Daniel Epron, Yan Xia, Reno Yoshida, Masanori Katsuyama, Wakana A. Azuma, Yoshiko Kosugi, Satoshi Nagai, Masako Dannoura
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引用次数: 0
Key message
Osmotically-driven radial transfer of water from xylem to phloem occurs during the day in the branches of hinoki cypress, even though branch diameter shrinks.
Abstract
The hydraulic coupling between xylem and phloem has been explicitly included in theoretical models of phloem transport; however, the predicted radial water transfer from xylem to phloem during the day has not yet been demonstrated experimentally. In a first experiment, we tested the hypothesis of a water transfer from xylem to the inner bark during the day, assuming that, if the transfer does not occur, phloem water would be isotopically enriched due to an influx of enriched water concomitant with sugar loading in the foliage. The inner bark water from branches of mature hinoki cypress was, however, only slightly enriched in 18O in the afternoon compared to sapwood water (δ18O of − 6.3 and − 6.6‰ respectively), but much less than foliage water (16.0‰ at noon and 18.9‰ in the afternoon). This suggests that the isotopically enriched leaf water concurrently loaded with sugars in the leaf phloem was mixed with the unenriched xylem water. In a second experiment, to confirm that water transfer from xylem to the inner bark during the day occurs in branches, deuterium-enriched water was sprinkled on the soil. Concomitant deuterium enrichment of xylem and inner bark water extracted from branches was observed during the day after labelling, earlier than in leaves, when branches were still shrinking. This provides experimental support for theoretical models of phloem transport that have predicted radial transfer of water from xylem to phloem along the path.
期刊介绍：
Trees - Structure and Function publishes original articles on the physiology, biochemistry, functional anatomy, structure and ecology of trees and other woody plants. Also presented are articles concerned with pathology and technological problems, when they contribute to the basic understanding of structure and function of trees. In addition to original articles and short communications, the journal publishes reviews on selected topics concerning the structure and function of trees.
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