Increasing the size of the microbial biomass altered bacterial community structure which enhances plant phosphorus uptake

Agricultural production can be limited by low phosphorus (P) availability, with soil P being constrained by sorption and precipitation reactions making it less available for plant uptake. There are strong links between carbon (C) and nitrogen (N) availability and P cycling within soil P pools, with microorganisms being an integral component of soil P cycling mediating the availability of P to plants. Here we tested a conceptual model that proposes (i) the addition of readily-available organic substrates would increase the size of the microbial biomass thus exhausting the pool of easily-available P and (ii) this would cause the microbial biomass to access P from more recalcitrant pools. In this model it is hypothesised that the size of the microbial population is regulating access to less available P rather than the diversity of organisms contained within this biomass. To test this hypothesis we added mixtures of simple organic compounds that reflect typical root exudates at different C:N ratios to a soil microcosm experiment and assessed changes in soil P pools, microbial biomass and bacterial diversity measures. We report that low C:N ratio (C:N = 12.5:1) artificial root exudates increased the size of the microbial biomass while high C:N ratio (C:N = 50:1) artificial root exudates did not result in a similar increase in microbial biomass. Interestingly, addition of the root exudates did not alter bacterial diversity (measured via univariate diversity indices) but did alter bacterial community structure. Where C, N and P supply was sufficient to support plant growth the increase observed in microbial biomass occurred with a concurrent increase in plant yield

Soliton phase near antiferromagnetic quantum critical point in Q1D conductors

In the frameworks of a nesting model for Q1D organic conductor at the antiferromagnetic (SDW) quantum critical point the first-order transition separates metallic state from the soliton phase having the periodic domain structure. The low temperature phase diagram also displays the 2nd-order transition line between the soliton and the uniformly gapped SDW phases. The results agree with the phase diagram of (TMTSF)$_2$PF$_6$ near critical pressure [T. Vuletic et al., Eur. Phys. J. B 25, 319 (2002)]. Detection of the 2nd-order transition line is discussed. We comment on superconductivity at lowest temperature.Comment: 4 pages, 1 figur

Study of the bacterial community affiliated to Hyalesthes obsoletus, the insect vector of “bois noir” phytoplasma of grape

Grape yellows caused by phytoplasmas afflict several important wine-producing areas of Europe. A grape yellows with increasingincidence in European vineyards is “bois noir” (BN), caused by ‘Candidatus Phytoplasma solani’. Its vector is the planthopperHyalesthes obsoletus Signoret (Hemiptera Cixiidae), occasionally feeding on grapevine. An innovative strategy for reducing thediffusion of the disease could be symbiotic control, exploiting the action of symbiotic microorganisms of the insect host. To investigatethe occurrence of possible microbial candidates for symbiotic control we performed a molecular characterization of thebacteria associated to H. obsoletus. Length heterogeneity PCR was applied for a preliminary population screening. Taxonomicaffiliations of the bacterial species were analyzed by denaturing gradient gel electrophoresis, showing, within the microbial diversity,the intracellular reproductive parasite Wolbachia pipientis and a Bacteroidetes symbiont with 92% nt identity with ‘CandidatusSulcia muelleri’. PCR essays specific for these bacteria showed they co-localize in several organs of H. obsoletus. Fluorescentin situ hybridization was performed to assess the distribution of these microorganisms within the insect body, showing interestinglocalization patterns, particularly in insect gonads and salivary glands. These results could be a starting point for a deeper investigationof functions and relationships between microbial species

Comparison of different primer sets for use in automated ribosomal intergenic spacer analysis of complex bacterial communities

ITSF and ITSReub, constituting a new primer set designed for the amplification of the 16S-23S rRNA intergenic transcribed spacers, have been compared with primer sets consisting of 1406F and 23Sr (M. M. Fisher and E. W. Triplett, Appl. Environ. Microbiol. 65:4630-4636, 1999) and S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 (L. Ranjard et al., Appl. Environ. Microbiol. 67:4479-4487, 2001), previously proposed for automated ribosomal intergenic spacer analysis (ARISA) of complex bacterial communities. An agricultural soil and a polluted soil, maize silage, goat milk, a small marble sample from the fac\ub8ade of the Certosa of Pavia (Pavia, Italy), and brine from a deep hypersaline anoxic basin in the Mediterranean Sea were analyzed with the three primer sets. The number of peaks in the ARISA profiles, the range of peak size (width of the profile), and the reproducibility of results were used as indices to evaluate the efficiency of the three primer sets. The overall data showed that ITSF and ITSReub generated the most informative (in term of peak number) and reproducible profiles and yielded a wider range of spacer sizes (134 to 1,387) than the other primer sets, which were limited in detecting long fragments. The minimum amount of DNA template and sensitivity in detection of minor DNA populations were evaluated with artificial mixtures of defined bacterial species. ITSF and ITSReub amplified all the bacteria at DNA template concentrations from 280 to 0.14 ng l 1, while the other primer sets failed to detect the spacers of one or more bacterial strains. Although the primer set consisting of ITSF and ITSReub and that of S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 showed similar sensitivities for the DNA of Allorhizobium undicula mixed with the DNA of other species, the S-D-Bact-1522-b-S-20 and L-D-Bact-132-a-A-18 primer set failed to detect the DNA of Pseudomonas stutzeri

Superconductivity and Antiferromagnetism in Quasi-one-dimensional Organic Conductors

We review the current understanding of superconductivity in the quasi-one-dimensional organic conductors of the Bechgaard and Fabre salt families. We discuss the interplay between superconductivity, antiferromagnetism, and charge-density-wave fluctuations. The connection to recent experimental observations supporting unconventional pairing and the possibility of a triplet-spin order parameter for the superconducting phase is also presented.Comment: (v1) 30 pages, 13 figures; Review article for the 20th anniversary of high-Tc superconductivity, to appear in J. Low Temp. Phys. (v2) 1 Ref. adde

How do Plants-Having Different Exudation Patterns-Shape a Similar Microbial Community?

