Occurrence and abundance of carbohydrates and amino compounds in sequentially extracted labile soil organic matter fractions

Purpose

The study aimed to describe the carbohydrates and amino compounds content in soil, the light fraction (LF), the >53 μm particulate organic matter (POM), and the mobile humic acid (MHA) fraction and to find out whether the carbohydrates and amino compounds can be used to explain the origin of SOM fractions.

Materials and methods

Soil samples were collected from two agricultural fields managed under organic farming in southern Italy. The LF, the POM, and the MHA were sequentially extracted from each soil sample then characterized. Seven neutral sugars and 19 amino compounds (amino acids and amino sugars) were determined in each soil sample and its correspondent fractions.

Results and discussion

The MHA contained less carbohydrate than the LF or the POM but its carbohydrates, although dominated by arabinose, were relatively with larger microbial contribution as revealed by the mannose/xylose ratio. The amino compounds were generally less in the LF or the POM than in the MHA, while the fungal (aspartic and serine) and bacterial (alanine and glycine) amino acids were larger in the MHA than in the LF or the POM, underlining the microbial contribution to the MHA. Results from both sites indicated that total carbohydrates content decreased moving from the LF (younger fraction) to the MHA (older fraction), which seems to follow a decomposition continuum of organic matter in the soil-plant system.

Conclusions

The study showed that the MHA is a labile humified fraction of soil C due to its content of carbohydrates and concluded that the content of carbohydrates and amino compounds in the LF, the POM and the MHA can depict the nature of these fractions and their cycling pattern and response to land management.

     

Do woodlice (Isopoda: Oniscidea) produce endogenous cellulases?

In studies on digestive processes and microorganisms in the gut of the common woodlouse, Porcellio scaber (Isopoda: Oniscidea), we observed marked contradictions between the activity of cellulolytic enzymes and the number of microorganisms. The anterior hindgut exhibited the highest cellulolytic activity, but was characterized by low microbial counts. Due to the presence of endosymbiotic bacteria in the midgut lobes that appear to produce cellulases, we suggest that the cellulases that are active in the hindgut of woodlice are of endogenous origin. Received: 4 April 1997     

Does leaf litter quality influence population parameters of the common woodlouse, Porcellio scaber (Crustacea: Isopoda)?

Population parameters (mortality of females, reproductive success, longevity of juveniles) of the common woodlouse, Porcellio scaber (Isopoda, Oniscidea), were examined with respect to the influence of varying leaf litter attributes: pH level, microbial cellulase activity, microbial dehydrogenase activity, protein content, nitrogen content, water content, tannin content, total phenol content and toughness of the leaves. These attributes were combined by using Principal Component Analysis. We obtained three Principal Components (PC) that were defined as “acidification,”“microorganisms” and “tree species.” The PCs explained 85% of the variance of leaf litter attributes. The PC “acidification” mainly influenced the mortality of females (P<0.001), while the longevity of juveniles showed significant correlation to the PC “microorganisms” (P<0.05). The PC “tree species” showed no influence on the observed population parameters, indicating that the leaf litter species itself had no direct influence on the population parameters of P. scaber. The reproductive success of females could not be explained by either of the PCs, but was influenced by cellulolytically active microorganisms (P<0.01). From these results, we conclude that acidification and reduced microbial activity in the field will cause a decrease in population density of P. scaber. Received: 30 July 1996     

Parameter sensitivity and field evaluation of SIDRA model

The simulation model SIDRA is based on a semi-analytical and semi-numerical solution to the Boussinesq equation. It has been developed on the ground of theoretical and field experimental results with the aim of a good prediction of both drainage peak and recession flow rates. Theoretical aspects and basic equations of the model are presented for the most general case where both soil physical properties and water table shapes are depth-dependent. The parameter sensitivity and field performances of the model are estimated in shallow loamy soils facing a seasonal waterlogging during winter season in France. Water table shape factors are the most sensitive parameters. Drainable porosity is slightly more sensitive than hydraulic conductivity for drainflow rate prediction whereas hydraulic conductivity is slightly more sensitive for water table elevation prediction. A comparison of experimental and simulated long term discharge and water table exceedance duration curves shows that the model could be a useful tool to assess the performances and control the relevance of a given subsurface drainage design.

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Résumé Le modèle de simulation SIDRA est basé sur une résolution semi-analytique et semi-numérique de l'équation de Boussinesq. Il a été développé à partir d'une approche théorique et de l'analyse de résultats d'expérimentations de terrain avec pour principal objectif d'atteindre une bonne prédiction des débits de pointe et de tarissement. Les principales équations du modèles sont présentées dans leur forme la plus générale qui permet de prendre en compte des propriétés hydrodynamiques et des formes de nappe dépendantes de la profondeur. L'étude de sensibilité aux paramètres et l'évaluation des performances du modèle sont réalisées dans le cas de sols limoneux peu profonds, sur la période hivernale où se manifeste l'engorgement des sols en France. Le modèle est très sensible aux variations des facteurs de forme de nappe. Concernant les paramètres hydrodynamiques, les débits simulés sont plus sensibles aux variations de la porosité de drainage qu'à celles de la conductivité hydraulique. A l'inverse les hauteurs de nappe simulées sont plus sensibles aux variations de conductivité hydraulique. Une comparaison sur une longue période des fréquences de dépassement de débits et hauteurs de nappe, simulées et observées, montre que le modèle peut constituer un bon outil de contrôle de l'efficacité d'un réseau de drainage et de son dimensionnement.

