Autecology of Atriplex Polycarpa from California

Atriplex polycarpa (Torr.) Wats. was a dominant, palatable shrub of the xeric Atripleto—Brometum disclimax in the San Joaquin valley of California. Overgrazing and agriculture during the past 100 years have restricted its present distribution to saline or fenced areas. Optimal germination temperatures (9—15°C) are close to those that prevail in nature in November, the month of utricle dispersal. Germination is rapid and can occur over a wide range of temperatures (3—33°C); it is reduced by light and NACl > 1%, but indifferent to temperature alternation and soil CaCO 3 content. It is unlikely that the bracteoles contain inhibitors. In a field plot in the Temblor Range of California, during a growing season with 115 mm precipitation, none of the seeds sown produced an established seedling, possibly because of competition by introduced annuals. Optimal growth conditions were 18—hour photoperiod, 24 ± 4°C. Growth at 12°C was quite slow. If conditions are favorable A. polycarpa can produce a large biomass, but it possesses a long juvenile stage of > 2 years prior to flowering. The base value of shoot water potential at no moisture stress is —18 bars, but this can be modified downward by pre—exposure to minor cycles of drought. This species can endure soil moisture below that which causes ultimate wilting or sunflower plants and can recover from a shoot water potential as low as —69 bars. Plants in nature, in August, exhibited a shoot water potential as low as —58 bars. This species was compared in a number of ways to Syrian ecological equivalents Haloxylon articulatum and Salsola vermiculata var. villosa.