ABSTRACT Microorganisms associated with plants have been shown to improve plant growth and yield participating in the biogeochemical cycles of elements in soil. For these reasons, the rhizosphere microbiome is considered one of the key determinants of plant health and productivity. Plants can influence the qualitative and quantitative composition of the rhizosphere microbial community by releasing different classes of organic compound. Yet, this release depends on several factors, such as plant genotype, soil properties, plant nutritional status, climatic conditions. Within a previous study, we showed that the rhizosphere microbial communities associated to both iron (Fe)-sufficient and Fe-deficient tomato and barley plants, grown in different agricultural calcareous soils, were surprisingly similar and formed by bacterial strains that exhibit plant growthpromoting (PGPR) traits

Magnetic Determination of Hc2H_{c2} under Accurate Alignment in (TMTSF)2_2ClO4_4

Cantilever magnetometry has been used to measure the upper critical magnetic field $H_{c2}$ of the quasi-one dimensional molecular organic superconductor (TMTSF)$_2$ClO$_4$. From simultaneous resistivity and torque magnetization experiments conducted under precise field alignment, $H_{c2}$ at low temperature is shown to reach 5T, nearly twice the Pauli paramagnetic limit imposed on spin singlet superconductors. These results constitute the first thermodynamic evidence for a large $H_{c2}$ in this system and provide support for spin triplet pairing in this unconventional superconductorComment: Submitted July 1, 2003, Accepted December 9, 2003, Physical Review Letter

Geometrical barriers and lower critical field in MgB2 single crystals

International audienceThe first penetration field sHpd has been deduced from local magnetization and specific heat measurements in magnesium diboride single crystals. For Ha ic, the geometrical barriers (GB) play a dominant role in the irreversibility mechanism. In thin samples, neglecting the GB in this direction would then lead to a large overestimation of Hc1 deduced from Hp through the standard elliptical formula. The lower critical field is found to be isotropic at low temperature (0.11±0.01 T)

Safe-site effects on rhizosphere bacterial communities in a high-altitude alpine environment

The rhizosphere effect on bacterial communities associated with three floristic communities (RW, FI, and M sites) which differed for the developmental stages was studied in a high-altitude alpine ecosystem. RW site was an early developmental stage, FI was an intermediate stage, M was a later more matured stage. The N and C contents in the soils confirmed a different developmental stage with a kind of gradient from the unvegetated bare soil (BS) site through RW, FI up to M site. The floristic communities were composed of 21 pioneer plants belonging to 14 species. Automated ribosomal intergenic spacer analysis showed different bacterial genetic structures per each floristic consortium which differed also from the BS site. When plants of the same species occurred within the same site, almost all their bacterial communities clustered together exhibiting a plant species effect. Unifrac significance value (P < 0.05) on 16S rRNA gene diversity revealed significant differences (P < 0.05) between BS site and the vegetated sites with a weak similarity to the RW site. The intermediate plant colonization stage FI did not differ significantly from the RW and the M vegetated sites. These results pointed out the effect of different floristic communities rhizospheres on their soil bacterial communities

Different pioneer plant species select specific rhizosphere bacterial communities in a high mountain environment

The rhizobacterial communities of 29 pioneer plants belonging to 12 species were investigated in an alpine ecosystem to assess if plants from different species could select for specific rhizobacterial communities. Rhizospheres and unvegetated soils were collected from a floristic pioneer stage plot at 2,400 m a.s.l. in the forefield of Weisskugel Glacier (Matsch Valley, South Tyrol, Italy), after 160 years of glacier retreat. To allow for a culture-independent perspective, total environmental DNA was extracted from both rhizosphere and bare soil samples and analyzed by Automated Ribosomal Intergenic Spacer Analysis (ARISA) and Denaturing Gradient Gel Electrophoresis (DGGE). ARISA fingerprinting showed that rhizobacterial genetic structure was extremely different from bare soil bacterial communities while rhizobacterial communities clustered strictly together according to the plant species. Sequencing of DGGE bands showed that rhizobacterial communities were mainly composed of Acidobacteria and Proteobacteria whereas bare soil was colonized by Acidobacteria and Clostridia. UniFrac significance calculated on DGGE results confirmed the rhizosphere effect exerted by the 12 species and showed different bacterial communities (P < 0.05) associated with all the plant species. These results pointed out that specific rhizobacterial communities were selected by pioneer plants of different species in a high mountain ecosystem characterized by oligotrophic and harsh environmental conditions, during an early primary succession