Understanding and modeling microbial responses and feedbacks to climate change is hampered by a lack of a framework in the pelagic environment by which to link local mechanism to large scale patterns. Where terrestrial ecology draws from landscape theory and practice to address issues of scale, the pelagic seascape concept...
Fluctuations in one system affect adjacent systems; mechanistic understanding of linkages helps conservation efforts be more effective by focusing on influential species and areas that facilitate connections between ecosystems. This study explored marine-derived nutrient inputs to adjacent terrestrial communities. We quantified wrack (seaweed and other organic matter) deposition at sites...
Biological di-nitrogen (N₂) fixation is a key process in open-ocean ecosystems, where the new nitrogen (N) provided by marine diazotrophs can support a large fraction of primary productivity and carbon (C) drawdown. Recent laboratory studies have shown that elevated pCO₂ enhances the rate of N₂ fixation by select laboratory isolates...
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RicardoM. Letelier
Biological di-nitrogen (N2) fixation is a key process in open-ocean
The biological transformation of dinitrogen gas (N2) into combined forms(termed N2 fixation) by certain genera of oceanic cyanobacteria represents the largest incoming flux of nitrogen to the global ocean. As such, biological nitrogen fixation
plays a significant role in the regulation of oceanic productivity and the export of
carbon and...
The North Pacific subtropical gyre (NPSG), once considered to be a biological desert due to low primary production (PP) and its associated variability, has been found more productive and variable than previously thought. The environmental conditions controlling this relatively high PP variability are yet to be elucidated, despite important implications...
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Mark R. Abbott, RicardoM. Letelier
The North Pacific subtropical gyre (NPSG), once
Our view of phytoplankton has historically revolved around their inability to
control their location in space. The term phytoplankton itself underscores this
particular difference between phytoplankton and their sessile terrestrial counterparts.
Yet there are other differences between land plants and the phytoplankton that are
perhaps equally important, beyond this sessile-planktonic...
Under conditions of fixed N-limitation, as with most oligotrophic systems, the process of biological N₂ fixation (diazotrophy) is favored, provided the necessary trace elements and vitamins are sufficient. Despite the well understood contributions of N₂
fixation in oligotrophic regions, the nutritional and ecological controls of marine diazotrophs have not been...
In ecological restoration, species that are sown to increase the native plant
diversity range in establishment ability. Some species readily establish, while others
rarely do. This study set out to investigate some of the potential processes influencing
species establishment, as well as the traits that are associated with the success...
Deep mixing events in the ocean’s surface layer act as physical drivers of carbon export by detraining dissolved and particulate organic matter, including surface phytoplankton communities, to depth. Once removed from the sunlit surface ocean environment, phytoplankton accumulation rates are dependent on the relative contributions of loss processes, such as...
We present a new nitrogen isotope model incorporated into the three-dimensional ocean component of a global Earth System Climate Model designed for millennial timescale simulations. The model includes prognostic tracers for the stable nitrogen isotopes, ¹⁴N and ¹⁵N, in the nitrate (NO₃ˉ), phytoplankton, zooplankton, and detritus variables of the marine...
Iron (Fe) is an important limiting nutrient that can affect the rate of ocean primary production because it is required by phytoplankton as an enzymatic cofactor in photosynthesis, nitrogen fixation, and other essential metabolic functions. Most Fe reaches the surface of the open ocean via atmospheric dust deposition, which is...
The concentrations of filamentous diazotroph Trichodesmium spp., present as free trichomes and in colonial assemblages, were measured at approximately monthly intervals at Stn ALOHA (22°45'N, 158°00'W) between October 1989 and December 1992. The average abundance of filaments in the upper 45 m of the water column was highly variable ranging...
The potential role of the diazotrophic cyanobacterium Trichodesmium spp. In nitrogen and phosphorus dynamics of the euphotic zone of the North Pacific subtropical gyre was investigated as one component of the Hawaii Ocean Time-series (HOT) program. Experiments were conducted with natural samples collected at Stn ALOHA (22° 45’ N, 158°...
