夏玉米叶片含水率及光合特性对不同强度持续干旱的响应

基于七叶期开始的夏玉米全生育期不同强度的干旱发生发展模拟试验资料,分析了不同强度的干旱发生发展对夏玉米叶片含水率及光合特性的影响。结果表明:夏玉米生育期内叶片含水率随干旱发生发展呈线性下降趋势,并与土壤相对湿度通过0.005水平的显著性检验,可表征玉米的受旱程度。玉米全生育期内叶片的光合速率、蒸腾速率和气孔导度均随干旱的发生发展呈显著下降趋势,且不同强度干旱的影响差异随时间推移而减小;而叶片水分利用效率则随干旱发生发展呈升高趋势,且随着干旱的发展不同强度干旱间的差异呈增加趋势。玉米全生育期内均出现了光合作用由气孔限制向非气孔限制的转换,转换时间分别为46、38、30和35 d,与干旱强度及持续时间呈反比。     

西南地区水稻干旱时空分布特征

从西南地区水稻生产特点和气候条件出发,改进相对湿润指数,建立计算偏离多年平均相对湿润指数值变化程度的湿润指数距平率（M_p）农业干旱监测模型,并采用农业干旱监测等级指标分析了1961—2010年西南地区水稻生育期间农业干旱时空分布特征,验证了M_p在西南地区水稻干旱监测方面的适用性.结果表明： 从年代际变化趋势来看,随着年代的增加,水稻受旱频率有降低趋势;从空间分布趋势来看,水稻受旱高频区主要分布在云南西北部和中东部,以及四川盆地东部、重庆东北部、贵州东南部局部区域;从各生长阶段发生干旱频率来看,水稻移栽至抽穗阶段发生干旱频率最高,其次是灌浆至成熟阶段,抽穗至灌浆期受旱频率最低.湿润指数距平率能较好地监测西南地区水稻的受旱情况,对于缺乏灌溉资料的地区采用该方法进行水稻干旱监测具有一定的实用价值.     

基于多源遥感数据的农业干旱监测模型构建及应用

干旱监测问题是干旱灾害模拟与预警及旱灾防灾减灾的关键。基于2001-2013年淮河流域40个气象站资料、28个土壤墒情站点和中分辨率成像光谱仪（MODIS）多源遥感数据,采用SEN趋势法和标准化降水蒸散指数（SPEI）等方法,综合了大气-植被-土壤相互作用等多元成因,构建了适用于淮河流域多源综合遥感干旱监测模型,探讨淮河流域干旱时空规律。研究表明：（1）基于多源数据构建综合干旱监测模型,利用土壤墒情和典型年份干旱监测对综合干旱监测模型适用性进行评价,通过了P < 0.01的显著性检验,构建的模型可综合反映出农业和气象干旱多源信息;（2）淮河流域干旱面积和干旱频率大都集中在4-5月和7-9月,9月份受旱面积最大。河南省是淮河流域受旱频率最高,其干旱面积占淮河流域多年平均干旱面积比重最大（38%）,其次是安徽（22%）,旱地受旱面积比重大于水田受旱面积比重;（3）淮河流域2、3和5月干旱有显著减弱趋势;而1、4和6月则有增强趋势。淮河流域小麦灌浆-成熟时期（4-6月）缺水对小麦粮食产量影响显著,综合淮河流域干旱趋势变化,需强化淮河流域4月份小麦的干旱监测与旱灾预警。     

