Tracing metabolic water in living tissues using triple oxygen isotopes

Animals and plants metabolize carbohydrates to acquire energy. The most common oxidant is air O₂, which comprises a distinct negative Δ’¹⁷O anomaly. Vertebrate bones and teeth inherit this anomaly providing a tool to approximate metabolic rates, aridity or paleo atmospheric compositions. In order to directly trace the Δ’¹⁷O anomaly in invertebrates, plants or soil water, we have developed a technique to quantitatively extract water from any organic tissue without heating or freeze drying. The method is based on water transfer from the organic matrix to initially dry, hygroscopic CaCl₂ salt in closed containers and is presented in detail by El-Shenawy et al. (this conference).

A sprouted potato is examined as an example for respiration by plant roots. Clear negative Δ’¹⁷O anomalies derived from air O₂ are observed within the water extracted from the tribes and especially the small fruits that only develop after prolonged time of spouting in a dark cabinet. Apparent evaporation trajectories evolve in δ¹⁸O vs. d-excess space, but these are mostly artifacts due to production of metabolic water with high δ¹⁸O within the potato and the tribes. Clearly, the production of such metabolic water within plants and soils must be accounted for, especially when interpreting δ¹⁸O vs. d-excess trajectories as evaporation slopes.

We examined Insect body water from lab reared beetles and silverfish as well as free ranging specimens form the Atacama Desert in Chile. A large interspecies range in δ¹⁸O vs. Δ’¹⁷O is observed, which is mainly interpreted to reflect variable water acquisition strategies. Metabolic water derived from air O₂ can make up large proportions of body water in some species, but not others. Respective body water mass balance models are presently constructed and will be presented.