Guangxi Key Laboratory of Plant Conservation and Restoration Ecology in Karst Terrain, Guangxi Institute of Botany, Guangxi Zhuang Autonomous Region and Chinese Academy of Sciences, Guilin, 541006, China.
Department of Biology, Lakehead University, Thunder Bay, ON, P7B 5E1, Canada.
BMC Ecol. 2018 Feb 7;18(1):5. doi: 10.1186/s12898-018-0159-y.
Camellia nitidissima, a rare and endangered shrub is narrowly distributed in South China and North Vietnam occurring in forest understory. Their light tolerance mechanism is unclear. We measured photosynthesis and related parameters on 2-years-old cuttings growing at 10, 30, 50 and 100% sunlight. Our research question was: At what light level are C. nitidissima cuttings responding most favorably, and what is the eco-physiological basis for their response to light? We hypothesized that as a forest understory growth of C. nitidissima would respond most favorably at low to intermediate light by optimizing photosynthetic activity, and high light will affect photosynthetic functions due to photoinhibition, damage of photosynthetic apparatus and concomitant enzyme activity.
With increasing light, the maximum net photosynthetic rate (P) and apparent quantum yield (AQY) decreased, while the light compensation point increased, and light saturation point first increased followed by a decrease. The P and AQY under 50 and 100% sunlight were significantly lower than that under 10 and 30% sunlight. The chlorophyll fluorescence parameters F, F, F/F all decreased under high light (> 50%). The contents of chlorophyll a (Chla), chlorophyll b (Chlb), and carotenoid (Car) decreased with increasing light. Relative conductivity, malondialdehyde (MDA) and proline contents in leaves were significantly increased in high light but we found no significant difference in these indices at 10 and 30% sunlight.
We conclude that C. nitidissima is a shade adapted plant with poor adaptability to high light (> 50%). The novelty of this research is the demonstration of the eco-physiological basis of its light tolerance (conversely, shade adaptation) mechanisms indicated by decreased photosynthetic activity, chlorophyll fluorescence, Chla, Chlb and Car contents and concomitant increase in relative conductivity, MDA and proline contents at high light causing photoinhibition. For artificial propagation of C. nitidissima we recommend growing cuttings below 30% sunlight. For in situ conservation of this valuable, rare and endangered shrub it is necessary to protect its natural habitats.
金花茶是一种分布范围狭窄的珍稀濒危灌木，仅分布于中国南方和越南北部的森林下层。其耐光机制尚不清楚。我们对生长在 10%、30%、50%和 100%光照下的 2 年生插条进行了光合作用及相关参数的测量。我们的研究问题是：金花茶插条在什么光照水平下反应最好，以及它们对光的反应的生态生理基础是什么？我们假设，作为森林下层的生长环境，金花茶在低到中等光照下通过优化光合作用活性反应最好，而高光会由于光抑制、光合器官损伤和伴随的酶活性而影响光合作用功能。
随着光照的增加，最大净光合速率（P）和表观量子产量（AQY）降低，而光补偿点增加，光饱和点先增加后降低。50%和 100%光照下的 P 和 AQY 明显低于 10%和 30%光照下的 P 和 AQY。高光（>50%）下叶绿素荧光参数 F、F、F/F 均降低。随着光照的增加，叶绿素 a（Chla）、叶绿素 b（Chlb）和类胡萝卜素（Car）的含量降低。高光下叶片相对电导率、丙二醛（MDA）和脯氨酸含量显著升高，但在 10%和 30%光照下这些指标无显著差异。
我们得出结论，金花茶是一种适应阴凉的植物，对高光（>50%）的适应能力较差。本研究的新颖之处在于，通过降低光合作用活性、叶绿素荧光、Chla、Chlb 和 Car 含量以及相对电导率、MDA 和脯氨酸含量的增加，同时伴随着光抑制的发生，证明了其耐光（反之，耐阴）机制的生态生理基础。因此，我们建议在 30%以下的光照下种植金花茶插条。为了保护这种有价值的、稀有和濒危的灌木的自然栖息地，有必要对其进行就地保护。
