Global environment change and simulated forage quality of wheat II. Water and nitrogen stress

Forage crops are frequently subjected to stress conditions resulting from inadequate supplies of water and N. Because forages grown under these stress conditions constitute an important resource in animal agriculture, this study was undertaken to assess possible changes in the nutritive value and productivity of forage crops as a consequence of global environment change. A relatively simple, mechanistic model of wheat was extended to simulate growth and important determinants of feed quality ([N], leaf:stem, dry matter digestibility) in an annual, temperate climate C₃ forage grass. Weather data for a semiarid region and different levels of applied N were used to examine the response of forage productivity to various levels of water and N availability. Not surprisingly, responses to global environment change were highly dependent on the availability of both water and N. When either resource was available at low levels, production of digestible dry matter was nearly unchanged by elevated [CO₂] or increased temperature. When compared at equivalent development stages, small increases in forage quality were simulated, mainly because higher temperature resulted in achievement of the initiation of grain fill at an earlier date. As N availability increased, differences in forage characteristics and productivity became more prominent. Elevated ambient [CO₂] increased vegetative mass, digestible dry matter, and concentration of digestible dry matter but decreased leaf:stem and [N]. Increased temperature generally had an effect on forage traits that was opposite to the elevated [CO₂] response. The combined effects of both factors sometimes cancelled each other, but usually one of the factors was dominant. Negative effects of temperature tended to be aggravated by dry conditions. At crop maturity, positive effects of elevated atmospheric [CO₂] on forage productivity and quality were severely decreased by nutrient and physiological constraints. These simulations indicate that when forage crops are grown under irrigation in semiarid regions, there may be substantial and complex changes in productivity and feed quality as a consequence of warmer temperature and elevated atmospheric [CO₂]. Under rainfed conditions, these differences could be quite erratic and virtually unpredictable within the current range of interannual variation in forage productivity and quality.     

Variability in grass forage quality and quantity in response to elevated CO2 and water limitation

Global climate change is expected to alter carbon dioxide concentration ([CO₂]) and water availability, with uncertain impacts on agriculture. Forage quality and quantity in grazing systems are of particular concern because C₃ and C₄ plants respond differently to altered environmental conditions. In a growth chamber, we compared crude protein content, biomass recovery and total crude protein across a set of perennial C₃ and C₄ grasses from the northern U.S. Great Plains under elevated [CO₂] and simulated drought. Simulated 95% confidence intervals indicate both C₃ and C₄ grasses increased forage quality and quantity under elevated [CO₂]. C₄ grasses were generally resistant to water limitation while forage quality and quantity of C₃ grasses declined under simulated drought. Our results are consistent with literature on forage quantity responses to elevated [CO₂] and drought, but forage quality responses contradict expectations. We suggest measuring plant functional traits might better elucidate response mechanisms and ameliorate methodological differences even if traits are not directly applicable to grazing management.     

Elevated atmospheric CO2 effects on N fertilization in grain sorghum and soybean

Increasing atmospheric CO₂ concentration has led to concerns about global changes to the environment. One area of global change that has not been fully addressed is the effect of elevated atmospheric CO₂ on agriculture production inputs. Elevated CO₂ concentration alterations of plant growth and C:N ratios may modify C and N cycling in soil and N fertility. This study was conducted to examine the effects of legume, soybean (Glycine max (L.) Merr.), and non-legume, grain sorghum (Sorghum bicolor (L.) Moench.) carbon dioxide-enriched agro-ecosystems on N soil fertility in a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults). The study was a split-plot design replicated three times with crop species (soybean and grain sorghum) as the main plots and CO₂ concentration (ambient and twice ambient) as subplots using open top field chambers. Fertilizer application was made with ${}^{15}\text{N}$-depleted NH₄NO₃ to act as a fertilizer tracer. Elevated CO₂ increased total biomass production in all 3 years of both grain sorghum (average 30%) and soybean (average 40%). With soybean, while no impact on the plant C:N ratio was observed, the total N content was greatly increased (average 29%) due to increased atmospheric N₂ fixation with elevated CO₂ concentration. With grain sorghum, the total N uptake was not affected, but the C:N ratio was markedly increased (average 31%) by elevated CO₂. No impact of elevated CO₂ level was observed for fertilizer N in grain sorghum. The results from this study indicated that while elevated CO₂ may enhance crop production and change N status in plant tissue, changes to soil N fertilizer application practices may not be needed.     

