Seasonal change of hydraulic resistance in Melilotus officinalis L. tissues under water deficit

The possible appearance of desertification phenomena in the Mediterranean zone necessitates the study of ecophysiological mechanisms of range plant tolerance to water deficit. Towards this direction several hydrodynamic (water potential, relative water content) and physiological parameters (stomatal conductance, transpiration) were measured while, at the same time, the seasonal change of hydraulic resistance was calculated in Melilotus officinalis (L.) under two different water regimes (well watered and water stressed plants). The results indicate that the well watered plants showed higher hydraulic resistance, possibly attributed to an effort of saving the soil water resources during the dry period. On the other hand, water stressed plants seemed to maintain their transpirational flow through a less sensitive stomatal apparatus, exhibiting a higher water transport capacity at the soil-plant-atmosphere continuum, indicating a capacity of phenotypic plasticity.