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Increases in net primary production (NPP) may not necessarily result in increased C sequestration since an increase in uptake can be negated by concurrent increases in ecosystem C losses via respiratory processes. Continuous measurements of net ecosystem C exchange between the atmosphere and two experimental cheatgrass (Bromus tectorum L.) ecosystems in large dynamic flux chambers (EcoCELLs) showed net ecosystem C losses to the atmosphere in excess of 300 g C m?2 over two growing cycles. Even a doubling of net ecosystem production (NEP) after N fertilization in the second growing season did not compensate for soil C losses incurred during the fallow period. Fertilization not only increased C uptake in biomass but...
A large reservoir of bioavailable nitrogen (up to approximately 10(4) kilograms of nitrogen per hectare, as nitrate) has been previously overlooked in studies of global nitrogen distribution. The reservoir has been accumulating in subsoil zones of arid regions throughout the Holocene. Consideration of the subsoil reservoir raises estimates of vadose-zone nitrogen inventories by 14 to 71% for warm deserts and arid shrublands worldwide and by 3 to 16% globally. Subsoil nitrate accumulation indicates long-term leaching from desert soils, impelling further evaluation of nutrient dynamics in xeric ecosystems. Evidence that subsoil accumulations are readily mobilized raises concern about groundwater contamination after...
Categories: Publication; Types: Citation
Turgor maintenance, solute content and recovery from water stress were examined in the drought-tolerant shrub Artemisia tridentata. Predawn water potentials of shrubs receiving supplemental water remained above ?2 MPa throughout summer, while predawn water potentials of untreated shrubs decreased to ?5 MPa. Osmotic potentials decreased in conjunction with water potentials maintaining turgor pressures above 0 MPa. The decreases in osmotic potentials were not the result of osmotic adjustment (i.e. solute accumulation). Leaf solute contents decreased during drought, but leaf water volumes decreased more than 75% from spring to summer, thereby passively concentrating solutes within the leaves. The maintenance of positive...
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 ?13C 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...
Categories: Publication; Types: Citation; Tags: AGU Fall Meeting Abstracts
Global change caused by anthropogenic activities may significantly modify the abundance, structure, and function of biological soil crusts. The components of global change can be grouped into (1) those that impact discreet sites but are occurring on a global scale, such as land-use change and invasive species, and (2) those that alter atmospheric chemistry resulting in changes in CO2 concentration, UV radiation, temperature, and precipitation (Vitousek 1994). In this chapter we will examine how landuse change, invasive species, elevated atmospheric CO2, increased UV radiation, and climate change may affect biological soil crusts and the ecosystems which they inhabit. Published in Biological Soil Crusts: Structure,...
Bromus tectorum (cheatgrass), an alien annual grass, has become naturalized in a variety of habitats ranging from arid steppe to mesic forest communities within the intermountain region of western North America. To examine the contribution of genetic differentiation to the success of cheatgrass, we measured photosynthesis, growth, phenology and biomass allocation in populations collected as seed from contrasting habitats and grown in a glasshouse. In addition, we examined the effects of drought and population seed source on characteristics of photosynthesis and growth. In general, leaf-level photosynthetic response to variation in light, temperature and soil moisture did not vary significantly among the different...
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...
Whole-plant and leaf nitrogen isotope composition are determined by the isotope ratio of the external nitrogen source and physiological mechanisms within the plant. Whole-plant isotope composition can reflect that of the nitrogen source when plant demand exceeds nitrogen supply. Uptake by mycorrhizae can cause the isotope ratio of the plant to deviate from the source. Intra-plant variation in isotope composition can be caused by multiple assimilation events, organ-specific loss of nitrogen, and resorption and reallocation of nitrogen. Future work must address acquisition of organic nitrogen from the soil solution, the role of mycorrhizae, and internal transformations within the plant. Published in Trends in Plant...
Growth of vegetative and reproductive structures in Artemisia tridentata is temporally separated during the growing season; vegetative growth occurs during spring and early summer when soil moisture is most abundant, while reproductive growth occur during summer and fall when soil moisture may be limiting. Vegetative and reproductive structures may therefore exhibit contrasting efficiencies of resource acquisition and investment resulting from temporal differences in resource availability during their development. We examined the effect of water stress on growth, photosynthesis, and resource investment for vegetative and reproductive modules of Artemisia tridentata by applying supplemental water. No differences...
