Plants Found To Share Water With Neighbors

By CAROL KAESUK YOON
Published: October 26, 1993

Tracking the global cycling of water from sky to earth and back again, scientists had thought they could count on at least one thing. The movement of water through plants, it seemed, was simple: up into the roots and out through the leaves as vapor. But now they are discovering that plants are not the passive water vaporizers they had been thought to be. Instead, researchers have found an unsuspected detour in the routing of water. And this discovery may enhance the understanding not only of how plants interact with one another but how ecosystems function and even how climate can change. ...

... Some researchers argue that scientists must now reconsider the role that these plants might play in global climate change, a process in which the global water cycle plays an integral role. ...

A version of this article appeared in print on October 26, 1993, on page C1 of the New York edition. The online article omits two drawings by Michael Rothman:

1) Captioned "A New View of How Trees Obtain and Share Water," a sugar maple is depicted, one-half at night, the other half in daylight. The caption reads, "Scientists are finding that plants that draw water from deep in the soil share the water with nearby plants. In a drought, the closer plants like trillium, lilies and goldenrod were to thirsty sugar maples, the better they did. Most of the tree's root system is above the hard fragipan layer of soil, with only a few roots penetrating to tap the deep water supply.

Text along the part of the tree in darkness, captioned, "Nightime hydraulic lifting," reads, "A long-rooted sugar maple is well equipped to pull up deep water. As it does not evaporate from leaves at night, it flows into the shallower roots and from there into the dry soil near the surface.

Text along the part of the tree in daylight, captioned, "Daytime water loss through leaves," reads, "It was known that during the day, the leaves of a tree lose water through the process of transpiration."

2) Captioned "Measuring the Flow of a Fountain in a Dry Landscape," a sugar maple is depicted with four rings drawn on the ground at distances of 0.5, 1.0, 1.5, 2.5 and 5.0 meters from the base of the tree. Beside that drawing is a table of plants -- herbs, shrubs, trees, and monocots -- and the time it took for water of known hydrogen-isotope composition to appear in their xylem (water-conducting tissue).

Fundamental to the study was the knowledge that "deep groundwater has a different hydrogen isotope content from that of fresh rainwater, so careful measurement of water from undergrowth harvested at precise distances from a sugar maple indicated how much the plants got from their tree benefactor."

The online version appends commentary from Dr. David Rind concerning the possible relationship between hydraulic lift and climate change.

The online version has an alternative description of the illustrations, and indicates that their source may be Oecologia.