CHAPTER 9 – Vascular Epiphytes
CHAPTER 9 – Vascular Epiphytes
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DOI：
10.1016/b978-012457553-0/50014-9
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发表时间：
2004
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影响因子：
--
通讯作者：
D. Benzing
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作者：
D. Benzing
温带地区的植物学家很少看到树皮是高等植物使用的多种基质中最密集利用的一种。许多藻类和苔藓植物栖息在中纬度和高纬度林地的树冠上，但很少有维管类型。热带森林讲述了一个完全不同的故事，特别是那些每公顷支持许多吨悬浮植被的森林，包括高达三分之一的当地维管植物群（例如，Gentry和Dodson 1987a； Freiberg和Freiberg 2000； Hsu等人2002；见图9-1）。事实上，大约有25000种，也就是维管植物的8%到10%，通常至少有一部分时间是作为附生植物度过的——实际上，它们在较大植物的冠上而不是在地上生根（见表9-1；Benzing 1990）。附生植物在这里的定义是使用它们的植物宿主或“光生植物”（字面意思是“支持植物”）仅仅是为了机械支持。由于缺乏地面植物进入土壤的途径和槲寄生的寄生习惯（见第10章），它们转而利用不太传统的替代品来获取水分和养分，例如蚂蚁的废物；湿透、腐烂的垃圾；和降水，因为它流过芽和根，其中一个或两个都可以适当地吸收（Benzing 1990）。化石表明，维管附生至少从石炭纪时期就存在了，对于许多现代物种来说，古老的模式仍然存在。例如，数百种现存的石松类和蕨类植物在腐植质席上扎根，就像大约2.5亿年前，Botryopteris在已灭绝的蕨类树Psaronius的树干上扎根一样（Rothwell 1991；见图9-2；见第七章）。从附生的分类分布（见表9-1；Benzing 1990）和现代植物实现这种生活方式的多种方式（见表9-2）来看，树皮已经被殖民过多次，并沿着许多进化途径。矛盾的是，在一些最大的开花植物家族中，如菊科、豆科和豆科，附生植物很少或没有。那么，为什么要在一篇专门讨论森林冠层生物学的文章中专门用一章来介绍一群主要生活在潮湿热带地区的植物呢？也许最令人信服的是刚刚提到的8%到10%的统计数据，但还有很多其他原因。维管附生植物也表现出非凡的适应性多样性，其中一些未确定的部分代表了对森林冠层栖息地或多或少特有的限制和机会的进化反应。同样重要的是这些植物影响赖以生存的生态系统的方式。
Botanists based in the temperate zone see little evidence that bark is one of the most intensively exploited of the many kinds of substrates used by higher plants. Numerous algae and bryophytes inhabit the canopies of mid and higher latitude woodlands, but few vascular types do. Tropical forests tell quite a different story, especially those that support many tons per hectare of suspended vegetation, including up to one-third of the local vascular flora (eg, Gentry and Dodson 1987a; Freiberg and Freiberg 2000; Hsu et al. 2002; see Figure 9-1). In fact, about 25,000 species, or somewhere between 8 and 10 percent of the vascular plants, routinely spend at least part of their lives as epiphytes—in effect, they root in the crowns of larger plants rather than on the ground (see Table 9-1; Benzing 1990).Epiphytes as defined here use their botanical hosts or “phorophytes”(literally meaning “supporting plant”) solely for mechanical support. Lacking the ground-based plant’s access to earth soil and the mistletoe’s parasitic habit (see Chapter 10), they instead draw on less conventional alternatives for moisture and nutrients, such as ant wastes; sodden, rotting litter; and precipitation as it flows over shoots and roots, either or both of which can be appropriately absorptive (Benzing 1990). Fossils indicate that vascular epiphytism has existed since at least the Carboniferous period, and for many modern species, ancient patterns persist. Hundreds of extant lycopods and ferns, for example, root in mats of humus, much like Botryopteris forensis did on the trunks of extinct tree fernlike Psaronius about 250 million years ago (Rothwell 1991; see Figure 9-2; see Chapter 7). Judging from the taxonomic scatter of epiphytism (see Table 9-1; Benzing 1990) and the variety of ways that modern flora accomplish this lifestyle (see Table 9-2), bark has been colonized many times and along numerous evolutionary pathways. Paradoxically, epiphytism is rare or absent in some of the largest families of flowering plants such as Asteraceae, Fabaceae, and Poaceae. So why devote a chapter in a text dedicated to forest canopy biology to a group of plants that predominately inhabit just the humid tropics? Perhaps most compelling is the 8 to 10 percent statistic just mentioned, but there are plenty of additional reasons. Vascular epiphytes also demonstrate extraordinary adaptive variety, some undetermined portion of which represents evolutionary response to constraints and opportunities more or less unique to the forest canopy habitat. No less important are the ways that these plants influence the ecosystems that host them.