CO2浓度升高条件下水稻蒸腾与N吸收的关系

利用FACE（Free Air Carbon Dioxide Enrichment）平台技术,用水培试验研究了低氮（14 mg/L）和高氮（28 mg/L）水平下,大气CO2浓度升高条件下水稻蒸腾与N吸收速率的相关关系。结果表明,在CO2浓度升高条件下,水稻生物量增加了36%（低N）和29%（高N）;总吸N量也增加达7%（低N） 和5%（高N）;而总蒸腾量减少28%（低N）和10%（高N）。由于促进更多分蘖的发生,高CO2浓度使分蘖期水稻平均N吸收速率提高了31%～156%（低N）和19%～87%（高N）,在其他时期无明显影响;而高CO2浓度对水稻平均蒸腾速率的影响主要表现在抽穗到灌浆末期。在对照条件下,平均蒸腾速率和平均N吸收速率呈显著正相关;但在CO2浓度升高条件下,两者相关关系不显著。说明人们所推测的“蒸腾效应”——高CO2浓度条件下降低了的蒸腾作用并非影响水稻N吸收的关键因素。     

Millet forage yield and silage quality as affected by water and nitrogen application at different sowing dates

This experiment was conducted to evaluate the effects of two irrigation regimes (control and water stress) and two nitrogen (N) levels (0 and 112.5 kg/ha) on forage yield and silage quality in millet. Bastan (Setaria italica (L.) P. Beauv) and Pishahang (Panicum miliaceum) were sown at two different dates during 2015 and 2016. Both cultivars exhibited reduced dry-matter (DM) yields (45% and 51% in Bastan and Pishahang respectively) due to drought stress. Proline and phenolic contents increased as a result of drought and were significantly and negatively correlated with DM yield and digestibility. Moreover, Pishahang had a reduced acid detergent fibre (ADF) content but improved leaf/stem ratio, digestible dry matter (DDM), relative feed value (RFV), net energy for lactation (NE_L), digestibility and silage quality as a result of drought stress, while no significant effects on these traits were observed in Bastan. Silage quality was greatly cultivar-dependent. Both cultivars had higher levels of DDM, RFV and NE_L at early sowing dates. Nitrogen supply had greater positive effects on increasing ash, crude protein (CP) content and DM yield under normal irrigation than under water-stress conditions. In summary, given the importance of the energy received per unit of forage from an animal husbandry viewpoint and the significance of DM yield per unit area from an agricultural viewpoint, the obtained results might help farmers in choosing not only the best sowing dates but also proper irrigation and N management practices to achieve their quantitative and qualitative objectives in forage production.     

Interactions between elevated atmospheric CO2 and defoliation on North American rangeland plant species at low and high N availability

Although common disturbances of grazing lands like plant defoliation are expected to affect their sensitivity to increasing atmospheric CO₂ concentration, almost no research has been conducted to evaluate how important such effects might be on the direct responses of rangelands to CO₂. This growth chamber experiment subjected intact plant–soil cylinders from a Wyoming, USA, prairie to a 3‐way factorial of CO₂ (370 vs. 720 μL L^?1), defoliation (non‐clipped vs. clipped) and soil nitrogen (control vs. 10 g m^?2 added N) under simulated natural climatic conditions. Above‐ and below‐ground biomass and N dynamics of the functional groups C₃ grasses, C₄ grasses and forbs were investigated. CO₂ and defoliation had independent influences on biomass and N parameters of these rangeland plants. Growth under CO₂‐enriched conditions enhanced above‐ground biomass 50% in C₃ grasses alone, while shoot N concentration declined 16% in both C₃ and C₄ grasses. Plant‐soil ¹⁵N uptake was unaffected by CO₂ treatment. In contrast, defoliation had no effect on biomass, but increased tissue N concentration 29% across all functional groups. Without additional N, forage quality, which is in direct relation to N concentration, will decline under increasing atmospheric CO₂. Increased dominance of C₃ grasses plus reduced forage quality may necessitate changes in grazing management practices in mixed‐species rangelands.     

