[en] Stable isotopes are a powerful tool for examining relationships between plants and their environments. Knowledge gained from studies using isotopes of H, C, N, O and S can inform decisions about management of agroforestry systems - in particular management of water and nutrients. Isotopes of carbon, oxygen and deuterium are now widely used to determine patterns of water use and environmental adaptations. Dual analysis of carbon and oxygen isotopes continues to provide new opportunities to gain a more detailed understanding of variation in ecophysiological processes of plants. For example, coupling a dual isotope approach with other disciplines, particularly dendrochronology, has expanded our ability to examine and compare short- and long-term temporal relationships between plants and their environment. Correlations between carbon and oxygen isotopes of tree rings of Callitris glaucophylla, growing in semi-arid, north-west Australia, reveal an apparent shift in the balance between photosynthesis and stomatal conductance. Between 1920 and 1960, the two isotopes are negatively correlated, while after 1960 they switch rapidly to a positive association. The shift to a positive correlation strongly suggests an increase in stomatal control to regulate water use, possibly a reflection of changes in rainfall patterns in north-west Australia. Detailed modelling of climate-isotope relationships also reveals a number of unusual relationships. Contrary to most studies, we found a significant correlation between δ¹⁸O values and climate of the preceding year. This suggests reduced oxygen re-exchange during cellulose synthesis than reported for other species. Variation in oxygen isotopes largely reflects relative humidity and rainfall early in the growing season, and temperature late in the preceding and current growing season. Again in contrast to other studies, carbon isotopes of tree rings of C. glaucophylla appear less useful than oxygen as a climate proxy, but reveal fundamental information about differences in physiology between conifers and broadleaf species. While carbon and oxygen are commonly used to examine relationships between trees and climate, deuterium isotopes are more commonly used to examine water sourcing by plants. In arid regions, dependence on rainfall or groundwater is largely a reflection of landscape position. For example, species adapted to growing in and along creek lines have access to groundwater and are less dependent on stored soil water. Conversely, species growing on floodplains are highly dependent on rainwater. A difference in access to water translates into differences in physiology and water use: rates of transpiration of creek line species varies little between seasons. These findings have implications for management of mixed systems and their adaptability to long-term changes in rainfall and groundwater supply. (author)