Effects of rapidly and gradually induced water stress on plant response in subterranean clover leaves

Summary The effect of rapidly vs. gradually induced soil water depletion in leaf gas exchange parameters was investigated in subterranean clover leaves in three different environments: growth room, outside late autumn (lower irradiance and evaporative demand) and late spring (higher irradiance and evaporative demand). The stomatal closure was the early response 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 developed before any substantial change in leaf water relations was achieved. During all of the experimental periods in the three contrasting environments, stomatal conductance was shown to be highly dependent on soil water availability (R 2 0.94, 0.55 and 0.74). The photosynthesis rate reductions were mainly explained by stomatal. closure variations (R 2 of 0.97–0.99). In the three contrasting environments, the slowly induced drought plants showed higher leaf water content and water potential for similar soil water availability. This was reflected in higher stomatal conductance and photosynthesis.