Effects of nitrogen rate on nitrate–nitrogen accumulation in forage kale and rape crops

Nitrogen fertilizer is applied to supplement soil nitrogen supply to maximize forage brassica crop dry-matter production. However, nitrogen fertilizer applications in excess of that required to maximize growth result in potentially toxic nitrate–nitrogen (NO₃–N) concentrations in grazeable plant tissues. Three experiments, two for forage kale at Lincoln (Canterbury) and one for forage rape at Hastings (Hawke's Bay) in New Zealand were grown under different rates of nitrogen (0–500 kg N ha⁻¹) to determine the effect of different rates of nitrogen on NO₃–N content of different plant parts of the crops. One of the kale experiments was grown with either full irrigation or no rain and no irrigation over summer, hereafter referred to as summer drought. The NO₃–N concentration on a whole plant (weighted average) basis increased from 0·1 mg g⁻¹ dry matter for the control plots to 2·30 mg g⁻¹ for the 500 kg N ha⁻¹ plots for forage kale. It increased from 0·99 for the control plots to 3·37 mg g⁻¹ for the 200 kg N ha⁻¹ plots for forage rape crops. However, NO₃–N concentration increased with N supply under the summer-drought plots from an average of 0·33 mg g⁻¹ when ≤120 kg N ha⁻¹ was applied to 2·30 mg g⁻¹ for the 240 kg N ha⁻¹ treatments but was unaffected by N supply under irrigation. The NO₃–N concentrations were higher in the stems and the petiole (which included the midrib of the leaf) than leaves in all three experiments. The NO₃–N concentration was highest at the bottom of the kale stem and decreased towards the top. We recommend N application rates based on soil tests results, and for conditions similar to the current studies up to 300 kg N ha⁻¹ under irrigation and adjusted lower N rates for regions prone to dry summers.     

Yield formation of CO2-enriched hybrid rice cultivar Shanyou 63 under fully open-air field conditions

Hybrid indica rice (Oryza sativa L.) cultivars play an important role in rice production system due to its heterosis, resistance to environmental stress, large panicle and high yield potential. However, no attention has been given to its yield responses to rising atmospheric [CO₂] in conjunction with nitrogen (N) availability. Therefore we conducted a free air CO₂ enrichment (FACE) experiment at Yangzhou, Jiangsu, China (119°42′0′′E, 32°35′5′′N), in 2004–2006. A three-line hybrid indica rice cv. Shanyou 63 was grown at ambient and elevated (ca. 570 μmol mol⁻¹) [CO₂] under two levels of supplemental N (12.5 g Nm⁻² and 25 g Nm⁻²). Elevated [CO₂] had no effect on phenology, but substantially enhanced grain yield (+34%). The magnitude of yield response to [CO₂] was independent of N fertilization, but varied among different years. On average, elevated [CO₂] increased the panicle number per square meter by 10%, due to an increase in maximum tiller number under enrich [CO₂], while productive tiller ratio remained unaffected. Spikelet number per panicle also showed an average increase of 10% due to elevated [CO₂], which was supported by increased plant height and stem dry weight per tiller. Meanwhile, elevated [CO₂] caused a significant enhancement in both filled spikelet percentage (+5%) and individual grain weight (+4%). Compared with the two prior FACE studies on rice, hybrid indica rice cultivar appears to profit much more from elevated [CO₂] than japonica rice cultivar (ca. +13%), not only due to its stronger sink generation, but also enhanced capacity to utilize the carbon sources in a high [CO₂] environment. The above data has significant implication with respect to N strategies and cultivar selection under projected future [CO₂] levels.     

