Balsamia (Sequestrate Helvellaceae, Ascomycota) in western North America.

Balsamia, a hypogeous, sequestrate genus in the Helvellaceae, has been characterized variously as having three to eight species in North America, and these have been considered either different from or conspecific with European species. No available modern systematic treatment of Balsamia exists to allow for accurate identification at the species level. We sequenced DNA from recent western North American Balsamia collections, assessed relationships by sequence similarity, and identified molecular taxonomic units. From these data, we determined which matched descriptions and types of named species. ITS sequences supported 12 Balsamia species in western North America, five originally described by Harkness and Fischer and seven new species that we describe here. No sequences from Balsamia collections in western North America were nested among those of European species. We found no clear evidence for separation of Balsamia into multiple genera.

High-Q nanomechanics via destructive interference of elastic waves.

Mechanical dissipation poses a ubiquitous challenge to the performance of nanomechanical devices. Here we analyze the support-induced dissipation of high-stress nanomechanical resonators. We develop a model for this loss mechanism and test it on Si(3)N(4) membranes with circular and square geometries. The measured Q values of different harmonics present a nonmonotonic behavior which is successfully explained. For azimuthal harmonics of the circular geometry we predict that destructive interference of the radiated waves leads to an exponential suppression of the clamping loss in the harmonic index. Our model can also be applied to graphene drums under high tension.

Real-time synchronous imaging of electromechanical resonator mode and equilibrium profiles.

Interferometric imaging of normal mode dynamics in electromechanical resonators, oscillating in the rf regime, is demonstrated by synchronous imaging with a pulsed nanosecond laser. Profiles of mechanical modes in suspended thin film structures and their equilibrium profiles are measured through all-optical Fabry-Perot reflectance fits to the temporal traces. As a proof of principle, the mode patterns of a microdrum silicon resonator are visualized, and the extracted vibration modes and equilibrium profile show good agreement with numerical estimations.

Stress and silicon nitride: a crack in the universal dissipation of glasses.

High-stress silicon nitride microresonators exhibit a remarkable room temperature Q factor that even exceeds that of single crystal silicon. A study of the temperature dependent variation of the Q of a 255 micromx255 micromx30 nm thick high-stress Si3N4 membrane reveals that the dissipation Q-1 decreases with lower temperatures and is approximately 3 orders of magnitude smaller than the universal behavior. Stress-relieved cantilevers fabricated from the same material show a Q that is more consistent with typical disordered materials. e-beam and x-ray studies of the nitride film's structure reveal characteristics consistent with a disordered state. Thus, it is shown that stress alters the Q-1, violating the universality of dissipation in disordered materials in a self-supporting structure.

Application of network theory to potential mycorrhizal networks.

The concept of a common mycorrhizal network implies that the arrangement of plants and mycorrhizal fungi in a community shares properties with other networks. A network is a system of nodes connected by links. Here we apply network theory to mycorrhizas to determine whether the architecture of a potential common mycorrhizal network is random or scale-free. We analyzed mycorrhizal data from an oak woodland from two perspectives: the phytocentric view using trees as nodes and fungi as links and the mycocentric view using fungi as nodes and trees as links. From the phytocentric perspective, the distribution of potential mycorrhizal links, as measured by the number of ectomycorrhizal morphotypes on trees of Quercus garryana, was random with a short tail, implying that all the individuals of this species are more or less equal in linking to fungi in a potential network. From the mycocentric perspective, however, the distribution of plant links to fungi was scale-free, suggesting that certain fungus species may act as hubs with frequent connections to the network. Parallels exist between social networks and mycorrhizas that suggest future lines of study on mycorrhizal networks.

Morphology and Stomatal Function of Douglas Fir Needles Exposed to Climate Change: Elevated CO2 and Temperature.

Climate change may have an impact on the productivity of conifer trees by influencing the morphology (size and surface characteristics) and function (capacity for gas exchange) of conifer needles. In order to test the responses of needles to climatic variables, Douglas fir (Pseudotsuga menziesii [Mirb.] Franco), saplings were grown in sunlit controlled environment chambers at ambient or elevated (+200 parts per million above ambient) CO2 and at ambient or elevated temperature (+4 degrees C above ambient). Needle characteristics, including length, width, area, stomatal density (stomata per mm2), percentage of stomatal occlusion, and the morphology of epicuticular wax, were evaluated. Needle function was evaluated as stomatal conductance to water vapor and transpiration. Needle length increased significantly with elevated temperature but not with elevated CO2. Neither elevated CO2 nor elevated temperature affected stomatal density or stomatal number in these hypostomatous needles. Epicuticular wax was less finely granular at elevated than at ambient temperature and was similar in appearance at elevated and ambient CO2. Stomatal conductance and transpiration increased with elevated temperature and associated increased vapor pressure deficit; however, neither conductance nor transpiration was affected by elevated CO2. These results indicate that simulated climate change influences Douglas fir needle structure and function.

Comparison of flagellated and nonflagellated sperm in plants.

Differences among flagellated and nonflagellated sperm in land plants are striking, but close examination reveals similarities in pattern of cytoskeleton and in nuclear structure. The microtubular cytoskeleton of flowering plant sperm consists of microtubule bundles arranged obliquely around the nucleus, terminating in cellular extensions. Microtubules are linked into bundles that branch and rejoin along the axis of the sperm cell, forming a cytoskeleton that determines cell shape but does not actively participate in cell movement. Generative cells and sperm share a pattern of microtubules not found in somatic cells. This pattern is initiated in the generative cell, one division before sperm formation, a situation parallel to spermatogenous cell development in vascular plants with flagellated sperm. Chromatin in flagellated and nonflagellated sperm is condensed by specialized histones.

Antibodies to pollen exines.

A polyclonal antiserum and monoclonal antibodies have been prepared to purified pollen exines of Calocedrus decurrens Florin. The location of the antigen is in the exine, as shown by light-and electron-microscopic immunocytochemistry. The greatest reduction in antibody binding follows treatment of the exine with chemicals known to alter sporopollenin. These results provide evidence that sporopollenin is antigenic. Exines of ten species of gymnosperms and angiosperms also bound the polyclonal antiserum, indicating similarity of sporopollenin structure.

beta-1, 3-Glucan Synthase from Lilium longiflorum Pollen.

A particulate fraction from pollen tubes and ungerminated pollen of Lilium longiflorum incorporated (14)C-glucose from UDP-glucose-(14)C into a lipid fraction and into beta-1, 3-glucan. Partial hydrolysis of the glucan yielded laminaribiose as the only radioactive disaccharide. The preferred substrate was UDP-glucose, and enzyme activity was stimulated by glucose and by beta-linked di- and trisaccharides. Enzyme from growing pollen tubes synthesized beta-1, 3-glucan more rapidly and produced a higher proportion of alkali-insoluble glucan than did enzyme from ungerminated pollen. The onset of pollen tube growth may be dependent on altered activity of beta-1, 3-glucan synthase.