Mineral composition of Medicago minima and Erodium cicutarium under various water regimes

Medicago minima and Erodium cicutarium are two annual, naturalized species in semi-arid, temperate rangelands of central Argentina. A field study was conducted to determine the effects of different levels of soil water availability on concentrations and partitioning of sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg) in various organs in these species. Aboveground plant parts and roots showed lower or similar, but not higher, Na concentrations under water stress than under irrigated conditions in both species and years. Concentrations of K, Ca, and Mg of aboveground plant parts and roots in both years for E. cicutarium and of Ca in 1989 for M. minima were greater under water stress than under irrigated conditions. Aboveground plant parts of both species had in general a lower Na and a greater K concentration than roots. Leaves and roots had similar Mg concentrations in M. minima. However, concentrations of this nutrient were greater or similar in roots than in leaves in E. cicutarium, and those of Ca were greater in leaves than roots in both species. Leaves and/or stems had greater Ca concentrations than fruits in both species and years under all water levels. The lowest concentrations of Na, Ca, K, and Mg among plant parts in both species were generally found in flowers. Aboveground plant parts of M. minima and E. cicutarium exceeded the Na, K, Ca, and Mg concentrations recommended for a balanced beef cattle diet under all water levels. Both species contained more Na, K, Ca, and Mg in shoots (all aboveground organs) than in roots in both years. Differences between species in the proportional allocation of whole plant Na, K, Ca, and Mg to the various aboveground and belowground organs under water stress, rainfed, and irrigated conditions are discussed.