Implications of Elevated CO2-Induced Changes in Agroecosystem Productivity

SUMMARY

Since CO₂ is a primary input for crop growth, there is interest in how increasing atmospheric CO₂ will affect crop productivity and alter cropping system management. Effects of elevated CO₂ on grain and residue production will be influenced by crop selection. This field study evaluated soybean [C₃; Glycine max(L.) Merr.] and grain sorghum [C₄; Sorghum bicolor (L.) Moench.] cropping systems managed under conservation tillage practices and two atmospheric CO₂ concentrations (ambient and twice ambient) for three growing seasons. Elevated CO₂ increased soybean and sorghum yield by 53% and 17% increase, respectively; reductions in whole plant water use were also greater for soybean than sorghum. These findings suggest that increasing CO₂ could improve future food security, especially in soybean production systems. Elevated CO₂ increased aboveground residue production by > 35% for both crops; such shifts could complement conservation management by increasing soil surface cover, thereby reducing soil erosion. However, increased residue could negatively impact crop stand establishment and implement effectiveness during tillage operations. Elevated CO₂ increased total belowground dry weight for both crops; increased root proliferation may alter soil structural characteristics (e.g., due to increased number and extent of root channels) which could lead to increases in porosity, infiltration rates, and subsequent soil water storage. Nitrate leaching was reduced during the growing season (due to increased N capture by high CO₂-grown crops), and also during the fallow period (likely a result of altered decomposition patterns due to increased C:N ratios of the high CO₂-grown material). Enhanced crop growth (both above-and be-lowground) under elevated CO₂ suggests greater delivery of C to soil, more soil surface residue, and greater percent ground coverage which could reduce soil C losses, increase soil C storage, and help ameliorate the rise in atmospheric CO₂. Results from this study suggests that the biodegradability of crop residues and soil C storage may not only be affected by the environment they were produced in but may also be species dependent. To more fully elucidate the relationships between crop productivity, nutrient cycling, and decomposition of plant materials produced in elevated CO₂ environments, future studies must address species effects (including use of genetically modified crops) and must also consider other factors such as cover crops, crop rotations, soil series, tillage practices, weed management, and regional climatic differences.     

Effect of reconstitution and Na2Co3 on tannin content and in vitro protein digestibility of faba bean cultivars

Two faba bean cultivars (317/99/81 and Giaz/402) obtained from Shambat Research Station in Northern Sudan, were used for this study. Investigation showed that the tannin contents of untreated seeds were 0.077% and 0.067% for cultivars 317/99/81 and Giza/402. In vitro protein digestibility values were 80.68% and 81.48% for the two cultivars, respectively. The extractable tannin content of the faba bean cultivars was markedly reduced by imbibing water or Na₂CO₃ solution into whole seeds and incubating them at 30°C for 1, 3, 6, 12 or 24 hours, or at 100°C for 5, 10 or 20 minutes. The extent of reduction depended on time, temperature, and Na₂CO₃ concentration; the percent tannin extracted and percent in vitro protein digestibility increased with time or Na₂CO₃ concentration, while application of high temperature reduced the time.     

CO2 Enrichment Effects on Forage and Grain Nitrogen Content of Pasture and Cereal Plants

SUMMARY

Increasing atmospheric CO₂ concentrations [CO₂] have the potential to enhance growth and yield of agricultural plants. Con-comitantly plants grown under high [CO₂] show significant changes of the chemical composition of their foliage and of other plant parts. Particularly, high [CO₂] result in a decrease of plant nitrogen (N) concentration, which may have serious consequences for crop quality. This presentation summarizes the results of a variety of CO₂ enrichment studies with pasture plants (Lolium spp., Trifolium repens) and cereal species (Triticum aestivum, Hordeum vulgare) which were conducted at our laboratory under different growth and CO₂ exposure conditions ranging from controlled environment studies to investigations under free air carbon dioxide enrichment (FACE). With the exception of clover in all experiments a CO₂-induced decline of forage and grain N concentration was observed. The magnitude of this reduction differed between species, cultivars, management conditions (N fertilization) and CO₂ exposure conditions. No unambiguous evidence was obtained whether N fertilization can contribute to meet the quality requirements for cereals and grass monocultures with respect to tissue N concentrations in a future high-CO₂ world. As shown in the FACE experiments current application rates of N fertilizers are inadequate to achieve quality standards.     

Intercropping of orchardgrass and alfalfa improves soil fertility,forage yield,feeding values and land use efficiency while limiting ruminal greenhouse gas emissions

