Comparative Ecology of Sarcobatus Baileyi and Sarcobatus Vermiculatus in Eastern California

—Greasewood (Sarcobatus) is a succulent-leaved, halophytic shrub of North American origin. The genus comprises 2 species: Sarcobatus baileyi and Sarcobatus vermiculatus. Sarcobatus vermiculatus is common throughout much of western North America, but S. baileyi is much more limited in distribution and was previously thought to be endemic to Nevada. Here we document and describe a S. baileyi population in eastern California, comparing its morphology and ecology to an adjacent S. vermiculatus population. Morphologically, S. baileyi is smaller in stature but produces larger seeds; however, fewer S. baileyi seeds germinated and survived a 20-day laboratory incubation compared to seeds of S. vermiculatus. Sarcobatus baileyi has higher leaf Na concentrations and operates at much lower plant water potentials than S. vermiculatus under field conditions; however, no significant differences were observed between the 2 species in long-term water-use efficiency as measured by leaf δ13C. Leaf Na concentrations were very low in both species. Overall, these species differ greatly in a number of traits that are consistent with the upland, nonphreatophytic character of S. baileyi, which is in stark contrast to the phreatophytic character of S. vermiculatus. Both species, however, are very salt tolerant and have low leaf N concentrations, indicating the low nutrient availability and the potentially high salinity of their extreme habitats. Further investigation of comparable desert ridge environments should be conducted to determine the extent of S. baileyi in eastern California, and common garden comparisons of the 2 species should be conducted to compare their ecophysiological traits. RESUMEN.—El "greasewood” (Sarcobatus) es un arbusto halofítico de origen norteamericano con hojas suculentas. El género consta de dos especies: Sarcobatus baileyi y Sarcobatus vermiculatus. Aunque S. vermiculatus es común en gran parte del oeste de Norteamerica, S. baileyi tiene una distribución mucho más limitada. Se pensaba anteriormente que S. baileyi era endémico a Nevada, pero aquí documentamos y describimos una población en el este de California, comparando su morfología y ecología con las de una población adyacente de S. vermiculatus. Morfológicamente, S. baileyi es más pequeña de altura, pero produce semillas más grandes. Sin embargo, menos semillas de S. baileyi germinaron y sobrevivieron a una incubación en laboratorio de 20 días, comparado con S. vermiculatus. Sarcobatus baileyi opera con potenciales de agua mucho más bajos que los de S. vermiculatus en condiciones de campo y tiene mayores concentraciones de Na en sus hojas. No obstante, no se observaron diferencias significativas en la eficiencia del uso de agua a largo plazo, medida en términos de δ13C entre las 2 especies. Las concentraciones de N en las hojas fueron muy bajas en ambas especies. En general, estas especies difieren mucho en varios rasgos que son consistentes con el carácter no freatofítico de S. baileyi de tierras altas, el cual contrasta claramente con el carácter freatofítico de S. vermiculatus. Ambas especies, sin embargo, son bastante tolerantes a la sal y tienen concentraciones bajas de N en hojas, lo cual indica la baja disponibilidad de nutrientes y la potencial alta salinidad en sus hábitats extremos. Investigaciones adicionales en ambientes comparables de bordes desérticos deberán llevarse a cabo para determinar la extensión S. baileyi en el este de California, además de comparaciones de las dos especies en jardín para comparar sus rasgos ecofisiológicos. 2011] COMPARATIVE ECOLOGY OF SARCOBATUS SPP. 235 Based on taxonomic descriptions and field observations, S. baileyi and S. vermiculatus differ in both morphology and ecology. Typically, S. baileyi shrubs have a shorter stature than S. vermiculatus shrubs (5–10 dm versus 5–21 dm; Hils et al. 2004), and branches of S. bai leyi are composed of short shoots arising from cushion-like pads, with the branch architecture forming an overall rounded appearance (Hils et al. 2004). The leaves of S. baileyi are grayish-green, and the flowers produce larger fruits with wider wings than do the flowers of S. vermiculatus (Hils et al. 2004). Rooting depth also differs between the species, with S. baileyi being more shallowly rooted than the phreato phytic S. vermiculatus. This morphological difference should translate into significant differences in the species’ water relations. The ecological breadth of these spe cies also differs. Sarcobatus baileyi has been documented only at elevations above 1200 m asl, typically in monoculture or in association with Atriplex confertifolia, whereas S. vermicu latus may be found at elevations as low as 100 m asl in saline lowlands, in dune systems, and around playas (Sanderson et al. 1999). Although S. vermiculatus often is the dominant shrub in more-saline areas, it can be codominant with other salt-tolerant shrub species including Allenrolfea occidentalis, Atriplex confertifolia, Atriplex lentiformis, and Atriplex parryi (Blank et al. 1998, James et al. 2005). In less saline areas, S. vermiculatus can be found in association with Artemisia tridentata, Chryso thamnus nauseosus, Tetradymia tetrameres, and Tetra dymia glabra (Toft and Elliott-Fisk 2002, Aanderud et al. 2008). We know of no common garden or reciprocal transplant experi ments comparing S. baileyi and S. vermiculatus. Moreover, there are no detailed comparisons of the species where they are growing in adjacent populations. While some differences in species traits may be due to site conditions, comparisons of adjacent populations will be useful for developing hypotheses regarding genetically versus phenotypically based ecological differences be tween the species. In the Coso Mountains south of the Owens (dry) Lake playa, California, we documented stands of S. baileyi. In subsequent forays, we collected data on community characteristics and individual shrub traits. Our goal in this research was to compare multiple traits of S. baileyi and S. vermiculatus growing in adjacent populations to illustrate ecological differences between the 2 species.