Agriculture's Role in Greenhouse Gas Mitigation

Examines technical, economic, and policy trends. Explores efforts to encourage farmers to adopt new agricultural practices that reduce agricultural greenhouse gas emissions. Reviews biofuel options, and related policy implications

The soil and plant biogeochemistry sampling design for The National Ecological Observatory Network

Human impacts on biogeochemical cycles are evident around the world, from changes to forest structure and function due to atmospheric deposition, to eutrophication of surface waters from agricultural effluent, and increasing concentrations of carbon dioxide (CO2) in the atmosphere. The National Ecological Observatory Network (NEON) will contribute to understanding human effects on biogeochemical cycles from local to continental scales. The broad NEON biogeochemistry measurement design focuses on measuring atmospheric deposition of reactive mineral compounds and CO2 fluxes, ecosystem carbon (C) and nutrient stocks, and surface water chemistry across 20 eco‐climatic domains within the United States for 30 yr. Herein, we present the rationale and plan for the ground‐based measurements of C and nutrients in soils and plants based on overarching or “high‐level” requirements agreed upon by the National Science Foundation and NEON. The resulting design incorporates early recommendations by expert review teams, as well as recent input from the larger natural sciences community that went into the formation and interpretation of the requirements, respectively. NEON\u27s efforts will focus on a suite of data streams that will enable end‐users to study and predict changes to biogeochemical cycling and transfers within and across air, land, and water systems at regional to continental scales. At each NEON site, there will be an initial, one‐time effort to survey soil properties to 1 m (including soil texture, bulk density, pH, baseline chemistry) and vegetation community structure and diversity. A sampling program will follow, focused on capturing long‐term trends in soil C, nitrogen (N), and sulfur stocks, isotopic composition (of C and N), soil N transformation rates, phosphorus pools, and plant tissue chemistry and isotopic composition (of C and N). To this end, NEON will conduct extensive measurements of soils and plants within stratified random plots distributed across each site. The resulting data will be a new resource for members of the scientific community interested in addressing questions about long‐term changes in continental‐scale biogeochemical cycles, and is predicted to inspire further process‐based research

Automated analysis of 15N and 14C in biological samples

Includes bibliographical references (page 947).An automated method for the simultaneous analysis of total N, total C, 15N and 14C in small plant and soil samples is described. A commercial C-N analyser - continuous flow isotope ratio mass spectrometer (ANCA-MS) has been extended to also measure CO2 and collect 14CO2 produced by sample combustion. Samples containing 20 - 200 μg N and up to 5 mg C can be analysed directly with no sample preparation other than drying and fine grinding. The precision of total elemental analysis is comparable to that by conventional methods. The average standard deviation of 15N analyses of plant material at natural abundance was ±1 ‰. This is accurate enough for all 15N studies except those using natural abundance and possibly long term studies of soil organic matter. Recovery of 14C in test samples was 100%. The instrument can be operated by graduate students under supervision and operating costs are primarily for sample cups, combustion catalyst and quartz tubes

Effects of cultivation on the organic matter of grassland soils as determined by fractionation and radiocarbon dating

Includes bibliographical references (pages 425-426).The effects of cultivation on the net mineralization of carbon and nitrogen in a lacustrine Brown clay (Sceptre) and two Orthic Black soils on glacial till (Oxbow) were assessed with the aid of fractionation and radiocarbon dating techniques. Fractionation of the soil organic matter of comparative virgin and cultivated soils by acid hydrolysis and peptization in dilute NaOH showed that the distribution of carbon and nitrogen among fractions of these soils was similar. There was no measurable alteration in the mean residence time (MRT) of the soil during the first 15 to 20 yr of cultivation, during which time the Sceptre soil had lost 19% of its carbon and the Oxbow, 35%. However, the MRT increased from 250 yr before present (BP) to 710 years BP after 60 yr of cultivation of the Oxbow soil. The losses for nitrogen were 10% lower than for carbon in the Oxbow soil due to the recycling of nitrogen in the soil. The rate of loss of carbon from the Oxbow soil during the cultivation period was simulated by expressing it as the sum of two first order reactions using fractionation and carbon dating data as the variables

