Atmospheric carbon dioxide (CO₂) concentration, temperature and nitrogen (N) are the key regulators of productivity and water use of plants under the changing climate. However, field scale studies on the interactive effect of the three above critical inputs are limited. Hence, this field study was conducted with three climate treatments (ambient (AC), elevated CO₂ (eC, ~550 µmol mol⁻¹) and co-elevation of both CO₂ and temperature (eCeT, ~550 µmol mol⁻¹ and temperature ~2 °C above ambient)) and four N treatments (0%, 50%, 100% and 150% of recommended N dose of 120 kg N ha⁻¹). The experiment was carried out in open top field chambers to study the effects of climate and N application on grain yield, evapotranspiration (ET) and water use efficiency (WUE) in wheat crop. Crop ET was estimated by field water balance method and WUE by taking the ratio of grain yield to crop ET. Elevation of CO₂ showed 9% yield gain over ambient (averaged across N levels), whereas, co-elevation of temperature reduced the yield gain to 4%. Further, N application significantly altered the level of CO₂ response. Under CO₂ enriched environment, the yield gain was 15% with N₁₀₀ as compared to 2% and 4% under N₀ and N₅₀, respectively, indicating CO₂ enrichment benefits in grain yield was N dependent. The three years’ pooled data showed significant effect of climate, N and their interaction on profile water storage, evapotranspiration and WUE. Elevation of CO₂ alone or with co-elevation of temperature resulted in significant decline in crop ET by 4–11 mm and significant increase in profile soil moisture and WUE. The WUE improved significantly, by 12% under eC and by 4% under eCeT, respectively, with the increase, more attributed to gain in grain yield. Quantitative derivation from the three years’ field experimentation could establish that under elevated CO₂ scenario (550 µmol mol⁻¹), an additional 1 °C rise in temperature would result in enhanced crop ET by 5 mm and yield loss of about 4%. This study thus revealed that limited N and increased temperature would potentially restrict the CO₂ mediated benefits in wheat yield and water use under the changing climate.

在不断变化的气候下，大气中二氧化碳（CO ₂）的浓度，温度和氮（N）是植物生产力和用水的关键调节器。但是，有关上述三个关键输入的交互作用的实地规模研究是有限的。因此，本实地研究是通过三种气候处理（环境（AC），升高的CO ₂（eC，〜550 µmol mol ^-1）和CO ₂和温度的共同升高（eCeT，〜550 µmol mol ^-1和温度〜高于环境温度约2°C））和四次N处理（建议的120 kg N ha ^-1的N剂量的0％，50％，100％和150％）。该实验在露天场中进行，研究了气候和氮肥施用对小麦作物籽粒产量，蒸散量（ET）和水分利用效率（WUE）的影响。通过田间水分平衡法和水分利用效率，通过估算谷物产量与作物ET的比值来估算作物ET。CO ₂升高显示相对于环境（在N水平上平均）的9％的产率增加，而温度的共同升高将产率增加降低至4％。此外，氮的施用显着改变了CO ₂响应的水平。在富含CO _2的环境下，使用N _100时，产量增加为15％，而在N ₀和N _50下分别为2％和4％，表明CO ₂谷物单产的富集效益与氮有关。三年的汇总数据显示，气候，氮及其相互作用对剖面水储量，蒸散量和水分利用效率有显着影响。单独升高CO ₂或与温度共同升高都会导致作物ET显着下降4-11 mm，并且剖面土壤水分和WUE显着提高。WUE显着提高，在eC下提高了12％，在eCeT下提高了4％，这更多地归因于谷物产量的增加。三年现场试验的定量推论可以证明，在CO ₂升高的情况下（550 µmol mol ^-1），温度每升高1°C，作物的ET升高5毫米，产量损失约4％。因此，这项研究表明，在不断变化的气候下，有限的氮素和升高的温度可能会限制CO ₂介导的小麦产量和水分利用效益。