Stomatal, mesophyll conductance and biochemical limitations to photosynthesis as affected by drought and leaf ontogeny in ash and oak trees

ABSTRACT 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 ( S L ) and non‐stomatal limitations ( NS L ) to light‐saturated net photosynthesis ( A max ), relative to the seasonal maximum rates obtained under conditions of optimal soil water content. Furthermore, based on combined gas exchange and chlorophyll fluorescence measurements, NS L was partitioned into a diffusive (due to a decrease in mesophyll conductance, MC L ) and a biochemical component (due to a…