LAUSR

Abstract. Plant growth and production are greatly affected by water deficit worldwide and particularly in Tunisia. In this context, a study was conducted to analyse the response of three vetch species (Vicia narbonensis, V. sativa and V. villosa) to four water treatments: 100% (Control), 80%, 60% and 40% of field capacity. Water stress led to important changes of both leaf physiology and anatomy. V. narbonensis kept cells turgor by adjusting the osmotic potential without changes in cell walls elasticity. V. sativa showed the most pronounced reductions of leaf water potential and the lowest osmotic adjustment under water stress although cell walls elasticity has not changed. However, V. villosa kept a higher fraction of apoplastic water over V. sativa that allowed it to maintain cells turgor despite the rigidity of its cell walls. Drought did not affect lamina thickness but increased the palisade parenchyma at the expense of spongy parenchyma. It was characterised by leaf lamina increase and constant thickness of the spongy parenchyma: a strategy to cope with drought. Moreover, stomata were reduced in size but were increased in number in order to avoid water loss.