Background, aim, and scope Fertilization is an important agricultural practice for increasing crop yields. In order to maintain the soil sustainability,
it is important to monitor the effects of fertilizer applications on the shifts of soil microorganisms, which control the
cycling of many nutrients in the soil. Here, culture-dependent and culture-independent approaches were used to analyze the
soil bacterial and fungal quantities and community structure under seven fertilization treatments, including Control, Manure,
Return (harvested peanut straw was returned to the plot), and chemical fertilizers of NPK, NP, NK, and PK. The objective of
this study was to examine the effects on soil microbial composition and diversity of long-term organic and chemical fertilizer
regimes in a Chinese upland red soil.
Materials and methods Soil samples were collected from a long-term experiment station at Yingtan (28°15′N, 116°55′E), Jiangxi Province of China.
The soil samples (0–20 cm) from four individual plots per treatment were collected. The total numbers of culturable bacteria
and fungi were determined as colony forming units (CFUs) and selected colonies were identified on agar plates by dilution
plate methods. Moreover, soil DNAs were extracted and bacterial 16S rRNA genes and fungal 18S rRNA genes were polymerase chain
reaction amplified, and then analyzed by denaturing gradient gel electrophoresis (DGGE), cloning, and sequencing.
Results The organic fertilizers, especially manure, induced the least culturable bacterial CFUs, but the highest bacterial diversity
ascertained by DGGE banding patterns. Chemical fertilizers, on the other hand, had less effect on the bacterial composition
and diversity, with the NK treatment having the lowest CFUs. For the fungal community, the manure treatment had the largest
CFUs but much fewer DGGE bands, also with the NK treatment having the lowest CFUs. The conventional identification of representative
bacterial and fungal genera showed that long-term fertilization treatments resulted in differences in soil microbial composition
and diversity. In particular, 42.4% of the identified bacterial isolates were classified into members of Arthrobacter. For fungi, Aspergillus, Penicillium, and Mucor were the most prevalent three genera, which accounted for 46.6% of the total identified fungi. The long-term fertilization
treatments resulted in different bacterial and fungal compositions ascertained by the culture-dependent and also the culture-independent
approaches.
Discussion It was evident that more representative fungal genera appeared in organic treatments than other treatments, indicating that
culturable fungi were more sensitive to organic than to chemical fertilizers. A very notable finding was that fungal CFUs
appeared maximal in organic manure treatments. This was quite different from the bacterial CFUs in the manure, indicating
that bacteria and fungi responded differently to the fertilization. Similar to bacteria, the minimum fungal CFUs were also
observed in the NK treatment. This result provided evidence that phosphorus could be a key factor for microorganisms in the
soil. Thus, despite the fact that culture-dependent techniques are not ideal for studies of the composition of natural microbial
communities when used alone, they provide one of the more useful means of understanding the growth habit, development, and
potential function of microorganisms from soil habitats. A combination of culture-dependent and culture-independent approaches
is likely to reveal more complete information regarding the composition of soil microbial communities.
Conclusions Long-term fertilization had great effects on the soil bacterial and fungal communities. Organic fertilizer applications induced
the least culturable bacterial CFUs but the highest bacterial diversity, while chemical fertilizer applications had less impact
on soil bacterial community. The largest fungal CFUs were obtained, but much lower diversity was detected in the manure treatment.
The lowest bacterial and also fungal CFUs were observed in the NK treatment. The long-term fertilization treatments resulted
in different bacterial and fungal compositions ascertained by the culture-dependent and also the culture-independent approaches.
Phosphorus fertilizer could be considered as a key factor to control the microbial CFUs and diversity in this Chinese upland
red soil.
Recommendations and perspectives Soil fungi seem to be a more sensitive indicator of soil fertility than soil bacteria. Since the major limitation of molecular
methods in soil microbial studies is the lack of discrimination between the living and dead, or active and dormant microorganisms,
both culture-dependent and culture-independent methods should be used to appropriately characterize soil microbial diversity. 相似文献
Dried soil samples from many sources have been stored in archives world-wide over the years, but there has been little research on their value for studying microbial populations. Samples collected since 1843 from the Broadbalk field experiment on crop nutrition at Rothamsted have been used to document changes in the structure and composition of soils as agricultural practices evolve, also offering an invaluable record of environmental changes from the pre- to post-industrial era in the UK. To date, the microbial communities of these soils have not been studied, in part due to the well-documented drop in bacterial culturability in dried soils. However, modern molecular methods based on PCR amplification of DNA extracted directly from soil do not require bacterial cells to be viable or intact and may allow investigations into the legacy of bacteria that were present at the time of sample collection.
