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A new system was designed that permits examination of long distance transport of water and nutrients through mycorrhizal hyphae without the architectural, nutritional, and physiological differences associated with comparing mycorrhizal and non-mycorrhizal plants. The "rhizobox" system consists of a rectangular box with a chamber where mycorrhizal plants are grown and an outer chamber where hyphae proliferate. The two chambers are separated by root-excluding screens and an air gap. Two slightly different experiments examined hyphal transport. The first experiment demonstrated the difficulties of comparing water use by mycorrhizal and nonmycorrhizal plants because of dissimilarities in plant architecture. The second experiment avoided the problem by comparing intact mycorrhizal plants with plants where hyphae passing to the outer chamber were severed. In the outer chamber, a 5 mM solution of RbCl was injected. Intact mycorrhizal plants transpired 35% more water than plants with severed hyphae in 16 h. The source of transpired water was the outer chamber, as suggested by lower soil moisture in the outer chamber and a higher Rb content in intact plants. This demonstrates an active role in water and nutrient transport by mycorrhizal hyphae, since plants were of a similar nature except for hyphal access to the outer chamber. Key words: water transport, mycorrhizal plants, rhizobox system, nutrient transport, hyphae.
Faber et al. (Tue,) studied this question.