Sorghum bicolor prioritizes the recovery of its photosynthetic activity when re-watered after severe drought stress,while manages to preserve it under elevated CO2 and drought

Understanding plant response and resilience to drought under a high CO₂ environment will be crucial to ensure crop production in the future. Sorghum bicolor is a C₄ plant that resists drought better than other crops, which could make it a good alternative to be grown under future climatic conditions. Here, we analyse the physiological response of sorghum under 350 ppm CO₂ (aCO₂) or 700 ppm CO₂ (eCO₂) with drought (D) or without drought (WW) for 9, 13 and 16 days; as well as its resilience under long (R1: 9D + 7R) or short (R2: 13D + 3R) recovery treatments. Sorghum showed elevated rates of gs under aCO₂ and WW, which resulted in a significant decrease in Ψ_w, gs, E, Φ_PSII, F_v’/F_m′ when exposed to drought. Consequently, A was greatly decreased. When re-watered, both re-watering treatments prioritized A recovery by restoring photosynthetic machinery under aCO₂, whereas under eCO₂ plants required little recovery since plant were hardly affected by drought. However, sorghum growth rate for aboveground organs did not reach control values, indicating a slower long-term recovery. Overall, these results provide information about the resilience of sorghum and its utility as a suitable candidate for the drought episodes of the future.     

Cultivar Specific Response of CO2 Fertilization on Two Tropical Mung Bean (Vigna radiata L.) Cultivars: ROS Generation,Antioxidant Status,Physiology, Growth,Yield and Seed Quality

Increasing atmospheric carbon dioxide concentration (CO₂) is an important component of global climate change that will have a significant impact on the productivity of crop plants. In recent years, growth and yield of agricultural crop plants have been shown to increase with elevated CO₂ (EC) and have enticed considerable interest due to variation in the response of crop plants. In this study, comparative response of two mung bean cultivars (HUM‐2 and HUM‐6) was evaluated against EC at different growth stages under near‐natural conditions for two consecutive years. The plants were grown in ambient as well as EC (700 ppm) in specially designed open‐top chambers. Under elevated CO₂, marked down‐regulation of reactive oxygen species (ROS) levels, membrane disruption and activities of superoxide dismutase and catalase were noticed in both the cultivars, but the extent of reduction was more in HUM‐6. As compared to ambient CO₂, EC increased total chlorophyll, photosynthetic rate, growth and yield parameters. Cultivar‐specific response was noticed as HUM‐6 showed higher increase in yield attributes than HUM‐2. Under CO₂ treatment, soluble protein and reducing sugars decreased while total soluble sugars and starch showed an opposite trend. Principal component analysis showed that both the cultivars responded more or less similarly to EC in their respective groupings of physiological and growth parameters, but the magnitude of ROS and antioxidative enzymes was variable. The experimental findings depict that both the cultivars of mung bean showed contrasting response against EC and paved the way for selecting the suitable cultivar having higher productivity in a future high‐CO₂ environment.     

Effects of Single and Multifactor Treatments with Elevated Temperature,CO2 and Ozone on Oilseed Rape and Barley

We investigated the effect of elevated [CO₂], [O₃] and temperature on plant productivity and if these climate factors interacted with each other in multifactor treatments. The climate effects were studied in 14 different cultivars/lines of European spring oilseed rape (Brassica napus L.) and spring barley (Hordeum vulgare L.). Seven genotypes of each species were cultivated in six single‐ and multifactor treatments with ambient or elevated CO₂ (385 ppm and 700 ppm), O₃ (20 ppb and 60 ppb) and temperature (12/19 °C and 17/24 °C). Growth and production parameters were measured. Elevated CO₂ increased yield and biomass. Seed number increased by about 47 % in barley and by 26 % in oilseed rape, but in oilseed rape, the TSW was significantly decreased, possibly because of shortening of the seed filling period. Higher temperatures decreased yield and biomass significantly in both species. A significantly decreased yield and thousand grain weight was also seen in barley due to elevated O₃. The multifactor combination of elevated CO₂, O₃ and temperature showed a decrease in growth and production in the two species, though not statistically significant for all parameters. This trend suggests that the expected increase in the plant production in northern Europe, indicated by Intergovernmental Panel on Climate Change (IPCC) as a consequence of increased [CO₂] and temperature, may not hold, due to interactions between these abiotic factors.     