The euphotic zone below the deep chlorophyll maximum layer (DCML) at Station ALOHA (a long-term oligotrophic habitat assessment; 22º45′N, 158º00′W) transects the nearly permanently stratified upper thermocline. Hence, seasonal changes in solar radiation control the balance between photosynthesis and respiration in this lightlimited region. Combining profiles of radiance reflectance, algal...
Based on a long-term set of observations and measurements at a station in the subtropical North Pacific Ocean, it now appears that contemporaneous rates of primary production in low-nutrient open ocean regions and perhaps in the ocean as a whole may be greater than had been considered in field studies...
Summertime wind stress along the coast of the northwestern United States typically exhibits intraseasonal oscillations (ISOs) with periods from ≈15 to 40 days, as well as fluctuations on the 2- to 6-day “weather-band” and 1-day diurnal time scales. Coastal upwelling of cool, nutrient-rich water is driven by extended periods of...
Variability of solar-induced (natural) fluorescence and chlorophyll were measured on scales of hours to weeks in the upper layer of a cyclonic eddy located south of the Antarctic Polar Front using a free-floating drifter. The fluorescence signal was analyzed both in terms of chlorophyll concentration and as an indicator of...
Ocean Acidification (OA) has emerged as a major threat to marine ecosystems, particularly regarding calcifying organisms. A growing body of literature describing laboratory investigations into pH stress indicates broadly deleterious effects for calcifiers, but responses vary greatly across taxa and can be influenced by variations in other environmental characteristics. Scaling...
Secondary metabolites (SMs) play an integral role in the life history of most fungal species. Fungal metabolomic studies provide insights into how fungi perform certain ecological functions, how they compete and interact with other organisms, and the breadth of fungal chemodiversity. Fungal SMs have also been utilized for a variety...
The Fukushima Daiichi nuclear disaster of 2011 made it apparent that releases of fission products to marine environments is a very real possibility. Additional data on the movement of material through marine environments can be used by radioecology personnel to assist with both ecosystem protection as well as environmental cleanup...
Photosynthetic energy allocation strategies were investigated in the marine diatom, Thalassiosira pseudonana, grown under a wide range of light limitation. Steady-state, continuous cultures were established at three light-limited growth rates. Simultaneous measurements of photosynthetic activity were made that targeted different points in photosynthetic energy flow from gross to net photosynthesis....
Few studies have examined the partitioning of organic matter in upwelling systems,
despite the fact that these systems play a key role in carbon and nitrogen budgets in the
ocean. We examined the production and partitioning of phytoplankton-derived organic
matter in deck incubations off Oregon during the upwelling season. During...
We report the development of a numerical model simulating vertical movement of the
cyanobacterium Trichodesmium spp. Given a range of physiological parameters derived from the literature,
resultant model solutions allow us to explore the ecological significance of vertical migration
by Trichodesmium colonies in a stratified oligotrophic oceanic system such as...
The eastern South Pacific (ESP) oxygen minimum zone (OMZ) is a permanent hydrographic feature located directly off the coasts of northern Chile and Peru. The ESP OMZ reaches from coastal waters out to thousands of kilometers offshore, and can extend from the near surface to depths greater than 700 m....
We examined variability in the natural fluorescence yield of a neritic diatom, Thalassiosira weissflogii, in continuous cultures. In this species, kinetics in natural fluorescence yield over time scales less than a photoperiod were characterized by sharp decreases, occurring at irradiance intensities that presumably coincide with the onset of nonphotochemical fluorescence...
We investigated the effects of elevated pCO₂ on cultures of the unicellular N₂-fixing cyanobacterium Crocosphaera watsonii
WH8501. Using CO₂-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions
approximating current atmospheric CO₂ concentrations (~400 ppm) as well as CO₂ levels corresponding to low- and...
