根茎禾草乳熟期净光合速率日变化的比较研究

对6种具有不同根茎长度的禾草乳熟期净光合速率日变化进行了比较研究．结果表明，除了中间偃麦草(Elytrigia intermedia)为“单峰”曲线外，另外5种禾草的净光合速率日变化曲线均呈“双峰型”，且其总体趋势是根茎越发达、根冠比越大，其净光合速率越迟到达第1峰、“午降”经历时间也越短，而大气相对湿度偏低(<55％)和叶片温度偏高(>36℃)是导致“午降”的重要因素．羊草(Leymus chinense)、茹莎娜牧冰草(Pascopyrum smithii)、赖草(Leymus secalinus)、大赖草(Leymus racemosus)、蒙古冰草(Agropyron mongolicum)、中间偃麦草(Elytrigia intermedia)的净光合速率第1峰值分别出现在10：12、10：00、9：51、9：39、9：06、8：13；“午降”经历时间分别是471、474、464、467和551min；“午降”期间的叶片温度均值分别是37．8、37．5、36．9、37．0和36．3℃．羊草和蒙古冰草、赖草和大赖草分别具有相似的净光合速率日变化曲线。在P=0．01时，r值分别是0．88和0．96。

Comparative study on daily change of photosynthesis rate of the rhizomatous grasses in milky ripe stage

Comparative study on daily change of photosynthesis rate of the rhizomatous grasses in their milky ripe stage was carried out, and the results showed that photosynthetic rate of five grasses appeared to be two-apex curve, except Elytrigia intermedia appeared to be one-apex curve. The general trend was that the higher the root/shoot ratio was, the later the first apex of the photosynthetic rate reached, and the shorter the noon break period was. Moreover, low relative humidity and high leaf temperature were the important factors for noon break. Leymus chinense, Pascopyrum smithii Rydb. cn. Rosana, Leymus secalinus, Leymus racemosus, Agropyron mongolicum and Elytrigia intermedia reached the first apex at 10:12, 10:00, 9:51, 9:39, 9:06 and 8:13, the noon break period was 471, 474, 464, 467 and 551 min, and the average leaf temperature during noon break was 37.8, 37.5, 36.9, 37.0 and 36.3 degrees C, respectively. Leymus chinense and Agropyron mongolicum, Leymus secalinus and Leymus racemosus had similar daily change in photosynthetic rate, respectively, and their r values were 0.88 and 0.96 respectively when R = 0.01.