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We examined the content and isotopic composition of nitrogen within soils of a juniper woodland and found that a cryptobiotic crust composed of cyanobacteria, lichens, and mosses was the predominant source of nitrogen for this ecosystem. Disturbance of the crust has resulted in considerable spatial variability in soil nitrogen content and isotopic composition; intercanopy soils were significantly depleted in nitrogen and had greater abundance of 15N compared to intra-canopy soils. Variations in the 15N\14N ratio for inter- and intracanopy locations followed similar Rayleigh distillation curves, indicating that the greater 15N/14N ratios for inter-canopy soils were due to relatively greater net nitrogen loss. Coverage...
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Invasion by the C3 annual grass Bromus tectorum has significantly increased the amount of relatively low quality (high lignin:nitrogen) plant litter deposited in arid Colorado Plateau grasslands. Our objectives were to determine what effects these changes have on microbial utilization of carbon (C) and nitrogen (N). We measured net C and N mineralization, and the δ13C of bulk organic matter, mineralized C, and bacterial fatty acids from soils of invaded and non-invaded C3 (Stipa hymenoides) and C4 (Hilaria jamesii) native grasslands. Carbon mineralization was greater in invaded compared to non-invaded sites (1.25 +/- 0.09 and 1.52 +/- 0.18 g CO2-C kg-1 soil h-1 respectively). Rates of net inorganic N mineralization...
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Although the variation in natural 15N abundance in plants and soils is well characterized, mechanisms controlling N isotopic composition of organic matter are still poorly understood. The primary goal of this study was to examine the role of NH3 volatilization from ungulate urine patches in determining 15N abundance in grassland plants and soil in Yellowstone National Park. We additionally used isotopic measurements to explore the pathways that plants in urine patches take up N. Plant, soil, and volatilized NH3d15N were measured on grassland plots for 10 days following the addition of simulated urine. Simulated urine increased 15N of roots and soil and reduced 15N of shoots. Soil enrichment was due to the volatilization...
Categories: Publication;
Types: Citation,
Journal Citation;
Tags: 15N,
Ammonia,
Biogeochemistry,
Grassland,
Herbivory, All tags...
Springer Netherlands,
Ungulate,
Volatilization,
Yellowstone National Park, Fewer tags
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Anthropogenic activity is causing dramatic changes in the nitrogen (N) cycle in many ecosystems. Most research has focused on the increase in N input caused by atmospheric deposition and invasion of N-fixing species, and on their effects on resource availability and species composition. However, in contrast to many ecosystems experiencing large increases in N input, many arid ecosystems are experiencing loss of nutrients due to land-use change. An important component of many arid ecosystems on a worldwide basis is the microbiotic crust, a biological soil crust composed of lichens, cyanobacteria, mosses, and algae. Nitrogen fixation by lichens and cyanobacteria comprising the crust is the primary source of N input...
Categories: Publication;
Types: Citation,
Journal Citation;
Tags: Canyonlands National Park,
Ecology,
Utah,
cryptogamic crusts,
land-use change, All tags...
microbiotic crusts,
microphytic crusts,
mineralization,
nitrification,
nitrogen,
stable isotopes, Fewer tags
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Microbiotic crusts are biological soil crusts composed of lichens, cyanobacteria, algae, mosses, and fungi. The biodiversity of these crusts is poorly understood; several cosmopolitan species dominate in most areas, but many species are confined to one or a few sites. Nitrogen fixation by organisms within the crust can be the dominant source of nitrogen input into many ecosystems, although rates of nitrogen input are limited by water availability, temperature, and nitrogen loss from the crust. Photosynthetic rates of the microbiotic crust can be 50% of those observed for higher plants, but the contribution of crusts to carbon cycling is not known. The microbiotic crust binds soil particles together, and this significantly...
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