Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064, USA.
New Phytol. 2011 Oct;192(2):449-61. doi: 10.1111/j.1469-8137.2011.03817.x. Epub 2011 Jul 12.
The ferns comprise one of the most ancient tracheophytic plant lineages, and occupy habitats ranging from tundra to deserts and the equatorial tropics. Like their nearest relatives the conifers, modern ferns possess tracheid-based xylem but the structure-function relationships of fern xylem are poorly understood. Here, we sampled the fronds (megaphylls) of 16 species across the fern phylogeny, and examined the relationships among hydraulic transport, drought-induced cavitation resistance, the xylem anatomy of the stipe, and the gas-exchange response of the pinnae. For comparison, the results are presented alongside a similar suite of conifer data. Fern xylem is as resistant to cavitation as conifer xylem, but exhibits none of the hydraulic or structural trade-offs associated with resistance to cavitation. On a conduit diameter basis, fern xylem can exhibit greater hydraulic efficiency than conifer and angiosperm xylem. In ferns, wide and long tracheids compensate in part for the lack of secondary xylem and allow ferns to exhibit transport rates on a par with those of conifers. We suspect that it is the arrangement of the primary xylem, in addition to the intrinsic traits of the conduits themselves, that may help explain the broad range of cavitation resistance in ferns.
蕨类植物是最古老的维管植物谱系之一，它们占据了从苔原到沙漠和赤道热带等各种生境。与它们最近的亲缘关系——松柏类植物一样，现代蕨类植物具有基于管胞的木质部，但蕨类植物木质部的结构-功能关系还了解甚少。在这里，我们对蕨类植物系统发育中的 16 个物种的叶片（大叶片）进行了采样，并研究了水力输送、干旱诱导的空化阻力、茎干木质部解剖结构以及羽片的气体交换响应之间的关系。为了进行比较，还提供了类似的松柏类数据集的结果。蕨类植物木质部与松柏类木质部一样，具有抗空化能力，但没有与抗空化相关的水力或结构权衡。在导管直径的基础上，蕨类植物木质部的水力效率可能高于松柏类和被子植物木质部。在蕨类植物中，宽大而长的管胞在一定程度上弥补了次生木质部的缺乏，使蕨类植物能够展示出与松柏类植物相当的运输速率。我们怀疑，除了导管本身的固有特性外，可能是初生木质部的排列方式有助于解释蕨类植物广泛的抗空化能力。
