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Response of wheat canopy CO2 and water gas-exchange to soil water contentunder ambient and elevated CO2

机译：环境和高CO 2条件下小麦冠层CO 2和水煤气交换对土壤水分的响应

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摘要

The nature of the interaction between drought and elevated CO2 partial pressure (pC(a)) is critically important for the effects of global change on crops. Some crop models assume that the relative responses of transpiration and photosynthesis to soil water deficit are unaltered by elevated pC(a), while others predict decreased sensitivity to drought at elevated pCa. These assumptions were tested by measuring canopy photosynthesis and transpiration in spring wheat (cv. Minaret) stands grown in boxes with 100 L rooting volume. Plants were grown under controlled environments with constant light (300 mu mol m(-2) s(-1)) at ambient (36 Pa) or elevated (68 Pa) PCa and were well watered throughout growth or had a controlled decline in soil water starting at ear emergence. Drought decreased final aboveground biomass (-15%) and grain yield (-19%) while elevated pC(a) increased biomass (+24%) and grain yield (+29%) and there was no significant interaction. Elevated PCa increased canopy photosynthesis by 15% on average for both water regimes and increased dark respiration per unit ground area in well-watered plants, but not drought-grown ones. Canopy transpiration and photosynthesis were decreased in drought-grown plants relative to well-watered plants after about 20-25 days from the start of the drought. Elevated pC(a) decreased transpiration only slightly during drought, but canopy photosynthesis continued to be stimulated so that net growth per unit water transpired increased by 21%. The effect of drought on canopy photosynthesis was not the consequence of a loss of photosynthetic capacity initially, as photosynthesis continued to be stimulated proportionately by a fixed increase in irradiance. Drought began to decrease canopy transpiration below a relative plant-available soil water content of 0.6 and canopy photosynthesis and growth below 0.4. The shape of these responses were unaffected by pC(a), supporting the simple assumption used in some models that they are independent of pC(a).
机译：干旱和较高的CO2分压（pC（a））之间相互作用的性质对于全球变化对农作物的影响至关重要。一些作物模型假定蒸腾作用和光合作用对土壤水分亏缺的相对响应不会因pC（a）的升高而改变，而其他一些模型则预测pCa升高时对干旱的敏感性降低。通过测量在生根体积为100 L的盒子中生长的春小麦（cv。Minaret）林冠层的光合作用和蒸腾作用来检验这些假设。在环境（36 Pa）或升高（68 Pa）的PCa恒定光照（300μmol m（-2）s（-1））的受控环境下生长植物，并在整个生长过程中浇水充足或土壤的受控下降水从耳朵出现开始。干旱降低了最终地上生物量（-15％）和谷物产量（-19％），而升高的pC（a）增加了生物量（+ 24％）和谷物产量（+ 29％），并且没有显着的相互作用。在水分充足的植物中，升高的PCa均使冠层的光合作用平均提高15％，并且每单位地上的暗呼吸增加，而干旱植物则没有。干旱开始后约20-25天，相对于灌溉良好的植物，干旱生长的植物的冠层蒸腾作用和光合作用降低。升高的pC（a）在干旱期间仅使蒸腾作用略有下降，但冠层的光合作用仍受到刺激，因此单位蒸腾净水量增长了21％。干旱对冠层光合作用的影响并不是最初光合作用能力下降的结果，因为光合作用继续受到辐照度的固定增加所成比例的刺激。干旱开始使冠层的蒸腾作用降低到相对植物可用土壤水分含量低于0.6时，冠层的光合作用和生长低于0.4。这些响应的形状不受pC（a）的影响，支持一些模型中使用的简单假设，即它们独立于pC（a）。

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