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*, Angelicque E. White, RicardoM. Letelier
Oregon State University, College of Earth, Ocean, and Atmospheric
A model to estimate chlorophyll-a concentration and yellow substance absorption at 440 nm from irradiance measurements made at varying depths is examined. The derivation of the model, requiring irradiance measurements at three wavebands, is presented and tested on data collected in oligotrophic (with low chlorophyll concentrations) waters and in coastal...
We report significant rates of dinitrogen (N₂) fixation in the central basins of the Gulf
of California (GC) during July–August 2005. Mixing model estimates based upon
δ¹⁵N values of particulate matter in the surface mixed layer indicate that N₂ fixation
provides as much as 35% to 48% of the phytoplankton-based...
We conducted laboratory experiments to assess the bioelemental plasticity of cultures of Trichodesmium
IMS101 under phosphorus (P)-replete, P-restricted, and light-limited conditions. The results reveal a high degree
of stoichiometric flexibility. Specifically, Trichodesmium IMS101 is capable of growth with carbon (C) : nitrogen
(N) : P ratios of C₅₈₅±₅₆ : N₉₀±₁₀...
We constructed an experimental apparatus that used lasers to provide the probe beams for measuring the transient absorption kinetics of bacterioplankton that contain proteorhodopsin, a microbial protein that binds retinal and is analogous to animal rhodopsin. With this approach we were able to observe photocycles characteristic of functioning retinylidene ion...
Despite the importance of the spring phytoplankton bloom off Oregon as a food source for zooplankton, little is known about the sources of phytoplankton seed stock for the bloom or its timing. Experiments were conducted in the late winter to determine if the benthic boundary layer (BBL) could be a...
We investigated the effects of elevated pCO₂ on cultures of the unicellular N₂-fixing cyanobacterium Crocosphaera watsonii
WH8501. Using CO₂-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions
approximating current atmospheric CO₂ concentrations (~400 ppm) as well as CO₂ levels corresponding to low- and...
We investigated the effects of elevated pCO₂ on cultures of the unicellular N₂-fixing cyanobacterium Crocosphaera watsonii
WH8501. Using CO₂-enriched air, cultures grown in batch mode under high light intensity were exposed to initial conditions
approximating current atmospheric CO₂ concentrations (~400 ppm) as well as CO₂ levels corresponding to low- and...
The grand plan of carbon neutralization and COP26 in Glasgow require a quick shift of energy sources from conventional fossil fuel to a more renewable substitute such as wind, or solar energy. However, the intermittency of those renewable energy sources does not meet the demand of the energy, which requires...
Oceanic crust covers nearly 70% of the Earth's surface, of which, the upper,
sediment layer is estimated to harbor substantial microbial biomass. Marine crust;
however, extends several kilometers beyond this surficial layer, and includes the
basalt and gabbro layers. In particular, the basalt layer has high permeabilities which
allows for...
The demand for the development of sustainable energy is an all time high as we burn through limited fossil fuel reserves and as environmental concerns rise every year. Renewable energy sources such as wind and solar power have limitations due to inconsistent power supply that cannot meet the regular needs...
In this dissertation, I present the results from three studies: (1) a phylogeny of Tenebrionoidea (Coleoptera) inferred from a seven-gene dataset derived from PCR and Sanger sequencing; (2) a phylogeny of Tenebrionidae, the largest family in Tenebrionoidea, inferred from a four-gene dataset also derived from PCR and Sanger sequencing; (3)...
Sustained time series have provided compelling evidence for progressive acidification of the
surface oceans through exchange with the growing atmospheric reservoir of carbon dioxide. However,
few long-term programs exist, and extrapolation of results from one site to larger oceanic expanses is
hampered by the lack of spatial coverage inherent to...
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., Church, M. J., Karl, D. M., Sadler, D. W., & Letelier, R. M. (2014).
Paired windward and leeward
We examined short-term (24–72 h) responses of naturally occurringmarine N2 fixing microorganisms (termed diazotrophs) to abrupt increases in the partial pressure of carbon dioxide (pCO2) in seawater during nine incubation experiments conducted between May 2010 and September 2012 at Station ALOHA (A Long-term Oligotrophic Habitat Assessment) (22°45′N, 158°W) in the...