The introduction of nonnative plant species may decrease ecosystem stability by altering the availability of nitrogen (N) for plant growth. Invasive species can impact N availability by changing litter quantity and quality, rates of N2-fixation, or rates of N loss. We quantified the effects of invasion by the annual grass Bromus tectorum on N cycling in an arid grassland on the Colorado Plateau (USA). The invasion occurred in 1994 in two community types in an undisturbed grassland. This natural experiment allowed us to measure the immediate responses following invasion without the confounding effects of previous disturbance. Litter biomass and the C:N and lignin:N ratios were measured to determine the effects on...
Pressure-volume measurements were made on Artemisia tridentata Nutt. ssp. tridentata samples rehydrated for 0, 1.5, 3, 6 or 24 h. Increasing rehydration time caused a significant increase in osmotic potential at turgor loss, cell elasiticity, and the relative water content at turgor loss, and a significant decrease in pressure potential at saturation. Osmotic potential at saturation was changed significantly by rehydration, but no consistent trend was observed. The symplastic water fraction did not differ significantly among treatments. The increase in the osmotic potential at turgor loss did not correspond with decreasing cell elasticity or synthesis of solutes. Instead, the leaf solute content remained constant...
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Biological soil crusts, composed primarily of photosynthetic cyanobacteria, algae, lichens and mosses, play a key role in many ecosystem functions of semi-arid and arid ecosystems around the world (Belnap and Lange 2001). They often cover plant interspaces in undisturbed areas (Kleiner and Harper 1972) and thus can constitute 70% or more of the living ground cover (Belnap 1995). These soil crusts are critical in the stabilization of soils and reduce both wind and water erosion (Belnap and Gillette 1997, 1998). They influence many processes that determine soil fertility, including carbon and nitrogen fixation, dust capture, and mineral chelation. They are often the dominant source of nitrogen (N) in desert ecosystems...
Categories: Publication; Types: Citation
Many serious ecosystem consequences of climate change will take decades or even centuries to emerge. Long-term ecological responses to global change are strongly regulated by slow processes, such as changes in species composition, carbon dynamics in soil and by long-lived plants, and accumulation of nutrient capitals. Understanding and predicting these processes require experiments on decadal time scales. But decadal experiments by themselves may not be adequate because many of the slow processes have characteristic time scales much longer than experiments can be maintained. This article promotes a coordinated approach that combines long-term, large-scale global change experiments with process studies and modeling....
A large reservoir of bioavailable nitrogen (up to approximately 10(4) kilograms of nitrogen per hectare, as nitrate) has been previously overlooked in studies of global nitrogen distribution. The reservoir has been accumulating in subsoil zones of arid regions throughout the Holocene. Consideration of the subsoil reservoir raises estimates of vadose-zone nitrogen inventories by 14 to 71% for warm deserts and arid shrublands worldwide and by 3 to 16% globally. Subsoil nitrate accumulation indicates long-term leaching from desert soils, impelling further evaluation of nutrient dynamics in xeric ecosystems. Evidence that subsoil accumulations are readily mobilized raises concern about groundwater contamination after...
Categories: Publication; Types: Citation, Journal Citation; Tags: Science
A large reservoir of bioavailable nitrogen (up to approximately 10(4) kilograms of nitrogen per hectare, as nitrate) has been previously overlooked in studies of global nitrogen distribution. The reservoir has been accumulating in subsoil zones of arid regions throughout the Holocene. Consideration of the subsoil reservoir raises estimates of vadose-zone nitrogen inventories by 14 to 71% for warm deserts and arid shrublands worldwide and by 3 to 16% globally. Subsoil nitrate accumulation indicates long-term leaching from desert soils, impelling further evaluation of nutrient dynamics in xeric ecosystems. Evidence that subsoil accumulations are readily mobilized raises concern about groundwater contamination after...
Categories: Publication; Types: Citation
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...
    map background search result map search result map Nitrogen deposition and UV stressor impacts in Canyonlands National Park as affected by climatic pulse events Nitrogen deposition and UV stressor impacts in Canyonlands National Park as affected by climatic pulse events