Diversity of fungal endophytic community in Quercus suber L. under different climate scenarios

Cork oak (Quercus suber L.) is an evergreen oak tree species, typically found throughout the Mediterranean Basin that presents a great ecological and economic importance in Portugal. The ecological importance is due to the role in the protection of the soil, biodiversity control, water quality and oxygen production. The cork production and processing confer cork oak a great economic relevance in Portugal. An increase of cork oak decline due to biotic and abiotic stresses has been reported, which could damage the ecosystem and lower cork production. Fungal species as D;plod;a corticola and Biscogniauxia mediterranea are cork oak pathogens that cause tree decline and affect cork productivity. The incidence of both diseases seems to increase when trees are under several environmental stresses, such as increased temperatures or drought. In this work, fungal endophytic species of cork oak were collected in different sites of Portugal (Bragança, Gerês, Alcobaça, Grândola e Gavião). The collection sites displayed differences in water availability and cork oak trees in different phytosanitary conditions. The community of fungal endophytes of young twigs and one/two-years old branches were studied by detecting fungal outgrowing from aseptic plant pieces and grouping them into morphotypes. A differentiation between live and death (xylem) branch tissue was considered by culturing the most superficial branch wood or the most inner wood. Collection sites with higher precipitation seem to display a more diverse community. Branches displayed a more diverse fungal community than young twigs, being the endophytic community, present in inner wood, more similar between sites, than young twigs or outer branch tissues. This study allowed the comparison of fungal endophytic communities living in cork oak trees with different water availability levels and disease symptoms. The results provide a good starting point towards the comprehension of the fungal community influence in disease occurrence.info:eu-repo/semantics/publishedVersio

Susceptibility Inhomogeneity and Non-Fermi-Liquid Behavior in Ce(Ru_{0.5}Rh_{0.5})_2Si_2

Magnetic susceptibility and muon spin rotation (\muSR) experiments have been carried out to study the effect of structural disorder on the non-Fermi-liquid (NFL) behavior of the heavy-fermion alloy Ce(Ru_{0.5}Rh_{0.5})_2Si_2. Analysis of the bulk susceptibility in the framework of disorder-driven Griffiths-phase and Kondo-disorder models for NFL behavior yields relatively narrow distributions of characteristic spin fluctuation energies, in agreement with \muSR linewidths that give the inhomogeneous spread in susceptibility. \muSR and NMR data both indicate that disorder explains the "nearly NFL" behavior observed above \sim2 K, but does not dominate the NFL physics found at low temperatures and low magnetic fields.Comment: 6 pages, 4 figures, REVTeX, submitted to Phys. Rev.

Non-Fermi-Liquid Scaling in Ce(Ru_{0.5}Rh_{0.5})_2Si_2

We study the temperature and field dependence of the magnetic and transport properties of the non-Fermi-liquid compound Ce(Ru_{1-x}Rh_x)_2Si_2 at x=0.5. For fields $\lesssim$0.1T the experimental results show signatures of the presence of Kondo-disorder, expected to be large at this concentration. For larger fields, however, magnetic and transport properties are controlled by the coupling of the conduction electrons to critical spin-fluctuations. The temperature dependence of the susceptibility as well as the scaling properties of the magnetoresistance are in very good agreement with the predictions of recent dynamical mean-field theories of Kondo alloys close to a spin-glass quantum critical point.Comment: 4 pages, 4 figures. Improved discussion. To appear in Phys. Rev. Let

Role of Disorder on the Quantum Critical Point of a Model for Heavy Fermions

A zero temperature real space renormalization group (RG) approach is used to investigate the role of disorder near the quantum critical point (QCP) of a Kondo necklace (XY-KN) model. In the pure case this approach yields $J_{c}=0$ implying that any coupling $J \not = 0$ between the local moments and the conduction electrons leads to a non-magnetic phase. We also consider an anisotropic version of the model ($X-KN$), for which there is a quantum phase transition at a finite value of the ratio between the coupling and the bandwidth, $(J/W)$. Disorder is introduced either in the on-site interactions or in the hopping terms. We find that in both cases randomness is irrelevant in the $X-KN$ model, i.e., the disorder induced magnetic-non-magnetic quantum phase transition is controlled by the same exponents of the pure case. Finally, we show the fixed point distributions $P_{J}(J/W)$ at the atractors of the disordered, non-magnetic phases.Comment: 5 pages, 3 figure

