Diurnal Changes of Chlorophyll Fluorescence Characteristics of Japanese Yew Seedlings under Different Light Conditions

In order to know the characteristics of light adaptation of Japanese yew for the efficient cultivation,we selected five-year seedlings to study the diurnal changes of chlorophyll fluorescence characteristics under three levels of the light control of full light( FL),60% full light( F1) and 30% full light( F2). From 7: 00 am to 17: 00,Foof seedlings under FL and F1 controls increased by 23. 0% and 14. 0%,respectively,and under F2 control Fofell slightly. Fmand Fv/ Fmof three groups of seedlings fell to the minimum and then rebounded,the Fmvalues of seedlings under FL,F1 and F2 light controls decreased at the most by 38. 0%,28. 0% and23. 0%,respectively,Fv/ Fmof seedlings under FL,F1 and F2 light controls decreased at the most by 14. 0%,6. 4% and 4. 2%,respectively. The ΦPSⅡof seedlings under F2 control reached the maximum and showed the raising tendency during the day,the tendency of ΦPSⅡunder FL and F1 light controls were similarity,the ΦPSⅡvalue under FL and F1 reached at a higher level at 9: 00,then decreased gradually,and at 15: 00 got the minimum value,and the ΦPSⅡvalue of the seedlings under FL control had the more lower level. The significant differences of ETR in three sample groups of seedlings appeared during 11: 00- 15: 00,the ETR of seedlings under F2 control got the maximum value during the time,and the ETR of seedlings under F1 maintained stable,and the ETR of seedlings under FL reached the minimum value. The q P of seedlings under F2 control was higher in value than the those under FL and F1 controls,the tendency under F2 was consistent with the daily light intensity change; the q P of seedlings under FL and F1 controls got the minimum in 13: 00 and 15: 00,respectively. The NPQ of seedlings under F2 control decreased during the day slightly,the NPQ under FL and F1 controls reached two times peak values at 9: 00 and 13: 00( 15: 00). Based on the above variation in fluorescence parameters,the photochemical reactions was the primary way in the optical utilization of the yew seedlings under F2 control during the day,and wasted lesser optical energy in the form of thermal energy radiation. The seedlings under FL and F1 controls appeared the photoinhibition in the high-light-temperature periods,at the time the seedlings improve the protection by increasing thermal dissipation, and the photosynthetic organ were not damaged.