The role physiological responses in survival of prolonged soil moisture deficit was investigated in vegetative plants of two Dactylis glomerata populations: KM2 (drought-resistant) and Lutetia (susceptible). The plants were grown in 1 m-deep soil columns in a controlled environment. After 56 d of full irrigation, water was withheld for 80 d, by which time all soil moisture had been consumed; the plants were then rewatered for a further 19 d. As drought progressed, leaf extension decreased to zero, water status declined, and water-soluble carbohydrates (WSC) at first increased and then decreased. The most pronounced differences between the two populations was that all KM2 tillers survived the drought, but 34% of Lutetia tillers died. In comparison with Lutetia, KM2 was characterized by (a) slower shoot growth rate, (b) greater root density at depth, (c) maintenance of higher lamina relative water content, (d) greater osmotic adjustment in leaf bases, (e) higher concentration of WSC in tiller bases, (f) greater ability to export WSC out of dying leaves, (g) lower content of metal ions but improved maintenance of P status, and (h) lower proline:amino acid ratio. The contribution of these responses to tiller survival under severe drought in controlled environments is contrasted with performance and persistence of swards in the field in the harsher Mediterranean environment.Copyright 1995, 1999 Academic Press

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