Effect of Phosphorus Nutrition on Growth and Physiology of Cotton Under Ambient and Elevated Carbon Dioxide

Phosphorous deficiency in soil limits crop growth and productivity in the majority of arable lands worldwide and may moderate the growth enhancement effect of rising atmospheric carbon dioxide (CO₂) concentration. To evaluate the interactive effect of these two factors on cotton (Gossypium hirsutum) growth and physiology, plants were grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.20, 0.05 and 0.01 mm ) under ambient and elevated (400 and 800 μmol mol^?1, respectively) CO₂. Phosphate stress caused stunted growth and resulted in early leaf senescence with severely decreased leaf area and photosynthesis. Phosphate stress led to over 77 % reduction in total biomass across CO₂ levels. There was a below‐ground (roots) shift in biomass partitioning under Pi deficiency. While tissue phosphorus (P) decreased, tissue nitrogen (N) content tended to increase under Pi deficiency. The CO₂ × Pi interactions were significant on leaf area, photosynthesis and biomass accumulation. The stimulatory effect of elevated CO₂ on growth and photosynthesis was reduced or highly depressed suggesting an increased sensitivity of cotton to Pi deficiency under elevated CO₂. Although, tissue P and stomatal conductance were lower at elevated CO₂, these did not appear to be the main causes of cotton unresponsiveness to elevated CO₂ under severe Pi‐stress. The alteration in the uptake and utilization of N was suggested due to a consistent reduction (18–21 %) in the cotton plant tissue N content under elevated CO₂.     

Do Increasing Atmospheric CO2 Concentrations Contribute to Yield Increases of German Crops?

The global atmospheric CO₂-concentration is increasing and there has been an increase in Germany of about 30 ppm from 340 ppm to 370 ppm CO₂ during the last two decades. The hectare yield of many crops has also increased during this time period. The objective of the present study was to estimate whether the past and future change in the atmospheric composition significantly contributes to the increase in hectare yield. Different crop species (beans, Phaseolus vulgaris, cv Pfälzer Juni; spring barley, Hordeum vulgare L., cvs. Alexis and Arena; spring wheat, Triticum aestivum L., cvs. Star and Turbo; maize, Zea mays L., cvs. Bonny and Boss) were grown at ambient (372 ppm) and at slightly elevated CO₂-concentrations (459 ppm and 539 ppm) in open-top chambers and the effect of the different CCVconcentrations on the growth and yield of the plants was measured. The past and future CO₂-effect was estimated from the slope of a linear CO₂-yield curve (percentage increase in yield per ppm CO_2′ 100% at 370 ppm) fitted to the data and those from previous studies on wheat and maize. The percentage increase in yield per ppm CO₂ is insignificant for beans, of borderline significance for silage maize (0.06 % per ppm), and 0.35 % per ppm and 0.26 % per ppm for barley and wheat, respectively. The COj-elevation primarily decreases the tiller dieback of the cereals. Considering the increase in CO₂ of 30 ppm and in the hectare yield of 25 % (barley) and 28 % (wheat) from 1970 to 1990, the contribution of CO₂ to the increase in the agricultural production is estimated to be one fourth up to one half of the increase in hectare yield of spring cereals. Given a recent yearly increase of 2 ppm the future CO_:-related increase in hectare yield is estimated to be about 0.5–0.7% per year.     

Effects of Free‐Air Carbon Dioxide Enrichment on Sap Flow and Canopy Microclimate of Maize Grown under Different Water Supply

The rise of atmospheric CO₂ concentration ([CO₂]) affects stomatal conductance and thus transpiration and leaf temperature. We evaluated the effect of elevated [CO₂] levels under different water supply on daily sap flow and canopy microclimate (air temperature (Tc) and vapour pressure deficit (VPD)) of maize. The crop was cultivated in circular field plots under ambient (AMB, 378 μmol mol^?1) and elevated [CO₂] (FACE, 550 μmol mol^?1) using free‐air CO₂ enrichment with sufficient water in 2007, while in 2008 a DRY semicircle received only half as much water as compared to the WET semicircle from mid of July. In 2007, sap flow was measured in WET simultaneously under AMB and FACE conditions and was significantly decreased by elevated [CO₂]. In 2008, sap flow was measured in all four treatments but not simultaneously. Therefore, data were correlated with potential evaporation and the slopes were used to determine treatment effects. Drought reduced whole‐plant transpiration by 50 % and 37 % as compared to WET conditions under AMB and FACE, respectively. Moreover, CO₂ enrichment did not affect sap flow under drought but decreased it under WET by 20 % averaged over both years. The saving of water in the period before the drought treatment resulted in a displacement of dry soil conditions under FACE as compared to AMB. Under WET, CO₂ enrichment always increased Tc and VPD during the day. Under DRY, FACE plots were warmer and drier most of the time in August, but cooler and damper short after the start of drought in July and from the end of August onwards. Thus, the CO₂ effect on transpiration under drought was variable and detectable rather easy by measuring canopy microclimate.     

