Physiological Response Of Calligonum Caput-medusae Seedlings To Drought And Salt Stress

The Taklimakan Desert Shelterbelt is mainly composed of shrubs belonging to three genera,Calligonum L.,Tamarix L.and Haloxylon Bunge,which ensures the long-term safety and unimpeded running of the desert highway and improves the environmental quality along the highway.In this paper,two-year-old seedlings of Calligonum caput-medusae were taken as the research object.In the experiment of salt stress,four treatments including 1,8,11 and 14 g/L of irrigation water were set,and 4.8g/L was used as the control.To study the adaptability of seedlings under salt stress of different degrees by measuring and analyzing the growth indexes and fluorescence parameters of seedlings.In the experiment of drought stress,normal irrigation cycle was taken as the control,and the drought stress treatments lasted for 20,30,40,50 and60 days,the changes of fluorescence parameters were measured under continuous drought stress.Through the systematic study of Calligonum caput-medusae seedlings on salt stress and drought stress,we expected to provide theoretical basis for the sustainable utilization and management of the Taklimakan Desert Highway Shelterbelt.The main results are as follows:（1）Saline irrigation with different salinity had significant influence on soil water and salt.During the whole period of salt stress,the maximum soil water content was observed at a depth about 20 cm soil layer under different salinity water irrigation in each irrigation cycle.Soil salt mainly accumulated in the soil surface（0-40 cm）,and it increased with the increasing salinity of irrigation water.（2）Salt stress had significantly influence on Calligonum caput-medusae seedlings.There was no significant difference on growth index and fluorescence index between different treatments and the control at the early stage of salt stress.The plant height,ground diameter,crown width,linear electron transfer（LEF）,actual photochemical efficiency(Y_（II）)and non-regulatory energy dissipation quantum yield(Y_（NO）)under 11g/L and 14 g/L were significantly lower than other treatments at the later stage of salt stress.However,non-photochemical quenching（NPQ）and regulatory energy dissipation quantum yield(Y_（NPQ）)were significantly higher than other treatments.According to the principal component analysis of the growth index and fluorescence index of the seedlings under different salt stress,the growth order of the seedlings was8 g/L>4.8 g/L>11 g/L>1 g/L>14 g/L,which means 8 g/L was the optimal salinity of irrigation water for Calligonum caput-medusae seedlings.（3）Drought stress had significanty influence on Calligonum caput-medusae seedlings.The litters of Calligonum caput-medusae increased by about 1 time after drought stress for 20 d and 30 d compared with the control,while the litters after drought stress for 40 d and 50 d increased by about 2 times.LEF and Y_（II）decreased gradually with the continuous drought stress.NPQ and Y_（NPQ）showed a gradually increasing trend with the continuous drought stress.The results indicated that drought stress can reduce the actual photochemical efficiency and electron transfer rate of the seedlings and consume the excess light energy by increasing heat dissipation.The daily average values of LEF,NPQ,Y_（II）,Y_（NPQ）and Y_（NO）of the normal growing assimilated shoots were significantly different from those of the young shoots and the dead shoots.The proportion of light energy utilization of Y_（II）,Y_（NPQ）and Y_（NO）in assimilated shoots with normal growth was close to 5:3:2,and the ratio of light energy utilization of Y_（II）,Y_（NPQ）and Y_（NO）in young shoots was close to 3:6:1,while the light energy absorbed by dry shoots was mainly used for Y_（NPQ）.In summary,continuous high salinity irrigation can reduce the actual photochemical efficiency and electron transport rate of Calligonum caput-medusae seedlings,consume excess light energy by increasing heat dissipation and other ways,and protect the internal photosynthetic structure from damage.Proper saline water irrigation will promote the growth of the seedlings of Calligonum caput-medusae.The damage of PSII response center was smaller in the seedlings under drought stress for30 days.When the drought stress exceeded 30 days,the PSII of the seedlings did not have irreversible photodamage,but the photoinhibition and the potential risk of photodamage caused by it increased.