Effects Of Soil Extreme Drought On Photo-physiological And Recovery Process Of Lonicera Japonica Thunb

Drought is one of the major limiting factors in the photosynthetic yield and organic matter synthesis of trees in the Yimeng mountain area and rehydration is one of the effective measures to reduce the decrease of plant productivity effectively.To elucidate the response of photosynthesis efficiency of Lonicera japonica to continuous soil drought,to reveal the mechanisms of the chlorophyll fluorescence redution underlying reduced photosynthetic efficiency,and the key water thresholds of plant rehydration were determined under different soil drought stress and different stress time.The recovery ability under the time,the critical water threshold point for the re-watering of plants was determined,which provided theoretical support for the reduction of productivity loss and high-efficiency water management of Lonicera japonica in the Yimeng area in extreme drought conditions.We studied the effects of drought stress on photosynthetic physiological processes of Lonicera japonica leaves and the response and mechanism of photosynthetic efficiency to sever drought and re-watering of Lonicera japonica leaves.First,using CIRAS-2 system and the Pocket PEA measured and analyzed the response characteristics of photosynthetic parameters and chlorophyll fluorescence-induced kinetic parameters to soil moisture.Second,four drought treatments?drought stress durations 0d,10d,20d,30d?were set at the determined 2 thresholds(RSWC_SL-NSL=29.7%?RSWC_wilting?Pn?0=11.4%).After the drought ended,the water resumed for30d,the changes of photosynthetic parameters and chlorophyll fluorescence induction kinetic parameters were determind and analyzed every 5 days.The results showed that:?1?The net photosynthetic rate?P_n?,stomatal conductance?G_s?,transpiration rate?T_r?and water use efficiency?WUE?in seedlings exhibited a clear threshold response to the relative soil water content?RSWC?.At RSWC below 29.7%,the limiting factor for P_n was non-stomatal.When RSWC=29.7%,the reason why P_n decrease was stomatal limitation to non stomatal limitation.When RSWC=11.4%,the P_n of the leaf was close to 0,and the photosynthetic apparatus was seriously damaged and the wilting of the plant tended to die at the same time.Based on this,the key water thresholds for the growth of Lonicera japonica under extreme soil drought were RSWC of stomatal limitation turning to non-stomatal limitation(RSWC_SL-NSL=29.7%),RSWC of leaves wilting(RSWC_wilting=11.4%)and RSWC when P_n was 0(RSWC_Pn?0=11.4%)(Definition:Threshold 1 was RSWC_SL-NSL=29.7%;Threshold 2 was RSWC_wilting,Pn?0=11.4%).?2?Based on the effects of soil drought stress on photosynthetic physiological processes and mechanisms of Lonicera japonica,it was known that mild soil drought had little effect on Lonicera japonica in Yimeng mountain area.An RSWC of 29.7%was the maximum allowable water deficit for the normal growth of seedlings of Lonicera japonica.At55.1%?RSWC?89.0%,the photosynthetic productivity of Lonicera japonica leaves was higherthan the average levels,and at 24.0%?RSWC?79.6%,the water utilization efficiency of Lonicera japonica leaves was higher than the average levels,so both P_n and WUE were higher than the average levels at 55.1%?RSWC?79.6%.?3?Drought stress at extreme drought threshold 1 and threshold 2 for 30 days,indicating that as the time of drought stress increases,the donor side of PSII?OEC?was seriously damaged,a large of Q_A^-was accumulated on the receptor side and he progression of the PSII electron transport chain was hindered.At the same time,the activity of PSII reaction center in leaves of Lonicera japonica decreased,and the photoinhibition was obvious.This indicated that the performance of the PSII reaction center was damaged,and the photosynthetic mechanism of Lonicera japonica was destroyed,which seriously affected the photosynthetic production of the Lonicera japonica.?4?After rewatering under different extreme drought conditions?stress different times under different thresholds?the photosynthetic gas exchange parameters,the fluorescence induced kinetic parameters and the activity parameters of PSII reaction center of Lonicera japonica leaves were obviously differences in recovery speed and recovery capatity.Extreme drought treatment-threshold 1 for 0 days?threshold 1?0??and 10 days?threshold 1?10??,and threshold 2 for 0 days?threshold 2?0??,P_n can be recovered to a higher level(P_n>P_nave),at this time the photosynthetic apparatus was reversibly damaged.After rehydration,the activity of the PSII reaction center recovered,and the photosynthetic apparatus performed well to ensure normal plant growth and development.And the recovery ability and recovery speed of P_n were threshold 1?0?>threshold 1?10?>threshold 2?0?.When the drought stress time continued to increase,the PSII reaction center of Lonicera japonica was seriously damaged and the overall performance was poor.The damage caused by the photosynthetic mechanism of Lonicera japonica was irreversible,and the growth was obviously inhibited.