Effects of Soil Water Stress on the Photosynthesis Characteristics and Chlorophyll Fluorescence Parameters of Cerasus humilis Seedling

Both Li-6400 photosynthesis system and OS1-FL chlorophyll fluorometer were used to measure the photosynthesis characteristic and chlorophyll fluorescence parameters of Cerasus humilis plant under soil water stress.The result showed:(1)The average photosynthesis rate reached the maximum under the low water stress,while that under the high soil water stress was the least.The stomatal conductance increased as a result of the increasing of PAR(Photosynthetically Active Radiation) under no soil water stress conditions and didn't variate under the mediums and high soil water stress conditions.Diurnal variation of photosynthesis rate presented a two-peaks curve and showed obvious noon depression.The variation of net photosynthesis rates under different water stress conditions are follows: 8.447±0.831,6.811±0.690,2.658±0.756,1.474±0.469 μmol·m-2·s-1.Significant variations of Pn happened between the conditions of the former two and the later two,Diurnal variations of Cond,Tr,WUE under different soil water stress conditions were similar to the variations of Pn.(2) The fluorescence parameter of Fo,NPQ increased with the increasing of water stress,while the Fv/Fm,Fv/Fo dereased.It means that with the increasing of the water stress,the reaction center of PSII was destroyed or a non-reversible deactivation occurred so that the photosynthesis was restrained.The photosynthetic apparatus of C.humilis was protected by exhausting the extra light energy through heat dissipation.(3) WUE reached its maximum(1.214±0.112 μmol·mmol-1)and the physiological parameters of photosynthesis were optimized under low soil water stress with water contents from 21%-24%.