Effects of Water Stress and Simulated Grazing on Leaf Elongation and Water Relations of an East African Grass, Eustachys paspaloides

Abstract

Eustachys paspaloides was studied under conditions of water stress and simulated grazing (clipping) in the laboratory. Leaf and soil water potentials and leaf elongation rate (LER) were monitored during a 41-day drying period, and following rewatering. Water relations characteristics of tillers were derived from pressure-volume curves during the drought and recovery periods.

Water stress developed more slowly in clipped than in unclipped plants; predawn water potentials declined at mean rates of 0.13 and 0.38 MPa day^-1 in clipped and unclipped plants, respectively. Consequently, leaf elongation of clipped plants continued approximately a week longer during the drying period than when plants were not clipped. Following rewatering, LER increased from zero to steady levels over 4 days.

Osmotic adjustment due to solute accumulation occurred in tillers of water-stressed plants. The difference in solute potential at full turgor between well-watered and stressed plants was 0.29 and 0.20 MPa for clipped and unclipped plants, respectively. The delay in permanent wilting afforded by lowered osmotic potential was about 1 day, indicating that osmotic adjustment is not a mechanism for reducing the effect of water stress on growth during long-term drought in Eustachys. However, osmotic adjustment may be an acclimation response to short-term drought during the growing season, and may aid in survival during the long dry season by limiting dehydration of the growing points.