| The process and mechanism of water metabolic and photosynthesis is the theoretical basic and technology auspice in the choice of water saving drought-resistant plant and right site type distribution for vegetation recovery in the arid and barren site conditions. Contraposing the problem of lacking study of shrubs and its correlative physiological ecology, the response characteristics to light intensity and CO2 concentration and diurnal change of photosynthetic efficiency parameters and chlorophyll fluorescence kinetic parameters of Vitex negundo , Cotinus coggygria Scop., Forsythia suspense, Rosa spp were studied under different soil moisture conditions. Discussed the response process and adaptive mechanism of photosynthesis and transpiration to water, light stress and CO2 concentration. Confirmed the quantitative relation of Photosynthesis, Transpiration and Water Use Efficiency on soil moisture, Photosynthetic Active Radiation and CO2 concentration. The following are the main results:1. Dural change characters and it's physiology mechanism of four shrubs were posted(1) Soil water had remarkable effect on the diurchange of four shrubs;Non-stoma restrict would happended under severe soil water stressSoil water stress had a remarkable effect on photosynthesis dural change of four shrubs. The types of dural change of Vitex negundo , Cotinus coggygria Scop., Rosa spp gradually transfered from single-peak curve to double-peak curve along with the aggravation of soil water stress. The critical value was respectively between 64.9%～81.2%, 40.5%～60.2% and 22.9%～44.7%. While the type of dural change of Cotinus coggygria Scop. was double-peak curve under each soil water. The the reason for photosynthetic siesta transfered from stoma restrict to non-stoma restrict double-peak along with the aggravation of soil water stress. The main reason for the descent of Pn of four shrubs at noon under light and middle water stress was stoma restrict. While The main reason for the descend of Pn of four shrubs at noon under severe water stress was non-stoma restrict.(2) The photosynthesis level of for shrubs were markedly different and descended with the drop of soil moisture. The sequence of photosynthesis rate and water utilization of four shrubs was Forsythia suspense>Vitex negundo> Rosa spp>Cotinus coggygria Scop.The photosynthesis level of for shrubs markedly descended with the drop of soil moisture. The sequence of photosynthesis rate and water utilization of four shrubs was Forsythia suspense>Vitex negundo> Rosa spp>Cotinus coggygria Scop.. For example, the average of four shrubs'diurnal Pn was Forsythia suspense(9.0μmol·m-2·s-1)>Vitex negundo (6.3μmol·m-2·s-1)>Rosa spp (5.9μmol·m-2·s-1)>Cotinus coggygria Scop.(3.6μmol·m-2·s-1),the average of four shrubs'diural WUE was Forsythia suspense (3.1μmol·mmol-1) > Vitex negundo(2.5μmol·mmol-1) > Rosa spp(2.3μmol·mmol-1) >Cotinus coggygria Scop.(1.2μmol·mmol-1).(3) Light restrain was taken place at noon, and was less effected by soil water; To adding heat dissipation is the main mechanism to resist light restrain The depress of four shrubs'Pn, Fm, Fv/Fm andΦPSⅡshowed that light restrain was taken place at noon. The hoist of NPQ showed that the add of heat dissipation was one of the main mechanism for four shrubs to resist light restrain.(4) The intenseness of soil water stress would aggravate the extent of light restrain. The photochemistry efficiency for PSII of Rosa spp and Cotinus coggygria Scop. was higher than Forsythia suspense and Vitex negundo.The average of four shrubs'diurnal Fv/Fm was Rosa spp (0.83)>Cotinus coggygria Scop. (0.82)>Forsythia suspense (0.81)>Vitex negundo (0.79). The average of four shrubs'diurnalΦPSⅡwas Cotinus coggygria Scop. (0.67)>Rosa spp (0.66)>Forsythia suspense (0.63)>Vitex negundo (0.62).2.The response character of four shrubs'photosynthesis efficency to light intensity and soil moisture was studied(1) The four shrubs had strong adaptability to light, they had higher Pn and WUE in strong light range.The four shrubs had strong adaptability to light, when PFD was between 550 and 1800μmol·m-2·s-1 the Vitex negundo had high-level photosynthesis rate, when PFD was between 800 and 1800μmol·m-2·s-1 the Cotinus coggygria Scop. and Forsythia suspense both had high-level photosynthesis rate, when PFD was between 600 and 1800μmol·m-2·s-1 the Rosa spp had high-level photosynthesis rate.