Coffee leaf and stem anatomy under boron deficiency

Boron deficiency in coffee is widely spread in Brazilian plantations, but responses to B fertilizer have been erratic, depending on the year, form and time of application and B source. A better understanding of the effects of B on plant physiology and anatomy is important to establish a rational fertilization program since B translocation within the plant may be affected by plant anatomy. In this experiment, coffee plantlets of two varieties were grown in nutrient solutions with B levels of 0.0 (deficient), 5.0 µM (adequate) and 25.0 µM (high). At the first symptoms of deficiency, leaves were evaluated, the cell walls separated and assessed for B and Ca concentrations. Scanning electron micrographs were taken of cuts of young leaves and branch tips. The response of both coffee varieties to B was similar and toxicity symptoms were not observed. Boron concentrations in the cell walls increased with B solution while Ca concentrations were unaffected. The Ca/B ratio decreased with the increase of B in the nutrient solution. In deficiency of B, vascular tissues were disorganized and xylem walls thinner. B-deficient leaves had fewer and deformed stomata.

Analysis of the near-intrinsic and extrinsic photocapacitance due to the EL2 level in boron implanted GaAs

A detailed analysis of the photocapacitance signal at the near‐band and extrinsic energetic ranges in Schottky barriers obtained on horizontal Bridgman GaAs wafers, which were implanted with boron at different doses and annealed at several temperatures, has been carried out by using the optical isothermal transient spectroscopy, OITS. The optical cross sections have been determined as well as the quenching efficiency of the EL2 level which has been found to be independent of the annealing temperature. Moreover, the quenching relaxation presents two significant features: (i) a strong increase of the quenching efficiency from 1.35 eV on and (ii) a diminution of the quenching transient amplitude in relation with that shown by the fundamental EL2 level. In order to explain this behavior, different cases are discussed assuming the presence of several energy levels, the existence of an optical recuperation, or the association of the EL2 trap with two levels located, respectively, at Ev+0.45 eV and Ec−0.75 eV. The theoretical simulation, taking into account these two last cases, is in agreement with the experimental photocapacitance data at low temperature, as well as at room temperature where the EL2 filling phototransient shows an anomalous behavior. Moreover, unlike the previous data reported for the EL2 electron optical cross section, the values found using our experimental technique are in agreement with the behavior deduced from the theoretical calculation. The utilization of the OITS method has also allowed the determination of another level, whose faster optical contribution is often added to that of the EL2 level when the DLOS or standard photocapacitance is used.

On the artificial creation of the EL2 center by means of boron implantation in gallium arsenide

In the present work, an analysis of the dark and optical capacitance transients obtained from Schottky Au:GaAs barriers implanted with boron has been carried out by means of the isothermal transient spectroscopy (ITS) and differential and optical ITS techniques. Unlike deep level transient spectroscopy, the use of these techniques allows one to easily distinguish contributions to the transients different from those of the usual deep trap emission kinetics. The results obtained show the artificial creation of the EL2, EL6, and EL5 defects by the boron implantation process. Moreover, the interaction mechanism between the EL2 and other defects, which gives rise to the U band, has been analyzed. The existence of a reorganization process of the defects involved has been observed, which prevents the interaction as the temperature increases. The activation energy of this process has been found to be dependent on the temperature of the annealing treatment after implantation, with values of 0.51 and 0.26 eV for the as‐implanted and 400 °C annealed samples, respectively. The analysis of the optical data has corroborated the existence of such interactions involving all the observed defects that affect their optical parameters

Boron extraction and vertical mobility in Paraná State oxisol, Brazil

The deficiency or excess of micronutrients has been determined by analyses of soil and plant tissue. In Brazil, the lack of studies that would define and standardize extraction and determination methods, as well as lack of correlation and calibration studies, makes it difficult to establish limits of concentration classes for analysis interpretation and fertilizer recommendations for crops. A specific extractor for soil analysis is sometimes chosen due to the ease of use in the laboratory and not in view of its efficiency in determining a bioavailable nutrient. The objectives of this study were to: (a) evaluate B concentrations in the soil as related to the fertilizer rate, soil depth and extractor; (b) verify the nutrient movement in the soil profile; (c) evaluate efficiency of Hot Water, Mehlich-1 and Mehlich-3 as available B extractors, using sunflower as test plant. The experimental design consisted of complete randomized blocks with four replications and treatments of five B rates (0, 2, 4, 6, and 8 kg ha-1) applied to the soil surface and evaluated at six depths (0-0.05, 0.05-0.10, 0.10-0.15, 0.15-0.20, 0.20-0.30, and 0.30-0.40 m). Boron concentrations in the soil extracted by Hot Water, Mehlich-1 and Mehlich-3 extractors increased linearly in relation to B rates at all depths evaluated, indicating B mobility in the profile. The extractors had different B extraction capacities, but were all efficient to evaluate bioavailability of the nutrient to sunflower. Mehlich-1 and Mehlich-3 can therefore be used to analyze B as well as Hot Water.

