L. H. Allen

Growth and yield responses of rice to carbon dioxide concentration

Rice plants ( Oryza saliva L., cv. IR30) were grown in paddy culture in outdoor, naturally sunlit, controlled-environment, plant growth chambers at Gainesville, Florida, USA, in 1987. The rice plants were exposed throughout the season to subambient (160 and 250), ambient (330) or superambient (500, 660, 900 μmol CO 2 /mol air) CO 2 concentrations. Total shoot biomass, root biomass, tillering, and final grain yield increased with increasing CO 2 concentration, thegreatest increase occurring between the 160 and 500 μmol CO 2 /mol air treatments. Early in the growing season, root:shoot biomass ratio increased with increasing CO 2 concentration; although the ratio decreased during the growing season, net assimilation rate increased with increasingCO 2 concentration and decreased during the growing season. Differences in biomass and lamina area among CO 2 treatments were largely due to corresponding differences in tillering response. The number of panicles/plant was almost entirely responsible for differences in final grain yield among CO 2 treatments. Doubling the CO2 concentration from 330 to 660 μmol CO 2 /mol air resulted in a 32 % increase in grain yield. These results suggest that important changes in the growth and yield of rice may be expected in the future as the CO 2 concentration of the earths atmosphere continues to rise.

Response of rice to carbon dioxide and temperature

Abstract The current increase in atmospheric carbon dioxide concentration ([CO 2 ]) along with predictions of possible future increases in global air temperatures have stimulated interest in the effects of [CO 2 ] and temperature on the growth and yield of food crops. This study was conducted to determine the effects and possible interactions of [CO 2 ] and temperature on the growth and yield of rice ( Oryza saliva L., cultivar IR-30). Rice plants were grown for a season in outdoor, naturally sunlit, controlled-environment, and plant growth chambers. Temperature treatments of 28/21/25, 34/27/31, and 40/33/37°C (daytime dry bulb air temperature/night-time dry bulb air temperature/paddy water temperature) were maintained in [CO 2 ] treatments of 330 and 660 μmol CO 2 mol −1 air. In the 40/33/37°C temperature treatment, plants in the 330 μmol mol −1 [CO 2 ] treatment died during stem extension while the [CO 2 ] enriched plants survived but produced sterile panicles. Plants in the 34/27/31°C temperature treatments accumulated biomass and leaf area at a faster rate early in the growing season than plants in the 28/21/25°C temperature treatments. Tillering increased with increasing temperature treatment. Grain yield increases owing to [CO 2 ] enrichment were small and non-significant. This lack of [CO 2 ] response on grain yield was attributed to the generally lower levels of solar irradiance encountered during the late fall and winter when this experiment was conducted. Grain yields were affected much more strongly by temperature than [CO 2 ] treatment. Grain yields declined by an average of approximately 7–8% per 1°C rise in temperature from the 28/21/25 to 34/27/31°C temperature treatment. The reduced grain yields with increasing temperature treatment suggests potential detrimental effects on rice production in some areas if air temperatures increase, especially under conditions of low solar irradiance.

Field techniques for exposure of plants and ecosystems to elevated CO2 and other trace gases

Carbon dioxide (CO{sub 2}) concentration of the atmosphere has varied considerably over geological time. Ice core data from the USSR Vostok Station showed that the Earth`s atmospheric CO{sub 2} ranged from as low as 180 to 200 {mu}mol mol{sup {minus}1} during the last two glacial maxima (13,000 to 40,000 and 130,000 to 160,000 years before present). However, following the rapid glacial melting, the concentration rose quickly to about 260 to 270 {mu}mol mol{sup {minus}1}. Since around 1700 AD, the CO{sub 2} concentration has increased from about 270 {mu}mol mol{sup {minus}1} to 315 {mu}mol mol{sup {minus}1} in 1958 and 355 {mu}mol mol{sup {minus}1} in 1991. 209 refs., 4 figs., 2 tabs.

Effects of enhanced UV-B radiation (280–320 nm) on ribulose-1,5-bisphosphate carboxylase in pea and soybean

