Fig. 10.

Schematic overview of the main experimental results on Populus nigra plants under moderate water stress (WS) and well-watered (WW) conditions: (1) in the leaf there is a clear daily trend where ABA regulates physiological parameters [stomatal conductance (g_s), mesophyll conductance (g_m) and leaf hydraulic conductance (K_leaf)] to optimize water transport and CO₂ assimilation; (2) in the stem ABA content may have a role in the regulation of water transport and carbohydrate metabolism; (3) ABA accumulates in the roots due to transport from the leaves where this hormone is synthesized. The increase in ABA content in the roots under water-stress conditions may enhance root hydraulic conductivity (L_p).