Seasonal microbial and nutrient responses during a 5-year reduction in the daily temperature range of soil in a Chihuahuan Desert ecosystem.

High daily temperature range of soil (DTRsoil) negatively affects soil microbial biomass and activity, but its interaction with seasonal soil moisture in regulating ecosystem function remains unclear. For our 5-year field study in the Chihuahuan Desert, we suspended shade cloth 15 cm above the soil surface to reduce daytime temperature and increase nighttime soil temperature compared to unshaded plots, thereby reducing DTRsoil (by 5 ºC at 0.2 cm depth) without altering mean temperatures.

Soil microbial and nutrient responses to 7 years of seasonally altered precipitation in a Chihuahuan Desert grassland.

Soil microbial communities in Chihuahuan Desert grasslands generally experience highly variable spatiotemporal rainfall patterns. Changes in precipitation regimes can affect belowground ecosystem processes such as decomposition and nutrient cycling by altering soil microbial community structure and function. The objective of this study was to determine if increased seasonal precipitation frequency and magnitude over a 7-year period would generate a persistent shift in microbial community characteristics and soil nutrient availability.

Natural transformation as a mechanism of horizontal gene transfer among environmental Aeromonas species.

Aeromonas species are common inhabitants of aquatic environments and relevant as human pathogens. Their potential as pathogens may be related in part to lateral transfer of genes associated with toxin production, biofilm formation, antibiotic resistance, and other virulence determinants. Natural transformation has not been characterized in aeromonads.

Choline and osmotic-stress tolerance induced in Arabidopsis by the soil microbe Bacillus subtilis (GB03).

Choline (Cho) is an essential nutrient for humans as well as the precursor of glycine betaine (GlyBet), an important compatible solute in eukaryotes that protects cells from osmotic stress caused by dehydrating conditions. The key enzyme for plant Cho synthesis is phosphoethanolamine N-methyltransferase (PEAMT), which catalyzes all three methylation steps, including the rate-limiting N-methylation of phosphoethanolamine. Herein, we report that the beneficial soil bacterium Bacillus subtilis (strain GB03) enhances Arabidopsis Cho and GlyBet synthesis associated with enhanced plant tolerance to osmotic stress.

Precipitation magnitude and timing differentially affect species richness and plant density in the sotol grassland of the Chihuahuan Desert.

Arid and semi-arid environments are dynamic ecosystems with highly variable precipitation, resulting in diverse plant communities. Changes in the timing and magnitude of precipitation due to global climate change may further alter plant community composition in desert regions. In this study, we assessed changes in species richness and plant density at the community, functional group, and species level in response to variation in the magnitude of natural seasonal precipitation and 25% increases in seasonal precipitation [e.

Linking microbial community structure and function to seasonal differences in soil moisture and temperature in a Chihuahuan desert grassland.

Global and regional climate models predict higher air temperature and less frequent, but larger precipitation events in arid regions within the next century. While many studies have addressed the impact of variable climate in arid ecosystems on plant growth and physiological responses, fewer studies have addressed soil microbial community responses to seasonal shifts in precipitation and temperature in arid ecosystems. This study examined the impact of a wet (2004), average (2005), and dry (2006) year on subsequent responses of soil microbial community structure, function, and linkages, as well as soil edaphic and nutrient characteristics in a mid-elevation desert grassland in the Chihuahuan Desert.

PCR-DGGE comparison of bacterial community structure in fresh and archived soils sampled along a Chihuahuan Desert elevational gradient.

The polymerase chain reaction coupled with denaturing gradient gel electrophoresis (PCR-DGGE) has been used widely to determine species richness and structure of microbial communities in a variety of environments. Researchers commonly archive soil samples after routine chemical or microbial analyses, and applying PCR-DGGE technology to these historical samples offers evaluation of long-term patterns in bacterial species richness and community structure that was not available with previous technology. However, use of PCR-DGGE to analyze microbial communities of archived soils has been largely unexplored.

Precipitation timing and magnitude differentially affect aboveground annual net primary productivity in three perennial species in a Chihuahuan Desert grassland.

Plant productivity in deserts may be more directly responsive to soil water availability than to precipitation. However, measurement of soil moisture alone may not be enough to elucidate plant responses to precipitation pulses, as edaphic factors may influence productivity when soil moisture is adequate. The first objective of the study was to determine the responses of the aboveground annual net primary productivity (ANPP) of three perennial species (from different functional groups) in a Chihuahuan Desert grassland to variation in natural precipitation (annual and seasonal) and a 25% increase in seasonal precipitation (supplemental watering in summer and winter).

Soil microbial community response to drought and precipitation variability in the Chihuahuan Desert.

Increases in the magnitude and variability of precipitation events have been predicted for the Chihuahuan Desert region of West Texas. As patterns of moisture inputs and amounts change, soil microbial communities will respond to these alterations in soil moisture windows. In this study, we examined the soil microbial community structure within three vegetation zones along the Pine Canyon Watershed, an elevation and vegetation gradient in Big Bend National Park, Chihuahuan Desert.

Characterization of the structural and functional diversity of indigenous soil microbial communities in smelter-impacted and nonimpacted soils.

