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Environmental and Stress Physiology

Oxygen-18 Content of Atmospheric Oxygen Does Not Affect the Oxygen Isotope Relationship between Environmental Water and Cellulose in a Submerged Aquatic Plant, Egeria densa Planch ¹

Department of Earth and Space Sciences, University of California, Los Angeles, California 90024

We determined that the oxygen isotopic composition of cellulose synthesized by a submerged plant, Egeria densa Planch., is related to the isotopic composition of environmental water by a linear function, ¹⁸O cellulose = 0.48 ¹⁸O water + 24.1%. The observation of a slope of less than 1 indicates that a portion of cellulose oxygen is derived from an isotopically constant source other than water. We tested whether this source might be molecular oxygen by growing plants in the presence of high concentrations of ¹⁸O in the form of O₂ bubbled into the bottom of an aquarium. Cellulose synthesized during this experiment did not have significantly different oxygen isotope ratios than that synthesized by control plants exposed to O₂ of normal ¹⁸O abundance. We propose that oxygen in organic matter recycled from senescent portions of the plant is incorporated into cellulose. Our findings indicate that paleoclimatic models linking the oxygen isotope composition of environmental water to cellulose from fossil plants will have to be modified to account for contributions of oxygen from this or other sources besides water.

³ Present address: Department of Earth Sciences, University of California, Santa Barbara, CA 93106.

¹ Supported by National Science Foundation grants DMB 84-05003 and DCB 88-96201 and Department of Energy grant DE-87ER60615.

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