The yield traits and physiological responses of three wheat genotypes were studied when subjected to heat and combined heat and drought stress at anthesis under either aCO₂ (400 ppm) or eCO₂ (800 ppm) in a greenhouse. The heat treatment was 7-days at day/night 35/28°C, and the combined heat and drought was withholding irrigation from the heat-stressed plants until the photosynthetic rate reached <5 μmol m⁻² s⁻¹. The LM62 genotype had higher photosynthetic rate compared with LM19, though no significant difference in grain yield was found. eCO₂ increased photosynthesis at 35°C and significantly lowered the electron transport rate at high intercellular CO₂ concentrations. Maximum velocity of Rubisco carboxylation (V_cmax) and the maximum velocity of RuBP regeneration in leaves (J_max) increased in 35°C compared with 25°C, though when normalized to 25°C both V_cmax and J_max decreased in the heat-stressed plants, indicating that an inhibition had occurred. The maximum photochemical efficiency of photosystem II (F_v/F_m) decreased under heat, which correlated with the yield loss caused by the stress. F_v/F_m also decreased under combined heat and drought, though it did not related to the declined yield. A small leaf area prolonged the drying period of Gladius, and it was the genotype with the lowest decrease in yield because of stress. It is concluded that the effects of heat and combined heat and drought stress on the gas exchange and photosynthetic capacity on leaf area basis are not directly linked to the yield performance among wheat genotypes, while the morphological characteristics of the plants are important determinants of grain yield in response to those abiotic stresses.

中文翻译：

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高温及热旱联合胁迫下，叶片光合性能不是影响春小麦产量的关键因素

研究了在温室中aCO ₂ (400 ppm) 或 eCO ₂ (800 ppm)下，三种小麦基因型在花期受到热以及热和干旱联合胁迫时的产量性状和生理反应。热处理持续7天，昼/夜35/28°C，热和干旱相结合，停止对热胁迫植物进行灌溉，直到光合速率达到<5 μmol m ^-2  s ^-1。LM62基因型与LM19相比具有更高的光合速率，但籽粒产量没有显着差异。eCO _{2在35°C 下增加光合作用，并在高细胞间CO 2}浓度下显着降低电子传输速率。与 25°C 相比，叶片中Rubisco 羧化的最大速度 ( V _cmax ) 和 RuBP 再生的最大速度 ( J _{max ) 在 35°C 下有所增加，但当归一化至 25°C 时，} V _cmax和J _max在高温下均下降-胁迫植物，表明发生了抑制。光系统II的最大光化学效率( F _v / F _m )在加热下下降，这与胁迫引起的产量损失相关。F _v / F _m在高温和干旱的共同作用下也下降，尽管这与产量下降无关。小叶面积延长了剑兰的干燥期，是因胁迫而减产最少的基因型。结论是，热和热干旱联合胁迫对叶面积气体交换和光合能力的影响与小麦基因型的产量表现没有直接关系，而植株的形态特征是籽粒产量的重要决定因素。以应对这些非生物胁迫。