Autecology of Salsola vermiculata var. villosa from Syria

Abstract

Salsola vermiculata var. villosa is one of the most important forage shrubs in the arid zones of Syria, the Middle East, and North Africa. Overgrazing, however, has restricted the species to nonsaline, rocky mountain slopes and to saline sebkhas. Optimal germination temperatures (12–18°C) closely correspond to those which predominate in nature during October and November, the months in which utricles become ready for dispersal. Germination is rapid, can occur over a wide range of temperature (3–33°C), and is insensitive to light and to temperature alternation. It is unlikely that fruit wings contain inhibitors, and in fact their removal reduces establishment. Germination is modestly improved by CaCO 3 , but reduced and delayed by 4% NaCl. At room temperature, seeds lost viability within 9 months. In a field plot in the Temblor Range of California (115 mm rain in 1969–70), 10% of sown seeds germinated, and some seedlings remained after the summer and winter of 1970. Optimal conditions for growth are 14-hour, 35/20°C. Floral buds are formed at temperatures above 12°C, but development of seeds and wing emergence require days shorter than 12 hours; consequently natural change in daylength synchronizes utricle maturation with the onset of rains in October. Clay loam, with no CaCO 3 , is the best medium for growth and reproduction, which contrasts with natural distribution on calcareoustsoils. Repeated seasonal clipping (simulating grazing pressure) did not delay flowering and did increase vegetative productivity. The base value of shoot pressure water potential (at little or no moisture stress) is −19 bars but this can be modified downward by preexposure to minor cycles of drought. This species can endure soil moisture below that which causes ultimate wilting of sunflower plants, and can sustain a shoot pressure water potential as low as −69 bars.