Quantum Griffiths effects and smeared phase transitions in metals: theory and experiment

In this paper, we review theoretical and experimental research on rare region effects at quantum phase transitions in disordered itinerant electron systems. After summarizing a few basic concepts about phase transitions in the presence of quenched randomness, we introduce the idea of rare regions and discuss their importance. We then analyze in detail the different phenomena that can arise at magnetic quantum phase transitions in disordered metals, including quantum Griffiths singularities, smeared phase transitions, and cluster-glass formation. For each scenario, we discuss the resulting phase diagram and summarize the behavior of various observables. We then review several recent experiments that provide examples of these rare region phenomena. We conclude by discussing limitations of current approaches and open questions.Comment: 31 pages, 7 eps figures included, v2: discussion of the dissipative Ising chain fixed, references added, v3: final version as publishe

Study of L-Arginine in Intestinal Lesions Caused by Ischemia-Reperfusion in Rats

examine whether treatment with L-arginine (ARG), a substrate of nitric oxide biosynthesis, attenuated intestinal dysfunction caused by ischemia (I) and reperfusion (R), we treated rats with ARG (100 mg/kg intravenously) or saline solution (SS) before 60 minutes of I produced by occlusion of the superior mesenteric artery and/or during 120 minutes of R. After I or I/R, we isolated 2-cm jejunal segments for mounting in an organ bath to study neurogenic contractions stimulated by electrical pulses or KCl with the use of a digital recording system. Thin jejunal slices were stained with hematoxylin and eosin for optical microscopy. Jejunal contractions were similar in the sham and I + ARG, but reduced in I + SS, I/R + SS, and I/R + ARG groups. Jejunal enteric nerves were damaged in I + SS, IR + SS, and IR + ARG, but not in the I + ARG group, suggesting that ARG attenuate intestinal dysfunctions due to I but not to R.Universidade Federal de São Paulo, Dept Surg, Escola Paulista Med, BR-04023900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Pharmacol, BR-04023900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biochem, BR-04023900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Morphol, BR-04023900 São Paulo, BrazilFed Univ Great Dourados, Sch Med, Dourados, BrazilUniversidade Federal de São Paulo, Dept Surg, Escola Paulista Med, BR-04023900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Pharmacol, BR-04023900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biochem, BR-04023900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Morphol, BR-04023900 São Paulo, BrazilWeb of Scienc

Crystal Field Triplets: A New Route to Non-Fermi Liquid Physics

A model for crystal field triplet ground states on rare earth or actinide ions with dipolar and quadrupolar couplings to conduction electrons is studied for the first time with renormalization group methods. The quadrupolar coupling leads to a new nontrivial, non-Fermi liquid fixed point, which survives in an intermediate valence Anderson model. The calculated magnetic susceptibility displays one parameter scaling, going as $T^{-\alpha}$ ($\alpha \approx 0.4$) at intermediate temperatures, reminiscent of the non-Fermi liquid alloy UCu_{5-x}Pd_x.Comment: 4 pages, 3 figures, REVTe

Disorder-to-order transition in the magnetic and electronic properties of URh_2Ge_2

We present a study of annealing effects on the physical properties of tetragonal single--crystalline URh_2Ge_2. This system, which in as-grown form was recently established as the first metallic 3D random-bond heavy-fermion spin glass, is transformed by an annealing treatment into a long-range antiferromagnetically (AFM) ordered heavy-fermion compound. The transport properties, which in the as-grown material were dominated by the structural disorder, exhibit in the annealed material signs of typical metallic behavior along the crystallographic a axis. From our study URh_2Ge_2 emerges as exemplary material highlighting the role and relevance of structural disorder for the properties of strongly correlated electron systems. We discuss the link between the magnetic and electronic behavior and how they are affected by the structural disorder.Comment: Phys. Rev. B, in print (scheduled 1 Mar 2000