Sustained time series have provided compelling evidence for progressive acidification of the
surface oceans through exchange with the growing atmospheric reservoir of carbon dioxide. However,
few long-term programs exist, and extrapolation of results from one site to larger oceanic expanses is
hampered by the lack of spatial coverage inherent to...
Sustained time series have provided compelling evidence for progressive acidification of the surface oceans through exchange with the growing atmospheric reservoir of carbon dioxide. However, few long-term programs exist, and extrapolation of results from one site to larger oceanic expanses is hampered by the lack of spatial coverage inherent to...
We conducted 11 independent short-term carbon dioxide (CO₂) manipulation experiments using colonies of
the filamentous cyanobacteria Trichodesmium isolated on three cruises in the North Pacific Subtropical Gyre
(NPSG). Dinitrogen (N₂) and carbon (C) fixation rates of these colonies were compared over CO₂ conditions
ranging from ~ 18 Pa (equivalent to...
In situ optical measurements of spectral absorption and beam attenuation provide information on the fine scale horizontal and vertical variations in phytoplankton pigments and other measures of phytoplankton photophysiology and ecology in coastal waters. Phytoplankton pigment ratios from discrete sample analyses with High Performance Liquid Chromatography were compared to in...
Mycobacterium avium subspecies paratuberculosis (MAP) is the causative agent of Johne's disease, a chronic inflammatory bowel disease that affects ruminant populations worldwide. The characteristic stages of the disease make diagnosis difficult, resulting in silent transmission among animals in a herd for years before proper detection of the infection. The extensive...
Ecosystems are facing increasing threats from human related activities, such as overfishing, pollution, habitat destruction, species invasions, and diseases, among others. While oceanic islands provide natural laboratories to understand ecological and evolutionary process, they are also particularly vulnerable to these impacts, given their usual isolation from the mainland and the...
Microscopic organisms inhabit virtually every niche on this planet, where they perform functions vital to all life on earth. Accordingly, humans host a complex community of microorganisms (i.e. the gut microbiome) that inhabit the gastrointestinal tract and modulate host physiology. Insight into the specific mechanisms through which gut microbes influence...
The Southern Ocean plays an important role in the ocean’s uptake of heat and carbon yet the processes controlling this uptake are not well understood. To date, more than 100 biogeochemical profiling floats that measure water column pH, oxygen, nitrate, fluorescence, and backscattering at 10-day intervals have been deployed throughout...
Modern upwelling conditions and corresponding oceanographic properties are investigated and reconstructed for the Late Quaternary. The oceanographic conditions considered influence diatom ecology and the record of fossil diatom frustules in the sediments.
Diatoms from modern sediments are evaluated as paleoceanographic proxies and transfer functions (TFs) are calibrated using the Imbrie...
Marine bacterioplankton play an important role in global elemental cycles because they return carbon dioxide and nutrients to the biosphere as they reduce organic matter. Furthermore, marine bacterioplankton are not uniformly active, and subpopulations of the in situ community may be more or less active at any given time. Defining...
The influence of mesoscale ocean eddies on near-surface ocean temperature, surface stress and phytoplankton communities is investigated by collocating numerous satellite measurements along with vertical profiles of oceanic temperature and salinity to the interiors of eddies identified and tracked in altimetric sea surface height maps.
The surface currents associated with...
Plant-parasitic nematodes cause more than US $100 billion in annual agriculture loss worldwide. Thorough knowledge of their genetic diversity, and interactions with endosymbionts and environment have the potential to provide valuable insights into the basic biology of these animals, and assist future efforts aimed at management of these plant parasites....
Algal chlorophyll and carotenoid distributions were measured periodically in the euphotic zone of Sta. ALOHA (22º45′N, 158º00′W) between February 1989 and October 1991 to document the variability in phytoplankton abundance and composition. The annual mean depth-integrated (O-200 db) concentration of Chl a displayed significant interannual variability. Seasonal patterns in Chl...
