对华山新麦草(Psathyrostachys huashanica Keng ex P. C. Kuo)营养叶的净光合速率(Pn)和蒸腾速率(Tr)的日变化曲线进行了分析,并在对叶温(Tl)、气孔阻力( Rs)、光合有效辐射强度( PAR)和气温( Ta)的日变化曲线进行测定的基础上分析了它们对华山新麦草 Pn 的影响规律。 结果表明:华山新麦草 Pn 的日变化曲线呈“三峰”型,峰值分别为 6. 5、6. 2 和 9. 0μmol· m^-2 · s^-1 ,依次出现在 9:30、11:30 和 16:30,而且具有明显的“午降”现象;Tr 的日变化曲线呈“单峰”型,最大值为 1. 7 mmol· m^-2 · s^-1 ,出现在 13:30;Tl、Rs、PAR 和 Ta 的日变化曲线均呈“单峰”型,峰值分别出现在 12:30、11:30、12:30 和 13:30。 华山新麦草的 Pn 对 Tl、PAR 和 Ta 的响应曲线均呈“抛物线”型,Pn 在一定范围内与 Tl、PAR 和 Ta 呈正相关,随着 Tl、PAR 和 Ta 的升高逐渐增加至最大值后逐渐降低;而 Pn 与Rs 则呈负相关,Pn 在一定范围内随 Rs 的增大逐渐降低。 根据拟合方程,华山新麦草营养叶的光补偿点和光饱和点分别为 1. 1 和 531. 5 μmol· m^-2 · s^-1 ,说明该种类具有很强的喜光性,且对光照强度的适应范围较广。 研究结果表明:较大的气孔阻力是造成华山新麦草叶片净光合速率偏低的主要原因。
 

The daily change curves of net photosynthetic rate (Pn) and transpiration rate (Tr) of foliage
leaf of Psathyrostachys huashanica Keng ex P. C. Kuo were analyzed, and on the bases of determination of daily change curves of leaf temperature ( Tl), stomatal resistance ( Rs), photosynthetically active radiation intensity (PAR) and air temperature (Ta), their influence rules on Pn were also analyzed. The results show that daily change curve of Pn is “three peaks” type with the peak values of 6. 5, 6. 2 and 9. 0 μmol· m^-2· s^-1, respectively, appearing successively at 9:30, 11:30 and 16:30, and there is an obvious “midday depression” phenomenon. The daily change curve of Tr is “ single peak” type with a maximum value of 1. 7 mmol· m^-2· s^-1 at 13:30. And the daily change curves of Tl, Rs, PAR and Ta are all “single peak” type, and their peaks appear respectively at 12:30, 11:30, 12:30 and 13:30. The response curves of Pn to Tl, PAR and Ta all are “parabola” type, and Pn positively correlates with Tl, PAR and Ta in a definite range, that is, Pn increases gradually to a maximum value and then decreases gradually with Tl, PAR and Ta enhancing. While Pn negatively correlates with Rs, that is, Pn decreases gradually in a certain range with Rs increasing. According to fitting equation, light compensation point and light saturation point of foliage leaf of P. huashanica are 1. 1 and 531. 5 μmol · m^-2 · s^-1, respectively, showing that P. huashanica possesses strong photophilic character, and adapts to a wide range of light intensity. It is suggested that greater stomatal resistance is the major reason for leading to
low net photosynthetic rate of P. huashanica.