Litter quality and nutrient cycling affected by grazing-induced species replacements along a precipitation gradient

One of the potential mechanisms for the impact of herbivores on nutrient cycling is the effect of selective grazing on litter quality through changes in species composition. However, the scarce evidence collected on this mechanism is controversial and seemingly influenced by site-specific variables. In this paper, we explored the consequences of grazing-induced changes in species composition on litter quality and nitrogen cycling with a regional perspective. Along a 900-mm of mean annual rainfall gradient, we selected species promoted and diminished by grazing from three natural rangelands of Argentina, analyzed their litter quality, and determined their decomposition and nutrient release kinetics under common greenhouse conditions. Litter quality and decomposition rates were strongly associated with plant response to grazing. However, the magnitude and direction of these differences depended on the ecosystem considered. In the wettest site, the species promoted by grazing (forbs) had higher nitrogen and phosphorus contents, faster decomposition rates, and higher release of nitrogen to the soil than species diminished by grazing (C₃ and C₄ grasses). In the intermediate and dry sites, species promoted by grazing had lower nitrogen and phosphorus contents, and slower decomposition rates than those diminished by grazing (C₃ grasses in both cases). Decomposition of the entire group of species was not correlated with mean annual rainfall, but when litter of the species diminished by grazing was analyzed, it was negatively correlated with precipitation. Nitrogen was immobilized more often than mineralized, even after one year of incubation. Immobilization was negatively correlated with precipitation. All these results indicate that grazing may significantly alter nutrient cycling by affecting litter quality through changes in species composition. These effects seem to be larger when species replacements induced by grazing either involve functional groups, as it was the case in our wettest site, or change root to shoot ratios. Therefore, the functional groups involved in the replacement of species as well as shifts between belowground and aboveground allocation should play a key role in grazing-induced changes on nitrogen cycling.     

Preferred conformation of peptides rich in Ac8c,a medium-ring alicyclic Cα,α-disubstituted glycine

A complete series of terminally blocked, monodispersed homo-oligopeptides (to the pentamer level) from the sterically demanding, medium-ring alicyclic C^α,α-disubstituted glycine 1-aminocyclooctane-1-carb oxylic acid (Ac₈c), and two Ala/Ac₈c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and ¹H-NMR. The molecular structures of the amino acid derivative Z-Ac₈c-OH, the dipeptide pBrBz- (Ac₈c)₂-OH and the tripeptide pBrBz-(Ac₈c)₃-OtBu were assessed in the crystal state by X-ray diffraction. Conformational energy computations were performed on the monopeptide Ac-Ac₈c-NHMe. Taken together, the results obtained strongly support the view that the Ac₈c residue is an effective β-turn and helix former. A comparison is also made with the conformational preferences of α-aminoisobutyric acid, the prototype of C^{α, α}-disubstituted glycines, and of the other members of the family of 1-aminocycloalkane-1-carboxylic acids (Ac_nc, with n=3, 5–7) investigated so far. The implications for the use of the Ac₈c residue in peptide conformational design are considered.     

Pathogenicity of Macroposthonia xenoplax to Walnut

Preplanting treatment of soil naturally infested with Macroposthonia xenoplax with 1,2-dibromoethane (ethylene dibromide) significantly increased the growth rate of Juglans hindsii seedlings. When seedlings of J. hindsii, J. regia CV "Serf" and J. regia CV Eureka were inoculated with M. xenoplax, their growth was signilicantly less than that of nematode-free controls. This retarded growth rate was accompanied hy feeder root necrosis, longitudinal cracks in the older roots, and distinct lesions in the secondary phloem.     

On the taxonomic status of a Dugesia species from Buenos Aires (Platyhelminthes: Turbellaria: Tricladida)

