DRY-WEIGHT PRODUCTION AND PARTITIONING IN MEDICAGO-MINIMA AND ERODIUM-CICUTARIUM UNDER WATER-STRESS

Medicago minima and Erodium cicutarium are two naturalized annual spec ies in extensive semi-arid, temperate rangelands of central Argentina. A field study was conducted during 1989 and 1990 to evaluate the effe cts of different levels of soil water availability on above- and below -ground dry weight production and partitioning in these species. Dry w eight production by M. minima was more sensitive to water stress than that by E. cicutarium. Although the response was more marked in M. min ima, both species allocated a larger proportion of total plant dry wei ght to fruits under water stress than under irrigated conditions durin g early spring. Percentage allocation of total plant dry weight into r eproductive organs in both species, and stems and peduncles in E. cicu tarium, was correlated with total dry weight of these organs; this mig ht indicate a correlation between sink size and strength. Persistence of both species in the local flora appears to be associated with their capacity to colonize open, degraded areas and grow in association wit h native perennial grasses, as well as to tolerate severe drought peri ods. (C) 1998 Annals of Botany Company.