Previous observations of light levels and phytoplankton abundances along the Oregon coast demonstrated that phytoplankton attenuated light sufficiently to potentially limit the growth of intertidal macrophytes and therefore structure local intertidal communities. Inspired by this observation, in spring 2004, I initiated a study to quantify the direct and indirect benthic...
Experiments were designed to answer key questions about diatom-derived organic matter cycling (i.e., production and degradation) in coastal systems. Dissolved organic matter (DOM) production was examined in axenic batch cultures of five diatom species. Dissolved organic carbon (DOC) release rates varied between species, but were significantly higher for all species...
Marine bacteria play vital roles in every niche of the ocean, from small-scale symbioses to large-scale productivity and the regulation of Earth’s climate. Recent advances in molecular tools now allow us to probe the genetic potential of entire microbial communities. The next step is linking these diverse communities to the...
Desert plant communities are among the most sensitive to changes in soil water conditions. In areas with shallow aquifers, it is important to understand both the effects of groundwater alterations on vegetation and how changes in surface-soil water affect plant water uptake. Studies in arid environments have evaluated the effect...
The apparent dissociation constants of carbonic acid were
determined as functions of temperature and salinity in seawater
at atmospheric pressure.
There is fair agreement between my values of K'₁ and those
of Buch et al. (1932), Lyman (1956), and Hansson (1971). My values,
on the average, are 6.7% lower than...
The particle size distribution (PSD) is a critical aspect of the oceanic ecosystem. Local variability in the PSD can be indicative of shifts in microbial community structure and reveal patterns in cell growth and loss. The PSD also plays a central role in particle export by influencing settling speed. Satellite-based...
During the summer of 2012, we used laser diffractometry to investigate the temporal and vertical variability of the particle size spectrum (1.25–100 µm in equivalent diameter) in the euphotic zone of the North Pacific Subtropical Gyre. Particles measured with this optical method accounted for ∼40% of the particulate carbon stocks...
Measurements at the Hawaii Ocean Time-series (HOT) Station ALOHA (22 degrees 45'N, 158 degrees W) have revealed a significant, approximately 50% increase in euphotic zone depth-integrated rates of primary production ( PP; mol C fixed m(-2) d(-1)) based on in situ C-14 experiments. The character of the nearly two-decade increasing...
Continuous records of upper water column (0–150 m) temperature profiles, spectral distribution of downwelling irradiance, and phytoplankton solar-induced fluorescence at 25 m depth were obtained during the inaugural deployment of the Hawaii Air-sea Logging Experiment, A Long-term Oligotrophic Habitat Assessment (HALE ALOHA) mooring, near the Hawaii Ocean Time-series (HOT) Station...
The subarctic-subtropical transition zone in the North Pacific represents the second largest sink of
atmospheric carbon dioxide in the world ocean, yet the relative importance of physical and biological processes in
this uptake is debated. In a step toward understanding the spatiotemporal variability of environmental,
physiological, and ecological factors that...
Time-series observations are critical to understand the structure, function, and dynamics of marine ecosystems. The Hawaii Ocean Time-series program has maintained near-monthly sampling at Station ALOHA (22°45′N, 158°00′W) in the oligotrophic North Pacific Subtropical Gyre (NPSG) since 1988 and has identified ecosystem variability over seasonal to interannual timescales. To further...
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Ferrón1,2, Jessica N. Fitzsimmons1,6, LaurieW. Juranek7,
Zbigniew S. Kolber1,8, RicardoM. Letelier1,7
Time-series observations are critical to understand the structure, function, and dynamics of marine ecosystems. The Hawaii Ocean Time-series program has maintained near-monthly sampling at Station ALOHA (22°45′N, 158°00′W) in the oligotrophic North Pacific Subtropical Gyre (NPSG) since 1988 and has identified ecosystem variability over seasonal to interannual timescales. To further...
