PREMISE Of all orchid species described, 70% live on phorophytes. Trees offer a vital space with characteristics that influence the successful establishment and life cycle of orchids. Field inventory and distribution analysis suggest that phorophyte selection is biased to certain tree species that would serve as better hosts. Phorophyte bark is known as an important factor that influences this preference, but the chemical and physical properties of bark that contribute to creating a favorable space for orchids are still poorly understood. In this work, the effect of bark physical characteristics on phorophyte preference of tropical orchids was studied. METHODS Orchids and their phorophytes were counted and identified along transects inside two natural reserves in Southeast Mexico. A rhytidome classification was used to describe the bark decoration patterns of the phorophytes. To quantify bark fissuring, we developed a new protocol based on image processing of light micrographs using free-access software. Bark topology characterization was complemented with scanning electronic microscopy. Maximum and minimum water content was also determined. RESULTS Analyses of bark decorations and bark fissuring were not enough to explain the preference found for some tropical trees. In contrast, a positive relationship was found among water-storage capacity, bark porosity, and phorophyte preference. The host trees preferred by most orchids have bark with higher pore density and higher water retention after draining. CONCLUSIONS Unexpectedly, the phorophytes preferred by orchids are not those with more fissured bark but those with a higher ability to retain minimum water content after draining, which is a bark property positively correlated with higher pore density. Our data indicate that the bark microenvironment, determined by topology and water storage capacity, has a pivotal role in phorophyte specificity, a key factor that affects orchid diversity and distribution in the world.

中文翻译：

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树皮蓄水能力影响附生兰花对寄主树的偏好

前提 在描述的所有兰花物种中，70% 以叶状植物为生。树木提供了一个重要的空间，其特征会影响兰花的成功建立和生命周期。田间清点和分布分析表明，叶状植物选择偏向于作为更好寄主的某些树种。Phorophyte 树皮被认为是影响这种偏好的一个重要因素，但树皮的化学和物理特性有助于为兰花创造有利的空间，我们仍然知之甚少。在这项工作中，研究了树皮物理特性对热带兰花枝叶植物偏好的影响。方法 沿墨西哥东南部两个自然保护区内的横断面对兰花及其叶状植物进行计数和鉴定。叶状体分类用于描述叶状植物的树皮装饰图案。为了量化树皮开裂，我们开发了一种基于使用免费软件对光显微照片进行图像处理的新协议。树皮拓扑表征与扫描电子显微镜相辅相成。还确定了最大和最小水含量。结果 对树皮装饰和树皮开裂的分析不足以解释对某些热带树木的偏爱。相比之下，在蓄水能力、树皮孔隙度和叶状植物偏好之间发现了正相关。大多数兰花喜欢的寄主树皮具有更高的孔隙密度和更高的排水后保水性。结论出乎意料，兰花喜欢的叶状植物不是那些树皮开裂较多的植物，而是那些排水后保持最低水分含量的能力较高的植物，这是一种与较高孔隙密度呈正相关的树皮特性。我们的数据表明，由拓扑结构和储水能力决定的树皮微环境在叶状植物特异性中起着关键作用，这是影响世界兰花多样性和分布的关键因素。