Short-term effects of aglime on inorganic- and organic-derived CO2 emissions from two acid soils amended with an ammonium-based fertiliser

Purpose

Aglime application can promote carbon dioxide (CO₂) emissions from acid soils. However, the controlling mechanisms are still poorly understood, particularly the role of fertiliser-ammonium oxidation. This study therefore assessed the effects of aglime on soil inorganic C (SIC)– and soil organic C (SOC)–derived CO₂ emissions from acid soils amended with ammonium.

Materials and methods

Ammonium at three N rates [0% (A0), 0.005% (A1), and 0.2% (A2) w/w] and labelled aglime (Ca¹³CO_3,¹³C 5.94% aa) at three rates [0% (L1), 0.067% (L1), and 0.392% (L2) w/w] were applied to two contrasting acid soils (Nariva series, Mollic Fluvaquents; and Piarco series, Typic Kanhaplaquults) and incubated in 1-l media bottles for 23 days. A calcareous soil (Princes Town series, Aquentic Eutrudepts, carbonate δ¹³C of ??4.79‰) was included as a control that only received ammonium at the three rates.

Results and discussion

The application of ammonium at the A2 rate significantly (p?<?0.05) increased cumulative SIC-CO₂ emissions by 15.8 and 27.1% in comparison to the A0 rate for the Nariva and Piarco soils, respectively, when they were limed at the L2 rate. The lower rate of ammonium (A1), however, had no effect on these emissions, which suggests that enough acidity may not have been generated at this rate to significantly enhance the release of SIC-CO₂. Furthermore, no effect of ammonium rates was observed on SIC-CO₂ emissions from the calcareous soil, which refutes the hypothesis that this amendment plays a greater role in regulating these emissions from calcareous soils compared with acid soils. Also, in contradiction to another hypothesis, the aglime-induced priming effect on SOC decomposition was more apparent in the low-C Piarco soil. This effect was also significantly (p?<?0.05) greater at the L2 rate (above the lime requirement for Piarco), which demonstrates the negative impact that over-liming could have on the sequestration of C in this soil. Our results also showed that ammonium addition may also help to reduce the magnitude of the aglime-induced priming effect in the Piarco soil when it is not over-limed.

Conclusions

Overall, the findings of this study suggest that ammonium fertiliser broadcast at conventional rates may not serve as a significant regulator of SIC-CO₂ emissions from highly to moderately acidic soils amended with aglime. Our findings also indicate a need to consider nitrogen management as an important factor regulating the effects of aglime on SOC-CO₂ emissions.

     

Above- and belowground biomass measurements in an unthinned stand of Sitka spruce (<Emphasis Type="Italic">Picea sitchensis</Emphasis> (Bong) Carr.)

Reporting carbon (C) stocks in tree biomass (above- and belowground) to the United Nations Framework Convention on Climate Change (UNFCCC) should be transparent and verifiable. The development of nationally specific data is considered ‘good practice’ to assist in meeting these reporting requirements. From this study, biomass functions were developed for estimating above- and belowground C stock in a 19-year-old stand of Sitka spruce (Picea sitchensis (Bong) Carr.). Our estimates were then tested against current default values used for reporting in Ireland and literature equations. Ten trees were destructively sampled to develop aboveground and tree component biomass equations. The roots were excavated and a root:shoot (R) ratio developed to estimate belowground biomass. Application of the total aboveground biomass function yielded a C stock estimate for the stand of 74 tonnes C ha⁻¹, with an uncertainty of 7%. The R ratio was determined to be 0.23, with an uncertainty of 10%. The C stock estimate of the belowground biomass component was then calculated to be 17 tonnes C ha⁻¹, with an uncertainty of 12%. The equivalent C stock estimate from the biomass expansion factor (BEF) method, applying Ireland’s currently reported default values for BEF (inclusive of belowground biomass), wood density and C concentration and methods for estimating volume, was found to be 60 tonnes C ha⁻¹, with an uncertainty of 26%. We found that volume tables, currently used for determining merchantable timber volume in Irish forestry conditions, underestimated volume since they did not extend to the yield of the forest under investigation. Mean stock values for belowground biomass compared well with that generated using published models.     

Limited effects of land use on soil dissolved organic matter chemistry as assessed by excitation–emission fluorescence spectroscopy and molecular weight fractionation

Dissolved organic matter (DOM) in soil solution represents a complex mixture of organic molecules and plays a central role in carbon and nitrogen cycling in plant–microbial–soil systems. We tested whether excitation–emission matrix (EEM) fluorescence spectroscopy can be used to characterize DOM and support previous findings that the majority of DOM is of high molecular weight (MW). EEM fluorescence spectroscopy was used in conjunction with MW fractionation to characterize DOM in soil solution from a grassland soil land management gradient in North Wales, UK. Data analysis suggested that three distinct fluorescence components could be separated and identified from the EEM data. These components were identified as being of humic‐like or fulvic‐like origin. Contrary to expectations, the majority of the fluorescence signal occurred in the small MW (<1 kDa) fraction, although differences between soils from the differently managed grasslands were more apparent in larger MW fractions. We conclude that following further characterization of the chemical composition of the fluorophores, EEM has potential as a sensitive technique for characterizing the small MW phenolic fraction of DOM in soils.     

