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Archaea are common and abundant members of biological soil crust communities across large-scale biogeographic provinces of arid North America. Regardless of microbial community development, archaeal populations averaged 2 � 107 16S rRNA gene copies per gram of soil, representing around 5% of the prokaryotic (total calculated bacterial and archaeal) numbers assessed by quantitative-PCR. In contrast, archaeal diversity, determined by denaturing gradient gel electrophoresis fingerprinting and clone libraries of 16S rRNA genes, was very restricted. Only six different phylotypes (all Crenarchaea) were detected, three of which were very dominant. Some phylotypes were widespread, while others were typical of Southern desert...
We examined mycobiota structure, diversity level, and density of microfungal isolates in the biological soil crusts (BSC) and non-crusted soil of the northern and central Negev desert in 10 locations along a southward rainfall gradient. A total of 87 species from 49 genera were isolated. The mycobiota of BSC (80 species) was characterized by dominance of melanin-containing fungi, the remarkable contribution of sexual ascomycete species, and low abundance of the genera Penicillium and Aspergillus. Species richness and the contribution of dark-colored fungi with large, multicellular spores negatively and significantly correlated with rainfall. The comparison with mycobiota of the non-crusted soil showed that in BSC...
Salt and sediment contributions to the Colorado River and its tributaries pose economic and environmental concerns for the United States and Mexico. Land use decisions promoting the aggregation of Mancos Shale derived soils are one way to reduce the transportation of salts and sediments to water resources. We used a simple field test of soil aggregate stability to determine the site characteristics influencing the soil stability of sedimentary marine shale in the Gunnison Gorge National Conservation Area in Southwestern Colorado. Ninety-six 1 m2 plots were intensively sampled to explore relationships between soil stability and the biological, chemical and physical site characteristics. Analysis of variance showed...
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In this study, we examined N gas loss as nitric oxide (NO) from N-fixing biologically crusted soils in Canyonlands National Park, Utah. We hypothesized that NO gas loss would increase with increasing N fixation potential of the biologically crusted soil. NO fluxes were measured from biologically crusted soils with three levels of N fixation potential (Scytonema-Nostoc-Collema spp. (dark)>Scytonema-Nostoc-Microcoleus spp. (medium)>Microcoleus spp. (light)) from soil cores and field chambers. In both cores and field chambers there was a significant effect of crust type on NO fluxes, but this was highly dependent on season. NO fluxes from field chambers increased with increasing N fixation potential of the biologically...
In some arid regions, rehabilitation of whole system N-fixation may be strongly facilitated by the recovery of populations of the lichen genus Collema. Identification of the limits to recovery of Collema in apparently suitable habitat should inform selection of rehabilitation techniques. We simultaneously tested the relative importance of three hypothetical limits to Collema recovery: active erosion, resource limitation, and propagule scarcity. We found that in our experimental system, active erosion had no effect on short-term establishment of Collema, whereas propagule addition did enhance recovery and microhabitat (a resource availability gradient) also exerted a strong influence. It is possible that attempts...
In this study, we examined N gas loss as nitric oxide (NO) from N-fixing biologically crusted soils in Canyonlands National Park, Utah. We hypothesized that NO gas loss would increase with increasing N fixation potential of the biologically crusted soil. NO fluxes were measured from biologically crusted soils with three levels of N fixation potential (Scytonema-Nostoc-Collema spp. (dark)>Scytonema-Nostoc-Microcoleus spp. (medium)>Microcoleus spp. (light)) from soil cores and field chambers. In both cores and field chambers there was a significant effect of crust type on NO fluxes, but this was highly dependent on season. NO fluxes from field chambers increased with increasing N fixation potential of the biologically...
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Summers on the Colorado Plateau (USA) are typified by harsh conditions such as high temperatures, brief soil hydration periods, and high UV and visible radiation. We investigated whether community composition and pigmention might vary in biological soil crusts as a result of such conditions. Representative surface cores were sampled on the ENE, WSW, and top microaspects of 20 individual soil crust pedicels at a single site in Canyonlands National Park, Utah, in spring and fall of 1999. Frequency of major cyanobacterial taxa and pigment concentrations were measured for each core. The frequency of major cyanobacterial taxa was lower in the fall compared to spring. The less-pigmented cyanobacterium Microcoleus vaginatus...
