为探明岩溶环境下稻田轮作黑麦草的高产机理,采用LI-6400光合测定仪对稻田轮作黑麦草的光合日变化特性进行测定.结果表明:1)从黑麦草光合生理指标的日变化看,净光合速率(Pn)呈双峰曲线,即在上午9:30～10:30、下午13:30～14:30分别出现一次高峰,但下午的峰值低于上午,两峰间在12:30出现一次低谷,并产生午休现象；叶片气孔导度(Gs)也呈双峰曲线,两峰出现在9:30和14:30,低谷出现在12:30,与净光合速率出现低谷的时间一致；叶片蒸腾速率(Tr)、光合有效辐射(PAR)、叶室温度(Tc)和叶片温度(TI)均呈单峰曲线,最大值均出现在中午12:30；相对湿度(RH)的日变化趋势正好与光合有效辐射相反,呈倒单峰曲线,其最小值也出现在12:30.2)从黑麦草光合生理指标的相互关系看,净光合速率出现的高峰先于气孔导度,蒸腾速率与净光合速率的日变化呈同步趋势；随着黑麦草光合有效辐射量的增加,胞间CO2浓度降低、水分利用效率提高、叶片净光合速率逐渐增强；相对湿度和有效辐射量过高或过低都不利于黑麦草进行光合作用.因此,每天上午10:30和下午14:30的有效辐射量最适合黑麦草叶片进行光合作用.%The photosynthetic diurnal variation characteristics of ryegrass leaves was determined by LI6400 photosyntometer to probe the high yield mechanism of ryegrass leaves under the paddy field rotation pattern in karst areas.The results showed that:1) The leaf Pn presented a bimodal curve at 9:30～10:30and 13:30～14:30 but the peak value at p.m was lower than that at a.m and the lower value appeared at 12:30.Leaf Gs presented a bimodal curve at 9:30 and 14:30 and the lower value appeared at 12:30 also.The maximum value of Tr,PAR,Tc and TI all appeared at 12:30 but the minimum value of RH appeared at 12:30; 2) The Pn peak was earlier than Gs and diurnal variation of Tr and Pn presented a synchronization trend.The intercellular CO2 concentration was reduced,water use efficiency was improved and leaf Pn enhanced gradually with increase of ryegrass photosynthetic effective radiant quantity.Higher or lower relative humidity and effective radiant quantity both were against ryegrass photosynthesis.The effective radiant quantity at 10:30 and 14:30 is benefial to ryegrass leaf photosynthesis.
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