ABSTRACT
Terrestrial ecosystems play a major role in the global carbon cycle. There is a great need, therefore, to understand how global changes, such as increasing atmospheric CO2 and enhanced levels of nitrogen deposition, will influence physiological responses of terrestrial vegetation, and how the vegetation can feedback to influence the global carbon cycle and the earth’s climate system. Despite significant progress in using micrometerological and remote sensing techniques, attempts to extend physiological measurements to large areas are often difficult for a variety of technical reasons. The source of water taken up by plants is precipitation and/or ground water, and since no fractionation occurs during water uptake by most plants, the isotope ratio of water in plant roots is the same as that of the water available in the soil.