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In this study, we conducted rainfall simulation experiments in a cool desert ecosystem to examine the role of biological soil crust disturbance and composition on dissolved and sediment C and N losses. We compared runoff and sediment C and N losses from intact late-successional dark cyanolichen crusts (intact) to both trampled dark crusts (trampled) and dark crusts where the top 1 cm of the soil surface was removed (scraped). In a second experiment, we compared C and N losses in runoff and sediments in early-successional light cyanobacterial crusts (light) to that of intact late-successional dark cyanolichen crusts (dark). A relatively high rainfall intensity of approximately 38 mm per 10-min period was used to...
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Biological soil crusts arrest soil erosion and supply nitrogen to arid ecosys- tems. To understand their recovery from disturbance, we studied performances of Collema spp. lichens relative to four experimental treatments plus microtopography of soil pedicels, oriented north-northwest to south-southeast in crusts. At sites in Needles (NDLS) and Island in the Sky (ISKY) districts of Canyonlands National Park, lichens were transplanted to NNW, SSE, ENE, WSW, and TOP pedicel faces and exposed to a full-factorial, randomized block experiment with four treatments: nutrient addition (P and K), soil stabilization with polyacrylamide resin (PAM), added cyanobacterial fiber, and biweekly watering. After 14.5 mo (NDLS) and...
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Biological soil crusts are an essential part of desert ecosystems throughout the world, as they are important in soil stabilization and soil fertility. Despite their importance, there have been few efforts to examine the population dynamics of the dominant species comprising these crusts or the effect of exotic plant invasions on these dynamics. In this study, we followed changes in lichen and moss cover for 8 years in plots dominated by native grasses or invaded by the exotic annual grass Bromus tectorum and across sites representing a range of land use histories. Our data showed that cover of both lichens and mosses can increase dramatically over short time periods, often going from just above 0% cover to as high...
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We present an approach to quantitatively assess nonnative plant invasions at landscape scales from both habitat and species perspectives. Our case study included 34 nonnative species found in 142 plots (0.1 ha) in 14 vegeta- tion types within the Grand Staircase–Escalante National Monument, Utah. A plot invasion index, based on nonnative species richness and cover, showed that only 16 of 142 plots were heavily invaded. A species invasive index, based on frequency, cover, and number of vegetation types invaded, showed that only 7 of 34 plant species were highly invasive. Multiple regressions using habitat characteristics (moisture index, elevation, soil P, native species richness, maximum crust development class,...
A novel black yeast-like fungus, Exophiala crusticola, is described based on two closely related isolates from biological soil crust (BSC) samples collected on the Colorado Plateau (Utah) and in the Great Basin desert (Oregon), USA. Their morphology places them in the anamorphic genus Exophiala, having affinities to the family Herpotrichiellaceae (Ascomycota). Phylogenetic analysis of their D1/D2 large subunit nuclear ribosomal RNA (LSU nrRNA) gene sequences suggests that they represent a distinct species. The closest known putative relative to Exophiala crusticola is Capronia coronata Samuels, isolated from decorticated wood in Westland County, New Zealand. The holotype for Exophiala crusticola anam. nov. is UAMH...
Transitions between atmosphere and soil, and between soil and roots, are two examples of small-scale boundaries across which the nutrient, water, and gas dynamics of ecosystems are modulated. Most atmospheric inputs to ecosystems have to pass through the soil; thus, the atmosphere?soil boundary influences the type and amount of materials and energy entering the soil. Belowground plant inputs occur through the rhizosphere, the zone of soil immediately adjacent to the root. This soil boundary layer affects root inputs to soil and root extraction of water and nutrients from soil. We discuss how water, carbon, nitrogen, and oxygen dynamics are affected by atmosphere?soil and soil?root boundaries and how light, soil...
Microbial activity in semiarid and arid environments is closely related to the timing, intensity, and amount of precipitation. The characteristics of the soil surface, especially the influence of biological soil crusts, can determine the amount, location, and timing of water infiltration into desert soils, which, in turn, determines the type and size of microbial response. Nutrients resulting from this pulse then create a positive feedback as increases in microbial and plant biomass enhance future resource capture or, alternatively, may be lost to the atmosphere, deeper soils, or downslope patches. When rainfall intensity overwhelms the water infiltration capacity of the plant interspace or the plant patch, overland...
Dryland ecosystems have long been considered to have a highly heterogeneous distribution of nutrients and soil biota, with greater concentrations of both in soils under plants relative to interspace soils. We examined the distribution of soil resources in two plant communities (dominated by either the shrub Coleogyne ramosissima or the grass Stipa hymenoides) at two locations. Interspace soils were covered either by early successional biological soil crusts (BSCs) or by later successional BSCs (dominated by nitrogen (N)-fixing cyanobacteria and lichens). For each of the 8 plant type�crust type�locations, we sampled the stem, dripline, and 3 interspace distances around each of 3 plants. Soil analyses revealed that...
