Gross N transformations were little affected by 4 years of simulated N and S depositions in an aspen-white spruce dominated boreal forest in Alberta, Canada

The effects of 4 years of simulated nitrogen (N) and sulfur (S) depositions on gross N transformations in a boreal forest soil in the Athabasca oil sands region (AOSR) in Alberta, Canada, were investigated using the ¹⁵N pool dilution method. Gross NH₄⁺ transformation rates in the organic layer tended to decline (P < 0.10, marginal statistical significance, same below) in the order of control (CK, i.e., no N or S addition), +N (30 kg N ha⁻¹ yr⁻¹), +S (30 kg S ha⁻¹ yr⁻¹), and +NS treatments, with an opposite trend in the mineral soil. Gross NH₄⁺ immobilization rates were generally higher than gross N mineralization rates across the treatments, suggesting that the studied soil still had potential for microbial immobilization of NH₄⁺, even after 4 years of elevated levels of simulated N and S depositions. For both soil layers, N addition tended to increase (P < 0.10) the gross nitrification and NO₃⁻ immobilization rates. In contrast, S addition reduced (P < 0.001) and increased (P < 0.001) gross nitrification as well as tended (P < 0.10) to reduce and increase gross NO₃⁻ immobilization rates in the organic and mineral soils, respectively. Gross nitrification and gross NO₃⁻ immobilization rates were tightly coupled in both soil layers. The combination of rapid NH₄⁺ cycling, negligible net nitrification rates and the small NO₃⁻ pool size after 4 years of elevated N and S depositions observed here suggest that the risk of NO₃⁻ leaching would be low in the studied boreal forest soil, consistent with N leaching measurements in other concurrent studies at the site that are reported elsewhere.     

Antibiotic Resistance in two Water Reclamation Systems for Space Applications

The purpose of this research was to evaluate the antibiotic resistance in two water reclamation systems developed from space missions. The first system is a small-scale water reclamation system operated at Johnson Space Center designed to reclaim wastewater during long-term space missions. The second system was a scaled-down version of the Johnson Space Center system operated at Texas Tech University. Antibiotic resistance patterns to 10 antibiotics were investigated before and after controlled doses of amoxicillin were added to the water reclamation systems. The results of this study indicate that bacteria in all systems were resistant to many antibiotics including beta-lactam antibiotics and a beta-lactam, beta-lactamase inhibitor combination, amoxicillin with clavulanic acid.     

Comparison of two methods that assess soil community level physiological profiles in a forest ecosystem

There are currently two approaches that use whole soil to determine community level physiological profiles (CLPP) based on C-substrate utilization. We assessed the Degens and Harris and MicroResp™ approaches for their ability to distinguish between previously mined and non-mined forest soils that are characterized by gradients in biological, chemical and physical properties. Surface soils (0-5 cm) were collected from two ages of forest rehabilitation (3- and 16-years post mining), within mounds and furrows (caused by contour ripping) and from adjacent non-mined forest soil. Microbial respiration response to individual substrates was six times greater from the Degens and Harris (1.84 μg CO₂-C g soil h⁻¹) than the MicroResp™ (0.31 μg CO₂-C g soil h⁻¹) approach. The MicroResp™ approach was able to distinguish between CLPP of the two ages of rehabilitation (P=0.05), whereas the Degens and Harris approach did not. Neither approach identified an overall difference between the CLPP of mined and adjacent non-mined forest. The MicroResp™ approach revealed a significant difference (P=0.03) in CLPP from mounds of the two rehabilitation ages but no differences between the furrows. In addition there was a difference (P=0.03) in CLPP between the mounds and furrows within the 3-year old rehabilitation but no difference between the mounds and furrows within the 16-year-old rehabilitation. However, the CLPP of mounds of the 3-year old rehabilitation were different (P=0.059) to adjacent non-mined forest, while the furrows were not. There was no difference in CLPP between the mounds or the furrows of the 16-year-old rehabilitation and adjacent non-mined forest. These results suggest that the aspect of microbial heterotrophic function measured in this study takes up to 3 years to re-establish in the furrows and between 3-16 years in the mounds of post-mined rehabilitation soils. Our results also indicated that the MicroResp™ was substantially better than the Degens and Harris approach in distinguishing between treatments; this is likely to be due to differences in substrate concentrations and soil water potentials between approaches. Testing of a more comprehensive range of organic compounds would likely provide greater ecological interpretation of the CLPP data.     

Ammonium oxidation coupled to dissimilatory reduction of iron under anaerobic conditions in wetland soils

In exploring the dynamics of iron and nitrogen cycling in sediments from riparian forests we have observed a redox reaction that has not been previously described. During incubations of soil slurries under strictly anaerobic conditions, we repeatedly measured an unexpected production of both nitrite () and ferrous iron [Fe(II)]. Using this indirect evidence we hypothesize that, under anaerobic conditions, there is a biological process that uses ferric iron [Fe(III)] as an electron acceptor while oxidizing ammonium () to for energy production. This oxidation under iron reducing anaerobic conditions is thermodynamically feasible and is potentially a critical component of the N cycle in saturated sediments.     

小城镇河流沉积物无机氮迁移循环研究

通过对河流柱状沉积物在通气下和厌气下进行避光短期静置模拟培养试验，研究了小城镇河流底泥-上覆水体系无机氮的迁移特征。结果表明，沉积物有机质降解对NH4的迁移有很大影响，通气和厌气下NH4的迁移均是向上覆水方向，NO3的迁移均是向沉积物方向，由于通气条件和静水环境引起的沉积物无机氮硝化作用和反硝化作用是影响沉积物一水界面体系氮迁移的最重要因素。     

氮素形态在土壤中的转化及对烤烟产量的影响

 试验研究了云南省玉溪地区气候、土壤条件下,铵态氮、尿素施入土壤中的转化,使用硝化抑制剂双氰胺（DCD）研究不同形态氮及其比例对烤烟生长的影响,以及施用秸秆、油饼对烤烟生长的影响。结果表明,施入土壤中的铵态氮、尿素其水解和硝化过程约在施肥后的1个月内完成,土壤中硝态氮含量随时间逐渐下降,1个月后土壤中铵态氮、硝态氨含量都降至痕量水平;硝化抑制剂对铵态氮硝化有显著的抑制效果;铵态氮、硝态氮对烤烟产量没有影响,秸秆、油饼则显著降低烤烟产量。     

Quantifying the contribution of dissolved organic matter to soil nitrogen cycling using N isotopic pool dilution

Dissolved organic matter (DOM) has been recognised as a key carbon and nitrogen (N) pool involved with soil-plant-microbe interactions. Yet few studies have quantified this contribution in agricultural soils. In this study we leached DOM from a sandy loam and sandy clay loam soil under either grassland or arable cropping. Two weeks after DOM removal microbial respiration from soils was not altered. However, a significant (P<0.05) decline in microbial biomass-N, potentially mineralizable-N, gross N mineralization and gross nitrification occurred after leaching. This data illustrate that whilst DOM is a small component of the soil OM it contributed up to 25% of microbial N supply within these agricultural soils.