Nitrogen transformations in soils previously amended with sewage sludge

Includes bibliographical references (pages 743-744).This short-term (10-d) incubation experiment established the rates of nitrogen (N) transformations occurring in sludge-amended and nonamended soil. Utilizing a nitrification block (C2H2) with (15NH4)2SO4, first-order rate constants were calculated for N immobilization, ammonification, nitrification, and denitrification. These rate constants were compared to values obtained after a long-term (87-wk) incubation performed on soils sampled from the same field plots. The short-term rates of ammonification were still higher than the controls 4 year after the last sludge addition. Sludge applications over an 8-yr period (180 Mg ha−1 yr−1) reduced soil nitrification potential compared to the controls when spiked with 15N. Denitrification did not cause a significant loss of N during either a short- or long-term incubation period. The microbial biomass in the sludge-amended soil contained more N, which resulted in a microbial C/N ratio of approximately 4:1 vs. 5:1 for the controls. Initial (short-term) N immobilization rate constants were 0.43 for the sludge-amended and 0.35 for the nonamended soil

Mineralizable soil nitrogen: amounts and extractability ratios

Includes bibliographical references (page 80).Studies were conducted on a 15N-labeled Weirdale loam, a Dark Gray Chernozemic soil (Boralfic Boroll) to (i) determine the amounts of N released by several methods previously used to obtain an estimate of potentially mineralizable N, (ii) determine their 15N enrichment and extractability ratios, and (iii) compare the results from the above with the N mineralized during incubation and NH+4 released by the chloroform fumigation incubation technique. The NH+4-N accumulated during 10 d in fumigated soils accounted for ∼1% of total N, was highly labeled, and had extractability ratios of 6.6 to 7.4. These ratios were similar to ones obtained for N mineralized during incubation of unfumigated soils. Ammonium-N extracted with dilute acidic permanganate solution (0.01M KMnO4 in 0.1 or 0.5M H2SO4) accounted for 0.72 to 0.84% of total N and had extractability ratios ranging from 3.4 to 3.9. A stronger solution of acidic permanganate extracted more N that was less enriched. Dilute sulfuric acid extracted NH+4 and organic N that had extractability ratios of < 3. Ammonium-N released by autoclaving the soil accounted for ∼1% of total N and had extractability ratios ranging from 0.6 to 0.9. Acid hydrolysis showed that 72% of total N was hydrolyzable, 32% was amino acid-N and 20% was NH+4 released on hydrolysis. The extractability ratio for NH+4 released on hydrolysis was 1.7 and was significantly (P < 0.01) greater than extractability ratios of hydrolyzable N and amino acid-N. The similarity and high extractability ratios of NH+4 released after fumigation and NO-3-N accumulating during aerobic incubation indicated that the fumigation extracted a biologically meaningful fraction. The biomass was responsible for only 15 to 25% of the net N mineralized during a 12-week incubation. Results indicated that (i) extraction of a highly labeled N pool in soil can only partly explain the source of N being mineralized, (ii) N is mineralized from several pools, and (iii) there is a remote possibility that a single extractant can extract the variety of N compounds undergoing mineralization and immobilization in soil

Extracellular Matrix Aggregates from Differentiating Embryoid Bodies as a Scaffold to Support ESC Proliferation and Differentiation

Embryonic stem cells (ESCs) have emerged as potential cell sources for tissue engineering and regeneration owing to its virtually unlimited replicative capacity and the potential to differentiate into a variety of cell types. Current differentiation strategies primarily involve various growth factor/inducer/repressor concoctions with less emphasis on the substrate. Developing biomaterials to promote stem cell proliferation and differentiation could aid in the realization of this goal. Extracellular matrix (ECM) components are important physiological regulators, and can provide cues to direct ESC expansion and differentiation. ECM undergoes constant remodeling with surrounding cells to accommodate specific developmental event. In this study, using ESC derived aggregates called embryoid bodies (EB) as a model, we characterized the biological nature of ECM in EB after exposure to different treatments: spontaneously differentiated and retinoic acid treated (denoted as SPT and RA, respectively). Next, we extracted this treatment-specific ECM by detergent decellularization methods (Triton X-100, DOC and SDS are compared). The resulting EB ECM scaffolds were seeded with undifferentiated ESCs using a novel cell seeding strategy, and the behavior of ESCs was studied. Our results showed that the optimized protocol efficiently removes cells while retaining crucial ECM and biochemical components. Decellularized ECM from SPT EB gave rise to a more favorable microenvironment for promoting ESC attachment, proliferation, and early differentiation, compared to native EB and decellularized ECM from RA EB. These findings suggest that various treatment conditions allow the formulation of unique ESC-ECM derived scaffolds to enhance ESC bioactivities, including proliferation and differentiation for tissue regeneration applications. © 2013 Goh et al

