Rooting pattern and water relations of three pasture grasses growing in drying soil.

Seedlings of perennial ryegrass (Lolium perenne L. S23), cocksfoot (Dactylis glomerata L. S37) and Timothy (Phleum pratense L. S48) were rooted into tubes of soil and plants were either watered well or remained unwatered for a period of seven days. Measurements were made of root water relations and of growth of roots and shoots. Root turgor of Dactylis was larger than that of Lolium and Phleum. As a result of accumulation of solutes, turgor of Dactylis and Lolium was maintained as the soil dried. Phleum roots lost turgor in drying soil and this characteristic correlated well with a water stress-induced reduction in root and shoot growth. Soil drying had marked effects on the rooting patterns of two of the three species. Phleum seedlings which, in wet soil are deep rooting were restricted in their depth of rooting, while roots of water-stressed Dactylis seedlings grew deeper into the profile than did roots of well-watered plants. When water was withheld from plants, deeper rooting apparently resulted in a more favourable shoot water balance which had a beneficial effect on shoot growth.