176,825 research outputs found
Metabolic pathways of Amino Acids, Monosaccharides and Organic Acids in Soils assessed by Position-Specific Labeling
No full textMicrobial carbon recycling: an underestimated process controlling soil carbon dynamics – Part 2: A C<sub>3</sub>-C<sub>4</sub> vegetation change field labelling experiment
No full textThe mean residence times (MRT) of different compound classes of soil organic
matter (SOM) do not match their inherent recalcitrance to decomposition. One
reason for this is the stabilization within the soil matrix, but recycling,
i.e. the reuse of "old" organic material to form new biomass may also play
a role as it uncouples the residence times of organic matter from the
lifetime of discrete molecules in soil.
We analysed soil sugar dynamics in a natural 30-year old labelling
experiment after a wheat-maize vegetation change to determine the extent of
recycling and stabilization by assessing differences in turnover dynamics
between plant and microbial-derived sugars: while plant-derived sugars are
only affected by stabilization processes, microbial sugars may be subject to
both, stabilization and recycling. To disentangle the dynamics of soil
sugars, we separated different density fractions (free particulate organic
matter (fPOM), light occluded particulate organic matter (≤ 1.6 g cm−3; oPOM1.6), dense occluded particulate organic matter
(≤ 2 g cm−3; oPOM2) and mineral-associated organic matter (> 2 g cm−3; mineral)) of a silty loam under long-term wheat and maize
cultivation. The isotopic signature of neutral sugars was measured by high
pressure liquid chromatography coupled to isotope ratio mass spectrometry
(HPLC/IRMS), after hydrolysis with 4 M Trifluoroacetic acid.
While apparent MRT of sugars were comparable to total
organic carbon in the bulk soil and mineral fraction, the apparent MRT of
sugar carbon in the oPOM fractions were considerably lower than those of the
total carbon of these fractions. This indicates that oPOM formation was
fuelled by microbial activity feeding on new plant input. In the bulk soil,
MRT of the mainly plant-derived xylose were significantly lower than those
of mainly microbial-derived sugars like galactose, rhamnose, fucose,
indicating that recycling of organic matter is an important factor
regulating organic matter dynamics in soil
Metabolic pathways of Amino Acids, Monosaccharides and Organic Acids in Soils assessed by Position-Specific Labeling
No full textMicrobial carbon recycling – an underestimated process controlling soil carbon dynamics – Part 1: A long-term laboratory incubation experiment
No full textIndependent of its chemical structure carbon (C) persists in soil for
several decades, controlled by stabilization and recycling. To disentangle
the importance of the two factors on the turnover dynamics of soil sugars,
an important compound of soil organic matter (SOM), a 3-year incubation
experiment was conducted on a silty loam soil under different types of land
use (arable land, grassland and forest) by adding 13C-labelled glucose.
The compound-specific isotope analysis of soil sugars was used to examine
the dynamics of different sugars during incubation.
Sugar dynamics were dominated by a pool of high mean residence times (MRT)
indicating that recycling plays an important role for sugars. However, this
was not substantially affected by soil C content. Six months after label
addition the contribution of the label was much higher for microbial biomass
than for CO2 production for all examined land use types, corroborating
that substrate recycling was very effective within the microbial biomass.
Two different patterns of tracer dynamics could be identified for different
sugars: while fucose and mannose showed highest label contribution at the
beginning of the incubation with a subsequent slow decline, galactose and
rhamnose were characterized by slow label incorporation with subsequently
constant levels, which indicates that recycling is dominating the dynamics
of these sugars. This may correspond to (a) different microbial growing
strategies (r and K-strategist) or (b) location within or outside the cell
membrane (lipopolysaccharides vs. exopolysaccharides) and thus be subject of
different re-use within the microbial food web. Our results show how the
microbial community recycles substrate very effectively and that high losses
of substrate only occur during initial stages after substrate addition. This
study indicates that recycling is one of the major processes explaining the
high MRT observed for many SOM fractions and thus is crucial for
understanding the global soil C cycle
Positive intercropping effects on biomass production are species-specific and involve rhizosphere enzyme activities: Evidence from a field study
No full text<jats:title>Abstract</jats:title><jats:p>Less attention has been given to soil enzymes that contribute to beneficial rhizosphere interactions in intercropping systems. Therefore, we performed a field experiment by growing faba bean, lupine, and maize in mono and mixed cultures in a moderately fertile soil. We measured shoot biomass and the kinetic parameters (maximal velocity (<jats:italic>V</jats:italic><jats:sub>max</jats:sub>) and Michaelis-constant (<jats:italic>K</jats:italic><jats:sub><jats:italic>m</jats:italic></jats:sub>)) of three key enzymes in the rhizosphere: Leucine-aminopeptidase (LAP), β-1,4-N-acetylglucosaminidase (NAG), and phosphomonoesterase (PHO). Faba bean benefitted in mixed cultures by greater shoot biomass production with both maize and lupine compared to its expected biomass in monoculture. Next, LAP and NAG kinetic parameters were less responsive to mono and mixed cultures across the crop species. In contrast, both the <jats:italic>V</jats:italic><jats:sub>max</jats:sub> and <jats:italic>K</jats:italic><jats:sub><jats:italic>m</jats:italic></jats:sub> values of PHO increased in the faba bean rhizosphere when grown in mixed cultures with maize and lupine. A positive relative interaction index for shoot P and N uptake for faba bean showed its net facilitative interactions in the mixed cultures. Overall, these results suggest that over-productivity in intercropping is crop-specific and the positive intercropping effects could be modulated by P availability. We argue that the enzyme activities involved in nutrient cycling should be incorporated in further research.</jats:p>