A century of mining and smelting activity at the Anaconda Smelter site in Anaconda, Montana, USA, has contaminated the surrounding soils and groundwater with metals. Soil microbial communities from six smelter-impacted sites and a nonimpacted site were compared to determine the long-term effects of a gradient of metal concentrations on microbial activity, biomass, functional diversity (Biolog microtiter plates), and structural diversity (denaturant gradient gel electrophoresis of 16S ribosomal DNA). Microbial activity and biomass were decreased in the smelter-impacted soils.

Sampling bias created by ampicillin in isolation media for Aeromonas.

Members of the bacterial genus Aeromonas are widely isolated from aquatic environments and studied in part for their ability to act as opportunistic pathogens in a variety of animals. All aeromonads, with the exception of Aeromonas trota, are generally thought to be resistant to ampicillin, so the antibiotic is frequently added to isolation medium as a selective agent. In this study, 282 aeromonads from environmental sources were isolated on a medium without ampicillin and their resistance to ampicillin determined.

Genotype, soil type, and locale effects on reciprocal transplant vigor, endophyte growth, and microbial functional diversity of a narrow sagebrush hybrid zone in Salt Creek Canyon, Utah.

When addressing the nature of ecological adaptation and environmental factors limiting population ranges and contributing to speciation, it is important to consider not only the plant's genotype and its response to the environment, but also any close interactions that it has with other organisms, specifically, symbiotic microorganisms. To investigate this, soils and seedlings were reciprocally transplanted into common gardens of the big sagebrush hybrid zone in Salt Creek Canyon, Utah, to determine location and edaphic effects on the fitness of parental and hybrid plants. Endophytic symbionts and functional microbial diversity of indigenous and transplanted soils and sagebrush plants were also examined.

Antimicrobial susceptibilities of Aeromonas spp. isolated from environmental sources.

Aeromonas spp. are ubiquitous aquatic bacteria that cause serious infections in both poikilothermic and endothermic animals, including humans. Clinical isolates have shown an increasing incidence of antibiotic and antimicrobial drug resistance since the widespread use of antibiotics began.

Metal distributions in New Orleans following hurricanes Katrina and Rita: A continuation study.

In late October 2005, twenty-seven metals were determined in soils and sediment layers deposited by floodwaters (flood sediments) within New Orleans, Louisiana. Samples originated from 43 sites along four transects, at an industrial canal, and near the Superdome. The sampling design encompassed flooded and nonflooded areas as well as differing economic strata within the city.

A microtiter plate procedure for evaluating fungal functional diversity on nitrogen substrates.

Ascertaining the effects of anthropogenic disturbance on belowground diversity is of paramount importance because pollution from agricultural practices and industrialization are increasing worldwide. Although we have methods for evaluating soil microbial function with respect to carbon use our ability to evaluate use of other compounds is limited. Because N cycling is of paramount importance in ecosystem stability, evaluation of the ability of saprophytic soil fungi to use a variety of N sources would provide important information on possible alterations in ecosystem stability with disturbance.

Assessment of pathogens and toxicants in New Orleans, LA following Hurricane Katrina.

Storm surge associated with Hurricane Katrina and the breach of levees protecting New Orleans, Louisiana allowed floodwaters from Lake Pontchartrain to inundate 80% of the city. Environmental samples were collected during September 16-18, 2005 to determine immediate human and wildlife health hazards from pathogens and toxicants in the floodwaters. Baseline information on potential long-term environmental damage resulting from contaminants in water and sediments pumped into Lake Pontchartrain was also collected.

Habitat disturbance and the diversity and abundance of ants (Formicidae) in the Southeastern Fall-Line Sandhills.

We examined habitat disturbance, species richness, equitability, and abundance of ants in the Fall-Line Sandhills, at Fort Benning, Georgia. We collected ants with pitfall traps, sweep nets, and by searching tree trunks. Disturbed areas were used for military training; tracked and wheeled vehicles damaged vegetation and soils.

Population patterns and antimicrobial resistance of Aeromonas in urban playa lakes.

Bacteria belonging to the genus Aeromonas are indigenous to aquatic environments. Once regarded as unimportant human pathogens, reports of opportunistic infections caused by these organisms have appeared increasingly in the medical literature. To estimate the potential for human infection by Aeromonas where limited water resources are being used intensively, we studied the spatial and temporal variation and incidence of antimicrobial resistance among environmental isolates of Aeromonas from two urban playa lakes in Lubbock, Texas.

Convergence across biomes to a common rain-use efficiency.

Water availability limits plant growth and production in almost all terrestrial ecosystems. However, biomes differ substantially in sensitivity of aboveground net primary production (ANPP) to between-year variation in precipitation. Average rain-use efficiency (RUE; ANPP/precipitation) also varies between biomes, supposedly because of differences in vegetation structure and/or biogeochemical constraints.

Plants retard litter decay in a nutrient-limited soil: a case of exploitative competition?

Litter was incubated in pasteurized and unpasteurized soils, with and without the presence of prairie grasses (Bouteloua gracilis or Schizachyrium scoparium), to determine if competition between plants and saprophytes altered rates of litter decay. A soil pasteurization treatment was included to ascertain if the presence of vesicular-arbuscular mycorrhizae inocula would affect the competitive interaction. Analyses of variance detected significant effects (P<0.