Use of tracers to determine the dynamic nature of organic matter, The

Includes bibliographical references (pages 31-43).Early experiments with 13C, 14C and 15N established the high rate of internal cycling of soil organic matter and reintroduced the concept of an active and passive phase in soil humus turnover. Later studies confirmed non-tracer investigations indicating that the percent decomposition of added materials is relatively independent of the rates of addition but dependent on its form and composition. The initial decomposition rate, plus the stabilization of microbial products in soil, must be taken into account when interpreting degradation of 14C enriched straw, roots, microbial tissue and specific components or in carbon dating naturally occurring 14C. Where initial decomposition data could be described by first order kinetics we calculated decay rate constants with and without the consideration of biosynthesis. Decay rates for laboratory systems were twice those for tropical field soils and eight times those calculated for temperate climates. The data were used in a model incorporating the concepts of microbial biosynthesis and recalcitrant and decomposable soil organic fractions which can both be physically protected. This realistically described the behaviour of soil-C in a Canadian grassland before and after cultivation

Effects of vesicular-arbuscular mycorrhiza on 14C and 15N distribution in nodulated fababeans

Includes bibliographical references (pages 249-250).A two-compartment growth chamber in which the aboveground plant materials were exposed to 14CO2 and the belowground portion was exposed to 15N2 under normal atmospheric pressure was designed for carbon and nitrogen transfer studies. Vicia faba infected with vesicular-arbuscular fungus Glomus mossae and non-mycorrhizal plants fixed similar quantities of N2 at an age of 6½ wk. Approximately 0.10 mg N was fixed ∙ g−1 dry plant materials ∙ day−1 and 40 mg C • g−1 dry matter day−1 were synthesized by mycorrhizal and non-mycorrhizal fababeans during 48 h exposure to 14CO2 at 6½ wk with no apparent difference in yield of dry matter. The non-mycorrhizal plants transferred 37% of the fixed 14C beneath ground. The mycorrhizal ones transferred 47% of the fixed 14C beneath ground. Most of the difference could be accounted for in the belowground respiration. The 14CO2 produced by root-microbial systems of the mycorrhizal fababeans was twice as great as that of the nonmycorrhizal; both contained active rhizobium

Fractionation of soil and 15N nitrogen to separate the organic and clay interactions of immobilized N

Includes bibliographical references (pages 211-212).Labelled 15N was added to two soils in cylinders in the field, and allowed to equilibrate for two summers of crop growth. The labelled soils were fractionated to provide information on the effect of organic and inorganic colloids on the stabilization of immobilized, 15N. Organic materials removed by 0.5 N NaOH without pretreatment contained more 15N than those extracted by the same reagent following decalcification and removal of sesquioxides with dithionite and HCl. Both extracts had similar amino acid (contents) and similar degrees of hydrolability. A fractionation system using an initial 0.1 M NaOH–0.1 M Na4P2O7 extraction followed by sonication and peptization in H2O yielded a humic acid fraction and a sedimentation fraction (< 0.04 μm) which differed markedly in degree of hydrolyzability, 15N content and amino acid-N content. The N associated with inorganic colloids < 0.04 μm, and that remaining in solution after the removal of larger particles accounted for 50% of the amino acid-N in a clay soil, and 40% in a fine sandy loam soil. Removal of sesquioxides followed by a second 0.5 N NaOH extraction reduced the N content of the colloidal size fractions of both soils, indicating that amorphous iron and aluminum compounds on the surface of clays are probably the active agents in bonding organic N to inorganic colloids. It is suggested that the nonhydrolytic technique, based largely on dispersion of the inorganic–organic colloids and analyses of the sediment, could be used to interpret the fate of microbiologically immobilized N compounds in the soil. Materials removed by 0.1 M Na4P2O7 were associated with polyvalent cations in the soil. Materials such as cytoplasmic constituents, released from the biomass during ultrasonic vibration or as lytic products would be expected to be adsorbed to inorganic colloids. They should be concentrated in the < 0.04 μm-size fraction. Cell wall and other particulate debris with a faster setting velocity would be expected to appear in larger-sized sedimentation fractions