干旱区生态环境知识资源中心

Along the margins of playas in northwestern Nevada, a salt-tolerant plant community occupies mounds that dot a largely unvegetated landscape. In this environment we studied soil development and plant-soil relationships. The mounds, averaging 0.3 m in height, are occupied by the shrubs Allenrolfea occidentalis (iodine bush), Sarcobatus vermiculatus (black greasewood), and Atriplex lentiformis ssp, torreyi (Torrey saltbush). Distichlis spicata (desert salt-grass) is the only herbaceous plant occupying this community. Soil salinity decreases with depth in this environment, and content of aqueous-extractable solutes is significantly influenced by site-specific vegetation. Content of silt, clay and salt in mound surface horizons suggests a chronosequence of mound formation, with the youngest at the barren playa interface and die oldest at the upland vegetation border. Plant demography and mound soil stratigraphy suggest that a pulse of plant recruit ment and mound building occurred during a time of neoglacial cooling. As a substrate for plant recruitment, mounds have a limited lifespan because deposition of eolian-transported salts and geochemical cycling by plants quickly render them too saline for seed germination. The apparent periodicity of mound formation precludes definitive conclusions regarding those mound characteristics favorable for plant recruitment and survivorship.