Use of stable isotopes in studies of forest-atmosphere H2O and CO2 exchange

ABSTRACT
Stable oxygen (18O/16O) and hydrogen (2H/1H) isotopes at natural abundance levels are useful tracers for studying water and carbon cycles in terrestrial ecosystems. Atmospheric water vapor contains fewer amounts of heavier water isotopes (2H and 18O) relative to the source water. In the case of surface water loss via vegetation (transpiration), this preferential loss of lighter water isotopologues result in enriched 2H and 18O contents in leaf water. Meanwhile, CO2 that diffuses into leaf intercellular space and later out of stomata become labeled by this enriched 18O signature. Scientists have used this labile 18O signal in studies of global carbon cycles and paleoclimatic reconstruction. Improving our understanding of leaf water 18O enrichment allows for the development of better process-based models to investigate biosphere-atmosphere water and carbon dioxide exchange processes spanning from ecosystem to global scales. Discussions will be emphasized on how biotic and abiotic factors influence diurnal and vertical variations of 2H and 18O in leaf water and water vapor in forest air.