Influence of Light Intensity on Growth and Photosynthetic Characteristics of Garcinia paucinervis seedlings

【Objective】In this paper, the light requirement and adaptation rules of the seedlings of Garcinia paucinervis, a rare and endangered plant, in karst mountains were studied, in order to provide a theoretical basis for its introduction, ex situ conservation, population rejuvenation, large - scale cultivation and ecological restoration of karst mountains. 【Method】The 3-year-old G. paucinervis seedlings were treated with different relative natural light intensities of 10%, 25%, 50% and 100% (marked as RI10%, RI25%, RI50% and RI100%, respectively) for two years. The dynamic changes of growth and leaf morphology features, biomass allocation, photosynthetic characteristics, photosynthetic pigment content in leaves and chlorophyll fluorescence parameters were compared, and the adaptation mechanisms of seedlings to different light environments were analyzed. 【 Result】 1) After two years of light treatment, the ground diameter, plant height and crown width of RI25% and RI50% treatments were significantly greater than those of RI10% and RI100% treatments. 2) The individual leaf area and leaf thickness of RI25% treatment were the greatest in the 4 treatments. The biomass, specific leaf area and leaf area ratio increased first and then decreased with the increase of light intensity. The root mass ratio and root to shoot ratio of RI100% treatment were the greatest, and significantly higher than that of RI10% treatment. 3) In the first year, the order of the maximum net photosynthetic rate (Pmax ) and apparent quantum yield (AQY) were RI50% > RI25% > RI100% > RI10%. The light saturation point (LSP), light compensation point (LCP) and dark respiration rate (Rd) increased with the increase of light intensity. There were no significant differences in Pmax and AQY values of RI50%, RI25% and RI10% in the second year, which however were higher than those of RI100% treatment. Except that the LSP of RI100% treatment was lower than that inthe first year, the LSP of the three shading treatments were higher than that in the first year. The highest value of net photosynthetic rate (Pn) in thewhole day was in the order of RI50% ≈ RI25% > RI10% > RI100%. In the most time of the whole day, Pn, stomatal limitation(Ls ), water use efficiency (WUE) and light use efficiency (LUE) of RI100% treatment were lower than those of the three shading treatments, and the internal cellular CO2 concentration(Ci ) of RI100% treatment was higher than those of the three shading treatments. 4) With the increase of light intensity, the contents of chlorophyll a, chlorophyll b and carotenoids in seedling leaves decreased significantly. The ratio of carotenoids to chlorophyll in RI100% treatment was significantly higher than that in the three shading treatments. 5) In the second year, variable fluorescence (Fv ), photochemical efficiency of PSII(Fv / Fo ) and maximum photochemical efficiency(Fv / Fm ), electron transfer rate(ETR) and photochemical quenching coefficient(qP ) were the highest in RI25% treatment, which changed significantly compared with the first year, while those parameters of RI100% treatment was significantly lower than the three shading treatments. 【 Conclusion】 G. paucinervis seedlings have the ability to adjust and adapt to the light environment in, the morphology and photosynthetic physiology. Seedlings grow slowly under stress in full light environment; Although the seedlings grow slowly under heavy shading, all photosynthetic physiological indexes are normal, indicating that they have adaptability to weak light; However, the seedlings grow well under 25% ~ 50% relative light intensity, and their seedling leaves can make full use of light energy by increasing the absorption capacity of light energy and the photochemical efficiency of PS Ⅱ. G. paucinervis seedlings cultivation needs moderate shade. It is speculated that the strong light stress caused by deforestation is one of the environmental factors for G. paucinervis endangerment. © 2022 Chinese Society of Forestry. All rights reserved.