气候变化背景下中国南方地区季节性干旱特征与适应Ⅳ.基于作物水分亏缺指数的玉米干旱时空特征

基于1959－2008年中国南方地区249个气象台站的地面观测资料,以作物水分亏缺指数为玉米干旱指标,计算其干旱频率和干旱站次比,分析中国南方地区春玉米和夏玉米各生育阶段发生干旱的时空分布特征.结果表明: 从干旱发生频率的空间分布看,春玉米在淮北、云南北部和华南南部发生的干旱较严重,在其他地区的干旱相对较轻;除了长江中下游地区、华南北部和西南东部的夏玉米在生育后期干旱较严重,研究区域内夏玉米在其生育前期和中期干旱较轻.从干旱面积和强度的变化趋势看,长江中下游地区春玉米在七叶到拔节阶段的干旱强度明显增加,在吐丝后到乳熟阶段的干旱面积和强度呈减小趋势;夏玉米在拔节后期到抽雄阶段以及吐丝后到乳熟阶段的干旱都呈减轻趋势.西南地区春玉米、夏玉米的干旱强度和范围没有明显趋势.从干旱面积和范围的年际和年代际变化看,长江中下游地区夏玉米的变化较大,而西南地区差异较小.     

土壤水分胁迫对玉米形态发育及产量的影响

未来气候变化可能加剧的干旱化将对我国主要粮食和最重要的饲料作物玉米产生严重影响。为增进玉米对干旱化响应与适应的理解及制定应对策略 ,利用大型活动遮雨棚及池栽对玉米进行了全程水分控制试验研究。对不同土壤水分胁迫下的玉米形态表征、生长发育及产量的分析表明 ,玉米受干旱胁迫的影响程度因受旱轻重、持续时间以及生育进程的不同而不同 ,受旱越重 ,持续时间越长 ,影响越甚。大喇叭口期前 ,玉米株高和生物产量受有限供水或轻度干旱影响不算很大 ,但从大喇叭口期后直至抽雄和灌浆期 ,轻度干旱胁迫持续久了也会对株高和生物产量产生较大不良影响。严重干旱胁迫则从拔节始至灌浆期均对株高和生物产量影响更为不利。进而引起果穗性状恶化 ,穗粒数和百粒重减小 ,最终导致经济产量大幅下降。说明玉米生育前期(大喇叭口期前 )进行有限的控水可行。而玉米生育前期干旱胁迫将使生育进程明显延缓 ,严重干旱胁迫可使抽雄、吐丝期较水分充足滞后 4 d左右 ,并引起成熟期推迟     

干旱对夏玉米苗期叶片权衡生长的影响

叶片是植物对干旱响应最敏感的器官之一,叶片性状变化及其权衡关系能够反映植物对资源的利用策略以及对干旱的适应对策。基于2014年6个初始土壤水分梯度的夏玉米持续干旱模拟试验研究表明,随着干旱的发展,夏玉米各叶片性状均会受到影响,但不同干旱程度的影响不一致。基于水分胁迫系数及干旱持续时间提出了干旱程度的定量表达,随着干旱的发生发展,干旱程度在0—1之间变化。当干旱程度小于0.21时,夏玉米叶片性状不会受到显著影响;0.21—0.76时,叶片性状大小受到影响,但变化趋势不会发生改变;0.76—0.91时,新叶形成补偿不了老叶脱落,有效叶片数、叶干重、绿叶面积和叶含水量等性状提前出现下降趋势;大于0.91时,叶片生长几乎停滞。夏玉米叶片性状在干旱条件下的适应性生长本质上体现了其在快速生长与维持生存之间的权衡,但不同干旱程度下,夏玉米叶片性状生长的权衡策略不同:未发生干旱时,夏玉米倾向于维持较高的代谢活性,一旦干旱程度大于0,夏玉米就会降低叶片代谢活性;当干旱程度小于0.48时,夏玉米倾向于通过迅速增加叶面积来吸收较多的能量,以获得较大的生长速率,为生殖器官的生长及产量形成储备能量;当干旱程度大于0.48时,夏玉米会减小单叶面积以减少水分散失,倾向于资源贮存以提高其生存能力。     