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. Kolber8, RicardoM. Letelier7, Sandra
Martínez-Garcia1,2, David P. Nicholson9, Kelvin J. Richards1
The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra spacecraft contains spectral bands that allow retrieval of solar-induced phytoplankton chlorophyll fluorescence emission radiance. Concurrent airborne laser-induced (and water-Raman normalized) phytoplankton chlorophyll fluorescence data is used to successfully validate the MODIS chlorophyll fluorescence line height (FLH) retrievals within Gulf Stream, continental...
We present a spatially extensive record of dinitrogen (N₂) fixation rates and distributions
of N₂ fixing microorganisms along with the results of exogenous phosphorus (P) addition experiments
conducted during a series of cruises in the North Pacific Subtropical Gyre (NPSG). We measured the
N₂ and carbon (C) fixation rates of...
The sagebrush steppe ecosystem of the Columbia Plateau has become degraded by a long history of alternative land use and associated perturbations. Protection of remnant stands of intact sagebrush steppe currently relies upon their preservation within the nation's network of parks and protected-areas. The John Day Fossil Beds National Monument,...
In 1976, John D. Isaacs proposed to use wave energy to invert the density structure of the ocean and pump deep, nutrient-rich water into the sunlit surface layers. The basic principle is simple: a length of tubing attached to a surface buoy at the top, and a one-way valve at...
The historical function of fire in sagebrush steppe has been altered by 19th century overgrazing, active fire suppression, annual grass invasion and encroachment of woody species. The significance of fire to these systems is known, but research on long-term fire effects are limited. The Sheep Rock management unit of the...
Continental margin carbon cycling is complex, highly variable over a range of space and time scales, and forced by multiple physical and biogeochemical drivers. Predictions of globally significant air–sea CO₂ fluxes in these regions have been extrapolated based on very sparse data sets. We present here a method for predicting...
Nitrate concentrations, chlorophyll a (Chl a) fluorescence, radiance, salinity, and
temperature were measured on the Hawaii Air-Sea Logging Experiment, A Long-Term
Oligotrophic Habitat Assessment (HALE ALOHA) mooring located near the Hawaii
Ocean Time-Series (HOT) Program’s Station ALOHA (22°45’N; 158°W). Nitrate
concentrations were determined with OsmoAnalyzers deployed at depths of 120...
Pseudomonas aeruginosa is a ubiquitous environmental microbe, opportunistic pathogen, and a highly social organism. P. aeruginosa utilizes a wide array of cooperative behaviors to adapt to the environmental conditions around it. These behaviors include quorum sensing (QS), a form a cell-to-cell signaling that coordinates the expression of secreted products in...
A carefully calibrated primitive-equation model from 41°N to 48°N is used to study the poleward undercurrent off the US west coast. Chapter 2 describes poleward flow over the slope from Eulerian and Lagrangian perspectives. The model is robust, in the sense of several characteristics being qualitatively consistent with observational and...
Guatemala is internationally recognized as a country suitable to invest in the forestry industry. The first Guatemalan Forest Incentive Program – PINFOR- was implemented in 1996 to foster local forestry through cost-sharing. However, it lacks both formal land use planning processes and mechanisms to assess economic potential of projects, so...
Satellite-derived data provide the temporal means and seasonal and nonseasonal
variability of four physical and biological parameters off Oregon and Washington
(41°–48.5°N). Eight years of data (1998–2005) are available for surface chlorophyll
concentrations, sea surface temperature (SST), and sea surface height, while six years of
data (2000–2005) are available for...
This study evaluated biomass production, water-use efficiency (WUE), biomass allocation, and water use characteristics of common plant species in Owens Valley, California, USA. The species studied were the grasses Distichlis spicata, Leymus triticoides, and Sporobolus airoides, the forbs Glycyrrhiza lepidota, Juncus arcticus, and Salsola tragus (annual), the desert shrubs Artemisia...
During austral summer 1997, satellite imagery revealed enhanced chlorophyll associated with the Antarctic Polar Front at 170°W. Phytoplankton growth conditions during the early stages of the spring increase were investigated on the Antarctic Environment and Southern Ocean Process Study Survey I cruise using flow cytometry (FCM) and microscopy to characterize...