Effects of free‐air CO2 enrichment and drought on root growth of field grown maize and sorghum

Increasing CO₂ concentration ([CO₂]) is thought to induce climate change and thereby increase air temperatures and the risk of drought stress, the latter impairing crop growth. The objective of this study was to investigate the effects of elevated [CO₂] and drought stress on root growth of one maize genotype (Zea mays cv. Simao) and two sorghum genotypes (Sorghum bicolor cv. Bulldozer and Sorghum bicolor × Sorghum sudanense cv. Inka) under the cool moderate climate of Central Europe. It was hypothesized that root growth stimulation due to elevated [CO₂] compensates for a reduced root growth under drought stress. Therefore, we established an experiment within a f ree‐a ir c arbon dioxide e nrichment system (FACE) in 2010 and 2011. Sorghum and maize genotypes were grown under ambient [CO₂] (385 ppm CO₂) and elevated [CO₂] (600 ppm CO₂) and in combination with restricted and sufficient water supply. Elevated [CO₂] decreased root length density (RLD) in the upper soil layers for all genotypes, but increased it in deeper layers. Higher [CO₂] enhanced specific root length (SRL) of “Simao” and “Bulldozer,” however, did not affect that of “Inka.” “Simao” achieved a higher SRL than the sorghum genotypes, indicating an efficient investment in root dry matter. Although elevated [CO₂] affected the root growth, no interaction with the water treatment and, consequently, no compensatory effect of elevated [CO₂] could be identified.     

Elevated atmospheric CO2 and the future of crop plants

Atmospheric CO₂ levels on Earth have risen steeply over the last 60 years and will continue to do so in future. CO₂ traps heat from earth's surface, which causes an increase in temperature and leads to other climatic changes. Crop plants are currently challenged by climate change. In general, elevated CO₂ increases photosynthetic rates, plant growth and the ability of plants to counteract stress. However, the effect of eCO₂ on respiration is not apparent. Plants growing at eCO₂ probably do not have sufficient respiratory ATP to drive cellular processes like nutrient uptake and transport, which impairs their nutritional quality. Here, we review how eCO₂ modulates growth and nutritional value of crop plants, emphasizing the contribution of photosynthesis and respiration. We highlight the mechanisms that modulate acclimation and adaptive responses of plants to eCO₂ and also discuss the ecological consequences. Finally, we project sorghum as a model for an eCO₂ ready crop.     

Does interspecific competition change the barley's response and recovery from heat wave?

Different species have different sensitivity to heat waves; therefore, interspecific competition may affect the crop response to heat waves. We investigated the effects of heat waves on spring barley (Hordeum vulgare L.) grown with and without wild mustard (Sinapis arvensis L.) as well as the recovery of barleys from stress. The plants were exposed to a 7‐day 35/28ºC (day/night) heat wave at ambient CO₂ (400 μmol/mol) and elevated CO₂ (800 μmol/mol). All seedlings were rehydrated and returned to control conditions (21/14ºC, CO₂ 400 μmol/mol) after the cease of heat wave and grown for a 7‐day period of recovery. Heat wave had more pronounced negative effect on the barley's aboveground biomass under competition with mustard, whereas the response of root biomass was not influenced by the presence of weeds. The heat wave induced reductions in barley's photosynthetic rate, stomatal conductance and water use efficiency under interspecific competition were higher compared to monocultured conditions. Interspecific competition impaired and delayed the recovery of barley's biomass production and leaf gas exchange parameters after heat wave. Elevated CO₂ slightly mitigated negative heat wave impact on the growth and leaf gas exchange parameters but had no effect during the recovery period.     