The nematode-trapping fungus Arthrobotrys oligospora in soilof the Bodega marine reserve: distribution and dependenceon nematode-parasitized moth larvae

Of the 13 nematode-trapping fungi previously detected at the Bodega Marine Reserve (BMR, Sonoma County, CA, USA), Arthrobotrys oligospora is by far the most abundant. Why A. oligospora is so abundant is unclear, but the answer may involve bush lupines (Lupinus arboreus), ghost moth larvae (Hepialus californicus), and insect-parasitic nematodes (Heterorhabditis marelatus). Previous research documented a dramatic increase of A. oligospora in BMR soil with the addition of an H. marelatus-parasitized moth larva. The current study tested two predictions based on the hypothesis that the H. marelatus-parasitized ghost moth larva is a unique and important resource for A. oligospora at BMR. First, because ghost moth larvae are concentrated in soil under bush lupines, we predicted that A. oligospora numbers would be greater under lupines than away from lupines. Second, we predicted that A. oligospora would be enhanced more by moth larvae containing living H. marelatus than by moth larvae containing dead H. marelatus or no H. marelatus or by nematodes alone. The first prediction was supported by data from a field study (A. oligospora population density was greater beneath lupines than in grasses 2 m away), but the difference was small. The second prediction was not supported by data from a laboratory experiment (dead moth larvae caused dramatic increases in A. oligospora numbers whether or not the dead moth larvae contained living nematodes). While H. marelatus are clearly unnecessary for the large increase in A. oligospora numbers, the importance of nematodes in general remains unclear because addition of dead moth larvae always resulted in large increases in bacterivorous nematodes and because addition of nematodes alone enhanced A. oligospora in one trial but not in two others.     

Mercury in the natural gas industry in Canada

There are an estimated 1,500 natural gas facilities across Canada, most of which used mercury (Hg) in metering equipment at one time or another. Although the use of mercury has ceased, many gas industry buildings still contain detectable levels of Hg in air. Air Hg levels are generally low but indoor remediation is suggested. Worker exposure to the air Hg levels is not considered a significant hazard. Very high soil Hg levels have been observed at numerous sites. Soil Hg levels do not pose an immediate human hazard but are sufficient to be hazardous to ecological receptors. The area of soil contamination, is generally within the buildings or within a few metres of the nearest door. Downward movement of the Hg does not generally extend more than one metre. Remediation of contaminated soil with on-site thermal desorption is recommended as the appropriate soil clean-up technology.     

Calorimetric measurements on chickens given diets with a range of energy concentrations

Eight diets with metabolisable energy (ME) concentrations ranging from 9–1 to 15–3 MJ/kg were given to groups of five chickens kept in respiration calorimeters for 3 to 4 d. Availability of ME ranged from 57% to 79%. One diet differed from the others, but for those groups of chickens on the other seven diets availability of ME was 80% when energy balance was negative and only 60% when positive.

Protein synthesis appeared to continue when chickens were in negative energy balance and fat was frequently catabolised when birds were in positive energy balance, apparently to support protein synthesis.     

Analysis of green hemp fibre reinforced composites using bag retting and white rot fungal treatments

The main objective of this project was to investigate two low cost treatment methods, namely bag retting and treatment with white rot fungi, which could be applied to hemp fibre with low environmental impact to improve its interfacial bonding with polypropylene. Wet chemical analysis, FTIR, scanning electron microscopy (SEM), X-ray diffraction (XRD), zeta potential and single fibre tensile testing were used to characterise the effect of treatment on hemp fibres. It was found that all the treatments increased the tensile strength of composites. White rot fungi Schizophyllum commune (S.com) treated fibre composites had the highest tensile strength of 45 MPa, an increase of 28% compared to composites using untreated fibre.     

Formation of a nematic fluid at high fields in Sr3Ru2O7

In principle, a complex assembly of strongly interacting electrons can self-organize into a wide variety of collective states, but relatively few such states have been identified in practice. We report that, in the close vicinity of a metamagnetic quantum critical point, high-purity strontium ruthenate Sr3Ru2O7 possesses a large magnetoresistive anisotropy, consistent with the existence of an electronic nematic fluid. We discuss a striking phenomenological similarity between our observations and those made in high-purity two-dimensional electron fluids in gallium arsenide devices.     

Radar soundings of the subsurface of Mars

The martian subsurface has been probed to kilometer depths by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express orbiter. Signals penetrate the polar layered deposits, probably imaging the base of the deposits. Data from the northern lowlands of Chryse Planitia have revealed a shallowly buried quasi-circular structure about 250 kilometers in diameter that is interpreted to be an impact basin. In addition, a planar reflector associated with the basin structure may indicate the presence of a low-loss deposit that is more than 1 kilometer thick.