Short-term population dynamics of ammonia oxidizing bacteria in an agricultural soil   总被引：2，自引：0，他引：2  

T.R. Cavagnaro  L.E. Jackson  K. Hristova  K.M. Scow 《Applied soil ecology》2008,40(1):13-18

Ammonia oxidizing bacteria (AOB) control the rate limiting step of nitrification, the conversion of ammonia (NH₄⁺) to nitrite (NO₂⁻). The AOB therefore have an important role to play in regulating soil nitrogen cycling. Tillage aerates the soil, stimulating rapid changes in soil N cycling and microbial communities. Here we report results of a study of the short term responses of AOB and net nitrification to simulated tillage and NH₄⁺ addition to soil. The intensively farmed vegetable soils of the Salinas Valley, California, provide the context for this study. These soils are cultivated frequently, receive large N fertilizer inputs and there are regional concerns about groundwater N concentrations. An understanding of N dynamics in these systems is therefore important. AOB population sizes were quantified using a real-time PCR approach. In a 15 day experiment AOB populations, increased rapidly following tillage and NH₄⁺ addition and persisted after the depletion of soil NH₄⁺. AOB population sizes increased to a similar degree, over a 1.5-day period, irrespective of the amount of NH₄⁺ supplied. These data suggest selection of an AOB community in this intensively farmed and C-limited soil, that rapidly uses NH₄⁺ that becomes available. These data also suggest that mineralization may play an especially important role in regulating AOB populations where NH₄⁺ pool sizes are very low. Methodological considerations in the study of soil AOB communities are also discussed.  相似文献   

Seed transmission of Pepino mosaic virus in tomato     

Inge M. Hanssen  Rick Mumford  Dag-Ragnar Blystad  Isabel Cortez  Beata Hasiów-Jaroszewska  Dimitrinka Hristova  Israel Pagán  Ana-Maria Pereira  Jeff Peters  Henryk Pospieszny  Maja Ravnikar  Ineke Stijger  Laura Tomassoli  Christina Varveri  René van der Vlugt  Steen Lykke Nielsen 《European journal of plant pathology / European Foundation for Plant Pathology》2010,126(2):145-152

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Host range and symptomatology of Pepino mosaic virus strains occurring in Europe     

Dag-Ragnar Blystad  René van der Vlugt  Ana Alfaro-Fernández  María del Carmen Córdoba  Gábor Bese  Dimitrinka Hristova  Henryk Pospieszny  Nataša Mehle  Maja Ravnikar  Laura Tomassoli  Christina Varveri  Steen Lykke Nielsen 《European journal of plant pathology / European Foundation for Plant Pathology》2015,143(1):43-56

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Impacts of different N management regimes on nitrifier and denitrifier communities and N cycling in soil microenvironments     

Kong AY  Hristova K  Scow KM  Six J 《Soil biology & biochemistry》2010,42(9):1523-1533

Real-time quantitative PCR assays, targeting part of the ammonia monooxygenase (amoA), nitrous oxide reductase (nosZ), and 16S rRNA genes were coupled with ¹⁵N pool dilution techniques to investigate the effects of long-term agricultural management practices on potential gross N mineralization and nitrification rates, as well as ammonia-oxidizing bacteria (AOB), denitrifier, and total bacterial community sizes within different soil microenvironments. Three soil microenvironments [coarse particulate organic matter (cPOM; >250 μm), microaggregate (53-250 μm), and silt-and-clay fraction (<53 μm)] were physically isolated from soil samples collected across the cropping season from conventional, low-input, and organic maize-tomato systems (Zea mays L.-Lycopersicum esculentum L.). We hypothesized that (i) the higher N inputs and soil N content of the organic system foster larger AOB and denitrifier communities than in the conventional and low-input systems, (ii) differences in potential gross N mineralization and nitrification rates across the systems correspond with AOB and denitrifier abundances, and (iii) amoA, nosZ, and 16S rRNA gene abundances are higher in the microaggregates than in the cPOM and silt-and-clay microenvironments. Despite 13 years of different soil management and greater soil C and N content in the organic compared to the conventional and low-input systems, total bacterial communities within the whole soil were similar in size across the three systems (∼5.15 × 10⁸ copies g⁻¹ soil). However, amoA gene densities were ∼2 times higher in the organic (1.75 × 10⁸ copies g⁻¹ soil) than the other systems at the start of the season and nosZ gene abundances were ∼2 times greater in the conventional (7.65 × 10⁷ copies g⁻¹ soil) than in the other systems by the end of the season. Because organic management did not consistently lead to larger AOB and denitrifier communities than the other two systems, our first hypothesis was not corroborated. Our second hypothesis was also not corroborated because canonical correspondence analyses revealed that AOB and denitrifier abundances were decoupled from potential gross N mineralization and nitrification rates and from inorganic N concentrations. Our third hypothesis was supported by the overall larger nitrifier, denitrifier, and total bacterial communities measured in the soil microaggregates compared to the cPOM and silt-and-clay. These results suggest that the microaggregates are microenvironments that preferentially stabilize C, and concomitantly promote the growth of nitrifier and denitrifier communities, thereby serving as potential hotspots for N₂O losses.  相似文献   

Quantitative and qualitative characterisation of humic products with spectral parameters     

Filcheva  Ekaterina  Hristova  Mariana  Nikolova  Pavlina  Popova  Todorka  Chakalov  Konstantin  Savov  Valentin 《Journal of Soils and Sediments》2018,18(8):2863-2867

Purpose

The application of different humic products for the treatment of soils and plants has increased in recent years. The characteristics of humic products, such as the content and composition of organic carbon and the maturity, provide valuable information which is essential for an adequate application. Such information is crucial for manufacturers, business consultants and users involved in the production, distribution and implementation of humic products. This article presents the correlation between the quantitative indicators of commercial humic products and their spectral characteristics via measurements in the ultraviolet spectrum at 300 nm, in the visible area at 445 and 665 nm and in the near-infrared spectrum at 850 nm.

Materials and methods

We evaluated humic products (liquid and solid) of different origins. Via wet combustion, the content of total organic carbon in humic products can be determined. The precipitation of humic acids from the starting solution determines the composition of the humic products in terms of humic acids (HAs) and fulvic acids (FAs). The dissolution of HAs determines their concentration by titration, while the specific extinction can be assessed via spectrophotometry via measuring the absorption of HAs spectra at the following wavelengths: 300, 465, 665 and 850 nm. The degree of aromaticity and condensation of humic products determines the optical density of the HAs via the E₄/E₆ ratio.

Results and discussion

The content of total organic carbon varied widely from 0.55 to 37.5% across all groups. The content of carbon in HAs, as a percentage of the total carbon in fulvic-type humic products, ranged from 1.29 to 16.00%, while in humic-type products, it ranged from 51.43 to 91.92%. The minimum value of the E₄/E₆ ratio was 2.97, while the maximum value was 6.35. We observed a direct relationship between the dominant type of acids in humic products and the E₄/E₆ ratio.

Conclusions

The optical density of HAs indicates their quality characteristics. The presented optical characteristics for humic products show that there is a direct relationship, especially between HAs/FAs and E₄/E₆ ratios. Measurement at 300 nm (E₃₀₀) in the near-ultraviolet area and at 850 nm (E₈₅₀) in the near-infrared area can increase the range of the spectral study.

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