(2) The Pnmax, LSP,Φ, LCP and Rd of four shrubs had obvious threshold responses to soil water.The Pnmax, LSP,Φ, LCP and Rd of four shrubs had obvious threshold responses to soil water, with the increase of soil water the Pnmax, LSP,Φ, Rd first increased, then they gradually decreased while the LCP first decreased, then it gradually increased. The critical value of soil moisture to the transition of photosynthesis efficency parameters was different. For example, The critical value of soil moisture of Vitex negundo, Cotinus coggygria Scop., Rosa spp was about 57.7%, 59.4%, 65.8% respectively, corresponding the maximal Pnmax, LSP,Φ, Rd and the minimal LCP. While when SWC was between 55.3% to 61.5%, Forsythia suspense had the maximal Pnmax, LSP,Φ, Rd, and when SWC was about 34.4% Forsythia suspense had the minimal LCP.(3) The RWC range for four shrubs to have higher Pn and WUE were different, the threshold range of Cotinus coggygria Scop. and Rosa spp is lager than Forsythia suspense and Vitex negundo; The drought-forbearing productivity of Vitex negundo and Cotinus coggygria Scop. was lager than Rosa spp and Forsythia suspense.The RWC range for four shrubs to have higher Pn and WUE (RWC for max) for Vitex negundo was 44.9%～88.1% (66.5%) and 39.5%～82.0% (60.7%), for Cotinus coggygria Scop. was 44.4%～94.1% (69.3%) and 47.0%～100% (73.8%), for Forsythia suspense was 45.7%～88.4% (67.1%) and 50.6%～97.9% (74.3%), for Rosa spp was 45.6%～92.5% (69.0%) and 50.8%～108.8% (79.8%). The fitting water deficit ranges for Vitex negundo , Cotinus coggygria Scop., Forsythia suspense, Rosa spp were 44.9%～82.0%, 47.0%～94.1%, 50.6%～88.4%, 50.8%～92.5%, in these ranges the four shrubs all have higher photosynthesis rate and water utilzation efficiency.3. The fitting models of four shrubs'light responses were confirmed The fitting models of four shrubs were different, and the fitting degree was less effected by soil water.Contrasted between three empirical models we found that the fitting effect s of photosynthesis response curve with non-rectangle hyperbolae model and index modle were better than rectangle hyperbolae model. The non-rectangle hyperbolae model is more appropriate to fit the light response processes of Vitex negundo and Cotinus coggygria Scop., while the fitting effects of photosynthesis response curve of Forsythia suspense and Rosa spp with index model were better than non-rectangle hyperbolae model under each soil water.4. The character of CO2 responses offour shrubs was studied(1) With the highten of CO2 concentration, the Pn and WUE remarkably elevated, while the Tr remarkably decended.The four shrubs had strong adaptability to CO2 concentration, with the increasing of CO2 concentration the net photosynthesis rate increased, the transpiration rate decreased while the water utilization efficiency increased gradually. when Cr was between 1000 and 1600μmol·mol-1 the Vitex negundo and Cotinus coggygria Scop. both had high-level photosynthesis rate, when Cr was between 1050 and 1600μmol·mol-1 the Forsythia suspense had high-level photosynthesis rate, when Cr was between 850 and 1600μmol·mol-1 the Rosa spp had high-level photosynthesis rate.(2) The CSP, CE,Γand Rp of four shrubs had obvious threshold responses to soil water.The CSP, CE,Γand Rp of four shrubs had obvious threshold responses to soil water, with the increase of soil water the CSP, CE, Rp first increased, then they gradually decreased while theΓfirst decreased, then it gradually increased. The critical value of soil moisture to the transition of photosynthesis efficency parameters was different. For example, The critical value of soil moisture of Vitex negundo, Cotinus coggygria Scop., Forsythia suspense, Rosa spp was respectively about 68.1%～90.4, 61.7%～73.6%, 69.1%, 66.9%.
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