Intercropping has been a globally accepted practice for forage production, however, consideration of multiple performance criteria for intercropping including forage production, feed use efficiency and ruminal greenhouse gas emissions needs to be further investigated. A two-year field study was conducted to evaluate forage dry matter (DM) yield, nutritive value, feeding values and land-use efficiency as well as ruminal carbon dioxide (CO₂) and methane (CH₄) emissions of intercropped orchardgrass (Dactylis glomerata) and alfalfa (Medicago sativa) sown in five intercropping ratios (100:0, 75:25, 50:50, 25:75, and 0:100, based on seed weight) and three nitrogen (N) fertilizer levels (0, 50, and 100 kg ha⁻¹). Increasing alfalfa proportion and N fertilizer level increased soil nutrients and the two-year total DM yield. Intercropping increased both land and nitrogen use efficiency (NUE) compared with monocultures. Greater NUE was obtained when N fertilizer was applied at 50 kg ha⁻¹, compared with 100 kg ha⁻¹. Increasing the proportion of alfalfa in intercrops increased the crude protein yield and rumen undegraded protein yield. Harvested forage intercrops were incubated with ruminal fluid for 48 h. Degraded DM yield, CO₂ and CH₄ emissions increased with increasing alfalfa proportion in intercrops. Overall, the 75:25 of orchardgrass-alfalfa intercrops was recommended as the best compromise between high forage productivity, superior feed use efficiency and low ruminal greenhouse gas emissions through complementary effects. The results indicate that the appropriate N fertilization level would be 50 kg ha⁻¹ for acquiring higher nitrogen use efficiency and forage productivity.     

Effect of two additives on the fermentation,in vitro digestibility and aerobic security of Sorghum–sudangrass hybrid silages

Two additives (Silo Guard (SG) and propionic acid (PA)) were tested for their effects on the quality and aerobic security of sorghum–sudangrass hybrid silages (JC‐1 and WC‐2). Two sorghum–sudangrass hybrid varieties were harvested for ensiling without additives (CK) or after the following treatments: SG at 0·5% of fresh forage or PA at 0·5% of fresh forage, with three replicates per treatment. The addition of SG and PA both affected the fermentation quality and chemical composition of the silages by lowering pH and NH₃‐N/TN and increasing lactic acid, the LA/TA ratio, WSC and CP concentrations compared with the untreated silages. In vitro DM digestibility (IVDMD), in vitro NDF digestibility (IVNDFD) and in vitro CP digestibility (IVCPD) were increased by SG in the JC‐1 silages and WC‐2 silages. Both additives improved the aerobic stability of sorghum–sudangrass hybrid silages. Furthermore, the additives reduced the mould counts and the aflatoxin and zearalenone levels compared with the untreated silages following aerobic exposure. Therefore, ensiling two sorghum–sudangrass hybrid varieties resulted in high‐quality silages. The addition of SG and PA improved silage quality, in vitro digestibility and aerobic security.     

Forage soybean performance in mediterranean environments

Livestock producers are interested in growing forage soybean [Glycine max (L.) Merr.] in summer and ensiling alone or in mixtures with corn or sorghum. Four row spacings (20, 40, 60, and 80 cm), four seeding rates (50, 100, 150, and 200 kg seeds per hectare) and four harvesting stages for forage production (V₅, R₂, R₄, and R₆) were evaluated under irrigated conditions in a randomized split–split plot design with three replications in three different locations in Turkey with Mediterranean-type climate in 2004 and 2005. Dry matter (DM) yield was significantly reduced with increased row spacings in all locations. There was no significant difference between 20, 40, or 60 cm row spacings while 80 cm provided the lowest yield. Increased seeding rates (50, 100, 150, and 200 kg seeds per hectare) generally increased DM yield, although the most suitable row spacing varied by location. DM yield was significantly affected by harvest maturity increasing with advancing maturity in all locations. DM constituent plant components were generally unaffected by row spacing and seeding rate but harvest maturity did significantly affect DM partitioning. As expected, leaf blade fractions decreased continually as plant maturity increased, while stem and flower plus pod fraction increased from V₅ to R₆. In general, row spacing and seeding rate did not significantly affect crude protein, degradable protein, and in vitro dry matter digestibility of soybean forage, but all decreased significantly with advancing maturity. These studies demonstrated soybeans managed for forage in a Mediterranean-type environment can average of 9.3 and 11.3 t ha⁻¹ dry matter yield at R₄ and R₆ stages, respectively, while averaging 13.3% crude protein, 8.2% degradable protein, and 60.6% in vitro dry matter digestibility.     

