991 experiment. Most of the isotopic analyses on the plants were performed on the holocellulose component. Soil organic carbon was obtained by first removing carbonate with HCl, floating off plant fragments with a NaCl solution, and picking out remaining plant fragments under magnification. The δ13C of the air above the FACE plots was approximately −15 to −19‰, i.e. much more 13C depleted than the background air of approximately −7.5‰. The δ13C values of plants and soils in the FACE plots were 10–12‰ and 2‰13C-depleted, respectively, compared with their control counterparts. The 14C content of the FACE cotton plants was approximately 40 pmC lower than tha tof the control cotton, but the 14C results from soils were conflicting and therefore not as revealing as the δ13C of soils. Soil stable-carbon isotope patterns were consistent, and mass balance calculations indicate that about 10% of the present organic carbon content in the FACE soil derived from the 3 year FACE experiment. At a minimum, this is an important quantitative measure of carbon turnover, but the presence of 13C-depleted carbon, even in the recalcitrant 6 N HCl resistant soil organic fraction (average age 2200 years before present (BP)), suggests that at least some portion of this 10% is an actual increase in carbon accumulation. Similar isotopic studies on FACE experiments in different ecosystems could permit more definitive assessment of carbon turnover rates and perhaps provide insight into the extent to which soil organic matter can accommodate the ‘missing’ carbon in the global carbon cycle.

Effects of free-air carbon dioxide enrichment on PAR absorption and conversion efficiency by cotton

The CO2 concentration of the atmosphere is predicted to double by the next century, and this is expected to increase significantly the growth and yield of many important agricultural crops. One consequence of larger and more vigorous plants may be increased crop evapotranspiration (ET) and irrigation water requirements. The objective of this work was to determine ET of cotton (Gossypium hirsutum L. cv. ‘Deltapine 77’) grown under ambient (about 370 μmol mol−1) and enriched (550 μmol mol−1) CO2 concentrations for both well-watered and water-stress irrigation managements. Studies were conducted in 1990 and 1991 within a large, drip-irrigated cotton field in central Arizona. Cotton ET was measured during the growing seasons using a soil water balance, based on neutron gauge soil water measurements. ET, for periods from 7 to 14 days, was not significantly different between ambient and enriched CO2 treatments at the 0.05 probability level, and the total seasonal ET for the CO2 treatments varied by 2% or less in either year. However, water-stress treatments, which were initiated on 3 July (day of year (DOY) 184) in 1990 and on 20 May (DOY 128) in 1991, had significantly lower (P < 0.05) ET than well-watered treatments starting at the end of July in 1990 and in early July in 1991 when the plants were about 75–90 days old. The result that CO2 enrichment to 550 μmol mol−1 did not significantly change the ET of cotton was consistent with the results of co-investigators who measured ET in the same experiments using stem flow gauges and an energy balance. This result implies that irrigation water use would not have to be increased to produce cotton in a future high-CO2 world. However, if a concomitant change in climate occurs, such as global warming, cotton evapotranspiration may change in response to the changed weather condition.

Sap flow measurements of transpiration from cotton grown under ambient and enriched CO2 concentrations

Anticipated changes in global climate and atmospheric CO2 concentrations have very important, albeit poorly understood consequences for production agriculture. Effects of these changes on plants have usually been examined in controlled-environment enclosures, glass-houses, or open-top field chambers. Beginning in 1989, an innovative experimental free-air CO2 enrichment (FACE) facility was operated in central Arizona to evaluate crop response to increased CO2 levels within a large, open-field production environment. Cotton (Gossypium hirsutum L.) was grown for three consecutive seasons under well-watered conditions and exposed to either ambient (control, about 370 μmol mol−1) or elevated (FACE, 550 μmol mol−1) CO2 concentrations. Deficit irrigation regimes supplying 75% (beginning in July 1990) or 67% (beginning in mid-May 1991) of the crops evapotranspiration requirement were included as additional treatment variables. Plant growth was monitored by periodic sampling. Canopy reflectances in visible (blue, 0.45-0.52 μm; green, 0.50-0.59 μm; red, 0.61-0.68 μm) and near-infrared (NIR; 0.79-0.89 μm) wavebands were measured frequently with an Exotech radiometer and related to absorbed photosynthetically active radiation (PAR; 0.4-0.7 μm) measured with a line quantum sensor. Dry biomass of plants in the FACE treatment was significantly (P < 0.05) greater than control values during each year of the study. The FACE plant canopy also absorbed significantly more PAR than controls during the early and middle portion of the 1990 and 1991 seasons. Light use efficiency (LUE, biomass produced per unit absorbed PAR) was significantly higher in FACE plots during each year. In the well-watered irrigation treatment, the 3 year mean LUE was 1.97 g MJ−1 for FACE and 1.56 g MJ−1 for controls. The deficit irrigation treatment in 1991 produced significantly smaller plants, which absorbed less PAR and had lower LUE than plants in the well-watered treatment (P < 0.05). No interaction was observed between CO2 and irrigation treatments. FACE research under realistic field conditions revealed positive consequences of increased CO2 on cotton plant biomass, PAR absorption, and LUE. It also demonstrated the effectiveness of this new technology for examining community-level plant responses to possible changes in global environment.

Canopy photosynthesis and transpiration of field-grown cotton exposed to free-air CO2 enrichment (FACE) and differential irrigation

Increasing atmospheric CO2 concentration has many implications for agriculture and forestry, one of which is the effect it will have on transpiration (T). The objective of this work was to quantify T of cotton (Gossypium hirsutum L.) grown in the field under ambient (370 μmol mol−1) and enriched (550 μmol mol−1) CO2 concentrations. Measurements were made in 1990 and 1991 at the Maricopa Agricultural Center, Arizona. Constant-power sap flow gauges were used to measure T. In 1990, three plants and in 1991, 10 plants were simultaneously instrumented with gauges in each of the CO2 treatments. Leaf area of plants with gauges was measured. T measured by sap flow was compared with evapotranspiration (ET) calculated by water balance in 1990 and with T calculated by water balance in 1991. Soil evaporation was measured using microlysimeters in 1991, and was found to be essentially equal (approximately 0.8 mm day−1, or about 10% of T) in the two CO2 treatments. There were no consistent differences in leaf area of plants with gauges between the two CO2 treatments. Sap flow, for periods from 15 min to 2 weeks, was not significantly different between the two CO2 treatments in either year, except for a few days in 1990. In 1991, the coefficient of variation of daily sap flow across plants was the same (about 30%) for both CO2 treatments throughout the year. The water balance ET (1990) and T (1991) were similar to sap flow in both years, and also showed no effect of CO2 treatment. These results show that for this crop, grown under well-watered and high-fertility conditions, there was no effect of CO2 on T, on a per unit ground area or per plant basis. These results are relevant for assessing the effects of increasing atmospheric CO2 concentrations on transpiration by cotton.