The Effect of Water Stress on the Vegetative Growth of White Clover (Trifolium repensL): Comparison of Long-term Water Deficit and a Short-term Developing Water Stress

Abstract

White clover plants were subjected to either a short-term developing water stress or long-term stable levels of water deficit on 'water stress columns'. The short-term stress reduced plant water status to —2 0 MPa over 15 d. The water stress columns imposed only mild levels of water stress (a reduction of 0 35 MPa in leaf water potential for the more severe treatment) but these were maintained for several weeks. The absolute growth of plants on the control columns was maintained throughout the experimental period. Vegetative growth was measured. Stolon, petiole, and lamina growth were all reduced to some extent when plants were grown symbiotically. The two regimes gave comparable results. When nitrate was supplied there was no effect of water stress. A considerably reduced absolute growth rate did not result in a similar decrease in final organ size. Stolon growth was most reduced by water stress. Leaf death during water stress was as important as changes in growth in determining final dry matter yield. Consequently, the yield of petiole and lamina from plants grown without supplied nitrate on the water stress columns was lower than that of stolon at the end of the treatment period. The merits of the water stress column system for imposing long-term water deficit are discussed.