Ground-layer plant community responses to even-age and uneven-age silvicultural treatments in Wisconsin northern hardwood forests

We evaluated ground-layer plant diversity and community composition in northern hardwood forests among uncut controls and stands managed with even-age or uneven-age silvicultural systems. Even-age treatments included diameter-limit cuttings (20-cm diameter at 30-cm stem height) in 1952 and shelterwood removals in 1964. Uneven-age treatments included three intensities of selection harvest (light, 20.6 m²/ha residual basal area after harvest; medium, 17.2 m²/ha residual basal area; and heavy, 13.8 m²/ha residual basal area) that were applied in 1952, 1962, 1972, and 1982. All treatments were winter logged over snow pack. In 1991, plant diversity and community composition were examined. Species richness for spring ephemerals ranged from 1 to 6 species/150-m², spring ephemeral diversity (Shannon's Index of Diversity) averaged 0.57 ± 0.04 and evenness averaged 0.45 ± 0.03. Summer flowering species richness ranged from 1 to 18 species/1-m², with an average diversity of 0.71 ± 0.07 and evenness of 0.42 ± 0.03. We found no significant differences among treatments for any of these variables, although power to detect a difference (at p = 0.05) was low in all cases (0.15–0.55) due to high variance and low replication. Community composition was not significantly different among the treatments, for either spring (p = 0.09) or summer (p = 0.79) flora. Few exotic species were found in any treatment. Lack of exotic invasions and minimal differences in plant diversity or composition among treatments may be due, in part, to the negligible amount of soil disturbance that resulted from winter logging. While other (unmeasured) ecosystem components may differ among these silvicultural treatments, our results suggest that ground-layer plant communities in northern hardwood ecosystems are either resistant to change or have recovered within the 40 years since disturbance in the even-age treatments and within 10 years since disturbance in the uneven-age treatments.     

Mechanical perturbation affects conductivity, mechanical properties and aboveground biomass of hybrid poplars

Xylem development in trees is affected by dynamic mechanical stresses imposed on stems by wind. To assess clonal differences in response to mechanical perturbation (MP), we subjected seven greenhouse-grown F1 hybrids of Populus trichocarpa Torr. and A. Gray. x P. deltoides Bartr. ex Marsh. to a standard MP treatment consisting of 20 manually imposed stem flexures per day for 70-90 days. Effects of MP on aboveground biomass, hydraulic conductivity (k(h)), specific conductivity (k(s)), flexural stiffness (EI), modulus of elasticity (MOE) and modulus of rupture (MOR) were determined. Treatment increased stem radial growth and decreased height growth, leaf area and total aboveground biomass. It also significantly decreased k(s), MOE and MOR, but significantly increased EI and wood specific gravity in most clones. Mechanical perturbation caused greater stem rigidity, without having a significant effect on whole-stem k(h) or percent loss of conductivity due to embolism. Maximum k(h) was positively correlated with EI in both control (r(2) = 0.54, P < 0.0001) and MP-treated (r(2) = 0.61, P < 0.0001) plants, and k(s) and MOE were positively correlated with percent vessel lumen area (r(2) = 0.45, P < 0.0001 and r(2) = 0.28, P = 0.002, respectively). Thus, contrary to our expectation of a trade-off between conductivity and wood strength, there may be an opportunity to select clones for woody biomass production that are superior in both mechanical strength and hydraulic conductivity, as is the triploid Clone 19-61.     

Phosphorus availability and farm structural factors: examining scarcity and oversupply in north‐east Germany

Assessing factors influencing phosphorus (P) availability in soils is important in preventing its overexploitation and excessive application in agricultural systems. Despite high historical P applications in the federal state of Brandenburg (Germany), county data on soil test P (STP) reveal considerable disparities in soil available P. In addition, negative soil balances as a result of small mineral P and manure inputs have been observed, raising questions about the factors leading to this situation. Our work focused on identifying possible causes operating at the farm management level by conducting a letter survey in two administrative districts of Brandenburg, the counties Barnim and Uckermark, linking farm management factors (ownership type, farm size, land tenure, animal husbandry with or without grassland and its intensity, presence of a biogas plant and organic production) to farmers’ self‐indicated levels of STP. Small‐ to medium‐sized individual farms tended to have (very) high STP, while large partnership farms and companies/cooperatives were sensitive to factors resulting in low STP. Farms with low shares of land ownership, the presence of grassland, extensive cattle farming and stockless organic farming had lower STP. On the other hand, biogas plants, partly in combination with intensive livestock (cattle) farming, were associated with larger STP. It was concluded that more care should be devoted to the design of agricultural policies and that further (inter‐ and transdisciplinary) research on this topic is needed.     