Microbial Metabolic Flux Analysis Using Position-Specific 13C-Labelled Glucose and Fragment 13C Analysis of Plfa
No full textSimulation of thermal plant optimization and hydraulic aspects of thermal distribution loops for large campuses
No full textFollowing an introduction, the author describes Texas A&M University and its utilities system. After that, the author presents how to construct simulation models for chilled water and heating hot water distribution systems. The simulation model was used in a $2.3 million Ross Street chilled water pipe replacement project at Texas A&M University. A second project conducted at the University of Texas at San Antonio was used as an example to demonstrate how to identify and design an optimal distribution system by using a simulation model. The author found that the minor losses of these closed loop thermal distribution systems are significantly higher than potable water distribution systems. In the second part of the report, the author presents the latest development of software called the Plant Optimization Program, which can simulate cogeneration plant operation, estimate its operation cost and provide optimized operation suggestions. The author also developed detailed simulation models for a gas turbine and heat recovery steam generator and identified significant potential savings. Finally, the author also used a steam turbine as an example to present a multi-regression method on constructing simulation models by using basic statistics and optimization algorithms. This report presents a survey of the author??s working experience at the Energy Systems Laboratory (ESL) at Texas A&M University during the period of January 2002 through March 2004. The purpose of the above work was to allow the author to become familiar with the practice of engineering. The result is that the author knows how to complete a project from start to finish and understands how both technical and nontechnical aspects of a project need to be considered in order to ensure a quality deliverable and bring a project to successful completion. This report concludes that the objectives of the internship were successfully accomplished and that the requirements for the degree of Degree of Engineering have been satisfied
Soil organic matter origin and composition along a 3200 m elevation gradient on Mount Kilimanjaro
No full textIntern experience at CH���M Hill, Inc.: an internship report
No full textIncludes author's vita"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirement for the degree of Doctor of Engineering."Includes bibliographical referencesA review of the author's internship experience with CH���M HILL, Inc.
during the period September 1975 through May 1976 is presented. During this nine month
internship the author worked as an Engineer II in the Industrial Processes discipline of this
large consulting engineering firm... The author's prime responsibility was as one of three
lead design engineers on the design of a large wastewater treatment facility for a pulp mill
in Hoquiam, Washington owned by ITT Rayonier Inc. The work generally consisted of the design
of individual treatment units and associated piping and pumping. The purpose of the project
was to provide wastewater treatment capabilities that would satisfy the effluent limitations
(standards) imposed upon the mill by the State of Washington Department of Ecology and the
U.S. Environmental Protection Agency. The author's assignment also entailed necessary
interaction with the project manager and other CH���M HILL design engineers and support staff
members, the client's representatives, and representatives of two other consulting engineering
firms working on the project. Thus, the internship position at CH���M HILL provided considerable
experience coordinating the author's work with the work of other engineers, guiding the design
and administrative efforts of a support staff, and interacting regularly with the client and
other consulting firms. This broad exposure to a variety of engineering and organizational
problems provided a valuable educational experience
Intern experience at the Texas Transportation Institute: an internship report
No full text"Submitted to the College of Engineering of Texas A&M University in partial
fulfillment of the requirements for the degree of Doctor of Engineering."Includes vita (leaf 91)Includes bibliographical references (leaf 57)This report discusses the author's engineering experience at the Texas
Transportation Institute (TTI), Texas A&M University from March 1974 through July 1977. A
report of this experience plus twelve additional hours of academic course work were
substituted for an internship according to requirements established by the College of
Engineering. Although the author could not retroactively establish objectives of the type
associated with a typical internship, the work experience gained could be related to the two
general objectives of an intership: 1. To demonstrate an identifiable contribution to the
organization in which the intern served, and 2. To enable the intern to become aware of the
non-technical aspects of working as an engineer in a non-academic environment. While a member
of the Texas Transportation Institute staff, the author worked on a number of projects in the
areas of highway traffic engineering research and the preparation of continuing education
courses for transportation engineering officials. These assignments were contained within the
Urban Transportation Systems Division of TTI. This report delineates the author's contribution
to four particular projects and discusses the technical as well as non-technical experience
gained from each. Having been exposed to more engineering situations than many of the other
Doctor of Engineering students, the author has already formulated some rather specific
milestones for the future. The Doctor of Engineering program is discussed in conjunction with
its potential for helping the author attain these career goals and objectives. Also, some
thoughts are presented regarding the Doctor of Engineering as a viable alternative to the
Ph.D. in preparing for a career in engineering higher education
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