Deuterium content in plants with short lifetime: preliminary results

Full text: The stable isotope concentration of hydrogen in the water contained in plants is strongly influenced by the environmental conditions and is dependent on physiological performances. The water in the cycle precipitation-soil-plants-atmosphere presents a varying isotopic composition due to the inter-annual changes in rainfall, temperature and humidity. The deuterium content of the water in the plant leaves with short life (vegetables) may identify the contribution of the ecosystem components to the exchange fluxes with the atmosphere. Soil water and leaf water are the sources of the evaporation-transpiration (ET) that transfers large quantities of water and energy between the land surface and the atmosphere. The deuterium content of the leaf water increases during plants growing in greenhouses (closed system for water cycle), the watering being reasonably constant during the growing period. This may be an indicator of trends in ET, but most probably is the plant aging. The deuterium content of leaf water is not yet well understood and can involve the following: 1. hydrogen isotope effects associated with leaf water enrichment due to the ET and equilibration with humidity of atmosphere; 2. the ability to use the hydrogen in photosynthetic and respiration processes; 3. the exchange of hydrogen isotopes during the transport of carbohydrates (such as sucrose) from leaves to developing xylem in shoots; 4. the isotopic fractionation associated with biochemical synthesis. The differences in isotopic discrimination between these processes need to be better characterized. (authors)