Variations in the natural abundance of oxygen‐18 and deuterium in plant carbohydrates

Abstract

Variations in the natural abundance of ^°0 and ^H in plant cellulose are influenced by the isotopic composition of the water directly involved in metabolism-^the metabolic water fraction. The isotopic distinction between the metabolic source water and total tissue water must reflect the formation of isotopic gradients within the tissue that are influenced by the rate of water turnover, by properties of the water conducting system and by environmental conditions, it seems that the ^^O abundance in the metabolic water is conserved in cellulose with a relatively constant isotope effect. The relationship of the ^H abundance between metabolic water and cellulose is more complex. Hydrogen incorporated into photosynthetic products during primary reduction steps is highly depleted in ^H. However, a large proportion of these hydrogens are subsequently replaced by exchange with water, leading to ^H enrichment during heterotrophic metabolism. Deciphering the oxygen isotope ratio of cellulose could help in providing insights into the carbon and oxygen fluxes exchanged between plants and the atmosphere. This is because the ^^O abundance in cellulose records the ^°0 abundance in the metabolic water, which in turn, controls the oxygen isotopic signatures of the CO2 and O2 released by plants into the atmosphere. The hydrogen isotope effects associated with carbohydrate metabolism provide insights into the autotrophic state of a plant tissue. This is because the hydrogen isotope ratio of carbohydrates must reflect the net effects of the two opposing isotope effects associated with photosynthesis and heterotrophic metabolism. NTRODUCTIONThe isotopic composition of precipitation recorded in different habitats provides the first level of control over

Oxygen Isotopes in Enamel Carbonate and their Ecological Significance

“…It is likely that A. bondi filled a similar niche in the past. The relative depletion of equids may also reflect their tendency to consume large quantities of grass stems, the water of which is depleted in heavy isotopes compared with grass leaves (Sternberg, 1989;Ziegler, 1989;Yakir, 1992).…”

“…Indeed, many mammals obtain all of their water from food. Water in plant roots and stems is isotopically similar to meteoric water, but leaf water is relatively enriched in H 2 18 O due to preferential evapotranspiration of the lighter H 2 16 O molecule (Gonfiantini, Gratziu & Tongiorgi, 1965;Dongmann et al, 1974;Epstein, Thompson & Yapp, 1977;Sternberg, 1989;Yakir, 1992). The isotopic composition of oxygen chemically bound in food is also variable.…”

“…The isotopic composition of oxygen chemically bound in food is also variable. For instance, plant leaf cellulose has higher 18 O values than root cellulose, which is generally enriched compared to animal foods (Epstein et al, 1977;Sternberg, 1989;Yakir, 1992;Tredget et al, 1993;Kohn, 1996).…”

Seasonally resolved stable isotope chronologies from northern Thailand deciduous trees

“…: (508) 289-3798; Fax: (508) lose. Greenhouse and field experiments show that the δ 18 O of tree cellulose is largely controlled by the isotopic signature of the tree's source water [1][2][3][4]. This value is typically offset following an evapo-transpiration enrichment of the leaf water used for photosynthesis [5].…”

Correlating δ13C and δ18O in cellulose of trees

“…1995a) have been shown to affect the carbon isotopic composition, often in agreement with the above-mentioned model. On the other hand, the processes which determine the oxygen isotope ratio in plant matter ar-e not as well understood (Yakir 1992). Many studies have dealt with 5' **O in leaf water, but r-elatively few with 5'^O in organic rnatler.…”