Abstract Pea (Pisum sativum (L.) cv. Little Marvel) and soybean (Glycine max (L.) Merr. cv. Bragg) were grown and exposed to UV-B radiation under greenhouse conditions. The effects of UV-B radiation on activities and kinetics of ribulose-1,5,-bisphosphate carboxylase (RuBPcase) in both pea and soybean and on growth, chlorophyll, carotenoids and soluble protein in pea were investigated. Plants were irradiated for 6 hr daily from the day of planting with supplemental UV-B radiation which was provided by two Westinghouse FS-40 fluorescent sun lamps filtered with 0.127 mm film of cellulose acetate (UV-B treatment) or 0.127 mm film of Mylar®S (Mylar control). Three UV-B radiation levels were used: 1.09 (treatment T1), 1.36 (treatment T2) and 1.83 (treatment T3) UV-Bseu where 1 UV-Bseu equals to 15.98 mW m−2 of weighted solar UV-B irradiance obtained by applying the weighting function,EXP-[(λ −265)/21]2, which was designed to simulate the DNA absorption spectrum. These UV-B levels corresponded to 6, 21 and 36% calculated decreases in stratospheric ozone concentration for treatment T1, T2 and T3, respectively. In pea plants, stem lengths, plant weights, chlorophyll, carotenoids and soluble protein decreased with increased levels of UV-B radiation. Leaf pigment extracted with 80% acetone from UV-B-treated pea plants showed an increase in absorption in the waveband from 330 to 400 nm. The Vmax (HCO3−1) of RuBP case from T3 pea plant leaves was 58% of that of the control. The Km (CO2) values were 22.4 and 33.9 μM for Mylar control enzyme and T3 enzyme, respectively. The Vmax (RuBP) value of RuBPcase of T3 leaf samples was 42% of that of the conrol. The Km (RuBP) values were 0.36 and 0.14 mM for RuBPcase of the Mylar control and T3 treatment, respectively.

Elevated CO2 increases water use efficiency by sustaining photosynthesis of water-limited maize and sorghum.

Maize and grain sorghum seeds were sown in pots and grown for 39 days in sunlit controlled-environment chambers at 360 (ambient) and 720 (double-ambient, elevated)μmol mol(-1) carbon dioxide concentrations [CO(2)]. Canopy net photosynthesis (PS) and evapotranspiration (TR) was measured throughout and summarized daily from 08:00 to 17:00h Eastern Standard Time. Irrigation was withheld from matched pairs of treatments starting on 26 days after sowing (DAS). By 35 DAS, cumulative PS of drought-stress maize, compared to well-watered plants, was 41% lower under ambient [CO(2)] but only 13% lower under elevated [CO(2)]. In contrast, by 35 DAS, cumulative PS of drought-stress grain sorghum, compared to well-watered plants, was only 9% lower under ambient [CO(2)] and 7% lower under elevated [CO(2)]. During the 27-35 DAS drought period, water use efficiency (WUE, mol CO(2)Kmol(-1)H(2)O), was 3.99, 3.88, 5.50, and 8.65 for maize and 3.75, 4.43, 5.26, and 9.94 for grain sorghum, for ambient-[CO(2)] well-watered, ambient-[CO(2)] stressed, elevated-[CO(2)] well-watered and elevated-[CO(2)] stressed plants, respectively. Young plants of maize and sorghum used water more efficiently at elevated [CO(2)] than at ambient [CO(2)], especially under drought. Reductions in biomass by drought for young maize and grain sorghum plants were 42 and 36% at ambient [CO(2)], compared to 18 and 14% at elevated [CO(2)], respectively. Results of our water stress experiment demonstrated that maintenance of relatively high canopy photosynthetic rates in the face of decreased transpiration rates enhanced WUE in plants grown at elevated [CO(2)]. This confirms experimental evidence and conceptual models that suggest that an increase of intercellular [CO(2)] (or a sustained intercellular [CO(2)]) in the face of decreased stomatal conductance results in relative increases of growth of C(4) plants. In short, drought stress in C(4) crop plants can be ameliorated at elevated [CO(2)] as a result of lower stomatal conductance and sustaining intercellular [CO(2)]. Furthermore, less water might be required for C(4) crops in future higher CO(2) atmospheres, assuming weather and climate similar to present conditions.

Crop Responses to Elevated Carbon Dioxide and Interaction with Temperature: Grain Legumes

SUMMARY Atmospheric carbon dioxide concentration ([CO2]) and other greenhouse gases have risen over the past few decades. If this continues, it could indirectly lead to increases in global temperature. Responses of grain legume crops (soybean, dry bean, peanut and cowpea) to elevated [CO2] and interactions with temperature are summarized. Our research shows that, in the absence of biotic (pests, diseases and weeds) or abiotic (temperature, water and nutrients) stresses, elevated [CO2] will increase yield due to increased photosynthesis and growth. However, at above optimum temperatures, the beneficial effects of elevated [CO2] are more than offset by negative effects of temperature on yield and yield-components, leading to lower seed yield and poor seed quality Future research should focus on developing genetic and agronomic crop management practices to improve crop productivity under changing climates.

