J. T. Ammons

RNA:protein ratio of the unicellular organism as a characteristic of phosphorous and nitrogen stoichiometry and of the cellular requirement of ribosomes for protein synthesis

BackgroundMean phosphorous:nitrogen (P:N) ratios and relationships of P:N ratios with the growth rate of organisms indicate a surprising similarity among and within microbial species, plants, and insect herbivores. To reveal the cellular mechanisms underling this similarity, the macromolecular composition of seven microorganisms and the effect of specific growth rate (SGR) on RNA:protein ratio, the number of ribosomes, and peptide elongation rate (PER) were analyzed under different conditions of exponential growth.ResultsIt was found that P:N ratios calculated from RNA and protein contents in these particular organisms were in the same range as the mean ratios reported for diverse organisms and had similar positive relationships with growth rate, consistent with the growth-rate hypothesis. The efficiency of protein synthesis in microorganisms is estimated as the number of active ribosomes required for the incorporation of one amino acid into the synthesized protein. This parameter is calculated as the SGR:PER ratio. Experimental and theoretical evidence indicated that the requirement of ribosomes for protein synthesis is proportional to the RNA:protein ratio. The constant of proportionality had the same values for all organisms, and was derived mechanistically from the characteristics of the protein-synthesis machinery of the cell (the number of nucleotides per ribosome, the average masses of nucleotides and amino acids, the fraction of ribosomal RNA in the total RNA, and the fraction of active ribosomes). Impairment of the growth conditions decreased the RNA:protein ratio and increased the overall efficiency of protein synthesis in the microorganisms.ConclusionOur results suggest that the decrease in RNA:protein and estimated P:N ratios with decrease in the growth rate of the microorganism is a consequence of an increased overall efficiency of protein synthesis in the cell resulting from activation of the general stress response and increased transcription of cellular maintenance genes at the expense of growth related genes. The strong link between P:N stoichiometry, RNA:protein ratio, ribosomal requirement for protein synthesis, and growth rate of microorganisms indicated by the study could be used to characterize the N and P economy of complex ecosystems such as soils and the oceans.

Mapping agricultural fields with GPR and EMI to identify offsite movement of agrochemicals

Offsite movement of waterborne agrochemicals is increasingly targeted as a non-point source of water quality degradation. Our research has indicated that subsurface water movement is variable and site-specific, and that a small soil volume frequently conducts a large volume of flow. This concentrated flow is usually caused by soil morphology, and it often results in water moving rapidly offsite from certain areas of fields; little or no lateral subsurface flow may occur in other areas. Identifying these subsurface regions is difficult using conventional soil survey and vadose zone sampling techniques. In this study, traditional surveying is combined with electromagnetic induction (EMI) and ground-penetrating radar (GPR) mapping to identify areas with high potential for subsurface offsite movement of agrochemicals, optimizing these identification techniques, and expanding the mapping procedures to make them useful at the field-scale for agricultural production practices. Conclusions from this research are: (1) EMI mapping provides rapid identification of areas of soil with a high electrical conductivity and presumably high potential for offsite movement of subsurface water, (2) GPR mapping of areas identified by EMI mapping provides a means to identify features that are known to conduct concentrated lateral flow of water, and (3) combining the capabilities of EMI and GPR instrumentation makes possible the surveys of large areas that would otherwise be impossible or unfeasible to characterize.

Mapping shallow underground features that influence site-specific agricultural production

Modern agricultural production practices are rapidly evolving in the United States of America (USA). These new production practices present significant applications for nonintrusive subsurface imaging. One such imaging technology is GPR, and it is now being incorporated within site-specific agriculture in the detection of soil horizons, perched water (episaturation), fragipans, hydrological preferential flow paths, and soil compaction. These features traditionally have been mapped by soil scientists using intrusive measurements (e.g., soil augers, soil pits, coring tools). Rather than developing a tool for soil mapping, our studies are targeting the identification, dimensioning, and position of subsurface features that directly influence agricultural productivity. It is foreseen that this information will allow for an increase in agricultural efficiency through infield machinery automation, and it will also greatly enhance development of highly efficient crop production strategies. The field sensing methodologies that we have developed using existing geophysical technologies are highly dependent upon both the soil and site characteristics due to seasonal variations. The GPR applications presented herein were conducted primarily in a region of loess soil that extends east of the Mississippi River into western Tennessee. GPR studies were also conducted in central Tennessee on the Cumberland Plateau within a region of shallow, sandy loam soils. Additional studies were conducted on the karst area of central Kentucky. Although targeting site-specific agriculture, our results and procedures may benefit the traditional users of GPR technology. We suggest that large-scale agricultural applications of the technology would be enhanced by integrating global positioning (GPS) technology in future hardware and software products.

