Effect Of Soil Drought Stress Degree And Duration On Photosynthesis Of Ziziphus Jujuba

Under the background of global climate change,droughts will occur more frequently.Drought will lead to severe reductions in food crops,deterioration of the ecological environment,and other adverse effects.How to deal with droughts and their impacts will become a scientific issue that needs urgent solution.Ziziphus jujuba is an economic shrub widely distributed in the mountainous and mountainous regions of northern China.It is a plant with strong adaptability to extreme climates,especially as a vanguard species of water and soil conservation in the hilly area of the Central Shandong Province.one.At present,the existing research mainly focuses on the artificial cultivation of wild jujube,and the study on the physiological mechanism of drought-resistance of wild jujube is still not deep enough.Therefore,it is necessary to carry out the research on the quantitative relationship between photosynthetic physiological processes and soil moisture in the hilly region of the Central Shandong Province.In this paper,the wild jujube in Luzhong area was taken as the research object to investigate the response mechanism of the wild physiological parameters of wild jujube under natural conditions to gradual drought in the soil in Luzhong area,and to clarify the quantitative relationship between it and soil moisture,to determine the key threshold points;reveal severe drought stress Effects on the photosynthetic and fluorescence parameters of wild jujube and the attempt to put forward the classification of soil water availability based on"production"and"effect";to clarify the recovery conditions and critical threshold of recovery of wild jujube under different threshold conditions.Two-year-old wild Ziziphus jujuba potted seedlings were used as experimental materials,artificial water supply and natural water consumption were combined to simulate soil drought under natural conditions,and the response process of photosynthesis and fluorescence parameters of wild Ziziphus jujuba leaves to soil water?RWC?was determined.mechanism.The main conclusions are:?1?The response of Ziziphus jujuba to drought stress is related to the degree of drought stress.The net photosynthetic rate?P_n?,transpiration rate?T_r?,and water use efficiency?WUE?of the gas exchange parameters of leaves of Choerospondias axillaris increased first and then decreased with the increase of soil water content.When RWC<38.5%,P_n decreased,intercellular carbon dioxide concentration?C_i?increased,stomatal limitation value?L_s?decreased,and the decline of leaf photosynthetic rate was mainly caused by non-stomatal limiting factors;The RWC ranged from 38.5%to 65.1%,and the Ziziphus jujuba P _n decreased with C_i and stomatal conductance?G_s?,and the photosynthetic rate of the leaves decreased at the stomatal limitation stage.In the process of gradual drought of soil?RWC range of21.5%-86.5%?,the maximum fluorescence?F_m?of jujube,the maximum photochemical efficiency of PSII?F_v/F_m?,and the actual photochemical efficiency of PSII(?_PS?)decreased gradually,the initial fluorescence?F_o?increased significantly,the photochemical quenching?qP?increased first and then decreased,and the non-photochemical quenching?NPQ?was too high?RWC>83.7%?or too low?RWC<38.5%?showed higher values under soil moisture,showing increased heat dissipation.Obviously,the gas exchange parameters and chlorophyll fluorescence parameters of the wild Ziziphus jujuba leaf had obvious threshold responses to the soil moisture,and the relative water content of the threshold point was about 38.5%.When the threshold value was lower than the threshold,the photosynthetic rate of the leaves changed from stomatal restriction to non-stomatal limitation.The main reason for the decrease of photosynthetic capacity of Choerospondias axillaris was that PSII was damaged,electron transport was blocked,and photosynthetic apparatus was damaged.In this paper,P_n is proposed to be produced,and WUE is proposed to be effective.The threshold value method is used to classify the soil moisture.When P_n=0,the corresponding water point is RWC=22.1%.When it is lower than this moisture point?RWC<22.1%?is defined as ineffective water;the soil water content below the average corresponding water point for P_n and WUE is defined as low-yielding and inefficient water,and the water content is between RWC 22.1%-44.9%or greater.92.9%;the soil water content above P_n is higher than its mean value but the WUE is lower than the water point corresponding to its mean value is middle-inefficient water with a moisture range of 44.9%-46.0%;both P_n and WUE are high.The soil moisture at the water point corresponding to its mean value is intermediate middle-effect water,and the water range is 46.0%-63.3%or 68.9%-80.5%;the P_n is at the saturation point,and the water corresponding to WUE is at the high efficiency point.The point is high-yield,high-efficiency water with a moisture range of 63.3%-68.9%.?2?The response of Ziziphus jujuba to drought stress is also related to the duration of drought stress.In the RWC=38.5%?from stomata to non-stomatal turning point?moisture,jujube P_n,T_r and WUE all decreased with the increase of stress duration,and the RWC was 21.5%?P_n=0?.The gas exchange parameter of Ziziphus jujuba under moisture is always at a low level with the increase of stress duration.The above two water points showed the same pattern of wild Ziziphus jujuba F _m,F _v/F _m,?_PS?,and qP.When the drought lasted 15 days under RWC=38.5%,the sour Ziziphus jujuba gas exchange parameters decreased rapidly.At the same time,the chlorophyll fluorescence parameters decreased rapidly and coincided with RWC=21.5%,and NPQ approached 0,indicating that RWC=38.5%.At this time,the photosynthetic apparatus was severely damaged,and the heat dissipation capacity was basically lost.When RWC=21.5%,in the process of intimidation continued,Ziziphus jujuba photosynthetic production and respiration consumption basic same,shown on the apparent to the status of the Pn=0,but the Tr and G_s>0,that drought under the water for 30 days Ziziphus jujuba still has biological activity,the plants did not die,showed stronger drought resistance.?3?The recovery of sour Ziziphus jujuba after severe drought threshold showed a significant gradient,that is,the degree of recovery and recovery decreased with the decrease of water and the increase of stress time.Under the RWC=38.5%moisture condition,when the drought stress time is less than 20 days,the middle-effect middle-effect water can be achieved after rehydration;when the stress time is more than 20 days and less than 30 days,the middle-product low-efficiency water can be achieved after rehydration;When the water is rehydrated immediately under this water condition,the jujube can be restored to high-yield and high-efficiency water.Under RWC=21.5%moisture,when the drought stress time is less than 10 days,the middle-aged low-effect water can be achieved after rehydration;when the stress time is more than 10 days and less than 30 days,only low-yield and low-effect water can be achieved after rehydration;When the water is rehydrated immediately under this water condition,the Ziziphus jujuba can only be restored to middle-inefficient water.Comparing two thresholds of severe drought?ie,RWC=38.5%,RWC=21.5%?,the recovery of rehydration under different stress conditions can be obtained,and the treatment under RWC=38.5%moisture is significantly better than that under RWC=21.5%moisture.The treatment shows stronger drought resistance and recovery.