Control of crops leaf growth by chemical and hydraulic influences

Three species of forage grasses (Festuca arundinacea, Eragrostis curvula, Sporobolus stapfianus) commonly grown in the Mediterranean region were subjected to a soil drying treatment. Leaf growth rate in F. arundinacea was highly sensitive to soil drying and low growth rates were associated with high laminar turgors. The production of ABA was stimulated by soil drying and there was a clear relation between increasing ABA accumulation and reduction in leaf growth, Leaf growth of E. curvula, a C-4 warm season grass, was relatively insensitive to soil drying which was not accompanied by a substantial increase in leaf ABA content, S. stapfianus, a resurrection plant, was highly sensitive to decreasing soil water availability, In these two latter species, leaf growth was substantially restricted before ABA accumulation occurred, It is suggested that reductions in laminar turgor of E. curvula and S. stapfianus may be limiting leaf growth as soil dries, The results indicated a different mechanism of sensing and responding to reduction in soil water availability for the three species studied. The relative importance of the chemical and hydraulic control of leaf growth is discussed.