摘要：

Gas exchange measurements were carried out on ash and oak trees in a forest plantation during three whole growing seasons characterized by different water availability (2001, 2002 and 2003). A quantitative limitation analysis was applied to estimate the effects of drought and leaf ontogeny on stomatal (SL) and non-stomatal limitations (NSL) to light-saturated net photosynthesis (Amax), relative to the seasonal maximum rates obtained under conditions of optimal soil water content. Furthermore, based on combined gas exchange and chlorophyll fluorescence measurements, NSL was partitioned into a diffusive (due to a decrease in mesophyll conductance, MCL) and a biochemical component (due to a decrease in carboxylation capacity, BL). During the wettest year (2002), the seasonal pattern of both Amax and stomatal conductance (gsw) was characterized in both species by a rapid increase during spring and a sli

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