Leaf Water Potential Trends in Three Grasses Native to Semiarid Argentina

Abstract

The natural grazing land of the semiarid region of central Argentina is subject to long and intense periods of drought during the hot season. The aim of the present study was to analyze the pattern of leaf water status for the cool-season grasses Piptochaetium napostaense and Stipa tenuis and the warm-season grass Pappophorum subbulbosum, which are important forage species in this grazing area. Leaf water potential, soil water potential, and relative humidity were measured during 1983 and 1984. At soil water potentials above -0.5 MPa, the leaf water potential of the 3 species showed high values at 0800, after nocturnal rehydratation, and minimum values at 1400, coincident with maximum atmospheric water demand. P. subbulbosum showed a greater capacity to withstand the drop in water potential at 1400 than did the cool-season species. During periods of low soil water potential the range of daily variation in leaf water potential was reduced in the 3 species because of marked decreases in the maximum and minimum values. Leaf water potential in the cool-season species correlated better with the deficit of atmospheric vapor pressure than with soil water potential. Leaf water potential of P. subbulbosum on the other hand showed a higher correlation with soil water potential than with atmospheric vapor pressure deficit.