Quantifying microbial biomass phosphorus in acid soils

 This study aimed to validate the fumigation-extraction method for measuring microbial biomass P in acid soils. Extractions with the Olsen (0.5 M NaHCO₃, pH 8.5) and Bray-1 (0.03 M NH₄F–0.025 M HCl) extractants at two soil:solution ratios (1 : 20 and 1 : 4, w/v) were compared using eight acid soils (pH 3.6–5.9). The data indicated that the flushes (increases following CHCl₃-fumigation) of total P (P_t) and inorganic P (P_i) determined by Olsen extraction provided little useful information for estimating the amount of microbial biomass P in the soils. Using the Bray-1 extractant at a soil:solution ratio of 1 : 4, and analysing P_i instead of P_t, improves the reproducibility (statistical significance and CV) of the P flush in these soils. In all the approaches studied, the P_i flush determined using the Bray-1 extractant at 1 : 4 provided the best estimate of soil microbial biomass P. Furthermore, the recovery of cultured bacterial and fungal biomass P added to the soils and extracted using the Bray-1 extractant at 1 : 4 was relatively constant (24.1–36.7% and 15.7–25.7%, respectively) with only one exception, and showed no relationship with soil pH, indicating that it behaved differently from added P_i (recovery decreased from 86% at pH 4.6 to 13% at pH 3.6). Thus, correcting for the incomplete recovery of biomass P using added P_i is inappropriate for acid soils. Although microbial biomass P in soil is generally estimated using the P_i flush and a conversion factor (k _P) of 0.4, more reliable estimates require that k _P values are best determined independently for each soil. Received: 3 February 2000     

Movement patterns of Brook Trout in a restored coastal stream system in southern Massachusetts

Coastal Brook Trout (Salvelinus fontinalis) populations are found from northern Canada to New England. The extent of anadromy generally decreases with latitude, but the ecology and movements of more southern populations are poorly understood. We conducted a 33‐month acoustic telemetry study of Brook Trout in Red Brook, MA, and adjacent Buttermilk Bay (marine system) using 16 fixed acoustic receivers and surgically implanting acoustic transmitters in 84 individuals. Tagged Brook Trout used the stream, estuary (50% of individuals) and bay (10% of individuals). Movements into full sea water were brief when occurring. GAMM models revealed that transitions between habitat areas occurred most often in spring and fall. Environmental data suggest that use of the saline environment is limited by summer temperatures in the bay. Movements may also be related to moon phase. Compared to more northern coastal populations of Brook Trout, the Red Brook population appears to be less anadromous overall, yet the estuarine segment of the system may have considerable ecological importance as a food resource.     

Evolution of Fusarium oxysporum f. sp. vasinfectum Races Inferred from Multigene Genealogies

ABSTRACT Fusarium wilt of cotton is a serious fungal disease responsible for significant yield losses throughout the world. Evolution of the causal organism Fusarium oxysporum f. sp. vasinfectum, including the eight races described for this specialized form, was studied using multigene genealogies. Partial sequences of translation elongation factor (EF-1alpha), nitrate reductase (NIR), phosphate permase (PHO), and the mitochondrial small subunit (mtSSU) rDNA were sequenced in 28 isolates of F. oxysporum f. sp. vasinfectum selected to represent the global genetic diversity of this forma specialis. Results of a Wilcoxon Signed-Ranks Templeton test indicated that sequences of the four genes could be combined. In addition, using combined data from EF-1alpha and mtSSU rDNA, the phylogenetic origin of F. oxysporum f. sp. vasinfectum within the F. oxysporum complex was evaluated by the Kishino-Hasegawa likelihood test. Results of this test indicated the eight races of F. oxysporum f. sp. vasinfectum appeared to be nonmonophyletic, having at least two independent, or polyphyletic, evolutionary origins. Races 3 and 5 formed a strongly supported clade separate from the other six races. The combined EF-1alpha, NIR, PHO, and mtSSU rDNA sequence data from the 28 isolates of F. oxysporum f. sp. vasinfectum recovered four lineages that correlated with differences in virulence and geographic origin: lineage I contained race 3, mostly from Egypt, and race 5 from Sudan; lineage II contained races 1, 2, and 6 from North and South America and Africa; lineage III contained race 8 from China; and lineage IV contained isolates of races 4 and 7 from India and China, respectively.     

Gyrate atrophy of the retina: inborn error of L-ornithin:2-oxoacid aminotransferase

Cultured fibroblasts from a patient with gyrate atrophy of the retina do not convert L-ornithine, uniformly labeled with carbon-14, to proline. This metabolic block is caused by deficient L-ornithine:2-oxoacid aminotransferase activity in the patient. Her heterozygote father has intermediate activity of this enzyme.     

A zinc-containing intraruminal device for facial eczema control in lambs

A zinc-containing intraruminal device has been developed for protecting lambs against facial eczema. The rate of release of zinc from the device has been optimised, and its safety in use established. Under both experimental and farm conditions, the device gave excellent protection against the liver injury associated with facial eczema. The device relies upon erosion for release of zinc, and disappears completely when its charge of zinc has been released, leaving no metal or plastic residue in the rumen. This device has the potential to greatly ameliorate the problem of facial eczema in New Zealand.     

Coherent optical control of the quantum state of a single quantum Dot

Picosecond optical excitation was used to coherently control the excitation in a single quantum dot on a time scale that is short compared with the time scale for loss of quantum coherence. The excitonic wave function was manipulated by controlling the optical phase of the two-pulse sequence through timing and polarization. Wave function engineering techniques, developed in atomic and molecular systems, were used to monitor and control a nonstationary quantum mechanical state composed of a superposition of eigenstates. The results extend the concept of coherent control in semiconductors to the limit of a single quantum system in a zero-dimensional quantum dot.     

Localization of metastable atom beams with optical standing waves: nanolithography at the heisenberg limit

The spatially dependent de-excitation of a beam of metastable argon atoms, traveling through an optical standing wave, produced a periodic array of localized metastable atoms with position and momentum spreads approaching the limit stated by the Heisenberg uncertainty principle. Silicon and silicon dioxide substrates placed in the path of the atom beam were patterned by the metastable atoms. The de-excitation of metastable atoms upon collision with the surface promoted the deposition of a carbonaceous film from a vapor-phase hydrocarbon precursor. The resulting patterns were imaged both directly and after chemical etching. Thus, quantum-mechanical steady-state atom distributions can be used for sub-0.1-micrometer lithography.