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The invasion of woody vegetation into deserts, grasslands and savannas is generally thought to lead to an increase in the amount of carbon stored in those ecosystems. For this reason, shrub and forest expansion (for example, into grasslands) is also suggested to be a substantial, if uncertain, component of the terrestrial carbon sink. Here we investigate woody plant invasion along a precipitation gradient (200 to 1,100 mm yr(-1)) by comparing carbon and nitrogen budgets and soil delta(13)C profiles between six pairs of adjacent grasslands, in which one of each pair was invaded by woody species 30 to 100 years ago. We found a clear negative relationship between precipitation and changes in soil organic carbon and...
Using interviews and participant observation at Pacific Northwest sustainable farming operations, this article analyzes the complex ways that class privileges and labor practices impact the social sustainability of sustainable agriculture. While the farmers in this study were highly aware of and reflexive about the class politics of sustainable agriculture, they also participated in a classed system that restricts access to sustainable farming as an occupation even as it exploits the labor of the farmer in order to regulate prices. In particular, the farmers in the study benefited from educational privileges and oftenlucrative off-farm income, they expressed a desire to make their goods more accessible and affordable...
Soils contain the largest near-surface reservoir of terrestrial carbon and so knowledge of the factors controlling soil carbon storage and turnover is essential for understanding the changing global carbon cycle. The influence of climate on decomposition of soil carbon has been well documented, but there remains considerable uncertainty in the potential response of soil carbon dynamics to the rapid global increase in reactive nitrogen (coming largely from agricultural fertilizers and fossil fuel combustion). Here, using 14C, 13C and compound-specific analyses of soil carbon from long-term nitrogen fertilization plots, we show that nitrogen additions significantly accelerate decomposition of light soil carbon fractions...
Plant species that colonize new environments tend to favour habitats with ample water and nutrients. But invasive plants can be more efficient in their use of resources than that observation might imply. Published in Nature, volume 446, on pages 985 - 986, in 2007.
The main concept currently in use in wind energy involves horizontal-axis wind turbines with blades of fiber composite materials. This turbine concept is expected to remain as the major provider of wind power in the foreseeable future. However, turbine sizes are increasing, and installation offshore means that wind turbines will be exposed to more demanding environmental conditions. Many challenges are posed by the use of fiber composites in increasingly large blades and increasingly hostile environments. Among these are achieving adequate stiffness to prevent excessive blade deflection, preventing buckling failure, ensuring adequate fatigue life under variable wind loading combined with gravitational loading, and...
There is now ample evidence of the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems and organizational hierarchies, from the species to the community levels. Despite continued uncertainty as to community and ecosystem trajectories under global change, our review exposes a coherent pattern of ecological change across systems. Although we are only at an early stage in the projected trends of global warming, ecological responses to recent climate change are already clearly visible. Published in Nature, volume 416, issue 6879, on pages 389 - 395, in 2002.
One of the most striking examples of self-organization in landscapes is the emergence of evenly spaced ridges and valleys. Despite the prevalence of uniform valley spacing, no theory has been shown to predict this fundamental topographic wavelength. Models of long-term landscape evolution can produce landforms that look realistic, but few metrics exist to assess the similarity between models and natural landscapes. Here we show that the ridge?valley wavelength can be predicted from erosional mechanics. From equations of mass conservation and sediment transport, we derive a characteristic length scale at which the timescales for erosion by diffusive soil creep and advective stream incision are equal. This length...
Categories: Publication;
Types: Citation,
Journal Citation;
Tags: Macmillan Publishers Limited. All rights reserved,
Nature
Most plants are known as C3 plants because the first product of photosynthetic CO2 fixation is a three-carbon compound. C4 plants, which use an alternative pathway in which the first product is a four-carbon compound, have evolved independently many times and are found in at least 18 families. In addition to differences in their biochemistry, photosynthetic organs of C4 plants show alterations in their anatomy and ultrastructure. Little is known about whether the biochemical or anatomical characteristics of C4 photosynthesis evolved first. Here we report that tobacco, a typical C3 plant, shows characteristics of C4 photosynthesis in cells of stems and petioles that surround the xylem and phloem, and that these cells...
Understanding energy and material fluxes through ecosystems is central to many questions in global change biology and ecology. Ecosystem respiration is a critical component of the carbon cycle and might be important in regulating biosphere response to global climate change. Here we derive a general model of ecosystem respiration based on the kinetics of metabolic reactions and the scaling of resource use by individual organisms. The model predicts that fluxes of CO2 and energy are invariant of ecosystem biomass, but are strongly influenced by temperature, variation in cellular metabolism and rates of supply of limiting resources (water and/or nutrients). Variation in ecosystem respiration within sites, as calculated...
Bats (Chiroptera) represent one of the largest and most diverse radiations of mammals, accounting for one-fifth of extant species. Although recent studies unambiguously support bat monophyly and consensus is rapidly emerging about evolutionary relationships among extant lineages, the fossil record of bats extends over 50 million years, and early evolution of the group remains poorly understood. Here we describe a new bat from the Early Eocene Green River Formation of Wyoming, USA, with features that are more primitive than seen in any previously known bat. The evolutionary pathways that led to flapping flight and echolocation in bats have been in dispute, and until now fossils have been of limited use in documenting...
