A Study On The Photosynthetic And Chlorophyll Flourescence Characteristics Of Three Desert Plants

Li-6400portable photosynthesis system was used to measure photosynthetic and chlorophyll fluorescence PARameters of Salix psammophila, Artemisia intramongolica, and Hedysarum scoparium. The objectives of this case are to understand their diurnal and seasonal dynamics, and to explore the main environmental factors that influence the PARameters of photosynthesis and chlorophyll fluorescence. The main results were:1. Diurnal changes of net photosynthetic rate (Pn) of Salix psammophila and Hedysarum scoparium showed one-peak curves.That of Artemisia intramongolicahad both one-peak curves and two-peak curves. Under favorable environmental conditions, the peak appeared at10:30,11:30, and11:30for three species (in an order that appeared above), respectively. Under harsh environmental conditions, the peak appeared earlier.2. Seasonal change of net photosynthesis rate of Salix psammophila, Artemisia intramongolica, Hedysarum scoparium showed two-peak curves, but the secondary peak of Hedysarum scoparium were not obvious. The maximum Pn of Salix psammophila was11.24μmol m-2s-1and appeared at mid-September. The maximum Pn of Artemisia intramongolicawas14.77μmol m-2s-1and appeared at late September. The maximum Pn of Hedysarum scoparium was6.13μmol m-2s-1and appeared at early July.3. Diurnal changes of transpiration rate (E) of Salix psammophila were one-peak curves. The peak was detected between10:30-14:30. That of Artemisia intramongolica and Hedysarum scoparium had both one-peak curves and two-peak curves.The peak of one-peak curves appeared at11:30and the main peak of two-peak curves appeared at9:30.4.The light response curves indicated that all the three species had wide photosynthetic ecological amplitude and strong adaptability to high Light intensity. Salix psammophila had the highest light use efficiency, carbon sequestration capacity and biological production potential, followed by Artemisia inframongolicaand Hedysarum scoparium.5.The major environmental factor influencing net photosynthetic rate of Salix psammophila was moisture content. The main environmental factors that affected Artemisia intramongolicawere temperature and relative humidity. The major environmental factor influencing net photosynthetic rate of Hedysarum scoparium was temperature and light intensity.6.Diurnal changes of PS Ⅱ maximum efficiency (Fv’/Fm’)、the efficiency of photosystemⅡ photochemistry (OPSⅡ),photochemical quenching (qp) of Salix psammophila, Artemisia intramongolica, Hedysarum scoparium were all "V" type curves. Diurnal changes of Nonphotochemical quenching (NPQ) of three species were one-peak curves. Diurnal changes of electron transport rate through PSⅡ (ETR) of Salix psammophila and Artemisia inframongolicahad both one-peak and two-peak curves. Two-peak curves were detected at mid-July and mid-August. Diurnal changes of ETR of Hedysarum scoparium were one-peak curves.7. Artemisia intramongolicahad the maximum ΦPSⅡ and qp, which indicated the highest efficiency of achieving and altering light energy. That means Artemisia intramongolicacan allocate more light energy for photochemical and can alter more light energy into chemical energy. Salix psammophila followed Artemisia intramongolicaand was higher than Hedysarum scopariumwere. Artemisia intramongolicahad the highest photosynthetic capacity with the largest ETR. The photosynthetic capacity of Hedysarum scopariumwere was lower than Artemisia intramongolicabut was higer than Salix psammophila. At later growth stage, photosynthetic capacity of Hedysarum scopariumwere was lower than Salix psammophila. Highest Fv’/Fm’ and NPQ indicated Artemisia intramongolicahad the highest efficiency of capturing excitation energy and had the highest ability to regulate light energy. Salix psammophila had a lower efficiency of capturing excitation energy than Hedysarum scopariumwere, but had a higher ability to regulate light energy. It was concluded that Artemisia intramongolicaadapted to the dry environment best.