Effect Of Low Light Stress On Photosynthetic And Growth Properties In Near-mature Oil-tea Camellia Plantation

Using six oil-tea camellia superior clones, with strong growth and high quality in both fruit and oil from Guangxi and Jiangxi, as materials, three natural light intensity artificial shading treatments (30%,60%and90%sun-shading) were set to reduce light levels to10%-70%full sun(FS,105.833K1x and69.556K1x in August and October, respectively), the FS treated as control to study the effect of low light on photosynthetic and growth properties in young growth period of Camellia oleifera. Results are summarized as follows:1. Diurnal variations of net photosynthetic rate of the six superior clones expressed single peak curves or double-apexes curves in low light levels. The average daily value of FS treatment was the highest with the range of6.52-8.35μmolCO2·m-2·s-1, and decreased along with the enhanced shading degree. Diurnal variations of net photosynthetic rate of Cen-ruan3, Cen-ruan22, Cen-ruan24, Changlin55and Changlin4changed with light level in August, bimodality under FS and30%sun-shading treatments, whose midday depression was remarkable, and single peak curve under60%and90%sun-shading, respectively. It was the stomatal factors that caused the midday decrease of net photosynthetic rate in Cen-ruan3, Cen-ruan22, Cen-ruan24and Changlin55under FS treatment, and after30%sun-shading, primarily is non-stomatal limitation, except Cen-ruan22. While in October, there was only one peak appeared in the curves of that in the six tested samples under the low light levels, and the photosynthetic midday depression disappeared. There were significant differences among net photosynthetic rate, intercellular CO2concentration, transpiration rate and water use efficiency in low light conditions.2. In low light levels, the physiological and ecological factors, including Gs, Ci,Tr, Ca and PAR, were closely linear related to net photosynthetic rate in oil-tea camellia. The decrease of net photosynthetic rate in oil-tea camellia under FS treatment was mainly affected by Gs, while illumination is the main ecological factor that had impact on it when in low light conditions.3. In August, the maximum photosynthetic efficiency in the leaves of the six tested samples varied from4.63to15.68μmolCO2·m-2·s-1, that in October ranged from3.31to 12.52μmolCO2·m-2·s-1. After being30%sun-shading, cen-ruan3, cen-ruan22and cen-ruan24showed stronger ability in photosynthesis, wider adaptation range of illumination, and had a better utilization ability of low light compared with other clones. In contrast, Changlin166, Changlin55and Changlin4were not suitable for prolonged growth in low light conditions.4. The content of chlorophyll a, chlorophyll b and total chlorophyll, especially that of chlorophyll b, increased significantly while the ratio of chlorophyll a/b showed downtrend with the reduce of light intensity. Chlorophyll b content in Changlin4under90%sun-shading treatment had an increase of83.6%compared with the control, that of cen-ruan22just had increased by16.92%, and the increase amplitude of the rest tested samples varied from30%to40%. In addition, the chlorophyll content in the leaves decreased while the ratio of chlorophyll a/b had a slight increase along with the prolonged shading time.5. There was a significantly positive relationship in soluble carbohydrate and soluble protein to the percentage of FS, with both variations dramatically reduced at low light levels. The soluble carbohydrate content of Changlin55declined greatest, when treated with30%sun-shading, it had a decrease of31.21%compared with the control; soluble carbohydrate content of Changlin166, Changlin55and Changlin4under FS treatment in October remarkably declined with a range of30.18%-35.4%as compared to that in August. There were not significantly differences between the soluble protein in cen-ruan3, cen-ruan22and cen-ruan24of30%sun-shading treatment and that of the FS treatment. The rate of descent in Changlin55under different shading treatments was the greatest, being18.39%,31.39%and41.26%, respectively, indicating the worst resistance to low light.6. The leaves of oil-tea camellia appeared to be larger and thinner in comparison to those from unshaded ones, specific leaf area increased while specific leaf weight decreased along with the enhanced shading degree. The height growth of the plants was restricted by the low light, yet new branches were helped stretched by30%sun shaded, contributing to the expansion of the plants.7. Fuzzy subordinative function value of shade tolerance of Cen-ruan3, Cen-ruan22, Cen-ruan24Changlin166and Changlin4varied from0.50-0.80, showed medium shade tolerance, that of Changlin55was the lowest. Shade tolerance of the samples also varied, following the order:Cen-ruan3's>Cen-ruan24's>Cen-ruan22's>Changlin166's> Changlin4's>Changlin55's, respectively. In addition, the suitable natural illumination for young growth period of oil-tea camellia in low light levels is approximately78.083Klx.