江淮地区夏玉米涝渍灾害时空分布特征和风险分析

为了定量评估江淮地区夏玉米涝渍灾害和揭示其时空分布特征,基于1961—2013年91个观测站点的日雨量数据,耦合夏玉米生育期和涝渍灾情数据,统计夏玉米不同生育时段、不同涝渍等级的灾害样本,采用偏相关分析、多元线性回归、正态性检验、区间估计等方法,构建了基于有效降雨量的夏玉米分生育时段涝渍灾害的等级指标,并验证了指标的合理性;分析了区域1961—2010年夏玉米涝渍灾害的时空分布和风险分布。结果表明:夏玉米涝渍灾害等级与当前涝渍过程降雨量和前2旬逐旬降雨量呈显著正相关;同一等级涝渍灾害,拔节-抽雄期指标阈值最高,抽雄-成熟期的次之,出苗-拔节期的最低;20世纪70年代涝渍灾害的发生有所减少,80年代后又逐渐增多;涝渍灾害的多发区主要分布在沿江、沿淮、沿湖和沿海地区,且随着生育进程的增加,多发区总体随雨带北移;近50年来出苗至抽雄阶段涝渍灾害的发生总体上呈增加趋势,抽雄至成熟阶段则以减少趋势为主;随着生育进程的增加,涝渍灾害风险指数的高值区逐渐由西南向东北移动。     

辽宁省玉米旱灾时空分布特征及综合风险评价

以辽宁省气象数据、空间数据和田间管理数据集为基础,首先,依据自然灾害风险形成理论,从危险性、脆弱性、暴露性和防灾减灾能力四因子入手,选择10个副指标,构建辽宁省玉米旱灾综合风险评价指标体系,并利用组合加权法和GIS空间分析方法,确定其权重及区域化。利用自然灾害风险指数法和加权综合评价方法,建立辽宁省玉米旱灾综合风险评价模型,并进行了辽宁省玉米旱灾时空分布特征分析及综合风险评价研究。结果表明：（1）自1960年以来,研究区干旱频率总体呈上升趋势,尤其2010年以后有明显增加态势。其中1970-1979年间干旱发生频率较低,2010-2019年间干旱频率最高。不管是月尺度、季节尺度、生长季尺度还是年际尺度,辽宁省西北部干旱频率普遍较高,而东南部干旱频率较低。干旱强度呈现从辽宁省中部地区向东西地区两个方向递减的趋势,高值出现在辽宁省中部的阜新、锦州、铁岭、辽阳、盘锦、鞍山、营口和大连等地。干旱历时从辽宁省东部向西部区域递减的趋势,其中高值出现在铁岭北部、盘锦、鞍山、营口和丹东南部等地,低值分布在朝阳西南部、葫芦岛西北部、本溪西部和丹东等地。（2）从4个因子角度来说,辽宁省朝阳西部和葫芦岛西北部玉米旱灾危险性指数较低以外其他区域玉米旱灾危险性指数均较高。然而,辽宁省西北玉米主产区玉米旱灾脆弱性指数和暴露性指数均较高,且防灾减灾能力较低。当4个因子加权综合评价时,辽宁省西北部玉米旱灾综合风险呈现较高的现象。研究结果可为保障辽宁省粮食安全及制定防灾减灾政策提供理论依据和科学指导。     

1961-2010年中国春玉米潜在种植分布的年代际动态变化

基于构建的中国春玉米种植分布-气候关系模型,对1961-2010年春玉米潜在种植分布年代际变化进行了分析.结果表明:春玉米潜在可种植面积呈增加趋势;气候最适宜种植面积波动式增加,近10年达5.3×105 km2;适宜种植面积明显扩大,近50年增加约8.2×105 km2,且呈东扩趋势;潜在种植北界呈波动式北移,最大北抬达1.4个纬度.表明,气候变化有利于中国扩大春玉米种植,但一些地区可能受水分条件的限制.     