Arbuscular mycorrhizal fungi (AMF) are plant symbionts that associate with the vast majority of terrestrial plants species. The AMF colonizes the plant roots by penetrating the root cortical cells, where the fungi exchanges mineral nutrients with the host plant for photosynthates. This association exists as a complex system in which...
We present a new nitrogen isotope model incorporated into the three-dimensional ocean component of a global Earth system climate model designed for millennial timescale simulations. The model includes prognostic tracers for the two stable nitrogen isotopes, 14N and 15N, in the nitrate (NO3−), phytoplankton, zooplankton, and detritus variables of the...
Western juniper (Juniperus occidentalis) encroachment has been associated with negative ecological and hydrological consequences including reductions in herbaceous production and diversity, deterioration for wildlife habitat, and higher erosion and runoff potentials. As a result, western juniper removal is a common and accepted rangeland management practice. Although studies evaluating the ecological...
Wetland degradation has negative influences on wetland functions and services. The understanding of wetland functions requires the intersection of two science disciplines, ecohydrology and plant physiology for a correct approach on wetland restoration and management. Although studies assessing ecohydrological relationships to protect wetlands are relatively common, studies evaluating both ecohydrological...
The local and remote sources of variability of the South Atlantic Ocean are investigated using a set of numerical experiments and satellite data. A global, eddy-permitting, numerical simulation is analyzed to investigate the dynamical links between the Antarctic Circumpolar Current (ACC) and the Malvinas Current (MC). The model results indicate...
Arbuscular mycorrhizal fungi (AMF) may exert profound influences on ecosystem resilience and invasion resistance in western North American sagebrush steppe and other arid rangeland plant communities. Maintenance of plant community structure through ecological feedbacks such as facilitation of nutrient cycling and uptake by host plants, physical and chemical contributions to...
Quaking aspen, Populus tremuloides, has experienced severe declines in recent years in part due to the effects of changing climate and extreme drought. As the dominant deciduous tree in Western North American forests, aspen plays a critical role in forest biodiversity and ecosystem function. Therefore, the persistence of this species...
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Ricardo Mata-Gonzalez
Quaking aspen, Populus tremuloides, has experienced severe declines
Within the sagebrush steppe ecosystem, invasive annual grasses are of growing management concern as they outcompete native vegetation, change the fundamental nutrient cycling processes, decrease biodiversity, and increase frequency of wildfires. The most widely used and effective management tool to decrease invasive annual grass abundance, is the use of pre-emergent...
Analytical and numerical models are used to study the effects of a meridional ridge on the propagation of barotropic Rossby waves produced by distant wind stress forcing. The analytical model illustrates the qualitative aspects of the problem by solving a simplified form of the potential vorticity equation. The analytical results...
After three decades of active research coupling hydrology and stream ecology, the connection among solute transport, metabolism and processing is still unresolved. These knowledge gaps obscure the functioning of stream ecosystems and how those ecosystems interact with other landscape processes. We must resolve these challenges to wisely manage water resources,...
In recent years, our ecological knowledge of tropical dry forests has increased dramatically. However, whole components of the ecosystem, like lichenized fungi, remain mostly unknown. Crustose lichens in these forests are so abundant, that they are responsible for the characteristic appearance of a “white bark forest” during the dry season....
Modifications of an ocean model are described, as the objective for which the model was used changed to study the kinematics and dynamics of an eastern-boundary poleward undercurrent.
5'-Deoxy-5'-methylthioadenosine phosphorylase catalyzes
the phosphorolytic cleavage of 5'-deoxy-5'-methylthioadenosine
to form 5'-deoxy-5'-methylthioribose-1-phosphate and
adenine in mammalian cells and plays an important role in
methionine and purine salvage. The enzyme is abundant in
normal tissues and in cell lines derived from normal cells.
However, several malignant tissues and cell lines have been...