Lloyd R. Frederick

Bio: Lloyd R. Frederick is an academic researcher from Iowa State University. The author has contributed to research in topics: Sulfur & Soil microbiology. The author has an hindex of 5, co-authored 7 publications receiving 699 citations.

Desiccation tolerance of four strains of Rhizobium japonicum

Abstract: The survival of different strains of Rhizobium japonicum was evaluated in three soils with two matric- and three osmotic-induced moisture potentials. Both drying and added NaCl significantly decreased populations. Strains CC 709 and USDA 110 were less affected by the matric- or osmotic-induced desiccation than strains CB 1809 and USDA 123. The survival of CC 709 and USDA 110 at 2 weeks with 0.7% added NaCI was 33 and 46% of initial counts in soils undergoing drying, and 70 and 69% in soils maintained at the 30kPa (0.3 bar) potential. Comparable survivals of CB 1809 and USDA 123 were 15 and 18% and 56 and 59%, respectively. The soil with the greatest clay and organic C contents maintained the highest populations during desiccation. Turbidity measurements indicated similar rates of growth of the four strains at a water activity ( A w ) of 0.999 in yeast mannitol broth (YMB). When the YMB was adjusted with glycerol to lower water activities, strains CC 709 and USDA 110 consistently showed greater growth than did strains CB 1809 and USDA 123. No growth of CB 1809 and USDA 123 was observed at an ( A w ) of 0.975. Water adsorption isotherms of freeze-dried cells showed that the more desiccation-susceptible strains (CC 709 and USDA 110) retained greater amounts of water at a given relative vapor pressure than did the two more tolerant strains.

A meta-analysis of the response of soil respiration, net nitrogen mineralization, and aboveground plant growth to experimental ecosystem warming

Abstract: Climate change due to greenhouse gas emissions is predicted to raise the mean global temperature by 1.0–3.5°C in the next 50–100 years. The direct and indirect effects of this potential increase in temperature on terrestrial ecosystems and ecosystem processes are likely to be complex and highly varied in time and space. The Global Change and Terrestrial Ecosystems core project of the International Geosphere-Biosphere Programme has recently launched a Network of Ecosystem Warming Studies, the goals of which are to integrate and foster research on ecosystem-level effects of rising temperature. In this paper, we use meta-analysis to synthesize data on the response of soil respiration, net N mineralization, and aboveground plant productivity to experimental ecosystem warming at 32 research sites representing four broadly defined biomes, including high (latitude or altitude) tundra, low tundra, grassland, and forest. Warming methods included electrical heat-resistance ground cables, greenhouses, vented and unvented field chambers, overhead infrared lamps, and passive night-time warming. Although results from individual sites showed considerable variation in response to warming, results from the meta-analysis showed that, across all sites and years, 2–9 years of experimental warming in the range 0.3–6.0°C significantly increased soil respiration rates by 20% (with a 95% confidence interval of 18–22%), net N mineralization rates by 46% (with a 95% confidence interval of 30–64%), and plant productivity by 19% (with a 95% confidence interval of 15–23%). The response of soil respiration to warming was generally larger in forested ecosystems compared to low tundra and grassland ecosystems, and the response of plant productivity was generally larger in low tundra ecosystems than in forest and grassland ecosystems. With the exception of aboveground plant productivity, which showed a greater positive response to warming in colder ecosystems, the magnitude of the response of these three processes to experimental warming was not generally significantly related to the geographic, climatic, or environmental variables evaluated in this analysis. This underscores the need to understand the relative importance of specific factors (such as temperature, moisture, site quality, vegetation type, successional status, land-use history, etc.) at different spatial and temporal scales, and suggests that we should be cautious in "scaling up" responses from the plot and site level to the landscape and biome level. Overall, ecosystem-warming experiments are shown to provide valuable insights on the response of terrestrial ecosystems to elevated temperature.

Bacterial and Fungal Contributions to Carbon Sequestration in Agroecosystems

Abstract: This paper reviews the current knowledge of microbial processes affecting C sequestration in agroecosystems. The microbial contribution to soil C storage is directly related to microbial community dynamics and the balance between formation and degradation of microbial byproducts. Soil microbes also indirectly influence C cycling by improving soil aggregation, which physically protects soil organic matter (SOM). Consequently, the microbial contribution to C sequestration is governed by the interactions between the amount of microbial biomass, microbial community structure, microbial byproducts, and soil properties such as texture, clay mineralogy, pore-size distribution, and aggregate dynamics. The capacity of a soil to protect microbial biomass and microbially derived organic matter (MOM) is directly and/or indirectly (i.e., through physical protection by aggregates) related to the reactive properties of clays. However, the stabilization of MOM in the soil is also related to the efficiency with which microorganisms utilize substrate C and the chemical nature of the byproducts they produce. Crop rotations, reduced or no-tillage practices, organic farming, and cover crops increase total microbial biomass and shift the community structure toward a more fungal-dominated community, thereby enhancing the accumulation of MOM. A quantitative and qualitative improvement of SOM is generally observed in agroecosystems favoring a fungal-dominated community, but the mechanisms leading to this improvement are not completely understood. Gaps within our knowledge on MOM-C dynamics and how they are related to soil properties and agricultural practices are identified.

Identifying the Dominant Soil Bacterial Taxa in Libraries of 16S rRNA and 16S rRNA Genes

Abstract: From near to far , from here to there , funny things are everywhere. —Dr. Seuss, One Fish Two Fish Red Fish Blue Fish In 1909, H. Joel Conn ([25][1]) expressed the hope that methods would soon be at hand by which the significance of the different bacteria present in any soil could be