Research On Photosynthetically And Ecophysiological Characteristics Of Typical Plants In Karst Area, Northwest Guangxi

Four pioneer plants in karst area in Northwest Guagnxi, Vitex negundo, Rhus chinensis Mill, Alangium chinense, and Alchornea trewioides, were chosen for the study on photosynthetic physioecological characteristics through the Li-6400 portable photosynthesis system. The results are as follows:â…°Differences existed in the diurnal curves of net photosynthetic rate (Pn) among the four pioneer plants, which is in the order of V. negundo (11.46), A. trewioides(9.33), R. Mill(7.81) and A. chinens e(6.98). The difference between V. negundo and other three species reached significant level (P>0.05), while the difference between the other three species was not significant (P>0.05). The transpiration rate had the same trend as net photosynthetic rate. The daily mean of water use efficiency presented in the order of V. negundo (2.60), A. trewioides(1.89), A. chinense (1.71), and R. chinensis (1.62). The difference was significant (P>0.05) between evry two species except A. chinense and R. chinensis. Correlation analysis showed that the most influencing factor on the Pn was PAR, followed by Gs, Ci, RH and Ta.â…±The variation of Pn wasquite different in the four seasons, and the values of Pn were largest in spring, followed in summer, autumn, and winter. Net photosynthetic rate for the four plants performed such as A. trewioides(9.34)>R. chinensis (9.33)>V. negundo (8.79)> A. chinense(8.24), but the differences was not significant (P>0.05); The seasonal variation of transpiration rate have the same characteristics as that of net photosynthetic. The seasonal variation of water use efficiency had different trends from net photosynthetic rate and transpiration rate, and it was in the order of A. trewioides (2.67)>A. chinense (2.55)>R. chinensis (2.53)>V. negundo (2.12) but with no significant difference.â…²The light compensation points were 19.45 for A. chinense,19.29 for R. chinensis,11.46 for V. negundo, and 11.46 for A. trewioides respectively. The photosynthetic quantum efficiency was in the order of R. chinensis (0.054), V. negundo (0.052), A. trewioides (0.052), and A. chinense(0.045), and net photosynthetic rate was A. trewioides> V. negundo> R. chinensis> A. chinense. All the above indicated that all the four plants were sunny. A. trewioides and V. negundo had the broadest adaptability to lighting environtment, followed by R. chinensis and A. chinense.â…³The CO2 compensation points for A trewioides, R. chinensis, V. negundo, and A. chinense were 47.92,65.43,68.21, and 84.95, respectively. The order of carbon assimilation efficiency was A. Trewioides (0.085), R. chinensis (0.081), V. negundo (0.075), and A. Chinense (0.036).â…´Through the synthetical comparison and analysis of the photosysthetic and ecophysiological indexes, all the four plants had hight photosynthetic efficiency, A. trewioides was the highest, followed by R. chinensis, V. negundo and A. chinens. The order of adaptability was as follows:A. trewioides>R. chinensis >V. negundo >A. chinense.