Dynamics of root growth and decay in two grasses native to semi-arid Argentina [Stipa tenuis; Piptochaetium napostaense; perennial forage grasses]

The pattern of root growth and decay in Stipa tenuis Phil, and Piptochaetium napostaense (Speg.) Hack, was examined under field conditions in root observation chambers. The roots of both species grew uninterruptedly throughout the whole year. Root elongation during spring, summer, and early autumn can be six and five times as high as that in the late autumn to winter period for S. tenuis and P. napostaense, respectively. Root decay was a continuous process in both species throughout the year, with maximum decay rates occurring from late spring through to the middle of autumn. Comparison of minimum and maximum values registered during the year showed a root decay ratio of about 4:1 for S. tenuis and one of 5:1 for P. napostaense. During the period of maximum root growth, both species showed a pulse‐like pattern of root elongation in response to rapid changes in water availability. In a semi‐arid region in which the soil is notably shallow, root growth behaviour of this kind should allow these species to respond opportunistically to water.