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3D Visualization of Water Transport in Ferns Print
Monday, 08 April 2013 00:00

 

Plants transport water through elongated cells called xylem. However, in trees such as eucalyptus or redwood, the xylem tissue—better known as wood—bears the weight of the branches and leaves, giving rise to the often massive canopies characteristic of these species. We know much about water transport in woody plants, but considerably less about primitive plants such as ferns. Not only have ferns played an important role in the evolution of trees and shrubs but collectively, these plant forms are a fascinating study in contrasts because ferns use xylem strictly for water transport, leaving structural support to other tissues. Given the global distribution and impressive diversity of ferns, how has their xylem evolved to deal with variable habitat water availability?

Data generated using x-ray microtomography (Beamline 8.3.2) reveals the 3D spatial organization of fern xylem networks, including the distribution and frequency of connections between xylem bundles. Reconstructing these xylem networks using traditional microscopy is an arduous task, and microtomography significantly expedites xylem analysis and visualization. Surprisingly, fern xylem has been shown to be an efficient water transport system, on par with other trees and shrubs. The ability of these species to adapt to the moist, shady understory or to open fields with seasonal drought illustrates a highly flexible water transport system. Indeed, microtomography imaging reveals that xylem organization in ferns is finely tuned to the environment and other physiological traits that allow each species to successfully compete for light, water, and nutrients.

The researchers looked at two species of ferns­—Pteridium aquilinum and Woodwardia fimbriata—with similar habitats but different survival strategies. P. aquilinum is fast-growing and drought-deciduous while W. fimbriata is slow-growing and evergreen. Left: Frond architecture of the two species and representative cross sections showing xylem organization. Right: Representative xylem maps, where each vertical line represents a vascular bundle and each white dot represents the location of a connection. The tightly packed vascular bundles in P. aquilinum promote rapid growth but are prone to air pockets (embolism) when water is scarce, and the fern loses its leaves during dry spells. The more conservative pattern in W. fimbriata results in slower growth but greater drought tolerance and frond longevity.

 

Watch a short ALS video on this topic:

 

Also, watch a more technical JoVE (Journal of Visualized Experiments) video about this research.


 

Work performed on ALS Beamline 8.3.2 .

Citations: C.R. Brodersen, L.C. Roark, and J. Pittermann, "The physiological implications of primary xylem organization in two ferns," Plant, Cell and Environment 35, 1898 (2012).

A.J. McElrone, B. Choat, D.Y. Parkinson, A.A. MacDowell, C.R. Brodersen, "Using High Resolution Computed Tomography to Visualize the Three Dimensional Structure and Function of Plant Vasculature," J. Vis. Exp. 74, e50162, doi:10.3791/50162 (2013).