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Communities of plants, biological soil crusts (BSCs), and arbuscular mycorrhizal (AM) fungi are known to influence soil stability individually, but their relative contributions, interactions, and combined effects are not well understood, particularly in arid and semiarid ecosystems. In a landscape-scale field study we quantified plant, BSC, and AM fungal communities at 216 locations along a gradient of soil stability levels in southern Utah, USA. We used multivariate modeling to examine the relative influences of plants, BSCs, and AM fungi on surface and subsurface stability in a semiarid shrubland landscape. Models were found to be congruent with the data and explained 35% of the variation in surface stability...
In arid and semiarid lands throughout the world, many of the open spaces between higher plants are covered by biological soil crusts, communities of cyanobacteria: algae, lichens, and bryophytes associated with bacteria and fungi. These crusts are miniature ecosystems between the atmosphere and soil, furnishing a habitat where microorganisms conduct nutrient recycles, especially nitrogen fixation, and contribute nutrients to the soils underneath. Photosynthetic components and ecosystem metabolism have been extensively studied, but the microfauna contributing to crust bacterial functioning have received little attention. This study of five crusts in southeastern Utah describes diversity and abundance of the protozoa,...
Biological soil crusts are an important component of desert ecosystems, as they influence soil stability and fertility. This study examined and compared the short-term vehicular impacts on lichen cover and nitrogenase activity (NA) of biological soil crusts. Experimental disturbance was applied to different types of soil in regions throughout the western U.S. (Great Basin, Colorado Plateau, Sonoran, Chihuahuan, and Mojave deserts). Results show that pre-disturbance cover of soil lichens is significantly correlated with the silt content of soils, and negatively correlated with sand and clay. While disturbance appeared to reduce NA at all sites, differences were statistically significant at only 12 of the 26 sites....
Biological soil crusts (BSC) are a dominant feature in arid and semi-arid ecosystems. BSC stabilize soils, contribute nitrogen and carbon, enhance vascular plant nutrition, and influence local hydrologic cycles. However, these ecological roles are determined by the species composition, morphology, and physiological functioning of the BSC. These factors, in turn, can be strongly affected by land use, invasive plants, and climate change. Soil surface disturbance and/or dominance by invasive plants both result in loss of lichens and mosses, leaving cyanobacteria dominating the soil surface. This loss reduces soil stability, carbon and nitrogen contributions, surface temperatures, and soil water retention times. Climate...
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Bromus tectorum is an exotic annual grass that currently dominates many western U.S. semi-arid ecosystems, and the effects of this grass on ecosystems in general, and soil biota specifically, are unknown. Bromus recently invaded two ungrazed and un-burned perennial bunchgrass communities in southeastern Utah. This study compared the soil food-web structure of the two native grassland associations (Stipa [S] and Hilaria [H]), with and without the presence of Bromus. Perennial grass and total vascular-plant cover were higher in S than in H plots, while quantities of ground litter were similar. Distribution of live and dead plant material was highly clumped in S and fairly homogenous in H. Soil food-web structure was...


map background search result map search result map Untangling the biological contributions to soil stability in semiarid shrublands Soil Biota in an Ungrazed Grassland: Response to Annual Grass (Bromus tectorum) Invasion Soil lichen and moss cover and species richness can be highly dynamic: The effects of invasion by the annual exotic grass Bromus tectorum, precipitation, and temperature on biological soil crusts in SE Utah Evaluating plant invasions from both habitat and species perspectives Temporal variation in community composition and pigmentation of desert cyanobacterial soil crusts Impacts of Biological Soil Crust Disturbance and Composition on C and N Loss from Water Erosion Treatment effects on performance of N-fixing lichens in disturbed soil crusts of the Colorado Plateau NO gas loss from biologically crusted soils in Canyonlands National Park, Utah Soil Biota in an Ungrazed Grassland: Response to Annual Grass (Bromus tectorum) Invasion Soil lichen and moss cover and species richness can be highly dynamic: The effects of invasion by the annual exotic grass Bromus tectorum, precipitation, and temperature on biological soil crusts in SE Utah Temporal variation in community composition and pigmentation of desert cyanobacterial soil crusts Impacts of Biological Soil Crust Disturbance and Composition on C and N Loss from Water Erosion Treatment effects on performance of N-fixing lichens in disturbed soil crusts of the Colorado Plateau NO gas loss from biologically crusted soils in Canyonlands National Park, Utah Evaluating plant invasions from both habitat and species perspectives Untangling the biological contributions to soil stability in semiarid shrublands