The Research Of Classification On Photosynthetic Characteristics Of Dioscorea Opposita Thunb

Dioscorea opposita Thunb. with a great variety has a wide range of origin, distribution and cultivation area. The classification of it has been investigated on many aspects such as photomorphology, nutritional quality and molecular level, but no unified classfication standard is established. What's more, the reports of photosynthetic characteristics on Dioscorea opposita Thunb. are insufficiency and the classification analysis on photosynthetic characteristics of it had not been reported. In this study, the classification analysis on photosynthetic characteristics of 76 Dioscorea opposita Thunb. strains which were sampled from Hainan, Fujian, Guangxi, Guangdong, Jiangxi and Yunnan Provinces was carried out and the main results were as follows:1. No obvious "midday depression" happened in the photosynthesis of Dioscorea opposita Thunb. Light saturation point (LSP) in PAR was roughly ranged from 1000 to 1500μmol·m-2·s-1, and from top to bottom the photosynthetic capacity in the fourth leaf was the largest among leaf positions.2. According to the photosynthetic physiological indicators,76 Chinese Yam strains were divided into six groups, and each group has the significant photosynthetic characteristic. The first group had lower CO2 fixation capacity and photosynthetic rate (Pn); the second group had higher water use capacity, CO2 fixation capacity and photosynthetic rate; and the third group was in the middle level; the CO2 fixation capacity and photosynthetic rate in the forth group were the highest; the fifth group had the lowest water use capacity and photosynthetic rate; while sixth group had the lowest CO2 fixation capacity and maintain lower level of photosynthetic rate.3. The cold resistance capacity of Hainan strains was lower than mainland strains:under low-temperature stress, the curve of photosynthetic-light response occurred abnormal and Pn declined.4.105# and 82# had higher photosynthetic capacity among the six mainland strains, while 81# and 210# had lower photosynthetic capacity. The main reason is that higher ability of water-absorbing in roots or higher ability of water-binding in leaves can maintain the water balance effectively which is benefical to increasing stomatal conductance (Cond), so as to reduce the restriction of stomatal factors on photosynthesis. In addition, compare in the difference between stomatal conductance and intercellular CO2 concentration (Ci) of 105# in groupⅢand 82# in groupⅣ, we found that 105# which had higher photosynthetic rate relying on higher stomatal conductance with higher CO2 supply capacity, while 82# relying on higher CO2 fixation capacity. 5. The photosynthetic capacity and photosynthetic characteristics of samples were chosen from the six groups according to the cluster analysis were consistent with the types they belonged to. This result showed that the classification analysis on photosynthetic characteristics of Dioscorea opposita Thunb. was an effective and feasible method.