In a preliminary study, to establish if dried soils can provide a historical record of bacterial communities, samples from the Broadbalk soil archive dating back to 1868 were investigated and plots treated with either farmyard manure (FYM) or inorganic fertilizer (NPK) were compared. As anticipated, the processes of air-drying and milling greatly reduced bacterial viability whilst DNA yields declined less and may be preserved by desiccation. A higher proportion of culturable bacteria survived the archiving process in the FYM soil, possibly protected by the increased soil organic matter. The majority of surviving bacteria were firmicutes, whether collected in 2003 or in 1914, but a wide range of genera was detected in DNA extracted from the samples using PCR and DGGE of 16S rRNA genes. Analysis of DGGE band profiles indicated that the two plots maintained divergent populations. Sequence analysis of bands excised from DGGE gels, from a sample collected in 1914, revealed DNA from - and β-proteobacteria as well as firmicutes. PCR using primers specific for ammonia oxidizing bacteria showed similar band profiles across the two treatments in recently collected samples, however older samples from the NPK plot showed greater divergence. Primers specific for the genus Pseudomonas were designed and used in real-time quantitative PCR to indicate that archived soil collected in 1868 contained 10-fold less pseudomonad DNA than fresh soil, representing around 105 genomes g−1 soil. Prior to milling, dramatically less pseudomonad DNA was extracted from recently collected air-dried soil from the NPK compared to the FYM plot; otherwise, the two plots followed similar trends. Overall bacterial abundance, diversity and survival during the archiving process differed in the two soils, possibly due to differences in clay and soil organic matter content. Nevertheless, the results demonstrate that air-dried soils can protect microbial DNA for more than 150 years and offer an invaluable resource for future research. 相似文献
Anatomic adaptations make birds more prone to open fractures with exposed bone parts losing vascularization. As a result of this exposure, fractures are colonized by different microorganisms, including different types of bacteria, both aerobic and anaerobic, causing osteomyelitis in many cases. For this reason, antibiotic treatment is common. However, carrying out antibiotic treatment without carrying out a previous antibiogram may contribute to increased resistance against antibiotics, especially in migratory wild birds. In this paper, bacterial counts regarding fracture type, bacterial identification and antibiotic resistance have been analysed in wild birds from wildlife rehabilitation centres in Spain. The results obtained showed that open fractures had higher bacterial counts (CFU/mL) than closed ones. Bacteria in family Enterobacteriaceae, identified were Escherichia spp., Enterobacter spp., Shigella spp., Hafnia alvei, Proteus mirabilis, Leclercia adecarboxylata and Pantoea agglomerans. Other bacteria present in wild birds’ fractures were Aeromonas spp., Enterococcus spp. Bacillus wiedmannii and Staphylococcus sciuri. All species found presented resistance to at least one of the antibiotics used. Wild birds can be implicated in the introduction, maintenance and global spreading of antibiotic resistant bacteria and represent an emerging public health concern. Results obtained in this paper support the idea that it is necessary to take this fact into account before antibiotic administration to wild animals, since it could increase the number of bacteria resistant to antibiotics. 相似文献
A study was conducted to estimate the record keeping, genetic selection, educational, and farm management effects on average
milk yield per cow (AYC), milk fat percentage, bacterial score, and bulk tank somatic cell count (BTSCC) of dairy farms in
the central region of Thailand. Farms were located in the provinces of Saraburi and Nakhon Ratchisima and were members of
the Muaklek dairy cooperative. Records from individual animals were unavailable. Thus, farm records of milk yield, milk fat
percentage, bacterial score, and BTCCC were collected from July 1, 2003 through June 30, 2006. Additional record keeping,
genetic selection, education, and farm management information was collected through a questionnaire in May of 2006. Data from
the Muaklek dairy cooperative and the questionnaire were then merged by a farm identification number. A single trait mixed
model was used to analyze AYC, milk fat percentage, and BTSCC, while a log linear model was used to analyze bacterial score.
Results showed that farms that kept records on individual animals had higher (P < 0.05) milk fat percentages and lower bacterial scores than farms that did not. Farms that used genetic information (EBV)
and phenotypes when selecting sires were higher (P < 0.05) for milk fat percentage than farms that used only phenotypes and personal opinion. Farms milking cows with a single
unit milking machine and by hand, had higher (P < 0.05) bacterial scores and BTSCC than farms using only a single or multi unit machine. Overall farms that kept individual
animal records, used EBV when selecting sires, used a single method for collecting milk, and used family labor achieved higher
performance from their herds than farms that did not. 相似文献