The taxonomic and distributional statuses of the freshwater planarians of South America are imperfectly understood, and a comprehensive review is sorely needed. The species known from the vicinity of Buenos Aires, Argentina, was first described by Böhmig (1902) under the name Planaria dubia Borelli, 1895. Subsequent authors (Kenk, 1930, 1974; Cazzaniga & Curino, 1987) have cast doubt on this assignation. Some have assigned it to Dugesia anceps Kenk; Hyman (1959) was inclined to regard the Buenos Aires planarian as a geographical variant of Dugesia sanchezi Hyman. A comparison of D. sanchezi from the mountainous region of central Chile with specimens from Buenos Aires confirms that the Argentinian material is a distinct species.The differences between the two species are subtle. The Argentinian specimens are distinctive in their possession of infranucleate epithelia of the atria, penis, and bursal canal, as well as in their penial structure. In both species, the epithelia of the atria and bursal canal are glandular. Those of D. sanchezi are nucleate and their secretions are cyanophilous. In the Argentinian specimens, these same epithelia are infranucleate; but while the secretion of the bursal canal is indeed cyanophilous, that of the atrium is erythrophilous. The presence, in these same specimens, of cyanophilous glands opening into the penial vesicles, and of erythrophilous glands whose secretions contribute to a viscous plug in the ejaculatory duct, suggests a difference in the physiology of copulation.It is apparent that the Argentinian specimens are distinct from D. sanchezi Hyman, and probably they represent a new species, one to be described in detail elsewhere. In any case, Hyman's (1959) suggestion that D. sanchezi occurs near Buenos Aires is mistaken; so also is Cazzaniga's & Curino's (1987) identification of specimens from Buenos Aires as D. anceps.     

A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques

After disulphide bonds are reduced with dithiothreitol, trans-3- (α-bromomethyl)-3’-[α- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this “tethered agonist” shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 μM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to “open-channel blockade” bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3’,bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel’s activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules.     

CD7 is a differentiation marker that identifies multiple CD8 T cell effector subsets

The adaptive immune response of human CD8 T cells to invading pathogens involves the differentiation of naive cells into memory and effector cells. However, the lineage relationship between memory and effector cells and the differentiation of CD8 T cells into distinct subsets of effector cell subpopulations are subjects of considerable debate. CD7 identifies three populations of CD8 T cells: CD7 high (CD7(high)), low (CD7(low)), and negative (CD7(neg)) that translate into subsets with distinct functional properties. The CD7(high) subset contains naive and memory cells and the CD7(low) and CD7(neg) subsets contain effector cells. The effector cells can functionally be divided into cytokine-secreting effector CD8 T cells and lytic effector CD8 T cells. These data provide a model of human CD8 T cell differentiation in which specialized distinct subpopulations can be identified by expression of CD7.     

Phytoplankton and chemico-physical parameters of the Scardovari Lagoon (Po Delta,North Adriatic Sea) during 1991 and 1992

Abstract

During research directed towards the employment of the biological resources of the North Adriatic lagoons, from January 1991 to December 1992, in both tidal phases, a survey was carried out on the phytoplankton and the chemico-physical parameters of the Scardovari lagoon. Data analyses allowed two different areas to be distinguished: one inner, which was generally characterized by high phytoplanktonic densities (St. 3–4), the other outer, which was more influced by marine load (St. 1–2). Photosynthetic picoplankton was dominant in terms of cell number in most samples. Phytoplanktonic fraction >2 μm was represented mainly by diatoms, which showed the higher species number. During the sample observation, some dinoflagellates, considered toxic or potentially toxic, were found. Their presence was important because of their effect on the bivalve mollusc cultures.     

Growth Monitoring: A Survey of Current Practices of Primary Care Paediatricians in Europe

Objective

We aimed to study current practices in growth monitoring by European primary care paediatricians and to explore their perceived needs in this field.

Methods

We developed a cross-sectional, anonymous on-line survey and contacted primary care paediatricians listed in national directories in the 18 European countries with a confederation of primary care paediatricians. Paediatricians participated in the survey between April and September 2011.

Results

Of the 1,198 paediatricians from 11 European countries (response rate 13%) who participated, 29% used the 2006 World Health Organization Multicentre Growth Reference Study growth charts, 69% used national growth charts; 61% used software to draw growth charts and 79% did not use a formal algorithm to detect abnormal growth on growth charts. Among the 21% of paediatricians who used algorithms, many used non-algorithmic simple thresholds for height and weight and none used the algorithms published in the international literature. In all, 69% of paediatricians declared that a validated algorithm to monitor growth would be useful in daily practice. We found important between-country variations.

Conclusion

The varied growth-monitoring practices declared by primary care paediatricians reveals the need for standardization and evidence-based algorithms to define abnormal growth and the development of software that would use such algorithms.