Cypripedium subtropicum is the only known winter-green species in the genus Cypripedium, whereas the other nearly 50 species keep their leaves for less than half the year. Life form has an important effect on carbon acquisition and adaptation of plants. However, the physiological mechanism behind it remains unclear. In this study, we investigated vegetative anatomy and photosynthetic performance of C. subtropicum across with its leaf ages. These anatomical and photosynthetic traits were also compared with typical Cypripedium spp. and other members of subfamily Cypripedioideae. The obtained results confirmed that this species exhibited many characters of shade plants, such as thin leaves, extremely low photosynthetic rate and light saturation point and high chlorophyll content. Unlike the strategy adopted by typical Cypripedium spp. that quickly achieve annual carbon gain with a high assimilation rate in a short growing season, C. subtropicum obtains its carbon through a low assimilation rate but a much longer leaf lifespan. The local climate and favourable light condition guaranteed the comparable carbon income in winter to compensate for its low photosynthetic capacity. The long-lived, thin leaves of C. subtropicum, differing from the long-lived, thick leathery leaves in conduplicate-leaved genera, represent a distinct adaptive strategy in subfamily Cypripedioideae. Our findings shed light on the divergent and convergent evolution in slipper orchids, and we hope these findings will contribute to the conservation of such an endangered orchid.

中文翻译：

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唯一已知的冬绿 Cypripedium 物种的植物解剖学和光合作用性能：对拖鞋兰的发散和收敛进化的影响

Cypripedium subtropicum 是 Cypripedium 属中唯一已知的冬绿物种，而其他近 50 种物种的叶子保持时间不到半年。生命形式对植物的碳获取和适应具有重要影响。然而，其背后的生理机制仍不清楚。在这项研究中，我们调查了 C. subtropicum 的营养解剖学和光合性能及其叶龄。这些解剖学和光合特性也与典型的 Cypripedium spp 进行了比较。和 Cypripedioideae 亚科的其他成员。所得结果证实，该树种具有叶片薄、光合速率和光饱和点极低、叶绿素含量高等遮荫植物的特点。与典型的 Cypripedium spp 采用的策略不同。C. subtropicum 在较短的生长季节以高同化率快速实现年碳增益，C. subtropicum 通过低同化率获得碳，但叶片寿命更长。当地的气候和有利的光照条件保证了冬季可比较的碳收入，以弥补其低光合能力。C. subtropicum 的长寿命、薄叶不同于复叶属的长寿命、厚革质叶，代表了 Cypripedioideae 亚科的独特适应性策略。我们的研究结果揭示了拖鞋兰花的发散和趋同进化，我们希望这些发现有助于保护这种濒临灭绝的兰花。subtropicum 通过低同化率但更长的叶片寿命获得碳。当地的气候和有利的光照条件保证了冬季可比较的碳收入，以弥补其低光合能力。C. subtropicum 的长寿命、薄叶不同于复叶属的长寿命、厚革质叶，代表了 Cypripedioideae 亚科的独特适应性策略。我们的研究结果揭示了拖鞋兰花的发散和趋同进化，我们希望这些发现有助于保护这种濒临灭绝的兰花。subtropicum 通过低同化率但更长的叶片寿命获得碳。当地的气候和有利的光照条件保证了冬季可比较的碳收入，以弥补其低光合能力。C. subtropicum 的长寿命、薄叶不同于复叶属的长寿命、厚革质叶，代表了 Cypripedioideae 亚科的独特适应策略。我们的研究结果揭示了拖鞋兰花的发散和趋同进化，我们希望这些发现有助于保护这种濒临灭绝的兰花。subtropicum 不同于复叶属的长寿命、厚革质叶，代表了 Cypripedioideae 亚科的独特适应策略。我们的研究结果揭示了拖鞋兰花的发散和趋同进化，我们希望这些发现有助于保护这种濒临灭绝的兰花。subtropicum 不同于复叶属的长寿命、厚革质叶，代表了 Cypripedioideae 亚科的独特适应策略。我们的研究结果揭示了拖鞋兰花的发散和趋同进化，我们希望这些发现有助于保护这种濒临灭绝的兰花。