气候变化背景下东北三省春玉米产量潜力的时空特征

以东北三省春玉米种植区为研究区域,利用当地地面气象观测资料、农业气象观测站春玉米多年试验资料和县级春玉米实际产量资料,使用验证后的农业生产系统模拟模型(APSIM-Maize),分析研究区域春玉米1961—2015年不同水平产量潜力及实际产量的时空分布特征,并解析气候波动对产量潜力的影响.结果表明: 1961—2015年,研究区域春玉米潜在产量平均值为12.2 t·hm^-2,且呈现明显的经向和纬向空间分布,即由南向北递减、西部高于东部.研究区域春玉米可获得产量平均值为11.3 t·hm^-2,与潜在产量呈相似的分布特征.在目前农户的栽培水平下,春玉米农户潜在产量和农户实际产量全区多年平均值分别为6.5和4.5 t·hm^-2.在品种和栽培管理措施不变的条件下,研究区潜在产量、可获得产量和农户潜在产量总体呈显著减少趋势,减幅分别为0.34、0.25和0.10 t·hm^-2·(10 a)^-1.农户实际产量呈增加趋势,增幅为1.27 t·hm^-2·(10 a)^-1.气候波动使东北三省春玉米潜在产量、可获得产量和农户潜在产量年际间波动范围分别为10.0～14.4、9.8～13.3和4.4～8.5 t·hm^-2.     

Hybrid rye performance under natural drought stress in Europe

Several rye growing regions of Central Europe suffered from severe drought stress in the last decade. Rye is typically grown on sandy soils with low water-holding capacity in areas with low rainfall, thus drought-tolerant varieties are urgently needed. The main objective of our study was to evaluate the drought stress tolerance of rye hybrids using large-scaled field experiments. Two biparental populations (Pop-A, Pop-B) each consisting of 220 F_2:4 lines from the Petkus gene pool and their parents were evaluated for grain yield testcross performance under irrigated (I) and rainfed (R) regime in six environments. We observed for most environments severe drought stress leading to an average grain yield reduction of 23.8 % for rainfed compared to irrigated regime in drought stress environments. A decomposition of the variance revealed significant (P < 0.01) genotypic and genotype × environment interaction variances but only a minor effect of drought stress on the ranking of the genotypes with regard to grain yield. In conclusion, separate breeding programs for drought-tolerant genotypes are not superior to the currently practiced selection under rainfed conditions without irrigation in hybrid rye breeding in Central Europe.     

Population structure in a wheat core collection and genomic loci associated with yield under contrasting environments

A set of 96 winter wheat accessions sampled from a variety of geographic origins, including cultivars and breeding lines, were characterized with 46 genome-wide SSR loci for genetic diversity and population structure. The genetic diversity within these accessions was examined using a genetic distance-based and a model-based clustering method. The model-based analysis identified an underlying population structure comprising of four distinct sub-populations which corresponded well with distance-based groupings. Information on the population structure is taken into account in an association mapping study of grain yield from a 3-years field trial incorporating fully irrigated, rainfed and drought stress treatments. A total of 21 marker-grain yield associations (P?<?0.01) were identified with nine SSR markers. Most associations were detected only in one to three environments (treatment/year combination), with an average R ² value around 13?%. However, marker gwm484 (on chromosome 2D) was associated with yield in six environments, including irrigated, rainfed and drought stress treatments, suggesting it could be used to improve grain yield across a range of environments. Variation in grain yield at this locus was associated with earliness, early vigour, kernels per spikelet and harvest index. Microsatellite locus psp3200 (on chromosome 6D) was associated with yield in dry and hot environments, which was related to earliness, early vigour, productive tillering and total biomass per plant. Partial least squares regression, with nine environmental factors, showed that precipitation from tillering to maturity was the main environmental factor causing marker?×?environment associations for grain yield.     

