Abstract:

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 (P_n) was measured under different light intensities condition, and then drawing the curve of P_n respond to light intensities according to the results. The diurnal variation of P_n 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 P_n 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 P_n of P. ternata (Fig1 & Fig3-a). P_n 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 P_n 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.

Key words: Pinellia ternate, Photosynthetic characteristics, Net photosynthetic rate, Light intensity, Transpiration rate