Survival of Perennial Cool-season Grasses .under Water Stress Conditions and after Establishment

A knowledge of the mechanism of abiotic stress tolerance in wild species of grasses is essential during
the first year after establishment in semi-arid areas, Perennial grasses are one of the keys to the
economic and environmental sustainability of pastures 'as well as 'livestock grazing in Iran. There is a
lack of know ledge about their drought tolerance during their initial growth stages and their response to re-watering during the first year of establishment. to evaluate the effects of soil ,water (field capacity,water holding and re-watering), a greenhouse experiment was conducted on root and shoot
development at initial growth stages and recovery of 36 populations of native cool-season grasses from 15 species of seven genera namely: Elymus, Agropyron, Secale, Hordeum, Bromus, Festuca, and
Dactylis. All measurements except root dry matter and length were .significantly affected by the
treatments(f<0.05). Water stress decreased root and ,shoot dry matter (about 50%), whereas root to
shoot ratio and recovery of dry matter increased at 22 and 43%, respectively. Decreasing soil water
from FC(-0}3 bar) to wilting point (-15 bar), reduced relative water content from 78 to 46% for all
species. 'Results indicated that Elymus elongatum and Bromus tomentellus were of the highest and
lowestyieldpotentials under water and stress conditions ,respectively ,Drought tolerant genotypes,
such as Elymus repense and Elymus elongatojorinis)howeda higher foot dry weight and responses to
rewatering , Root extention and carbohydrate storage were associated with greater drought tolerance as
well as recovery yield.