BACKGROUND Leaf water conservation and pseudobulb water storage are two of the strategies commonly employed by epiphytic plants to adapt to dry environments. During the flowering period, a great deal of water transpires through the flowers, which then influences water-related processes. However, there is little research on the coordinated relationship between the different structures of epiphytes. Our study explored the phylogenetic conservation and evolutionary correlations between structural traits of 8 species in the genus Dendrobium by using phylogenetic independent contrast (PIC) analysis. RESULTS Leaf dry mass, leaf water content, leaf dry matter content, specific leaf area, stomatal density, stomatal area index, pseudobulb length, pseudobulb width, and flower dry mass show strong phylogenetic signals. Pseudobulb length is significantly positively correlated with stomatal volume but significantly negatively correlated with mesophyll thickness according to both species mean values and PIC values. Pseudobulb internode length is also positively correlated with stomatal volume but negatively correlated with stomatal density according to PIC values. Pseudobulb width is significantly positively correlated with leaf dry mass, stomatal density, stomatal area index, flower petal vein number and flower dry mass but negatively correlated with specific leaf area according to species mean values. However, these correlations are insignificant when PIC values are analyzed. Stomatal volume is positively correlated with flower dry mass, and after phylogeny is considered, this correlation is still significant. Leaf dry mass is positively correlated with flower petal vein number according to species values. Flower number per pseudobulb is negatively correlated with upper epidermal cell size according to species values but negatively correlated with stomatal area index according to PIC values. There are no correlations between pseudobulb and flower water-related traits according to PIC values. CONCLUSIONS A trade-off should exist in epiphytic plants between the two drought-tolerant strategies of pseudobulb storage and leaf water retention. Plants possessing thick blades with a few large stomata tend to use the pseudobulb water storage strategy to adapt to drought. Small flowers and low flower dry mass should be associated with the leaf water retention strategy. In addition, flowers and leaves exhibit an obvious water balance and should share common selection pressures. The present study provides a case with which to understand the coordinated adaptation of different structures in epiphytic plants.

中文翻译：

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石end植物不同结构之间水相关性状的进化相关性。

背景技术叶片水的保存和假鳞茎的水储存是附生植物通常用来适应干燥环境的两种策略。在开花期，大量的水从花中渗出，进而影响与水有关的过程。但是，关于附生植物的不同结构之间的协调关系的研究很少。我们的研究通过系统发育独立对比（PIC）分析探索了石D属中8种物种的系统发育保守性和进化相关性。结果叶片干重，叶片含水量，叶片干物质含量，比叶面积，气孔密度，气孔面积指数，假鳞茎长度，假鳞茎宽度和花干质量均显示出强的系统发生信号。根据物种平均值和PIC值，假鳞茎长度与气孔体积显着正相关，而与叶肉厚度显着负相关。根据PIC值，假鳞茎节间长度也与气孔体积呈正相关，而与气孔密度呈负相关。假鳞茎宽度与叶片干重，气孔密度，气孔面积指数，花瓣叶脉数和花朵干重呈显着正相关，但根据物种平均值，与特定叶面积呈负相关。但是，当分析PIC值时，这些相关性并不重要。气孔体积与花干重呈正相关，并且在考虑系统发育后，这种相关仍然很显着。根据种类值，叶片干重与花瓣静脉数成正相关。根据物种值，每个假鳞茎的花数与上表皮细胞大小负相关，而根据PIC值，与假气孔面积指数负相关。根据PIC值，假鳞茎和与花水有关的性状之间没有相关性。结论附生植物应在假球贮藏和叶片保水两种耐旱策略之间进行权衡。叶片较厚，气孔较小的植物倾向于使用假鳞茎贮水策略来适应干旱。小花和低花干质量应与叶片保水策略相关。此外，花和叶表现出明显的水平衡，应具有共同的选择压力。本研究提供了一个案例，以了解附生植物中不同结构的协调适应。