Abstract:

Tangtsinia nanchuanica is a kind of rare plants, a class Ⅱ protected species in China. Its wild individuals have been hardly found. In this paper, the eco-physiological characteristics of Tangtsinia nanchuanica and its relative Cephalanthera falcata were compared. Using the LI COR6400 Portable Photosynthesis System, we measured some eco-physiological indicators of the two plants. Except the indicators such as stomatal conductivity (Con), water use efficiency (WUE) and internal CO₂ concentration(Ci), Tangtsinia nanchuanica and Cephalanthera falcata had not significant differences in net photosynthetic rate(P_n), transpiration rate(E) and other indicators. The P_n, dark respiration rate(Rd),E, Con, Ci, Light compensation point (LCP) , light saturation point (LSP) , solar energy use efficiency (SUE) and WUE of Tangtsinia nanchuanica were 6.16(±0.4) μmol·m^-2s-1,0.47(±0.04) μmol·m^-2s-1,2.7(±0.2) mmol·m^-2s-1, 0.114(±0.02) mol·m^-2s-1, 206(±29) μmol·mol^-1, 10 μmol photons·m^-2s-1, 200 μmol photons·m^-2s-1, 9.6(±0.9)%, 3.1(±0.2) mmol CO₂·mol^-1 H₂O respectively. Accordingly, the P_n,Rd, E, Con, Ci, LCP, LSP, SUE and WUE of Cephalanthera falcata were 5.8 (±1.1) μmol·m^-2s-1, 0.45(±0.06) μmol·m^-2s-1, 2.6(±0.3) mmol·m^-2s-1, 0.101(±0.03) mol·m^-2s-1, 173(±51) μmol·mol^-1, 10 μmol photons·m^-2s-1, 200 μmol photons·m^-2s-1, 9.1(±1.1)%, 2.7(±0.7) mmol CO₂·mol^-1 H₂O. In the greenhouse, the high P_n values of the orchids were observed from 9:00 to 13:00 and the midday photosynthetic depression was not observed on sunny days in summer. According to the light response of P_n, Tangtsinia nanchuanica and Cephalanthera falcata were both shade tolerant plant but could tolerate strong lights less than 1 000 μmol photons·m^-2s-1. Based on the temperature response of P_n, the favorable temperature for the two orchids was 15～25℃. By the stepwise multiple regression, it was found that E, WUE, Con, Ci, air temperature and PAR were the most dominant factors affecting the P_n of Tangtsinia nanchuanica, and the Con, Ci, air CO₂ concentration, E, PAR, relative humidity and SUE were the most dominant factors affecting the P_n of Cephalanthera falcata.

Key words: Tangtsinia nanchuanica, Cephalanthera falcata, Photosynthesis rate, Transpiration rate