EFFECTS OF RAPIDLY AND GRADUALLY INDUCED WATER-STRESS ON PLANT-RESPONSE IN SUBTERRANEAN CLOVER LEAVES

The effect of rapidly vs, gradually induced soil water depletion in le af gas exchange parameters was investigated in subterranean clover lea ves in three different environments: growth room, outside late autumn (lower irradiance and evaporative demand) and late spring (higher irra diance and evaporative demand). The stomatal closure was the early res ponse to soil water depletion and it showed a common pattern for both water stress methods in all three contrasting environments. This early response (around 40 % reduction in respect to irrigated plants) was d eveloped before any substantial change in leaf water relations was ach ieved. During all of the experimental periods in the three contrasting environments, stomatal conductance was shown to be highly dependent o n soil water availability (R(2) 0.94, 0.55 and 0.74). The photosynthes is rate reductions were mainly explained by stomatal closure variation s (R(2) Of 0.97-0.99). In the three contrasting environments, the slow ly induced drought plants showed higher leaf water content and water p otential for similar soil water availability. This was reflected in hi gher stomatal conductance and photosynthesis.