Different hydraulic strategies under drought stress between Fraxinus mandshurica and Larix gmelinii seedlings

Persistent and severe drought induced by global climate change causes tree mortality mainly due to the hydraulic imbalance of conduit systems, but the magnitude of injury may be species dependent. A water-exclusion experiment was carried out on seedlings of two tree species with distinct characteristics, i.e., Fraxinus mandshurica and Larix gmelinii to examine hydraulic responses of leaf, stem, and root to drought stress. The two species displayed different hydraulic strategies and related traits in response to drought stress. L. gmelinii reduced its leaf hydraulic conductance by quick stomatal closure and a slow decline in leaf water potential, with a more isohydric stomatal regulation to maintain its water status. In contrast, F. mandshurica was more anisohydric with a negative stomatal safety margin, exhibiting strong resistance to embolism in stem and leaf-stem segmentation of hydraulic vulnerability to preserve the hydraulic integrity of stem. These differences in hydraulic behaviors and traits between the two species in response to drought stress provide a potential mechanism for their co-existence in temperate forests, including which in the forest modeling would improve our prediction of tree growth and distribution under future climate change.