Categories: Publication;
Types: Citation,
Journal Citation;
Tags: Nature,
Nature Publishing Group,
Wyoming,
animal physiology,
chiroptera,
Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.
This research examines in detail the technology and economics of substituting biodiesel for diesel #2. This endeavor examines three areas. First, the benefits of biodiesel are examined, and the technical problems of large-scale implementation. Second, the biodiesel production possibilities are examined for soybean oil, corn oil, tallow, and yellow grease, which are the largest sources of feedstocks for the United States. Examining in detail the production possibilities allows to identity the extent of technological change, production costs, byproducts, and greenhouse gas (GHG) emissions. Finally, a U.S. agricultural model, FASOMGHG was used to predict market penetration of biodiesel, given technological progress,...
Coal is a critical component in the international energy portfolio, used extensively for electricity generation. Coal is also readily converted to liquid fuels and/or hydrogen for the transportation industry. However, energy extracted from coal comes at a large environmental price: coal combustion can produce large quantities of ash and CO2, as well as other pollutants. Advanced technologies can increase the efficiencies and decrease the emissions associated with burning coal and provide an opportunity for CO2 capture and sequestration. However, these advanced technologies increase the severity of plant operating conditions and thus require improved materials that can stand up to the harsh operating environments....
The main concept currently in use in wind energy involves horizontal-axis wind turbines with blades of fiber composite materials. This turbine concept is expected to remain as the major provider of wind power in the foreseeable future. However, turbine sizes are increasing, and installation offshore means that wind turbines will be exposed to more demanding environmental conditions. Many challenges are posed by the use of fiber composites in increasingly large blades and increasingly hostile environments. Among these are achieving adequate stiffness to prevent excessive blade deflection, preventing buckling failure, ensuring adequate fatigue life under variable wind loading combined with gravitational loading, and...
Cyanobacteria develop as large, cryptic populations in the topsoil of arid land, where plant cover is restricted, water is scarce and harsh microenvironmental conditions prevail. Here we show that some cyanobacteria can actively move in response to wetting or drying events by migrating to the soil surface or retreating to their refuge below. This ability to follow water, which to our knowledge has not been demonstrated before in microbes, may turn out to be important for microbial terrestrial populations in general. Published in Nature, volume 413, issue 6854, on pages 380 - 1, in 2001.
Categories: Publication;
Types: Citation,
Journal Citation;
Tags: Cyanobacteria,
Cyanobacteria: physiology,
Nature,
Soil,
Soil Microbiology,
Renewable Energy Technologies (RETs) are often recognized as less competitive than traditional electric energy conversion systems. Obstacles with renewable electric energy conversion systems are often referred to the intermittency of the energy sources [1] and the relatively high maintenance cost. However, due to an intensified discourse on climate change and its effects, it has from a societal point of view, become more desirable to adopt and install CO2 neutral power plants. Even if this has increased the competitiveness of RETs in a political sense, the new goals for RET installations must also be met with economical viability. We propose that the direction of technical development, as well as the chosen technology...
The concentration of carbon dioxide (CO2) in the Earth's atmosphere is rising rapidly1, with the potential to alter many ecosystem processes. Elevated CO2 often stimulates photosynthesis2, creating the possibility that the terrestrial biosphere will sequester carbon in response to rising atmospheric CO2 concentration, partly offsetting emissions from fossil-fuel combustion, cement manufacture, and deforestation3,4. However, the responses of intact ecosystems to elevated CO2 concentration, particularly the below-ground responses, are not well understood. Here we present an annual budget focusing on below-ground carbon cycling for two grassland ecosystems exposed to elevated CO2 concentrations. Three years of experimental...
Shallow groundwater, the primary water source in the Bengal Basin, contains up to 100 times the World Health Organization (WHO) drinking-water guideline of 10 μg l−1 arsenic (As), threatening the health of 70 million people. Groundwater from a depth greater than 150 m, which almost uniformly meets the WHO guideline, has become the preferred alternative source. The vulnerability of deep wells to contamination by As is governed by the geometry of induced groundwater flow paths and the geochemical conditions encountered between the shallow and deep regions of the aquifer. Stratification of flow separates deep groundwater from shallow sources of As in some areas. Oxidized sediments also protect deep groundwater through...
Hydrates in nature have been known for a long time. In the last couple of decades the possibility of commercial utilization of natural hydrates has arisen as an alternative energy source. This paper asks 21 questions that, in the author’s opinion, need to be addressed and answered correctly before one can be confident one understands the scope of the problem one is facing in attempting to address the role of natural hydrates, both commercially and geologically.
No species can maximize growth, reproduction and competitive ability across all environments, so the success of invasive species is habitat-dependent. Nutrient-rich habitats often experience more invasion than resource-poor habitats, a pattern consistent with traits generally associated with successful invaders (high growth rates, early reproduction and many offspring). However, invaders do colonize resource-poor environments, and the mechanisms that allow their success in these systems are poorly understood. Traits associated with resource conservation are widespread among species adapted to resource-poor environments, and invasive species may succeed in low-resource environments by employing resource conservation...
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