| Forsythia suspensa was used in the experiment.The laws of photosynthetic characteristics of F. suspensa was studied during the seasons of growth using the technology of gas exchange and analyzing chlorophyll fluorescence. Moreover, different shaded treatments in summer, including shading 43%, 70% and 97% PAR, were adopted in order to study the effects of environment on the photosynthetic characters and chlorophyll fluorescence parameters. Therefore, photosynthetic ability was improved and accumulation of photosynthetic products was increased.We expected to provide theoretical foundation and actual meanings at the same time for cultivating the F. suspensa was scientifically. The main results were as follows:1. The photosynthetic characteristics of F. suspensa was demonstrated seasonal variation obviously. Seasonal changes of net photosynthetic rate in F. suspensa showed a single peak curve the peak appeared at 6,7 month. The environmental conditions such as temperature humidity and so light is ideal for the qrowth of F. suspensa,which was an important period of accumlation of photosynthetic products ,then decreased accordingly cooler weather in september minimun value of the rapid decline.2. The diurnal variation of F. suspensa was inerratic. The diurnal curve of photosynthes'rate (Pn) in F. suspensa presented a single peakcurve without mid-depression. The peak appeared at noon then deereased. The diurnal curves of leaf transpiration rate and stomatal conductance were identical to Pn, but negatively with internal CO2 concentration. Pn was significantly positively related with transpiration rate and stomatal conductance. The principal environmental factors affecting Pn were PAR. The maximal PSII fficiency(Fv/Fm) and PSII potential efficiency(Fv/Fo) displayed a significant midday ecline, being as low as the lowest valuein a day under the strong light of the noon.3. F. suspensa was LCP is between 20.1～26.3μmol·m-2·s-1,LSP is bewteen 863～1529μmol·m-2·s-1,CCP is bewteen 35.2～81.8μmol·mol-1,in spring and summer the CSP was higher than 2 000μmol·mol-1, and CSP is bewteen 1550μmol·mol-1 in autumn. These re-sults indicated that F. suspensa was a C3 plant.4. Through shaded treatments, the light compensation point (LCP), light saturation point (LSP)and dark respiration rate (DP) of the F. suspensa plant were at a low level, the value of which decreased with the increasing of shade degree. The diurnal variation of net photosynthetic rate (Pn) presented only one peak under both full day light and all shade conditions, the daily maxmium and average of net photosynthetic rate decreased significantly with increasing of shade degree, and there by efficiency of the solar energy utilization increased.The diurnal variations of transpiration rate and stomata conductance in leaves were smiilar to that of net photosynthetic rate, the values of transpiration rate and stomata conductance also decreased as increasing of the shade degree. The net photosynthetic rate, transpiration rate and stomata conductance under full day light and all shade conditions showed a positive correlation.The content of chlorophyll a+b, chlorophyll a and chlorophyll b in leaves grown under all shades conditions were significant higher than those under full day light, and increased with increasing of shade degrees, mean while the chlorophyll a/b decreased. Fv/Fm and Fv/Fo were significantly higher than those under full day light and increased with increasing of shade degrees under all shade conditions. |
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