Factors affecting summer maize yield under climate change in Shandong Province in the Huanghuaihai region of China

Clarification of influencing factors (cultivar planted, cultivation management, climatic conditions) affecting yields of summer maize (Zea mays L.) would provide valuable information for increasing yields further under variable climatic conditions. Here, we report actual maize yields in the Huanghuaihai region over the past 50 years (1957–2007), simulated yields of major varieties in different years (Baimaya in the 1950s, Zhengdan-2 in the 1970s, Yedan-13 in the 1990s, and Zhengdan-958 in the 2000s), and factors that influence yield. The results show that, although each variety change has played a critical role in increasing maize yields, the contribution of variety to yield increase has decreased steadily over the past 50 years (42.6%–44.3% from the 1950s to the 1970s, 34.4%–47.2% from the 1970s to the 1990s, and 21.0%–37.6% from the 1990s to the 2000s). The impact of climatic conditions on maize yield has exhibited an increasing trend (0.67%–22.5% from the 1950s to the 1970s, 2.6%–27.0% from the 1970s to the 1990s, and 9.1%–51.1% from the 1990s to the 2000s); however, interannual differences can be large, especially if there were large changes in temperature and rainfall. Among climatic factors, rainfall had a greater positive influence than light and temperature on yield increase. Cultivation measures could change the contribution rates of variety and climatic conditions. Overall, unless there is a major breakthrough in variety, improving cultivation measures will remain important for increasing future summer maize yields in the Huanghuaihai region.     

Root System Dynamics of Miscanthus × giganteus and Panicum virgatum in Response to Rainfed and Irrigated Conditions in California

Miscanthus (Miscanthus × giganteus) and switchgrass (Panicum virgatum) are large perennial grass bioenergy crops in the USA and Europe. Despite much research into their agronomic potential, few studies have examined in situ root growth dynamics under irrigation and soil water deficits, particularly as they relate to shoot performance. We grew miscanthus and switchgrass in outdoor mesocosms under irrigated and rainfed conditions and assessed the spatial distribution and abundance of roots using minirhizotron images and whole root system sampling. Despite surviving an extended period of drought, shoot and root biomass, root length density, numbers of culms, and culm height were reduced in both species under rainfed (dry) conditions. However, rainfed switchgrass far outperformed rainfed miscanthus in all shoot and root growth metrics. The rainfed (drought) treatment reduced switchgrass and miscanthus whole plant biomass by 83 and 98 %, culm production by 67 and 90 %, and root length density by 67 and 94 % compared to irrigated plants, respectively. Root nitrogen concentration was higher for miscanthus (3-fold) and switchgrass (4-fold) in the rainfed treatment compared to irrigated plants and did not significantly differ between species. Unlike miscanthus, switchgrass grew roots continuously into regions of available soil moisture as surface soil layers grew increasingly dry, indicating a drought avoidance strategy. Our study suggests that switchgrass is more likely to tolerate drought by mining deep wet soils, while miscanthus relies on shallow rhizome production to tolerate dry soils.     

QTLs linked to leaf epicuticular wax,physio-morphological and plant production traits under drought stress in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Drought stress is the major constraint to rice (Oryza sativa L.) production and yield stability in rainfed ecosystems. Identifying genomic regions contributing to drought resistance will help to develop rice cultivars suitable for rainfed regions through marker-assisted breeding. Quantitative trait loci (QTLs) linked to leaf epicuticular wax, physio-morphological and plant production traits under water stress and irrigated conditions were mapped in a doubled haploid (DH) line population from the cross CT9993-5-10-1-M/IR62266-42-6-2. The DH lines were subjected to water stress during anthesis. The DH lines showed significant variation for epicuticular wax (EW), physio-morphological and plant production traits under stress and irrigated conditions. A total of 19 QTLs were identified for the various traits under drought stress and irrigated conditions in the field, which individually explained 9.6%–65.6% of the phenotypic variation. A region EM15_10-ME8_4-R1394A-G2132 on chromosome 8 was identified for leaf EW and rate of water loss i.e., time taken to reach 70% RWC from excised leaves in rice lines subjected to drought stress. A large effect QTL (65.6%) was detected on chromosome 2 for harvest index under stress. QTLs identified for EW, rate of water loss from excised leaves and harvest index under stress in this study co-located with QTLs linked to shoot and root-related drought resistance traits in these rice lines and might be useful for rainfed rice improvement.     

