Spatial Heterogeneity of the Root System of Grasses in the Patagonian Arid Steppe

Abstract

SORIANO, A., R. A. GOLLUSCIO AND E. SATORRE (Depto. Ecol., Facultad Agron., Univ. Buenos Aires, Av. San Martin 4453, 1417-Buenos Aires, Argentina). Spatial heterogeneity of the root system of grasses in the Patagonian arid steppe. Bull. Torrey Bot. Club 114:103-108. 1987.Root biomass distribution and root growth into traps buried in the soil have been studied in the three dominant grasses (Stipa speciosa Trin. et Rupr., S. humilis Vahl and Poa ligularis Nees ap. Steud.) of extensive plant communities of the Patagonian arid steppe. Root biomass decreases sharply from center to the periphery of young and old plants of the three species. As a result of this attenuation, low root density pockets, corresponding to bare soil patches between tussocks, are found in the upper soil layer. At these pockets, water from small rains would be underutilized. Comparison of root biomass and spring root growth into traps supports the conclusion that, in a growing season, the three grasses were able to rebuild the roots only to the size previous to ablation provoked by trap installation. It is, therefore, postulated that lack of full colonization of low density root pockets by established root systems is determined by morphological constraints that limit their size and geometry. Potentiality seems to exist for the establishment of new individuals that would contribute to the formation of a continuous layer of uniform root density in the upper soil. Better use would thus be made of small rains, amounting to 57% of total rainfall events.