O-isotopes in plants - mechanisms and application

Understanding the effects of global environmental change on the biogeochemical properties of ecosystem functions remains a major challenge for ecologists. In this respect, stable isotopes have been a highly valuable tool to study for example water or carbon fluxes between the biosphere, atmosphere or geosphere. In particular oxygen isotopes (d18O) are now beginning to be established as a promising tool to study water relations of plants and ecosystems. It has been suggested that through the development of new d18O models, d18O from plant organic material could be used as a simple and integrative measure to determine transpiration patterns from a large number of different plants, which would require a vast logistical effort, using traditional gas exchange methods. Such integrative methods are essential in ecosystem studies in order to include complex factors such as species composition or biodiversity in the analyses. The development of d 18O models is, however, in the initial stages, which limits the application of these models in ecosystem science. It remains for example unclear, if in addition to environmental parameters, species-specific effects such as different leaf morphologies or different physiological properties need to be considered in the models for a precise prediction of d 18O. The work proposed here aims to clarify these open questions. In three experiments I will test, if species-specific leaf morphologies affect d18O values of mean lamina leaf water (E1), if species-specific morphological and ecophysiological parameters affect the d 18O ratio of plant organic material (E2), how existing d18O models need to be improved to realistically reflect transpiration patterns for different species in ecosystem studies (E3). Using 15 selected plant species E1 and E2 will be tested in controlled environments to differentiate species-specific effects from environmental effects on d 18O. These results will be used in E3 to improve existing d 18O models, which I will validate in two different Californian ecosystems. The expected results will help to better understand the ecophysiological mechanisms behind the d18O signal in plant material and to develop d 18O models that realistically reflect a plant`s water relations. The proposed work will be conducted at the University of California in Berkeley in the lab of Prof. Todd Dawson. Prof. Dawson is a leading expert in the field of stable isotope based plant ecophysiology. His lab is therefore the ideal host institution for a successful accomplishment of the proposed work.