Stomatal, mesophyll and biochemical limitations to soil drought and rewatering in relation to intrinsic water-use efficiency in manchurian ash and mongolian oak

The balance between stomatal and mesophyll conductance has been reported to directly influence intrinsic water-use efficiency (WUE_i), but it is unclear whether variations in stomatal and mesophyll limitations (l_sc and l_m, respectively) affect WUE_i during soil drought and rewatering. Limitations (l_sc, l_m and biochemical limitation, l_b) and WUE_i were measured in Manchurian ash (Fraxinus mandshurica Rupr.) and Mongolian oak (Quercus mongolica Fish. ex Ledeb) saplings exposed to two levels of water stress (moderate and severe) and rewatering in this study. The primary limiting factors for photosynthesis among l_sc, l_m, and l_b and their correlations with WUE_i were assessed. Both l_sc and l_m increased with water stress, while l_b decreased, and during recovery, l_sc and l_m decreased, while l_b increased. Photosynthesis limitations directly influenced WUE_i, with WUE_i being larger after rewatering than during water stress, increasing as biochemical capacity weakened at the expense of diffusional limitations (l_sc and l_m). Stomatal closure was more limiting to net photosynthesis in Mongolian oak than in Manchurian ash during the drought and recovery treatments; consistently higher WUE_i was measured in the former species, possibly due to a more developed root system and larger leaf hydraulic conductance and stem vessel diameter in the former species.