Effects of soil rewatering on mesophyll and stomatal conductance and the associated mechanisms involving leaf anatomy and some physiological activities in Manchurian ash and Mongolian oak in the Changbai Mountains.

The recoveries of mesophyll (g) and stomatal conductance to CO (g) after soil rewatering have received considerable attention in recent years, but the recovery mechanisms involving leaf anatomy and physiological activities are poorly understood. Moreover, it is also unclear whether leaf gas-phase conductance (g) or liquid-phase conductance (g) is the main factor promoting g recovery. By simultaneously using gas exchange and chlorophyll fluorescence, we measured the recoveries of g and g in saplings of Manchurian ash (Fraxinus mandshurica Rupr.) and Mongolian oak (Quercus mongolica Fish. ex Ledeb) exposed to two initial water stress (medium water stress, MW, and severe water stress, SW) and following rewatering. Furthermore, leaf anatomical characteristics and the activities of aquaporin (AQP) and carbonic anhydrase (CA) were measured to explain the mechanisms of g and g recoveries. The results showed that (i) both g and g were partly recovered after rewatering, and the recoveries decreased with initial water stress in both species. (ii) The g recovery was much greater in Mongolian oak than in Manchurian ash, while the g recovery was much greater in Manchurian ash. Consequently, the photosynthesis recovery in Manchurian ash was mostly affected by g recovery, while that in Mongolian oak was mostly affected by g recovery. (iii) The g recovery mainly resulted from the great increase in leaf g after rewatering rather than that in g, as g had a negative effect on g recovery. The stomatal opening status improved after rewatering, as the stomatal pore size (SS) increased, greatly promoting g recovery. In addition, the activities of both AQP and CA increased after rewatering, which improved CO transmembrane transports and greatly promoted g and g recoveries.