Developmental responses of rice to photoperiod and carbon dioxide concentration

Abstract The documented increase in the carbon dioxide concentration of the Earths atmosphere has stimulated interest in the effects of CO 2 on plants and in particular the future prospects for the worlds food supplies. While rice is a major food crop, relatively little is known about the effects of CO 2 concentration on the timing of physiological growth stages and total growth duration, which are important aspects of a rice cultivars adaptability to the environment of a particular geographic region. The objective of this study was to determine the developmental responses of a modern, improved rice cultivar ( Oryza sativa , cultivar ‘IR-30’) to a range of CO 2 concentrations under two contrasting photoperiods. Rice plants were grown season-long in an outdoor, naturally lit, computer-controlled environment, plant growth chambers in CO 2 , concentrations of 160, 250, (subambient) 330 (ambient), 500, 660 and 900 (superambient) μmol CO 2 mol −1 air. The entire experiment was conducted twice during 1987. The first or early planted rice (EPR) experiment was conducted with photoperiod extension lights during the vegetative phase of development, while the second or late-planted rice (LPR) experiment was conducted using only naturally occurring photoperiod. In both experiments, mainstem leaf developmental rates were greater during vegetative rather than reproductive growth stages and leaf appearance rates increased with CO 2 treatment during vegetative development. In the LPR experiment, panicle initiation and boot stage occurred earlier and total growth duration was shortened for rice plants in the superambient compared with ambient and subambient CO 2 treatments. This acceleration of plant development with increasing CO 2 treatment was associated with a CO 2 -induced decrease in the number of mainstem leaves formed during the vegetative phase of growth. The reduced developmental response of rice plants to CO 2 in the EPR compared with the LPR experiment was attributed to the artificially extended photoperiod during the EPR experiment forcing a delay in the onset of reproductive development particularly in the superambient treatments. The CO 2 -induced acceleration of development and shortening of total growth duration should become a topic of interest for rice agronomists and breeders involved with selecting rice cultivars and agronomic practices for a particular geographic region in view of the continued increases in global atmospheric CO 2 concentration.

Dynamic Computer Control of Closed Environmental Plant Growth Chambers. Design and Verification

ABSTRACT CONTROLLED-environment chambers can be used to closely investigate plant responses to well-defined and -maintained conditions. This paper describes the theoretical and practical basis for the design and development of a computer-based growth chamber control system that can produce a wide range of constant or time-varying environments. Analyses of energy, humidity, and CO2 balances, expressed in terms of dry bulb temperature, dewpoint temperature, and CO2 concentration, were developed to relate the effects of external environmental conditions and internal biological and physical processes to the direct regulation of chamber conditions. These relationships were used to match cooling (air conditioners) and heating power to the maximum anticipated latent energy loads and sensible energy requirements. In practice, the theoretical control equations were transformed into digital software algorithms that suited the characteristics of the sensors and hardware in each control sub-system. Design of plant chamber control systems may be hampered by the lack of heat exchanger design information over the range of interest. Controls of outdoor plant chambers are difficult because of the large energy and mass flows relative to system capacitance. Nevertheless, this system demonstrates that feedback-feedforward control algorithms can be used to control several chambers by multiplexing gas samples through CO2 analyzers and dewpoint hygrometers. The combined system of software, sensors and control elements has been successfully used in several CO2 enrichment studies. Dry bulb temperature was regularly controlled to within ±1° C, dewpoint to within ±1.5° C and CO2 concentration to within 5% of desired values.

Interactions of CO2 enrichment and temperature on carbohydrate accumulation and partitioning in rice

Abstract The objective of this study was to determine the long-term effects of CO 2 concentration and temperature on carbohydrate partitioning and status in rice ( Oryza sativa L. cv. IR-30). The plants were grown season-long in sunlit, controlled-environment chambers with CO 2 concentrations of 330 or 660 μmol mol −1 , and daytime air temperatures of 28, 34 or 40°C. In leaf blades, the priority between partitioning of carbon into storage or into export changed with CO 2 concentration and temperature. Leaf sucrose concentration increased with CO 2 enrichment at all temperature regimes. Over the season, elevated CO 2 resulted in an increase in total non-structural carbohydrate (TNC) concentration in leaf blades, leaf sheaths and culms at all temperature treatments. Elevated CO 2 had no effect on carbohydrate concentration in the grain at maturity, however, grain TNC concentration was significantly lowered by increasing temperature. Under the highest temperature regime, the plants in the 330 μmol mol −1 CO 2 treatment died during stem extension while the CO 2 enriched plants survived but produced sterile panicles. The results suggest that CO 2 -enriched plants could survive and maintain carbohydrate production rates at higher temperatures than the non-enriched plants; however, the optimum temperature for TNC accumulation was 28°C at both CO 2 concentrations.

SIMULATION AS A TOOL FOR ANALYZING CROP RESPONSE TO CLIMATE CHANGE

ABSTRACT Simulations of soybean and com (maize) growth for the southeastern U.S.A. were run for 30 baseline years of weather data, 1951-80, for 19 locations with and without supplemental irrigation, using SOYGRO and CERES-Maize crop models. Runs were also made for climatic changes predicted by two General Circulation Models (GCMs) for a doubling of atmospheric carbon dioxide. One climate change scenario resulted in over 50% reduction in rainfed seed yields for both crops, while the impact of the second scenario was negligible. Under irrigation, the simulated results indicated doubled CO2 produced 20% less corn and 14% more soybean, somewhat independent of the climate change scenario. Irrigation water demand was significantly increased.