Study On Photosynthetic Characteristics Of Vitis Vinifera L.cv. Cabernet Sauvignon In Weibei Rainfed Highland

The photosynthetic characteristics of the Vitis vinifera L. cv Cabernet Sauvignon were studied with LI-6400 portable photosynthesis system in two vineyards (hilly and plain area) in the Yaozhou area of Shaanxi province, from May to August in the year 2006. Some photosynthetic parameters were separately measured in the hilly and plain area, such as diurnal and monthly variation of net photosynthetic rate (Pn), and the effects of various environmental factors on Pn, and responsive characteristics of Pn to photosynthetic active radiation (PAR) and CO₂ concentration were also systematically studied. Some significant results obtained were as follows.1. Diurnal variation of Pn of Cabernet Sauvignon in Weibei Rainfed HighlandThe diurnal variation of net photosynthetic rates (Pn) of leaves either in the hilly area or in the plain area showed a double-peak curve with a lower value of the second peak, and the Pn curve in the hilly area was above the curve in the plain area. PAR and Transpiration (Tr) were the main factors that affected photosynthesis in the both areas.2. Monthly variation of Pn of Cabernet Sauvignon in Weibei Rainfed Highland The common monthly variation of Pn of Cabernet Sauvignon between the hilly area and the plain area obeyed the following order: berry expanding stage (July) > Turning-color period (May) > Anthesis (August), while there was still some difference, and during most time of the growing season, the average value of Pn in the hilly area was higher than that in the plain area. The results of regression analysis of main factors in the both areas showed that the major physiological factors that affected the monthly variation of Pn of Cabernet Sauvignon were: PAR > stomatal conductance (Gs) > intercellular CO₂ concentration (Ci), >Transpiration (Tr) > relative humidity (RH) > Ta.3. Response curve of Pn to PAR level of grapevine in Weibei Rainfed HighlandThe PAR response curve followed a quadratic function either in the hilly area or in the plain area, with their according light saturation points (LSP) at 1390¹472(μmol·m^-2·s^-1) and 1287¹410(μmol·m^-2·s^-1), light compensation points (LCP) at 38.7⁴7.0(μmol·m^-2·s^-1) and 36.7⁴2.6(μmol·m^-2·s^-1), appearance quantum yield (AQY) at 0.028⁰.036(mol·m^-2·s^-1) and 0.019⁰.034(mol·m^-2·s^-1). Compared with the plain area, the leaves in the hilly area had lower LCP and higher LSP, which suggests that the leaves in the hilly area have much better efficiency of light utilization, and when the LSP was reached in the grapevine leaves, the higher P max and AQY in the hilly area means that the leaves have stronger capacity of making photosynthate.4. Response curve of Pn to CO₂ level of grapevine in Weibei Rainfed Highland Response curve of CO₂ was a quadratic equation either in the hilly or in the plain area, with their according CO₂ saturation points (CSP) at 743⁷96 (μmol·m^-2·s^-1) and 813⁸46 (μmol·m^-2·s^-1), CO₂ compensation points (CCP) at 46.08⁴8.27 (μmol·m^-2·s^-1) and 51.20⁵4.40 (μmol·m^-2·s^-1), carboxylation efficiency (CE) at 0.056⁰.073 (mol·m^-2·s^-1) and 0.036⁰.043 (mol·m^-2·s^-1). The leaves in the hilly area had higher CE and lower CO₂ saturation point, which indicates that the grapevine in the hilly region has higher CO₂ utilization ratio than that in the plain area.5. Comparison of photosynthetic characteristics of grapevine in the hilly and plain area The Pn and Tr of the leaves in the hilly area were significantly higher (p < 0.05), and the Gs and Ci were also higher (P > 0.05) than those in the plain area, while the WUE of the leaves was less than that in the plain area. The P max of the leaves in the both areas reached its biggest level during the period of berries expansion, followed by the color-changing period, and flowering was the last, which was consistent with the change of CE levels. In our research, under the conditions of a hilly area, the photosynthetic characteristics of the leaves of Cabernet Sauvignon such as P max and CE had better performances than those under the conditions of a plain area, which suggests that Cabernet Sauvignon cultivated in a hilly area has more powerful capacity of photosynthesis.