Seasonal and annual changes in leaf delta13C in two co-occurring Mediterranean oaks: relations to leaf growth and drought progression

摘要

Change in delta13C (a measure of the ratio of photosynthesis to transpiration, used as an index of long-term water use efficiency), and its relations with leaf development, biochemical characteristics and water stress were monitored over a 2-yr period in two co-occurring Mediterranean oak species (the deciduous Quercus pubescens and the evergreen Quercus ilex) at 4 sites near Montpellier, southern France. The time course of leaf delta13C showed different patterns in the two species. Young Q. pubescens leaves had a high delta13C, with a marked decrease occurring during leaf growth. In contrast, leaves at budburst and maturity did not differ significantly in Q. ilex. It is suggested that the difference between delta13C of young leaves was linked todifferential use of reserves of carbon compounds in the two species. delta13C values of mature leaves were negatively correlated with minimum seasonal values of predawn water potential, suggesting that a functional adjustment to water resources occurred.There was a significant correlation between individual delta13C values for two successive years. This interannual dependence showed that delta13C rankings between trees were constant through time.