Mobilized Surveying of Soil Conductivity Using Electromagnetic Induction

Established and emerging geophysical technologies offer many promising applications for precise near–surface surveying. Scientists are investigating these non–invasive surveying techniques to enhance soil mapping and research. A non–invasive soil surveying system was developed to rapidly map soil characteristics. This system employs an all–terrain utility vehicle towing a nonmetallic carriage that cradles a commercially available ground conductivity meter. Autonomous data streams of time–stamped soil conductivity data and global positioning system (GPS) data are immediately downloaded to a computer after a survey. Both data sets are automatically merged using the time stamp data as an index. Using geographical information software (GIS), conductivity maps of increased data density are produced on–site. The mobile surveying system increased total conductivity sampling rate by a factor of >100, and increased data density by a factor of >10 over a conventional manual survey method when operating over a 1–ha open test site. For open fields that can be easily traversed with a utility vehicle, the mobile surveying system was found to greatly enhance data quality by increasing data density, and to dramatically increase both data acquisition efficiency and data post–processing speeds.

Deep weathering of calcareous sedimentary rock and the redistribution of iron and manganese in soil and saprolite

Iron and Mn redistribute in soil and saprolite during weathering. The geological weathering fronts ofcalcareous sedimentary rock were investigated by examining the bulk density, porosity, and distribution ofCa, Fe, and Mn. Core samples were taken ofsoil, saprolite, and bedrock material from both summit (HHMS-4B) and sideslope (HHMS-5A) positions on an interbedded Nolichucky shale and Maryville limestone landform in Solid Waste Storage Area 6 (SWSA-6). This is a low-level radioactive solids waste disposal site on the Dept. ofEnergy (DOE) Oak Ridge Reservation in Roane County Tennessee. This work was initiated because data about the properties of highly weathered sedimentary rock on this site were limited. The core samples were analyzed for pH, calcium carbonate equivalence (CCE), hydroxylamine-extractable (HA) Mn, and dithionite-citrate (CBD)-extractable Fe and Mn. Low pH values occurred from the soil surface down to the depth of the oxidized and leached saprolite in both cores. The CCE and HA-extractable Mn results were also influenced by the weathering that has occurred in these zones. Extractable Mn oxide was higher at a lower depth in the oxidized and leached saprolite compared with the Fe oxide, which was higher in the overlying soil solum. Amounts of Mn oxides were higher in the sideslope core (HHMS-5A) than in the summit core (HHMS-4B). Iron was more abundant in the deeper weathered summit core, but the highest value, 39.4 g kg -1 , was found at 1.8 to 2.4 m in the sideslope core. The zone encompassing the oxidized and partially leached saprolite down to the unoxidized and unleached bedrock had higher densities and larger quantities of CaCO 3 than the soil solum and oxidized and leached saprolite. The overlying soil and oxidized and leached saprolite had lower pH and CCE values and were higher in Fe and Mn oxides than the oxidized and unleached saprolite. The distribution of Fe and Mn is important when evaluating soil and saprolite for hazardous waste disposal site assessment.

