LEAF WATER POTENTIAL LEAF WATER-DEFICIT RELATIONSHIP FOR 10 SPECIES OF A SEMIARID GRASSLAND COMMUNITY

The relationship between water potential and relative water content (w ater content in percentage of full hydration) is a characteristic of p lant tissues, that may vary with environmental conditions. It is used here to compare leaf water relations of ten species coexisting in a se miarid grassland community (Festucetum vaginatae danubiale) in Hungary . Three groups of species can be distinguished. In two of these leaf w ater potential changes only moderately with decreasing leaf water cont ent. These are either short-lived, drought escaping spring plants rely ing on seasonally favourable water supply (group 1) or xerophytes with very deep root system having access to permanent water resources (gro up 2, only one species studied here). Xerophytes with moderately deep roots (group 3) display a rapid drop of leaf water potential with incr easing leaf water deficit. This generates a steep water potential grad ient in the soil-plant continuum that in turn enhances water uptake by roots. There is a positive correlation between the rate of water pote ntial decline and degree of sclerophylly (proportion of dry material i n the water-saturated leaf), and both variables show seasonal change i n perennial species.