Physiological and yield responses of recombinant chromosome substitution lines of barley to terminal drought in a Mediterranean‐type environment

Physiological traits and productivity of the recombinant chromosome substitution lines (RCSLs) of barley, developed through the cross of Hordeum vulgare ssp. vulgare cv. Harrington and the wild ancestor Hordeum vulgare ssp. spontaneum, were measured in plants growing in microplots (with and without irrigation) and in field conditions in two Mediterranean‐type environments, Cauquenes (rainfed) and Santa Rosa (irrigated). The objectives were to assess the degree of phenotypic variability in response to terminal drought stress and to test whether the introgression of the wild ancestor into cv. Harrington can increase the terminal drought tolerance of RCSLs of barley. Days from emergence to anthesis and from anthesis to maturity of the 80 RCSLs were reduced in only 2–4 days under water stress, in microplots. Specific leaf area (SLA) and stomatal conductance (gs) of 80 RCSLs and cv. Harrington decreased greatly under water stress in plants growing in microplots and field conditions (in 2004/05 growing season). No G × E interaction was detected except for SLA in the microplot experiment. The principal component analysis provided a clear distinction between RCSLs. Along the first principal component, it was possible to identify 24 RCSLs which represent the whole range of grain yield (GY), gs and SLA observed in the 80 RCSLs. The selected 24 RCSLs were evaluated in field conditions at Cauquenes and Santa Rosa, during two growing seasons (2007/08 and 2008/09). The gs and carbon isotope discrimination in grains (Δ¹³C) were significantly (P < 0.001) lower in the rainfed condition (Cauquenes), but the water‐soluble carbohydrates (WSC) in stems at anthesis and maturity was significantly (P < 0.001) higher than in well‐irrigated condition (Santa Rosa). Grain yield was reduced by 63% under drought conditions. Differences between RCSLs in gs, WSC and GY were significant (P < 0.001) in 2007/08. The stress tolerance index (STI) was highly (P < 0.01) correlated with GY in all environments (rainfed and irrigated conditions and the two growing seasons). The relationship between STI and Δ¹³C under rainfed condition allowed identifying drought tolerant and susceptible RCSLs; the former were high yielding lines under rainfed and irrigated conditions (and higher STI values), but with similar GY to cv. Harrington, but presented higher grain Δ¹³C values than cv. Harrington. The drought susceptible lines presented lower GY, STI and Δ¹³C values than cv. Harrington. These results suggest that H. spontaneum has contributed alleles that increase terminal drought tolerance to some of the RCSLs.     

小麦抗旱种质资源的遗传多样性

在雨养和灌水条件下,田间栽培小麦抗旱材料。根据结实器官建成与物候期、生育期的对应关系,通过供试材料产量构成因素的旱、水表现,分析在各因素形成时期的抗旱性。分别以抗旱系数和抗旱指数作为评价抗旱性的指标,通过聚类分析供试材料的遗传多样性。结果发现有些材料表现为全生育期抗旱,而有些材料只在苗期、拔节期、开花期和灌浆期等一个或几个生育时期表现抗旱;有的材料表现为抗旱高产,但有的材料产量水平较低;同时还发现部分抗旱种质资源在灌水条件下有较大的增产潜力。     

Excessive rainfall leads to maize yield loss of a comparable magnitude to extreme drought in the United States