Wheat grain quality under increasing atmospheric CO2 concentrations in a semi-arid cropping system

We investigated wheat (Triticum aestivum) grain quality under Free Air CO₂ Enrichment (FACE) of 550 ± 10% CO₂ μmol mol⁻¹. In each of two full growing seasons (2008 and 2009), two times of sowing were compared, with late sowing designed to mimic high temperature during grain filling. Grain samples were subjected to a range of physical, nutritional and rheological quality assessments. Elevated CO₂ increased thousand grain weight (8%) and grain diameter (5%). Flour protein concentration was reduced by 11% at e[CO₂], with the highest reduction being observed at the late time of sowing in 2009, (15%). Most of the grain mineral concentrations decreased under e[CO₂] - Ca (11%), Mg (7%), P (11%) and S (7%), Fe (10%), Zn (17%), Na (19%), while total uptake of these nutrients per unit ground area increased. Rheological properties of the flour were altered by e[CO₂] and bread volume reduced by 7%. Phytate concentration in grains tended to decrease (17%) at e[CO₂] while grain fructan concentration remained unchanged. The data suggest that rising atmospheric [CO₂] will reduce the nutritional and rheological quality of wheat grain, but at high temperature, e[CO₂] effects may be moderated. Reduced phytate concentrations at e[CO₂] may improve bioavailability of Fe and Zn in wheat grain.     

Wheat grain quality under increasing atmospheric CO2 concentrations in a semi-arid cropping system

We investigated wheat (Triticum aestivum) grain quality under Free Air CO₂ Enrichment (FACE) of 550 ± 10% CO₂ μmol mol⁻¹. In each of two full growing seasons (2008 and 2009), two times of sowing were compared, with late sowing designed to mimic high temperature during grain filling. Grain samples were subjected to a range of physical, nutritional and rheological quality assessments. Elevated CO₂ increased thousand grain weight (8%) and grain diameter (5%). Flour protein concentration was reduced by 11% at e[CO₂], with the highest reduction being observed at the late time of sowing in 2009, (15%). Most of the grain mineral concentrations decreased under e[CO₂] - Ca (11%), Mg (7%), P (11%) and S (7%), Fe (10%), Zn (17%), Na (19%), while total uptake of these nutrients per unit ground area increased. Rheological properties of the flour were altered by e[CO₂] and bread volume reduced by 7%. Phytate concentration in grains tended to decrease (17%) at e[CO₂] while grain fructan concentration remained unchanged. The data suggest that rising atmospheric [CO₂] will reduce the nutritional and rheological quality of wheat grain, but at high temperature, e[CO₂] effects may be moderated. Reduced phytate concentrations at e[CO₂] may improve bioavailability of Fe and Zn in wheat grain.     

Effect of CO2 Concentration,Temperature and N Fertilization on Biomass Production of Soybean Genotypes Differing in N Fixation Capacity

Abstract

We tested the hypothesis that elevated CO₂ concentration [CO₂]-induced enhancement of biomass production of soybean is greater in a genotype that has a higher nitrogen (N) fixation capacity. Furthermore, we analyzed theinteractive effects of N fertilization, temperature and [CO₂] on biomass production. Three genetically related genotypes: Enrei (normally-nodulating genotype), Kanto 100 (supernodulating genotype), and En1282 (non-nodulating genotype) were grown in pots, with or without N fertilizer for two years (2004, 2005). They were then subjected to two different [CO₂] (ambient and elevated (ambient + 200 ?mol mol-¹)) × two temperature regimes (low,high (low + 4~5ºC)). Top dry weight at maturity was the greatest in the elevated [CO₂] × high temperature regime, irrespective of genotype and N fertilization. The [CO₂] elevation generally enhanced N acquisition and dry matter production during the vegetative growth stage, and the enhancement was more pronounced in the nodulating genotypes (Enrei and Kanto 100) than in the non-nodulating genotype (En1282), indicating that N supply through N fixation contributes to elevated [CO₂]-induced biomass production in soybean. However, the relative responsiveness ofbiomass production to elevated [CO₂] was not necessarily higher in the supernodulating genotype than the normally-nodulating genotype. The N utilization efficiency to produce biomass was inferior in the supernodulating genotype than in the normally-nodulating and non-nodulating genotypes. These results did not fully verify the hypothesis that elevated [CO₂]-induced enhancement of biomass production of soybean is greater in a genotype with a higher N fixation capacity.     

