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Downy brome (Bromus tectorum L.) is an alien grass that dominates disturbed ground in shrub-steppe ecosystems of the western United States. Responses of downy brome to added nitrogen and water were evaluated using intact soil cores obtained from an old field. Gas exchange data were gathered at the leaf and canopy scales. Stomatal conductance and net photosynthesis rates were greater at the leaf scale than at the canopy scale, decreased with time from germination, and were weakly affected by treatments. Water-use efficiency was weakly related to time from germination and treatments. Biomass was greater in the nitrogen-plus-water (7.4 g) treatment, compared with water (3.6 g), nitrogen (4.5 g), and control (3.3 g)...
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Desert plants can influence the pattern of resources in soil resulting in small-scale enriched zones. Although conceptually simple, the shape, size, and orientation of these "resource islands" are difficult to study in detail using conventional sampling regimes. To demonstrate and alternative approach, we sampled soil under and around individual Artemisia tridentata (sagebrush), a dominant shrub of cool desert environments, and analyzed the samples with univariate statistics and geostatistics. Univariate Halvorson, Jonathan J, Harvey Bolton Jr, Jeffrey L Smith, and Richard E Rossi. ?Geostatistical analysis of resource islands under Artemisia tridentata in the shrub-steppe.? Western North American Naturalist 54,...
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Disturbance of shrub-steppe soils and alterations in plant cover may affect the distribution, size and activity of soil microorganisms and their ability to biogeochemically cycle essential nutrients. Therefore, the soil microbial biomass and activity and selected soil enzyme activities were determined for two arid ecosystems, an undisturbed perennial shrub-steppe and annual grassland, which was initially shrub-steppe and has been an annual grassland since the disturbance caused by farming ceased in the 1940s. Soils were sampled at 0?5 and 5?15 cm depths beneath sagebrush (Artemisia tridentata Mutt.), bluebunch wheatgrass [Elytrigia spicata (Pursh) D.R. Dewey] and cryptogamic soil lichen crust at the perennial site...
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