用LI-6400型便携式光合作用测定系统对半夏的光合特性进行研究。结果表明半夏是喜阴植物, 光补偿点为19.19 μmol photons·m-2·s-1。半夏的初始表观量子效率高, 因此对光的利用率高。光合作用受叶片内部气孔调节和外部空气相对湿度、光照强度等因子影响, 半夏净光合速率的日变化呈双峰曲线。相关性分析表明,光照强度和蒸腾速率是影响半夏净光合速率的主要因子。因此，在栽培时，可采取与其他作物间作的方式, 对其遮荫, 缓解午休现象, 提高光合作用日同化量。对来自不同地区的16个居群的净光合速率进行测定，用SPSS软件对测定结果进行统计分析，结果表明，不同居群间的净光合速率差异显著，以来自四川崇州的PT3居群的净光合速率最大，为22.4 μmol CO2·m-2·s-1；有14个居群内部个体的净光合速率差异不显著, 有两个居群（PT7和PT15）内部个体的净光合速率差异极显著。
Pinellia ternata (Thunb.) Breit. is a wild medical plant. Their tubers were a crude drug of traditional Chinese medicine. For satisfying the demand of the drug market, some farmers began to cultivate this species in the field. The knowledge concerning physiological characteristics of P. ternata was an important guidance to its domestication, cultivation and cultivar breeding. This study focused on the photosynthetic characteristics of P. ternata, and expected to provide a scientific basis for choosing reasonable cultivation habitat and sieving preferential germplasm resource for field production of this crude drug.
The photosynthetic characteristics of live mature leaves in P. ternata plants were determined with the LI-6400 portable photosynthesis system. The net photosynthetic rate (Pn) was measured under different light intensities condition, and then drawing the curve of Pn respond to light intensities according to the results. The diurnal variation of Pn was measured at sunny day from 7:00–7:00 pm. From 9:00–11:00 am was the time for measuring the Pn of P. ternata populations. Ten plants were chosen at choice from a population, and each plant was measured 3 times. The mean values were used to describe the Pn of the given populations. In all the measuring course, the photosynthetically active radiation was controlled stably at 1 000 μmol photons·m-2·s-1 with the red-blue light source provided by the LI-6400 portable photosynthesis system. Original data were dealt with by MS Excel 2000 and analyzed by SPSS 11.0.
The results showed that the light compensation point of P. ternata was 19.19 μmol photons·m-2·s-1(Fig.1), indicating that P. ternata is a shade-loving plant. The initial apparent quantum efficiency of P. ternata was high up to 0.0604, indicating its high use efficiency of the light. Leaf photosynthesis was regulated by stoma and affected by relative humidity and light intensity .The curve of diurnal variation of net photosynthetic rate from leaves of P. ternata had two peaks (Fig.2). Fig.3 showed the effect of light intensity (Fig.3-a), temperature (Fig.3-b), relative humidity (Fig.3-c), stomatal conductance (Fig.3-d), intercelluar CO2 concentration (Fig.3-e), transpiration rate (Fig.3-f) on Pn of P. ternata. And it was correlated significantly with light intensity and transpiration rate, with the correlation coefficient of 0.820 and 0.713 respectively (Table 1). It was suggested that intercropping of P. ternata with tall crops would get shadowy environment, decrease midday depression of photosynthesis, and increase photosynthetic daily assimilation amount. The light intensity is one of the main factors of influencing Pn of P. ternata, and the midday depression of this species was observed in this investigation. But what causes midday depression of P. ternata couldn’t be light intensity (Fig.3-a). Although the light intensity was high up to 1055.7 μmol photons·m-2·s-1 at midday, it was not too high to result in decrease Pn of P. ternata (Fig1 & Fig3-a). Pn of 16 populations of P. ternata was measured and analyzed by SPSS 11.0, showing the very significant difference among them (Table 3). The Pn of the population PT3 that derived from Chongzhou Country, Sichuan Province, was 22.4 μmol CO2·m-2·s-1, which was the maximum among all the investigated populations (Table 2). Besides, there were other two populations, PT4 and PT6 which respectively derived from Zhongjiang and Shehong, also expressed very high Pn value. Theses three populations were considered adaptive to cultivation in the field. There were 14 of 16 populations in which individual plants showed the same Pn in statistics in the same population, which indicating to some extent that genotypes of individual plants are homozygous in these populations. And the other two populations PT7 and PT15, which respectively derived from Luxian and Guangan, were statistically different in Pn of individual plant, which means that the genetic diversity exist in these two populations. Therefore, in order to get the consistent cultivation type of photosynthetic characteristic, artificial choice is necessary.
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