Elevated carbon dioxide and temperature effects on rice yield,leaf greenness,and phenological stages duration

The present field experiment was conducted during two consecutive cropping seasons in central Portugal to study the effects of simultaneous elevation of carbon dioxide concentration ([CO₂]) (550 μmol mol^?1) and air temperature (+2–3 °C) on japonica rice (Oryza sativa L. “Ariete”) yield, crop duration, and SPAD-values across the seasons compared with the open-field condition. Open-top chambers were used in the field to assess the effect of elevated air temperature alone or the combined effect of elevated air temperature and atmospheric [CO₂]. Open-field condition was assessed with randomized plots under ambient air temperature and actual atmospheric [CO₂] (average 382 μmol mol^?1). Results obtained showed that the rice “Ariete” had a moderate high yielding under open-field condition, but was susceptible to air temperature rise of +2–3 °C under controlled conditions resulting in reduction of grain yield. The combined increase of atmospheric [CO₂] with elevated air temperature compensated for the negative effect of temperature rise alone and crop yield was higher than in the open-field. SPAD-readings at reproductive stage explained by more than 60 % variation the straw dry matter, but this finding requires further studies for consolidation. It can be concluded that potential increase in air temperature may limit rice yield in the near future under Mediterranean areas where climate change scenario poses a serious threat, but long term field experiments are required.     

Effects of elevated CO2 concentration on growth and photosynthesis of Chinese yam under different temperature regimes

Chinese yam (‘yam’) was grown at different carbon dioxide concentrations ([CO₂]), namely, ambient and elevated (ambient + 200 μmol mol^?1), under low- and high-temperature regimes in summer and autumn, separately. For comparison, rice was also grown under these conditions. Mean air temperatures in the low- and high-temperatures were respectively 24.1 and 29.1 °C in summer experiment and 20.2 and 24.9 °C in autumn experiment. In summer experiment, yam vine length, leaf area, leaf dry weight (DW), and total DW were significantly higher under elevated [CO₂] than ambient [CO₂] in both temperature regimes. Additionally, number of leaves, vine DW, and root DW were significantly higher under elevated [CO₂] than under ambient [CO₂] in the low-temperature regime. In autumn experiment, tuber DW was significantly higher under elevated [CO₂] than under ambient [CO₂] in the high-temperature regime. These results demonstrate that yam shows positive growth responses to elevated [CO₂]. Analysis of variance revealed that significant effect of [CO₂] × air temperature interaction on yam total DW was not detected. Elevated-to-ambient [CO₂] ratios of all growth parameters in summer experiment were higher in yam than in rice. The results suggest that the contribution of elevated [CO₂] is higher in yam than in rice under summer. Yam net photosynthetic rate was significantly higher under elevated [CO₂] than under ambient [CO₂] in both temperature regimes in summer. Elevated [CO₂] significantly affected on the rate in yam but not in rice in both experiments. These findings indicate that photosynthesis responds more readily to elevated [CO₂] in yam than in rice.     

Effects of free air carbon dioxide enrichment and nitrogen supply on growth and yield of winter barley cultivated in a crop rotation

The increase in atmospheric CO₂ concentration [CO₂] has been demonstrated to stimulate growth of C₃ crops. Although barley is one of the important cereals of the world, little information exists about the effect of elevated [CO₂] on grain yield of this crop, and realistic data from field experiments are lacking. Therefore, winter barley was grown within a crop rotation over two rotation cycles (2000 and 2003) at present and elevated [CO₂](375 ppm and 550 ppm) and at two levels of nitrogen supply (adequate (N2): 262 kg ha⁻¹ in 1st year and 179 kg ha⁻¹ in 2nd year) and 50% of adequate (N1)). The experiments were carried out in a free air CO₂ enrichment (FACE) system in Braunschweig, Germany. The reduction in nitrogen supply decreased seasonal radiation absorption of the green canopy under ambient [CO₂] by 23%, while CO₂ enrichment had a positive effect under low nitrogen (+8%). Radiation use efficiency was increased by CO₂ elevation under both N levels (+12%). The CO₂ effect on final above ground biomass was similar for both nitrogen treatments (N1: +16%; N2: +13%). CO₂ enrichment did not affect leaf biomass, but increased ear and stem biomass. In addition, final stem dry weight was higher under low (+27%) than under high nitrogen (+13%). Similar findings were obtained for the amount of stem reserves available during grain filling. Relative CO₂ response of grain yield was independent of nitrogen supply (N1: +13%; N2: +12%). The positive CO₂ effect on grain yield was primarily due to a higher grain number, while changes of individual grain weight were small. This corresponds to the findings that under low nitrogen grain growth was unaffected by CO₂ and that under adequate nitrogen the positive effect on grain filling rate was counterbalanced by shortening of grain filling duration.