Effects of water stress and night temperature preconditioning on water relations and morphological and anatomical changes of Lotus creticus plants

The water relations and anatomical and morphological changes of Lotus creticus sub. creticus seedlings to two irrigation treatments (water stress and control) and temperature (unheated and night-heated greenhouse) was investigated in nursery conditions. Shoot and root growth, leaf stomatal density, leaf trichome density, xylem vessels in roots and stems and water relations were studied because of their relation with drought resistance. Water stress led to substantial losses in dry weight, leaf area, root dry weight and length. The limited osmotic adjustment reached by the plants may not maintain leaf turgor and growth. In general deficit irrigation produced Lotus plants with greater leaf trichome densities and number of xylem vessels of stems and roots. Night-time heating had little influence on these aspects, temperature reduced leaf water potential of water stressed plants but had no effect on well-watered plants. Deficit irrigation under nursery conditions induced a suite of morphological and physiological adaptations (reduction in leaf area, development of osmotic adjustment, increments of leaf hairs and number of xylem vessels of stem and roots) that might allow a considerable capacity to adapt to adverse conditions after transplanting.This work has been supported by Projects CICYT (AGF96-1136-CO2-02), FEDER (1FD97 0420 CO2 01) and SENECA (PI-75/00819/FS/01)Peer reviewe