| Water condition is the main factor to influence growth and distribution of dominant shrub and herbaceous plant living in shell ridge region of the yellow river delta.While Periploca sepium Bunge is the dominant shrub which has the stronger function of wind prevention,sand fixation,as well as water and soil conservation.But the growth of Periploca sepium Bunge is greatly limited by soil water.In order to clearly investigate the response rules and adaptive mechanism of photosynthetic efficiency and water deprivation of Periploca sepium Bunge on shell-sand moisture,the research took 4a-Periploca sepium Bunge as the study object.And long-term 4 kinds of water adaptive treatments and short-term 12 series water response treatments were set respectively.Li-6400XT portable photosynthesis system,FMS-2 portable fluorescence system,and Dynamax packaged stem sap flow gauge based on stem-heat balance method etc.were adopted to determine and analyze photoresponse of gas exchange parameter,chlorophyll fluorescence parameter and physiological and biological indexes for leaves of Periploca sepium Bunge,and stem sap flow parameters of Periploca sepium Bunge.The water response rule of photosynthetic efficiency for Periploca sepium Bunge was discussed.The physiological and ecological adaptive mechanism of Periploca sepium Bunge adapting itself to draught threat of shell-sand was revealed.And the water condition facilitating Periploca sepium Bunge in keeping higher photosynthetic efficiency was clearly confirmed.The research results can act as a reference for vegetation restoration of shell ridge of bohai gulf and selection of matching species with the site.The research results are as follows:?1?Photosynthetic efficiency,transpiration rate and respiration effect of Periploca sepium Bunge decreased apparently under drought and water logging stress of shell-sand,while drought stress had more serious effect than water logging stress on Periploca sepium Bunge.The Periploca sepium Bunge had the highest water use efficiency when drought stress was moderate?the relative water content?RWC?of shell-sand is 50.27%?.The optimum water content range?RWC?of shell sand to maintain high photosynthesis and water use efficiency was 63.22%-69.98%,Among the range,69.40%for RWC was the water condition which facilitated Periploca sepium Bunge in the most vigorous photosynthetic effiency.36.61%for RWC is the threshold value of conversion from stomatal limitation to non-stomatal limitation.?2?Under the condition of drought stress,the yield of light quantum and electron transfer velocity in PS?of leaves of Periploca sepium Bunge apparently declined,and the process of photosynthesis was seriously influenced by photoinhibition.Luminous energy used for heat dissipation in PS?increased,and initial fluorescence value ascended?when RWC was 23.50%,it was 257.62?.Photosynthetic mechanism was damaged.While the change inclination of various fluorescence parameters in water logging stress were weaker than that in severe drought stress.At this time,the photosynthetic mechanism was not damaged.?3?With the increase of drought stress in shell-sand,the chlorophyll content for the leaves of Periploca sepium Bunge were significantly decreased;the activity of superoxide dismutase?SOD?ascended first and then decreased,while the activity of peroxidase?POD?increased all along.The content of proline and soluble sugar increased significantly,and the content of Malondialdehyde?MDA?increased first and then decreased.Periploca sepium Bunge showed the characteristics of enhancing the osmotic adjustment substances,increasing the activity of antioxidant enzymes,and reducing the membrane lipid peroxidation product to resist and adapt to shell-sand drought stress.?4?With the development of drought stress of shell-sand,the instantaneous daily rate and daily accumulated quantity of stem sap flow for Periploca sepium Bunge gradually reduced,which was characterized by advancing or delaying actively reaching peak time of the stem sap flow.When RWC of shell-sand was 57.4%-84.7%,the instantaneous stem sap flow rate and daily water consumption(142.48-220.6 g·d-1)of Periploca sepium Bunge kept the higher level.And when RWC was 69.40%,the daily water consumption of stem sap flow of Periploca sepium Bunge could reach the highest value of 220.6 g/d.The daily water consumption of Periploca sepium Bunge was apparently lower than that under the condition of water logging stress under the condition of drought stress of shell-sand.It was obvious that stronger photosynthetic physiological adjustment capacity and water adaptive plasticity were demonstrated on Periploca sepium Bunge under drought stress of shell-sand. |
PDF Full Text Request