     

RADIOGRAPHIC, COMPUTED TOMOGRAPHIC AND HISTOPATHOLOGIC APPEARANCE OF A PRESUMED SPINAL CHORDOMA IN A DOG

A 4-year-old Labrador Retriever presented for urinary incontinence and constipation of 2 weeks duration. There was a tender abdomen, lumbar pain and conscious proprioceptive deficits in both pelvic limbs. Depressed pelvic limb reflexes were present consistent with a lower motor neuron lesion. In radiographs of the lumbar spine there was narrowing of the intervertebral disc space at L5-L6 with irregular, multifocal areas of mineralized opacities dorsal to the intervertebral disc space, presumably within the vertebral canal. On computed tomography, an intramedullary, partially mineralized mass was identified in the spinal cord at the level of caudal L5 through cranial L6. At necropsy there was a four-centimeter enlarged, irregular segment of spinal cord at the level of L5-L6. When sectioned, the spinal cord bad a mineralized texture. Histologically there were variable sized cells that were stellate in appearance with vacuolated cytoplasm (physaliferous cells) and mucinous background consistent with a chordoma. Chordoma is a rare, skeletal neoplasm that originates from mesoderm-derived notochord and has been reported in humans and animals. Extraskeletal development of a chordoma within the spinal cord is a rare manifestation of this neoplasm. However, based on other reports in dogs, solitary extraskeletal locations of chordomas may be the typical expression of this neoplasm in the dog. Differentiation of similar histologically appearing tumors, such as a parachordoma or myxoid chondrosarcoma, will require immunohistochemical characterization of these tumors in veterinary patients.     

Crystal structure of the potassium channel KirBac1.1 in the closed state

The KirBac1.1 channel belongs to the inward-rectifier family of potassium channels. Here we report the structure of the entire prokaryotic Kir channel assembly, in the closed state, refined to a resolution of 3.65 angstroms. We identify the main activation gate and structural elements involved in gating. On the basis of structural evidence presented here, we suggest that gating involves coupling between the intracellular and membrane domains. This further suggests that initiation of gating by membrane or intracellular signals represents different entry points to a common mechanistic pathway.     

GlyR alpha3: an essential target for spinal PGE2-mediated inflammatory pain sensitization

Prostaglandin E2 (PGE2) is a crucial mediator of inflammatory pain sensitization. Here, we demonstrate that inhibition of a specific glycine receptor subtype (GlyR alpha3) by PGE2-induced receptor phosphorylation underlies central inflammatory pain sensitization. We show that GlyR alpha3 is distinctly expressed in superficial layers of the spinal cord dorsal horn. Mice deficient in GlyR alpha3 not only lack the inhibition of glycinergic neurotransmission by PGE2 seen in wild-type mice but also show a reduction in pain sensitization induced by spinal PGE2 injection or peripheral inflammation. Thus, GlyR alpha3 may provide a previously unrecognized molecular target in pain therapy.     

Response of lactating dairy cows fed different supplemental zinc sources with and without evaporative cooling to intramammary lipopolysaccharide infusion: metabolite and mineral profiles in blood and milk

The objective of this study was to determine the effect of evaporative cooling and dietary supplemental Zn source on blood metabolites, insulin and mineral concentrations, and milk mineral concentrations following intramammary lipopolysaccharide (LPS) infusion. Seventy-two multiparous Holstein cows were assigned to one of four treatments with a 2 × 2 factorial arrangement. Treatments included two environments: with or without evaporative cooling using fans and misters over the freestall and feedbunk, and two dietary sources of supplemental Zn: 75 mg/kg of dry matter (DM) supplied by Zn hydroxychloride (inorganic Zn; IOZ) or Zn hydroxychloride (35 mg of Zn/kg of DM) + Zn–Met complex (ZMC; 40 mg of Zn/kg of DM). A subset of cows (n = 16; 263 ± 63 d in milk) was infused with 10 μg of LPS or a saline control in the left or right rear quarters on day 34 of the environmental treatment. Individual milk samples collected from LPS-infused quarters at −4, 0, 6, 12, 24, 48, 72, 96, and 144 h relative to infusion were analyzed for minerals. Blood samples were collected at the same time with an additional sample collected at 3 h post-infusion to analyze glucose, nonesterified fatty acids (NEFA), insulin, and minerals. Cooling by time interactions (P ≤ 0.07) were observed for plasma glucose, NEFA, and serum insulin. Compared with cooled cows, non-cooled cows had lower concentrations of plasma glucose except at 3 h following intramammary LPS infusion, greater serum insulin at 3 and 12 h, and lower plasma NEFA at 24 and 48 h after infusion. Relative to cooled cows, non-cooled cows tended (P = 0.07) to have lower serum K concentration and had lower (P < 0.01) serum Zn 6 h following infusion (cooling by time interaction: P < 0.01). Relative to ZMC cows, IOZ cows had greater (P ≤ 0.09) concentrations of plasma Se, skim milk Na and Se, and skim milk Na to K ratio. Regardless of treatment, intramammary LPS infusion reduced (P < 0.01) serum or plasma concentrations of Ca, Mg, Zn, Fe, and Se, but increased (P < 0.01) their concentration in skim milk. In conclusion, deprivation of cooling resulted in more rapid and prolonged insulin release and influenced the systemic and mammary mineral metabolism during mammary inflammation induced by LPS of lactating dairy cows. Dietary supplementation of Zn–Met complex reduced blood and milk Se concentrations compared with cows fed Zn from an inorganic source.