Light and carbon dioxide (CO2) are two essential components for plant photosynthesis. To understand the effects of elevated CO2 concentration on photosynthetic characteristics of hybrid rice under different light conditions, two hybrid rice varieties (YLY900 and YY538) were grown in the field using a free-air CO2 enrichment facility (FACE) in 2017 with two CO2 concentration treatments (ambient CO2 and elevated 200 μmol·mol-1 above ambient CO2), the photosynthesis traits of top full expansion leaves were measured in both sunny and cloudy days at jointing and grain filling stages. Elevated CO2 increased net photosynthetic rate (Pn) of two rice varieties. The increase in sunny days (31%) was greater than in cloudy days (21%), and the increase at jointing stage (37%) was greater than at grain filling stage (21%). There were significant interactions between CO2 with weather, and between CO2 with growth stage. Water use efficiency (WUE) of leaves in response to elevated CO2 showed the similar trend as Pn. Elevated CO2 decreased stomatal conduc-tance (gs) and transpiration rate (Tr), and the decreases in sunny days were greater than that in cloudy days. The Pn, gs, Tr, WUE and stomatal limit (Ls) measured in cloudy days were significantly lower than that measured in sunny days by 41%, 18%, 41%, 26% and 27%, respectively. Results from the correlation analyses showed that the Pn, gs, and Tr in sunny days were significantly positively correlated with the corresponding parameters in cloudy days. The results indicated that cloudy weather conditions reduced photosynthesis and its response to elevated CO2 of two hybrids rice varieties at middle and late growth stages. Therefore, weather variation should be considered when assess rice yield potential in the future environment.光和二氧化碳(CO2)是绿色植物光合作用的两个基本条件.为了明确不同光照条件下,高CO2浓度对不同杂交水稻光合特性的影响,2017年利用稻田大型FACE平台,以‘Y两优900’和‘甬优538’为供试材料,设置环境CO2和高CO2浓度(增200 μmol·mol-1)两个水平,分别在拔节期和灌浆期同时测定阴、晴天气条件下顶部全展叶光合特性参数.结果表明: 高CO2浓度使不同天气情况下两品种叶片的净同化率(Pn)均呈增加趋势,其中晴天条件下的增幅(31%)大于阴天(25%),拔节期的增幅(37%)大于灌浆期(21%),CO2与天气、CO2与生育期均存在显著的互作效应.叶片水分利用效率(WUE)对高CO2浓度的响应趋势与Pn一致.高CO2浓度环境下叶片气孔导度(gs)、蒸腾速率(Tr)均呈下降趋势,晴天条件下的降幅略大于阴天.与晴天相比,阴天条件下叶片Pn、gs、Tr、WUE和Ls平均分别下降41%、18%、41%、26%和27%,差异均达显著或极显著水平.相关分析表明,晴天Pn、gs、Tr均与阴天时的参数呈极显著正相关关系.表明阴天使水稻生育中、后期叶片光合参数及其对高CO2浓度的响应均大幅降低,且两品种表现一致.评估未来水稻产量潜力需要考虑天气条件.

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