Coupling water sources and carbon metabolism of natural vegetation at integrated time and space scales

The linkage between water utilization and photosynthetic processes is investigated using stable isotopes and eddy covariance techniques, allowing integration of physiological pro- cesses both at time and space scales, respectively. Using the ratio of the stable isotopes of hydrogen (hydrogen vs. deuterium) and discrimination of 13C vs. ~2C, the relationship between water sources (rain water vs. ground water) utilization and intercellular carbon dioxide con- centration is analysed for various species of two different ecosystems: an alpine forest and a Mediterranean macchia. As an example of space scale integration of water-carbon coupling, the relationship between canopy carbon dioxide assimilation and bulk stomatal conductance, measured with eddy covariance, is presented for a macchia community and a low-productivity grassland.