The effect of initial stomatal opening on the dynamics of biochemical and overall photosynthetic induction

We analyzed stomatal behaviors, the role of initial stomatal conductance (at onset of light, g (ini)), and contemporaneous effects on two types of photosynthetic induction, namely overall (stomatal and mesophyll effects included) and biochemical induction (mainly RuBisCO activity). Studies were performed in sun leaves of four species (Alnus glutinosa (L.) Gaertn., Betula pubescens Ehrh., Fagus sylvatica L., and Helianthus annuus L.) differing in shade-tolerance: A species-specific g (ini)-threshold, namely g (ini(crit)), was found, being decisive for time courses of induction. When g (ini) was above g (ini(crit)), induction half-times (t (50%)) were reached within 5 min, almost completely independent of stomatal limitations, and both induction types did not differ between species. Large variations in t (50%) (4-36 min) were observed when g (ini) < g (ini(crit)). These correlated linearly with lag times before onset of stomatal opening in response to light (t (lag)). t (lag) is generally the longer the lower g (ini). Total overall and total biochemical induction correlated highly significantly with velocities of stomatal opening. Different induction times between species occurred as a result of stomatal behavior rather than photosynthetic parameters. Any induction process is initially more limited by the biochemical component. When g (ini) < g (ini(crit)), this biochemical limitation shifts towards stomata-dominated limitation at a lower induction state. Consequentially, stomata limit the induction process over most of the induction course. When g (ini) > g (ini(crit)) and stomata open fast, then induction is (almost) completely dominated by biochemical limitations and proceeds much faster. This study confirms the very important role of g (ini(crit)) in photosynthetic induction irrespective of species and discusses implications for modeling.