Effect of tillage and crop on arbuscular mycorrhiza

Large-scale inoculation with arbuscular mycorrhizal fungi (AMF) is generally impractical in most regions and we have little understanding of the factors that determine inoculation success. Nevertheless, the ability to take full advantage of indigenous AMF for sustainable production needs to be developed within cropping systems. We used part of a long-term field experiment to understand the influence of tillage and the preceding crop on AMF colonization over the growing season. Arbuscular mycorrhiza colonization rate was more affected by treatment (tillage or the combination of crop and preceding crop) than by the total number of AMF spores in the soil. Conventional tillage (CT) had a statistically significant negative effect (P £ 0.05) on spore numbers isolated from the soil, but only in the first year of study. However, the AMF colonization rate was significantly reduced by CT, and the roots of wheat, Triticum aestivum, L, cv. Coa after sunflower, Helianthus annuus L., were less well colonized than were those of triticale, X Triticosecale Wittmack, cv. Alter after wheat, but the affect of tillage was more pronounced than was the effect of crop combination. Under no-till there was a significant increase in AMF colonization rate throughout the sampling period in both wheat and triticale,indicating that the extraradical mycelium previously produced acted as a source of inoculum. In general, triticale showed greater AMF colonization than wheat, despite the preceding crop being less mycotrophic. Under these experimental conditions, typical of Mediterranean agricultural systems, AMF colonization responded more strongly to tillage practices than to the combination of crop and preceding crop

Laser pulse detection method and apparatus

A sensor is described for detecting the difference in phase of a pair of returned light pulse components, such as two components of a light pulse of an optical gyro. In an optic gyro, the two light components have passed in opposite directions through a coil of optical fiber, with the difference in phase of the returned light components determining the intensity of light shining on the sensor. The sensor includes a CCD (charge coupled device) that receives the pair of returned light components to generate a charge proportional to the number of photons in the received light. The amount of the charge represents the phase difference between the two light components. At a time after the transmission of the light pulse and before the expected time of arrival of the interfering light components, charge accumulating in the CCD as a result of reflections from components in the system, are repeatedly removed from the CCD, by transferring out charges in the CCD and dumping these charges

VLA observations of 6-cm excited OH

The VLA was used to determine precise positions for 4765-MHz OH maser emission sources toward star-forming regions which had been observed about seven months earlier with the Effelsberg 100-meter telescope. The observations were successful for K3-50, DR21EX, W75N, and W49A. No line was detected toward S255: this line had decreased to less than 5 per cent of the flux density observed only seven months earlier. The time-variability of the observed features during the past 30 years is summarised. In addition, to compare with the Effelsberg observations, the 4750-MHz and 4660-MHz lines were observed in W49A. These lines were found to originate primarily from an extended region which is distinguished as an exceptional collection of compact continuum components as well as by being the dynamical centre of the very powerful H_2 O outflow.Comment: 11 pages, will require MN style file to process. MNRAS, accepted Oct 15, 200

NO-TILL PROVIDES THE OPPORTUNITY TO MANAGE UNDERGROUND INTERACTIONS BETWEEN ARBUSCULAR MYCORRHIZAL FUNGI, WEEDS AND CROP PLANTS UNDER MEDITERRANEAN CONDITIONS

Early colonization of crop roots by arbuscular mycorrhiza (AM) is considered beneficial but its importance likely depends on the possible stresses faced by the host plant. Manganese toxicity is one such stress that AM can alleviate. Colonization initiated by extraradical mycelium (ERM) is faster than other sources of inoculum. No-till creates the possibility of encouraging inoculation via this source. At seeding time the ERM available for colonizing plants under no-till would have developed in association with previous crops or those weeds that germinated after the first autumn rain. However, the long, hot and dry summer under Mediterranean conditions might reduce the effectiveness of the ERM to colonize the new crop. The hypothesis that an intact ERM developed by weeds can affect the earlier AM colonization of wheat and alleviate Mn toxicity was tested in a pot experiment. Two mycotrophic (Ornithopus compressus L., Lolium rigidum Gaudin), and one non-mycotrophic (Silene galica L) weed species were grown for 7 weeks before being controlled with Glyphosate (the ERM remaining intact) or by mechanical disturbance (which also disrupted the ERM). Wheat was then planted and allowed to grow for 21 days. AM colonization, plant dry weight and shoot nutrient content were evaluated for both weeds and wheat. When an intact mycelium was present at the seeding of wheat (treatments with Ornithopus compressus and Lolium rigidum controlled by Glyphosate) there was a threefold increase in the AM colonization rate and growth of the crop compared with results for all the other treatments. The enhanced growth of wheat was associated with an alleviation of Mn toxicity, consistent with the hypothesis. However, there was a significant difference of the wheat growth after Ornithopus and Lolium (1.9 times), suggesting functional diversity within mycotrophic weeds and crops