Response of Growth and Yield of Rice (Oryza sativa) to Elevated Atmospheric Carbon Dioxide in the Subhumid Zone of Sri Lanka

Increasing atmospheric CO₂ is recognized as a major aspect of global climate change that would have a significant impact on the productivity of major agricultural crops. Two field experiments were done, with the objective of quantifying the response of a short‐duration rice (Oryza sativa) variety (BG‐300) to elevated atmospheric carbon dioxide, in the low elevation, subhumid zone of Sri Lanka. The experiment contained three treatments. In the elevated CO₂ treatment, rice was grown at a CO₂ concentration of 570 µmol/mol within open top chambers (OTC s). The ambient CO₂ treatment included crops grown within OTC s, but maintained at the ambient CO₂ concentration of 370 µmol/mol. The third treatment was a crop grown in the open field under ambient CO₂ concentration. Grain yields of rice crops grown under elevated CO₂ were 24 % and 39 % greater than the respective ambient treatments in the maha (January – March 2001) and yala (May – August, 2001) seasons. Significant increases in total biomass at harvest (23 % and 39 %, respectively, in maha and yala) were more responsible for the above yield increases than the slight increases in the harvest index (4 % and 2 %). Yields of the ambient and open field treatments did not differ significantly. Among the yield components, the number of panicles per hill was significantly higher in the elevated treatment and showed significant positive correlations with grain yield in both seasons. In addition, grain yield showed significant positive correlations with the percentage of filled grains in maha and the number of grains per panicle in yala. Significant increases in the number of tillers per hill under elevated CO₂ were responsible for its greater leaf area index and the greater numbers of panicles per hill. Crops under elevated CO₂ accumulated biomass faster than those grown under ambient CO₂ during the vegetative and grain‐filling stages. The results of this study demonstrate that elevated CO₂ causes significant yield increases in rice, even when it is grown in warm, subhumid tropical climates.     

Effects of CO2 Enrichment and Drought on Photosynthesis,Growth and Yield of an Old and a Modern Barley Cultivar

Susceptibility of crops to drought may change under atmospheric CO₂ enrichment. We tested the effects of CO₂ enrichment and drought on the older malting barley cultivar Golden Promise (GP) and the recent variety Bambina (BA). Hypothesizing that CO₂ enrichment mitigates the adverse effects of drought and that GP shows a stronger response to CO₂ enrichment than BA, plants of both cultivars were grown in climate chambers. Optimal and reduced watering levels and two CO₂ concentrations (380 and 550 ppm) were used to investigate photosynthetic parameters, growth and yield. In contrast to expectations, CO₂ increased total plant biomass by 34 % in the modern cultivar while the growth stimulation was not significant in GP. As a reaction to drought, BA showed reduced biomass under elevated CO₂, which was not seen in GP. Grain yield and harvest index (HI) were negatively influenced by drought and increased by CO₂ enrichment. BA formed higher grain yield and had higher water‐use efficiency of grain yield and HI compared to GP. CO₂ fertilization compensated for the negative effect of drought on grain yield and HI, especially in GP. Stomatal conductance proved to be the gas exchange parameter most sensitive to drought. Photosynthetic rate of BA showed more pronounced reaction to drought compared to GP. Overall, BA turned out to respond more intense to changes in water supply and CO₂ enrichment than the older GP.     

Heat,wheat and CO2: The relevance of timing and the mode of temperature stress on biomass and yield

Atmospheric CO₂ enrichment affects C3 crops both directly via increased carbon gain and improved water use efficiency and indirectly via higher temperatures and more frequent climatic extremes. Here we investigated the response of spring wheat (Triticum aestivum L. cv. Triso) to CO₂ enrichment (550 vs. 380 µmol/mol) and heat, applied as a constant +4°C increase or a typical heat wave either before or after anthesis, or as two typical heat waves before and after anthesis. We applied a climate chamber approach closely mimicking ambient conditions. CO₂ enrichment increased above‐ground biomass and yield by c. 7 and 10%, but was not able to compensate for adverse heat stress effects, neither before nor after anthesis, with few exceptions only. Yield depression due to heat stress was most severe when two heat waves were applied (?19%). This adverse effect was, however, compensated by CO₂ enrichment. Applying heat stress before or after anthesis did not exert different effects on yield for both +4°C warming and heat wave application. However, +4°C depressed yield more than a heat wave at ambient CO₂, but not so at elevated CO₂. Thus, the interactive effects were complex and prediction of future wheat yield under CO₂ enrichment and climate extremes deserves more attention.     