Increasing drought and extreme rainfall are major threats to maize production in the United States. However, compared to drought impact, the impact of excessive rainfall on crop yield remains unresolved. Here, we present observational evidence from crop yield and insurance data that excessive rainfall can reduce maize yield up to ?34% (?17 ± 3% on average) in the United States relative to the expected yield from the long‐term trend, comparable to the up to ?37% loss by extreme drought (?32 ± 2% on average) from 1981 to 2016. Drought consistently decreases maize yield due to water deficiency and concurrent heat, with greater yield loss for rainfed maize in wetter areas. Excessive rainfall can have either negative or positive impact on crop yield, and its sign varies regionally. Excessive rainfall decreases maize yield significantly in cooler areas in conjunction with poorly drained soils, and such yield loss gets exacerbated under the condition of high preseason soil water storage. Current process‐based crop models cannot capture the yield loss from excessive rainfall and overestimate yield under wet conditions. Our results highlight the need for improved understanding and modeling of the excessive rainfall impact on crop yield.     

洛阳旱地夏玉米生产潜力长周期定量模拟与评价

以洛阳孟津地区气象数据库、土壤数据库、作物数据库和多年田间试验数据库为基础,应用DSSAT作物生长模型估算了当地夏玉米光温生产潜力和光温水生产潜力,并对节水潜力开发现状及途径进行了分析.结果表明,洛阳孟津地区47a夏玉米光温生产潜力为6900.00～15805.00 kg · hm-2,均值为12039.96 kg · hm-2,可作为补灌区平均最高产量的上限参考值;光温水生产潜力为1529.31～13742.00 kg · hm-2,均值为8894.42 kg · hm-2,仅占光温生产潜力82%左右,可作为雨养夏玉米平均最高产量的上限参考值.夏玉米生育期内平均降水量为356.22mm,年际间波动幅度较大,平均水分满足率为71.9%,不同土壤类型及不同降雨年型夏玉米潜在水分利用效率变幅较大,波动范围为8.04～37.46 kg · hm-2 · mm-1,47a均值为26.424 kg · hm-2 · mm-1.近8a旱作夏玉米现实水分利用效率仅占潜在水分利用效率的45.87%,平均光温水生产潜力开发度为47.55%.夏玉米节水潜力非常大,采用合理的节水农业措施,加强农田建设,改善地力状况,增强土壤储水蓄水稳定能力,高效利用降水资源,提高水分利用效率是今后提高夏玉米产量的重要途径.     

The combined and separate impacts of climate extremes on the current and future US rainfed maize and soybean production under elevated CO2

Heat and drought are two emerging climatic threats to the US maize and soybean production, yet their impacts on yields are collectively determined by the magnitude of climate change and rising atmospheric CO₂ concentrations. This study quantifies the combined and separate impacts of high temperature, heat and drought stresses on the current and future US rainfed maize and soybean production and for the first time characterizes spatial shifts in the relative importance of individual stress. Crop yields are simulated using the Agricultural Production Systems Simulator (APSIM), driven by high‐resolution (12 km) dynamically downscaled climate projections for 1995–2004 and 2085–2094. Results show that maize and soybean yield losses are prominent in the US Midwest by the late 21st century under both Representative Concentration Pathway (RCP) 4.5 and RCP8.5 scenarios, and the magnitude of loss highly depends on the current vulnerability and changes in climate extremes. Elevated atmospheric CO₂ partially but not completely offsets the yield gaps caused by climate extremes, and the effect is greater in soybean than in maize. Our simulations suggest that drought will continue to be the largest threat to US rainfed maize production under RCP4.5 and soybean production under both RCP scenarios, whereas high temperature and heat stress take over the dominant stress of drought on maize under RCP8.5. We also reveal that shifts in the geographic distributions of dominant stresses are characterized by the increase in concurrent stresses, especially for the US Midwest. These findings imply the importance of considering heat and drought stresses simultaneously for future agronomic adaptation and mitigation strategies, particularly for breeding programs and crop management. The modeling framework of partitioning the total effects of climate change into individual stress impacts can be applied to the study of other crops and agriculture systems.