Optical fiber coupling method and apparatus

Systems are described for coupling a pair of optical fibers to pass light between them, which enables a coupler to be easily made, and with simple equipment, while closely controlling the characteristics of the coupler. One method includes mounting a pair of optical fibers on a block having a large hole therein, so the fibers extend across the hole while lying adjacent and parallel to one another. The fibers are immersed in an etchant to reduce the thickness of cladding around the fiber core. The fibers are joined together by applying a liquid polymer so the polymer-air interface moves along the length of the fibers to bring the fibers together in a zipper-like manner, and to progressively lay a thin coating of the polymer on the fibers

OH Maser sources in W49N: probing differential anisotropic scattering with Zeeman pairs

Our analysis of a VLBA 12-hour synthesis observations of the OH masers in W49N has provided detailed high angular-resolution images of the maser sources, at 1612, 1665 and 1667 MHz. The images, of several dozens of spots, reveal anisotropic scatter broadening; with typical sizes of a few tens of milli-arc-seconds and axial ratios between 1.5 to 3. The image position angles oriented perpendicular to the galactic plane are interpreted in terms of elongation of electron-density irregularities parallel to the galactic plane, due to a similarly aligned local magnetic field. However, we find the apparent angular sizes on the average a factor of 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred earlier. The average position angle of the scattered broadened images is also seen to deviate significantly (by about 10 degrees) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, we find significant differences in the scatter broadened images for the two hands of polarization, even when apparent velocity separation is less than 0.1 km/s. Here we present the details of our observations and analysis, and discuss the interesting implications of our results for the intervening anisotropic magneto-ionic medium, as well as a comparison with the expectations based on earlier work.Comment: 5 pages, 3 figures, submitted to the Proceedings of the IAU Symposium 287: "Cosmic masers - from OH to H0

Ranging system which compares an object reflected component of a light beam to a reference component of the light beam

A system is described for measuring the distance to an object by comparing a first component of a light pulse that is reflected off the object with a second component of the light pulse that passes along a reference path of known length, which provides great accuracy with a relatively simple and rugged design. The reference path can be changed in precise steps so that it has an equivalent length approximately equal to the path length of the light pulse component that is reflected from the object. The resulting small difference in path lengths can be precisely determined by directing the light pulse components into opposite ends of a detector formed of a material that emits a second harmonic light output at the locations where the opposite going pulses past simultaneously across one another

Tumor-Like Growth of Antlers in Castrated Fallow Deer: An Electron Microscopic Study

Male deer regenerate new sets of antlers each year. When fully grown, rising levels of testosterone promote antler ossification, cutting off the blood flow and causing the velvet integument to be shed. After the mating season, the old antlers fall off to be replaced by new ones. When the adult fallow deer is castrated in autumn or winter, its bony antlers are shed and replaced by usually shorter regenerates that remain permanently viable and in velvet. If prevented from winter freezing, these antlers continue to grow thicker each year, eventually giving rise to amorphous outgrowths, or antleromas, from their sides. These growths mushroom out from the antler as clusters of nodules, developing in unpredictable locations, but commonly at the bases and ends of the antlers. Their integument contains numerous hair follicles. Internally, antleromas are composed of masses of collagen together with fibroblasts actively engaged in ribonucleic acid and protein synthesis. Thin basal laminae surround the blood vessels, and in the skin separate the overlying epidermis from the collagenous substance of the antleroma. Despite their superficial resemblance to hypertrophic scars, antleromas lack many of the characters by which they are diagnosed. They may be classified as benign tumors, at least in the generic sense. Antleromas would appear to represent a sustained expression of antler regeneration uncoupled from those morphogenetic influences responsible for the configurations into which deer antlers normally develop