Effect of drought on growth, carbohydrates, and soil water use by perennial ryegrass, tall fescue, and white clover

In irrigated pastures of the semiarid, high-elevation western USA, perennial ryegrass (Lolium perenne L.) persistence is poor, and over time white clover (Trifolium repens L.) often dominates mixtures. Irrigation is often not available during autumn, when these perennial plants store carbohydrate reserves for spring 0regrowth. Our objective was to compare the effect of water stress on growth, carbohydrates, and soil water use of perennial ryegrass, white clover, and tall fescue (Festuca arundinacea Schreb.) in a greenhouse study. These three species were grown separately in a Kidman fine sandy loam, in 15-cm-diam, 1-m-deep pots and irrigated for 81 d (4 plants/pot). Paired pots were then either irrigated or subjected to water deficit (drought) for 30 d, followed by 10 d of recovery with irrigation. At 10-d intervals, four paired pots of each species were destructively sampled to determine leaf and storage organ dry matter and carbohydrate and simple sugar concentrations in storage organs. Root length density and soil water content were also sampled at 20-, 60-, and 90-cm soil depths. Leaf dry matter was lower in water-stressed plants than in irrigated plants by the end of the drought, but did not differ among species. After 10 d of recovery, storage carbohydrate concentration in droughted perennial ryegrass was lower than in white clover, and the ratio of simple sugars (droughted:irrigated) in perennial ryegrass was higher than in white clover. Tall fescue performed similarly to both species. Before the drought, grasses had similar, extensive root systems that withdrew more soil water from the 90-cm soil depth than did white clover. By the end of the 30-d drought, white dover had reduced soil water at all depths as much as the grasses. White clover survived drought and conserved carbohydrate reserves after 10 d of recovery better than did perennial ryegrass and similarly to tall fescue.