Effect of drought stress and water recovering on physiological characteristics of Sinocalycanthus chinensis seedlings

The effect of soil drought stress on photosynthetic physiological characteristics of seedling leaves had been studied using 2-year-old pot-cultured Sinocalycanthus chinensis seedlings as experimental materials under different levels of drought stress: no stress(75%80% of field capacity),light stress(60%65% of field capacity),medium stress(50%55% of field capacity)and severe stress(35%-40% of field capacity).The results showed that the net photosynthesis rate(Pn) was reduced and its diurnal pattern shifted from a typical doublepeaked curve gradually to a single-peaked one under drought stress conditions.According to the criteria suggested by Farquhar and Sharkey,the peak value depression of photosynthesis under the medium drought conditions may be attributed to stomatal limitation,while that may be linked to non-stomatal limitation under the severe stress.light compensation point(LCP),CO2 compensation point (CCP) and stomatal resistance(Rs) increased with the increasing intense of drought stress,while the light saturation point(LSP),apparent quantum yield(AQY),maximal Pn(Pmax),carboxylation efficiency(CE),Fv/Fm and transpiration rate(Tr) decreased.Dark respiration rate(Rd) was enhanced with increases under light stress and then declined under severe stress while intercellular CO2 concentration(Ci) showed a diverse trend.The photosynthetic ability could not be recovered under the severe stress.These results suggest that Sinocalycanthus chinensis is vulnerable to be damaged by severe drought stress.