Ulcerative keratitis

Ulcerative keratitis comprises an important proportion of presenting ocular complaints in small animals. Because of its high frequency, corneal ulceration may not routinely stimulate the clinical concern for rigorous diagnosis, attentive management, and aversion of potential complications that it merits. Only by maintaining an appreciation for the pathologic processes at work during corneal injury and repair can busy clinicians competently diagnose, successfully treat, and forestall the complications of corneal ulceration.     

High-Resolution Imaging by Fourier Transform X-ray Holography

Fourier transform x-ray holography has been used to image gold test objects with submicrometer structure, resolving features as small as 60 nanometers. The hologram-recording instrument uses coherent 3.4-nanometer radiation from the soft x-ray undulator beamline X1A at the National Synchrotron Light Source. The specimen to be imaged is placed near the first-order focal spot produced by a Fresnel zone plate; the other orders, chiefly the zeroth, illuminate the specimen. The wave scattered by the specimen interferes with the spherical reference wave from the focal spot, forming a hologram with fringes of low spatial frequency. The hologram is recorded in digital form by a charge-coupled device camera, and the specimen image is obtained by numerical reconstruction.     

The crystal structure of a T cell receptor in complex with peptide and MHC class II

The crystal structure of a complex involving the D10 T cell receptor (TCR), 16-residue foreign peptide antigen, and the I-Ak self major histocompatibility complex (MHC) class II molecule is reported at 3.2 angstrom resolution. The D10 TCR is oriented in an orthogonal mode relative to its peptide-MHC (pMHC) ligand, necessitated by the amino-terminal extension of peptide residues projecting from the MHC class II antigen-binding groove as part of a mini beta sheet. Consequently, the disposition of D10 complementarity-determining region loops is altered relative to that of most pMHCI-specific TCRs; the latter TCRs assume a diagonal orientation, although with substantial variability. Peptide recognition, which involves P-1 to P8 residues, is dominated by the Valpha domain, which also binds to the class II MHC beta1 helix. That docking is limited to one segment of MHC-bound peptide offers an explanation for epitope recognition and altered peptide ligand effects, suggests a structural basis for alloreactivity, and illustrates how bacterial superantigens can span the TCR-pMHCII surface.     

Kinetics and postmucosal effects on urinary recovery of 5 intravenously administered sugars in healthy cats

The objective of this study was to describe the kinetics of urinary recovery and to evaluate the effects of postmucosal factors on urinary recovery of 5 intravenously administered saccharides. Ten cats received an isotonic sugar solution containing lactulose, rhamnose, xylose, methylglucose, and sucrose intravenously. These sugars were selected because of their prior use for intestinal permeability and mucosal function testing in humans and dogs. Urethral catheterization with a closed collection system was used for collection of cumulative urine samples prior to and 2, 4, 6, 8, 10, 12, and 24 h after administration of the sugar solution. High-pressure anion exchange liquid chromatography with pulsed amperometric detection was used to measure the concentrations of each sugar in the urine and calculate urinary recovery. Twenty-four hour cumulative urinary recovery for each sugar from the cats, was lower than expected compared to dogs and humans. All 5 sugars had the highest percentage of urinary recovery during the first 2 h after administration. Mean sugar elimination rate constants and half-lives ranged from 0.268/h for methylglucose to 0.415/h for lactulose and 1.67 h for lactulose to 2.59 h for methylglucose, respectively. Metabolism and incomplete urine collection are possible reasons for lower cumulative urinary recoveries of these 5 sugars in cats compared with dogs. Although these 5 sugars are not ideal marker molecules, they may still be useful for intestinal permeability and mucosal function testing in cats.     

猪败血型链球菌病的诊疗报告

本文阐述了猪链球菌病的临床症状、实验室检验及防治方法，力求为科学防控猪链球菌病提供有益的探索和参考。