The Alleviating Effect of Elevated CO2 on Heat Stress Susceptibility of Two Wheat (Triticum aestivum L.) Cultivars

This study analysed the alleviating effect of elevated CO₂ on stress‐induced decreases in photosynthesis and changes in carbohydrate metabolism in two wheat cultivars (Triticum aestivum L.) of different origin. The plants were grown in ambient (400 μl l^?1) and elevated (800 μl l^?1) CO₂ with a day/night temperature of 15/10 °C. At the growth stages of tillering, booting and anthesis, the plants were subjected to heat stress of 40 °C for three continuous days. Photosynthetic parameters, maximum quantum efficiency of photosystem II (PSII) photochemistry (F_v/F_m) and contents of pigments and carbohydrates in leaves were analysed before and during the stress treatments as well as after 1 day of recovery. Heat stress reduced P_N and F_v/F_m in both wheat cultivars, but plants grown in elevated CO₂ maintained higher P_N and F_v/F_m in comparison with plants grown in ambient CO₂. Heat stress reduced leaf chlorophyll contents and increased leaf sucrose contents in both cultivars grown at ambient and elevated CO₂. The content of hexoses in the leaves increased mainly in the tolerant cultivar in response to the combination of elevated CO₂ and heat stress. The results show that heat stress tolerance in wheat is related to cultivar origin, the phenological stage of the plants and can be alleviated by elevated CO₂. This confirms the complex interrelation between environmental factors and genotypic traits that influence crop performance under various climatic stresses.     

Including root architecture in a crop model improves predictions of spring wheat grain yield and above‐ground biomass under water limitations

Although the root length density (RLD) of crops depends on their root system architecture (RSA), the root growth modules of many 1D field crop models often ignored the RSA in the simulation of the RLD. In this study, two model set‐up scenarios were used to simulate the RLD, above‐ground biomass (AGB) and grain yield (GY) of water‐stressed spring wheat in Germany, aiming to investigate the impact of improved RLD on AGB and GY predictions. In scenario 1, SlimRoot, a root growth sub‐model that does not consider the RSA of the crop, was coupled to a Lintul5‐SlimNitrogen‐SoilCN‐Hillflow1D crop model combination. In scenario 2, SlimRoot was replaced with the Somma sub‐model which considered the RSA for simulating RLD. The simulated RLD, AGB and GY were compared with observations. Scenario 2 predicted the RLD, AGB and GY with an average root mean square error (RMSE) of 0.43 cm/cm³, 0.59 t/ha and 1.03 t/ha, respectively, against 1.03 cm/cm³, 1.20 t/ha and 2.64 t/ha for scenario 1. The lower RMSE under scenario 2 shows that, even under water‐stress conditions, predictions of GY and AGB can be improved by considering the RSA of the crop for simulating the RLD.     

Effects of CO2 enrichment on young plant growth of 96 genotypes of tomato (Lycopersicon esculentum)

Summary The early growth of 96 genotypes of tomato was studied at 320 ppm CO₂ and at 750 ppm CO₂ in separate climate rooms. Plants were harvested at 40 and 55 days after sowing. Fresh and dry weights were determined. Large differences between genotypes were found for average plant fresh and dry weights and for relative growth rates. The average overall growth enhancement by CO₂ enrichment was 2.3. Two genotypes showed significant genotype x CO₂ interaction. The consequences of these results for tomato breeding are discussed.     

Use of barley seed vigour to discriminate drought and cold tolerance in crop years with high seed vigour and low trait variation

Seed vigour is a precondition for early and homogenous field emergence of barley, in addition to effective malting. This study aimed to assess the selection of barley varieties by using seed vigour as the indicator. Seed vigour of barley (quantified as the germination percentage) was evaluated under drought (?0.2 MPa) and temperature stress (10°C). At two locations over a 3‐year period, 1 population of 133 Derkado × B83‐12/21/5 doubled haploid (DH) lines (and parents) was evaluated for seed vigour, of which 108 DH lines were assessed for three malting parameters. The relatively high values of vigour during the 3‐year period (overall average 94–95%) probably impeded high variations in genetic potential. A total of 27 DH lines of the 133 evaluated showed transgression for vigour (up to 98%) in comparison with the parents (Derkado: 96%; B83: 92%). In conclusion, caution should be applied when selecting for seed vigour, even in good crop years with high levels of seed vigour and low trait variations. Such selection might improve vigour, particularly in crop years with unsuitable weather conditions.     

