Light response model and photosynthetic dynamics at different phenological stages of Dongzao jujube

Abstract:【Objective】At present, facility cultivation has become the main cultivation method for jujube, which is a kind of artificially-created way of cultivation, by construction of greenhouses and/or other protective facility, to provide favorable environmental conditions for the growth and to reduce the impact of the natural environment on the growth of the plant. At the same time, facility cultivation can also adjust the photosynthetic ability of jujube plants. Although facility cultivation has great advantages, jujube farmers’knowledge on controlling the internal environment of facility is still not enough, and the growth characteristics of Dongzao jujube and other related understandings are insufficient, resulting in the current facility cultivation being prone to improper regulation, which will directly affect the development and yield. However, the optimal photosynthetic model of jujube and the dynamic change pattern at different phenological periods under different facility cultivation modes are still unclear. This study carried out model fitting and light response curve analysis for Dongzao jujube tree in different phenological periods under three facility cultivation modes.【Methods】The photosynthesis of Dongzao jujube tree was assessed through a randomized sampling of plants grown in the greenhouse, rain shelter and open field. During the various phenological stages, including the budding stage, full-flowering stage, young- fruit stage, expanding stage, crisp- ripening stage and post- harvest stage, measurements were conducted in more than three sunny days status. For accurate data collection, plants with identical growth were selected, and measurements were performed choosing 3-6 leaves from four different directions of the canopy. The photoresponse parameters were determined, including net photosynthetic rate, intercellular carbon dioxide concentration, stomatal conductance transpiration rate and water use efficiency. Subsequently, the average values of these parameters were calculated for a comprehensive analysis. The measurement was performed from 09:00 a.m. to 11:00 a.m. The leaves were stimulated for 20 minutes with 2200 μmol· m^{- 2} ·s ^{- 1} light intensity. Prior to measuring, wipe the dust on the surface of the leaf with a paper towel. The exponential model, non-rectangular hyperbola model, rectangular hyperbola model and its modified form were all applied to fitting, with the certainty coefficient, mean square error and mean absolute error serving as criteria for evaluating the accuracy of the fittings. Finally, the photosynthetic physiological characteristics of Dongzao jujube under different phenological periods were compared. Simultaneously, during the flowering season (mid-July), were measured the diurnal variation in photosynthesis and their light response curve. The correlation indexes of photosynthesis between girdling and treatments were compared to analyze the effect of girdling on the photosynthetic efficiency.【Results】The results showed that, by comparing the fitting effects of four models, nongirdling i.e. right-angled hyperbola modified model, right-angled hyperbola model, non-right-angled hyperbola model and exponential model, R2 , MSE and MAE were introduced to analyze the fitting accuracy of the fitting data. The analysis showed that there was a certain deviation between the fitting points of the four models and the measured values, and the fitting results of the four models were in a descending order as follows: non-rectangular hyperbola model ＞ rectangular hyperbola model ≈ measured value ≈ rectangular hyperbola modified model ＞ exponential model. By combining the results of R2 , Pnmax, LSP and LCP, as well as MSE and MAE, the light response curve of Dongzao jujube was best fitted by the right- angle hyperbolic modified model, which was closest to the measured value and could fit the light response curve of Dongzao jujube under different cultivation modes. The LCP, LSP, AQY and Pnmax of Dongzao jujube at different phenological stages were the lowest at the full-flowering stage, and then gradually recovered to the highest value at the crisp-maturity stage. In addition, the Pnmax, LSP, LCP and AQY values of the girdling plants were lower than those of the non-girdling plants at the full-flowering stage, and the net photosynthetic rate of the non-girdling plants was significantly higher than that of the girdling plants. Under high light-intensity conditions, girdling not only changed the growth potential of Dongzao jujube but also inhibit the photosynthetic capacity. This effect is not restored until the crisp-ripening stage.【Conclusion】This study fitted the optimal light response model of Dongzao jujube, through which the photosynthetic characteristics could be accurately evaluated, the influence of different facility cultivation models on the photosynthesis was also clarified, and the pattern of light demand in the whole growth process was revealed, which provided theoretical instruction for the regulation of photosynthetic environment in facility cultivation and the promotion of growth and fruit setting for jujube trees.