EVALUATING GPR AND EMI FOR MORPHOLOGICAL STUDIES OF LOESSIAL SOILS

Development of a rapid and nonintrusive method for obtaining accurate soil morphological information is critical for pinpointing areas that are prone to leaching. The purpose of this study was to evaluate the suitability of using ground-penetrating radar (GPR) and electromagnetic induction (EMI) techniques in combination to gather soil morphological information on loessial soils. A survey of apparent electrical conductivity (ECa) was conducted in southwestern Tennessee at 10-m increments throughout a 1-ha field. Based on variation in the EMI data, a 36-m transect was selected for further investigation by GPR using a 200-MHz antenna. A hydraulic excavator was used to trench the site to a depth of 3 m, and a complete soil morphological investigation was performed along the trench face at 6-m increments. Readings from the EMI showed a moderate correlation with percent fragic properties (r = 0.40). Average depth to the loess/alluvium interface interpreted from the GPR was 1.20 m, and to the alluvium/Tertiary sand interface, 1.88 m. The loess/alluvium and alluvium/Tertiary sand interfaces interpreted from the GPR data had strong relationships to the measured depths, R2 = 0.90 and 0.88, respectively. Results from this study show that using precursory EMI data to pinpoint GPR surveys is a precise, accurate, and rapid means of acquiring field-scale soil morphological information.

Integration of Real-Time Global Positioning with Ground-Penetrating Radar Surveys

Precision agriculture, environmental mapping, and rural construction benefit from subsurface imaging by revealing the spatial variability of underground features. Features surveyed of agricultural interest are bedrock depth, soil horizon thicknesses, and buried–object features such as drainage tile. For these applications, ground–penetrating radar (GPR) is an effective near–surface imaging technology. GPR technologies are used to survey large, open land tracts, whereby subsurface features are ultimately geo–referenced using a geographic information system (GIS) database. This article describes the concept of employing a differentially corrected global position system (DGPS) to provide real–time position location. The system automatically embeds distance referencing markers within the GPR image file, essentially acting as a virtual survey wheel. Markers containing geo–referenced position information are generated “on–the–go” at predefined travel increments. This GPR surveying system supplies high automation and has increased our overall survey and image post–processing efficiency.

DETECTING VERTICAL ANOMALIES WITHIN LOESSIAL SOILS USING GROUND–PENETRATING RADAR

Ground–penetrating radar (GPR) data were collected over a 10–year period on sites composed of loess over alluvium over Tertiary sands. During wet periods, radargrams exhibited ephemeral columnar patterns occurring in and around the alluvium/Tertiary sand interface. Following prolonged dry periods, radargrams did not exhibit the columnar patterns. Extracted soil cores contained vertical preferential flow paths and vertical macro pores. A trench excavation revealed increased preferential flow paths in those areas that exhibited columnar patterns. Conductivity shifts and sharper dielectric contrasts of localized moisture ponded or drained at this interface may cause reverberation patterns beneath.

SURVEYING PERCHED WATER ON ANTHROPOGENIC SOILS USING NON–INTRUSIVE IMAGERY

Wetland soils of anthropogenic origin are difficult to map using conventional soil surveying methods. While traditional soil profile classifications are highly accurate at the borehole, beyond the sampling point the soil–unit boundaries must be visually extrapolated from the surrounding natural terrain. Anthropogenic soils are often erratic, many possessing unpredictable morphologies. Mapping precision is limited by additional sampling expense and site restrictions to excessive borings. In order to increase mapping precision, this project compared measurements of shallow water table depth in copper–mine tailings as determined by (1) intensive conventional soil morphology classification, (2) ground–penetrating radar (GPR), and (3) electromagnetic induction (EMI). Ground–penetrating radar and EMI results were in agreement with water table depths as determined by soil morphology. Wherever a well–formed densic contact was present, GPR and EMI interpretations of water table depths when used alone were inconclusive. The combined technologies, employed in tandem, detected the densic contact layer. Non–intrusive technologies improved mapping precision when combined and supplemented with conventional soil mapping techniques.

Ground-Penetrating Radar Mapping of Agricultural Landforms within the New Madrid Seismic Zone of the Mississippi Embayment

Cataclysmic earthquakes have repeatedly shattered the alluvial landforms about the Missouri Bootheel, the most recent being the 1811-1812 New Madrid earthquakes. During these immense earthquakes, the ground surfaces split apart spewing sands, sulfuric steam, and charcoal. Volcanic-like venting left behind sand blow craters pockmarking the surface. Sand-filled vents are now embedded between the subsurface and surface. These sand vents and fissures serve as rapid water-transport channels extending from just beneath the surface into the water table, rapidly draining surface water much like sink holes and abandoned wells.