Elevated CO2 modulates the effects of drought and heat stress on plant water relations and grain yield in wheat

To investigate the interactive effects of drought, heat and elevated atmospheric CO₂ concentration ([CO₂]) on plant water relations and grain yield in wheat, two wheat cultivars with different drought tolerance (Gladius and Paragon) were grown under ambient and elevated [CO₂], and were exposed to post‐anthesis drought and heat stress. The stomatal conductance, plant water relation parameters, abscisic acid concentration in leaf and spike, and grain yield components were examined. Both stress treatments and elevated [CO₂] reduced the stomatal conductance, which resulted in lower leaf relative water content and leaf water potential. Drought induced a significant increase in leaf and spike abscisic acid concentrations, while elevated [CO₂] showed no effect. At maturity, post‐anthesis drought and heat stress significantly decreased the grain yield by 21.3%–65.2%, while elevated [CO₂] increased the grain yield by 20.8% in wheat, which was due to the changes of grain number per spike and thousand grain weight. This study suggested that the responses of plant water status and grain yield to extreme climatic events (heat and drought) can be influenced by the atmospheric CO₂ concentration.     

Stage Sensitivity of Mungbean (Vigna radiata L. Wilczek) to an Elevated Level of Carbon Dioxide

An experiment was undertaken using open‐top chambers to study the effect of CO₂ enrichment on crop growth and to assess the variation related to the time of CO₂ exposure. In general, enriched CO₂ conditions (600 ± 50 p.p.m.) in the chamber positively affected the growth and development of mungbean (Vigna radiata), a short‐duration (60–65 days) summer pulse crop. However, there was significant variability in the effect of the crop stage/time of CO₂ exposure. It was observed that high CO₂ exposure at an early growth stage [0–20 days after germination (DAG)] had a larger effect than that at a later growth stage (21–40 DAG). The experiment also provided a means of assessing the short‐ and long‐term effects of elevated CO₂ on the carbon exchange rate at both stages of exposure. The study revealed that the sensitivity of plants to high CO₂ was more pronounced with respect to net photosynthetic rate. The overall photosynthetic activity gave greater growth and development of plants under high CO₂.     

Can additional N fertiliser ameliorate the elevated CO2‐induced depression in grain and tissue N concentrations of wheat on a high soil N background?

Elevated CO₂ stimulates crop yields but leads to lower tissue and grain nitrogen concentrations [N], raising concerns about grain quality in cereals. To test whether N fertiliser application above optimum growth requirements can alleviate the decline in tissue [N], wheat was grown in a Free Air CO₂ Enrichment facility in a low‐rainfall cropping system on high soil N. Crops were grown with and without addition of 50–60 kg N/ha in 12 growing environments created by supplemental irrigation and two sowing dates over 3 years. Elevated CO₂ increased yield and biomass (on average by 25%) and decreased biomass [N] (3%–9%) and grain [N] (5%). Nitrogen uptake was greater (20%) in crops grown under elevated CO₂. Additional N supply had no effect on yield and biomass, confirming high soil N. Small increases in [N] with N addition were insufficient to offset declines in grain [N] under elevated CO₂. Instead, N application increased the [N] in straw and decreased N harvest index. The results suggest that conventional addition of N does not mitigate grain [N] depression under elevated CO₂, and lend support to hypotheses that link decreases in crop [N] with biochemical limitations rather than N supply.     

Vulnerability of lodging risk to elevated CO2 and increased soil temperature differs between rice cultivars

Anthropogenic increases in atmospheric carbon dioxide concentration [CO₂], and subsequent increases in surface temperatures, are likely to impact the growth and yield of cereal crops. One potential means for yield reduction is for climate parameters to increase the occurrence of lodging. Using an in situ free-air CO₂ enrichment (FACE) system, two morphologically distinct rice cultivars, KH (Koshihikari) and SY (Shan you 63), were grown at two [CO₂]s (ambient and ambient + 200 μmol mol⁻¹) and two soil temperatures (ambient and ambient ± 1.8 °C) over a two year period to assess and quantify lodging risk. Elevated [CO₂] per se had no effect on lodging resistance for either cultivar. However, elevated [CO₂] and higher soil temperature increased the lodging risk for SY, due to a relatively higher increase in plant biomass and height at the elevated, relative to the ambient [CO₂] condition. Elevated soil temperature per se also increased lodging risk for both cultivars and was associated with longer internodes in the lower portion of the tillers. These findings illustrate that lodging susceptibility in rice, an important cereal crop, can be increased by rising [CO₂] and soil temperature; however, variation observed here between rice cultivars suggests there may be sufficient intraspecific variability to begin choosing rice lines that minimize the potential risk of lodging.