Photosynthetic Characteristics of Potentilla Discolor Bunge and Their Response to Light Intensity in Loess Hilly Area

Photosynthetic rate (P_n),transpiration rate (T_r),stoma conductance (G_s),and light response curve of Potentilla discolor Bunge were measured in the field using an open gas exchange system,Li—6400 Portable Photosynthesis System in the hilly area of the Loess Plateau.Results showed that the diurnal varia- tion of net photosynthetic rate presented a single-bottom curve.The maximal P_n was 14.91μmol/(m~2·s) at 8:00 a.m and the minimum P_n,0.13μmol/(m~2·s) at 14:00 p.m.Potentilla discolor Bunge got into the state of photosynthetic noon break.The light compensation point,the light saturation point,and apparent quantum efficiency of Potentilla discolor Bunge were 51.4,527,and 0.0566μmol/(m~2·s),respectively. This indicated that Potentilla discolor Bunge was a typical sun plant.During the course of light response, with R_(PA) increasing,T_r rose and its diurnal variation was in agreement with G_s.There was an exponent rela- tionship between T_r and G_s.The water use efficiency (WUE) of Potentilla discolor Bunge abided with a pa- rabola model as R_(PA) increased.At the beginning,WUE increased greatly and the maximum appeared at 4.68 mmol/mol when R_(PA) was 800μmol/(m~2·s).Then WUE decreased with a less variation.