Sun Mei, Feng Chun-Hui, Liu Zhen-Ya, Tian Kun
National Plateau Wetlands Research Center, Southwest Forestry University, Kunming, 650224, Yunnan, China.
Ecological Research Station of Dianchi in Yunnan, Jinning, 650600, Yunnan, China.
Bot Stud. 2020 May 16;61(1):16. doi: 10.1186/s40529-020-00292-4.
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.
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.
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.
叶片水分保持和假鳞茎水分储存是附生植物适应干旱环境常用的两种策略。在开花期，大量水分通过花朵蒸腾，进而影响与水分相关的生理过程。然而，关于附生植物不同结构之间的协同关系研究较少。我们的研究通过系统发育独立对比（PIC）分析，探究了石斛属8个物种结构性状之间的系统发育保守性和进化相关性。
叶片干质量、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、假鳞茎宽度和花朵干质量显示出较强的系统发育信号。根据物种平均值和PIC值，假鳞茎长度与气孔体积显著正相关，但与叶肉厚度显著负相关。根据PIC值，假鳞茎节间长度也与气孔体积正相关，但与气孔密度负相关。根据物种平均值，假鳞茎宽度与叶片干质量、气孔密度、气孔面积指数、花瓣维管束数量和花朵干质量显著正相关，但与比叶面积负相关。然而，分析PIC值时，这些相关性不显著。气孔体积与花朵干质量正相关，考虑系统发育后，这种相关性仍然显著。根据物种值，叶片干质量与花瓣维管束数量正相关。根据物种值，每个假鳞茎的花朵数量与上表皮细胞大小负相关，但根据PIC值与气孔面积指数负相关。根据PIC值，假鳞茎和花朵与水分相关的性状之间没有相关性。
附生植物在假鳞茎储存和叶片保水这两种耐旱策略之间应该存在权衡。拥有厚叶片和少量大气孔的植物倾向于采用假鳞茎水分储存策略来适应干旱。小花和低花朵干质量应该与叶片保水策略相关。此外，花朵和叶片表现出明显的水分平衡，应该受到共同的选择压力。本研究提供了一个理解附生植物不同结构协同适应的案例。
