On the enrichment of H2 18O in the leaves of transpiring plants

Abstract

ummary. The vapor pressure difference botween H~ 1so and tt~ l~O is the reason for the accumulation of the heavy molecule in transpiring leaves. Since photosynthcsis on land is the main sourco of atmospheric oxygen, this mechanism is important for the remarkable enrichment of iso in atmosphoric O 3 (Dole effect). Using a simple box model for transpiring lcaves a quantitative understanding of the isotope fractionation is possible which is woll con-firme4 by the results of model experiments as well as by measurements on trees. Maximum enrichment of H 2 iso in the water of leaves (relative to seil water) is 25 7~ (theoretically, for dxy air) and was foun4 untier natural conditions to be 21 ~ (for 28 % relative humidity); minimum theoretical enrichment is zero (observed 2.5 %°). IntroduetionThe atmospheric reservoir of free oxygen is involved in the global biocyele on land: O S is liberated from water during photosynthesis, and consumed by the respirative proeesses. Both reactions are seleetive, to some degree, for the isotopie masses of oxygen which leads to a stationary excess of the heavy isotope, 1sO, in atmospherie 0 3. A quantitative understanding of this phenomenon (Dole effeet [i2]) is of aetual interest in the context of global environmental studies, e.g. the gas exchange between atmosphere and ocean [t8].The isotope fraetionation oeeurring during respiration has been studied by Lane and Dole [~2], but is not suffieient to aeeount for the 180 exeess actually present. The other prineipal eontribution has been overlooked a long time, sinee the mechanism is somewhat peculiar: it is not the aet of photosynthesis itself whieh is responsible for the isotope fraetionation, but the vapor pressure differenee of isotopie water moleeules in transpiring leaves --the most common place of land photosynthesis [7,9].The purpose of the presënt paper is a first approaeh to a quantitative understanding of this contribution to atmospherie 1so enriehment on the basis of a box model for transpiring leaves. Computation of the isotopie eomposition of oxygen from land photosynthesis, on the global average, will be presented in a following paper.1. Theoretieal Considerations (G. Dongmann, K. Wagener) A Model el the H 2180 Enrichment in the Water o/LeavesFor the water transport through leaves the compartment model in Fig. i is eonsidered.

Investigating climate at the Upper Palaeolithic site of Kraków Spadzista Street (B), Poland, using oxygen isotopes

“…Although based on a small number of data-points, if the sampled mammoth are assumed to have lived in both D-O warm and cold periods, these values will approximate to a long-term average of δ 18 O in these regions (Arppe and Karhu, 2010 is also equal to or smaller than any of these mixed assemblages (see Table 3 second, the water in the river networks that provided a major source of drinking water for mammoth would have been continually replenished from local groundwater reservoirs, meaning their isotopic composition would have been relatively immune to change from evaporative influences (Darling et al, 2006); and, third, because mammoth consumed a relatively large proportion of their water each day by drinking rather than as water consumed through food, the latter being more susceptible to evapotranspiration effects (Dongmann et al, 1974). Evaporation has also been rejected as a primary factor in previous isotopic studies involving mammoth in…”

“…When interpreting isotopic signatures, however, it is also important to consider influences that may modify the isotopic composition of ingestion waters prior to their consumption by animals. These include changing seasonality of rainfall (Rozanski et al, 1993), and the evaporative enrichment of surface and leaf waters, which is primarily controlled by ambient aridity rather than ambient temperature (Dongmann et al, 1974;Gibson and Reid, 2010). Surface waters c.7‰ higher in δ 18 O are known from cold arid environments (Gibson and Reid, 2010), while enrichment of leaf waters can be much greater, elevating δ 18 O by over 20‰ relative to surface water in some instances (Dongmann et al, 1974).…”

Needle cell elongation and maturation timing derived from pine needle cellulose δ18O

“…The factors controlling leaf-water d 18 O and leaf-cellulose d 18 O have gradually been identified and quantified over the years, resulting in increasingly sophisticated physiological models (Dongmann et al . 1974;Flanagan, Comstock & Ehleringer 1991;Farquhar & Lloyd 1993;Aucour, HillaireMarcel & Bonnefille 1996;Roden, Lin & Ehleringer 2000;Gan et al .…”

Oxygen Isotopes in Enamel Carbonate and their Ecological Significance

“…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.…”