中文摘要：

【目的】研究长期遮荫对小麦旗叶光合作用及叶绿素荧光参数的影响。【方法】以扬麦158、扬麦11、南农9918和南农02Y393等4个冬小麦（Triticum aestivumL.）品种为材料,从拔节至成熟期进行遮光22%和33%处理。【结果】灌浆前中期,遮荫对较耐荫的品种扬麦158和南农02Y393旗叶SPAD（Soil-PlantAnalysesDevelopment）值无显著影响,而降低不耐荫品种扬麦11和南农9918的旗叶SPAD值,但遮荫显著提高了灌浆后期小麦旗叶SPAD值。遮荫降低了小麦旗叶光合速率（Pn）、PSⅡ实际光化学效率（ΦPSⅡ）和光化学荧光猝灭系数（qP）与干物质积累量,而提高了光系统Ⅱ的初始荧光强度（Fo）和最大光化学转化效率（Fv/Fm）。【结论】遮荫主要是通过降低叶片光系统Ⅱ的实际光化学效率和光化学荧光猝灭系数,引起单叶光合速率下降,最终降低小麦干物质积累。

英文摘要：

【Objective】Study the effect of long term shading on photosynthesis and chlorophyll fluorescence in flag leaves. 【Method】Four winter wheat （Triticum aestivum L.） varieties, Yangmai 158, Yangmai 11, Nainong 9918, and Nainong 02Y393, were used, obstruction of about 22% and 33% of the total incident photosynthetically active radiation （PAR） to the canopy between jointing and maturity was made. 【Result】Shading showed little effect on flag leaf SPAD value of shading-resistant variety Yangmai 158 and Nannong 02Y393 while decreased Soil-Plant Analyses Development （SPAD） value of shading-sensitive variety Yangmai 11 and Nannong 9918 during the early grain filling stage. However, shading significantly increased leaf SPAD value at late grain filling stage for all varieties. Shading decreased flag leaf net photosynthetic rate （Pn）, photosynthetic system II （PSⅡ） actual photochemical efficiency （ΦPSⅡ）, photochemical quenching of chlorophyll fluorescence （qP） and dry matter accumulation, while increased leaf original fluorescence （Fo） and maximum photochemical efficiency （Fv/Fm）. 【Conclusion】Under shading conditions, the low Pn of flag leaves is related to decrease of ΦPSII and qP, and thereafter, the dry matter accumulation in plant.