Phloem mobility of Boron in two eucalypt clones

Boron deficiency causes large productivity losses in eucalypt stands in extensive areas of the Brazilian Cerrado region, thus understanding B mobility is a key step in selecting genetic materials that will better withstand B limitation. Thus, in this study B mobility was evaluated in two eucalypt clones (68 and 129), under B sufficiency or B deficiency, after foliar application of the 10B isotope tracer to a single mature leaf. Samples of young tissue, mature leaves and roots were collected 0, 1, 5, 12 and 17 days after 10B application. The 10B:11B isotope ratio was determined by HR-ICP-MS. Samples of leaves and xylem sap were collected for the determination of soluble sugars and polyalcohols by ion chromatography. Boron was translocated within eucalypt. Translocation of foliar-applied 10B to the young tissues, mature leaves and roots was higher in clone 129 than in 68. Seventeen days after 10B application to a single mature leaf, between 14 and 18 % of B in the young tissue was originated from foliar B application. In plants with adequate B supply the element was not translocated out of the labeled leaf.

Boron mobility in eucalyptus clones

Understanding the magnitude of B mobility in eucalyptus may help to select clones that are more efficient for B use and to design new practices of B fertilization. This study consisted of five experiments with three eucalyptus clones (129, 57 and 58) where the response to and mobility of B were evaluated. Results indicated that clone 129 was less sensitive to B deficiency than clones 68 and 57, apparently due to its ability to translocate B previously absorbed via root systems to younger tissues when B in solution became limiting. Translocation also occurred when B was applied as boric acid only once to a single mature leaf, resulting in higher B concentration in roots, stems and younger leaves. The growth of B-deficient plants was also recovere by a single foliar application of B to a mature leaf. This mobility was greater, when foliar-applied B was supplied in complexed (boric acid + manitol) than in non-complexed form (boric acid alone). When the root system of clone 129 was split in two solution compartments, B supplied to one root compartment was translocated to the shoot and back to the roots in the other compartment, improving the B status and growth. Thus, it appears that B is relatively mobile in eucalyptus, especially in clone 129, and its higher mobility could be due to the presence of an organic compound such as manitol, able to complex B.

Compared boron uptake and translocation in cotton cultivars

The mobility of boron (B), a commonly deficient micronutrient in cotton, has been shown to be low in the plant phloem. Nevertheless, studies have indicated that cotton cultivars can respond differently to B application. A greenhouse experiment was conducted to compare B absorption and mobility in cotton cultivars grown in nutrient solution. Treatments consisted of three cotton cultivars (FMT 701, DP 604BG and FMX 993), and five B rates (0.0, 2.5, 5.0, 10.0, and 20.0 µmol L-1). Plant growth and development were monitored for four weeks from the appearance of the first square. The time of onset and severity of B deficiency symptoms varied among cotton cultivars. Initial B uptake of cv. DP 604BG was lower than of the other cultivars, but a greater amount of available B in the nutrient solution was required to prevent deficiency symptoms in this cultivar. Boron deficiency impairs cotton growth, with no differences among cultivars, regardless of the time of appearance and intensity of B deficiency symptoms.

The Lithium, Boron and Beryllium content of serpentinized peridotites from ODP Leg 209 (Sites 1272A and 1274A): Implications for lithium and boron budgets of oceanic lithosphere

Despite the key importance of altered oceanic mantle as a repository and carrier of light elements (B, Li, and Be) to depth, its inventory of these elements has hardly been explored and quantified. In order to constrain the systematics and budget of these elements we have studied samples of highly serpentinized (>50%) spinel harzburgite drilled at the Mid-Atlantic Ridge (Fifteen-Twenty Fracture zone, ODP Leg 209, Sites 1272A and 1274A). In-situ analysis by secondary ion mass spectrometry reveals that the B, Li and Be contents of mantle minerals (olivine, orthopyroxene, and clinopyroxene) remain unchanged during serpentinization. B and Li abundances largely correspond to those of unaltered mantle minerals whereas Be is close to the detection limit. The Li contents of clinopyroxene are slightly higher (0.44-2.8 mu g g(-1)) compared to unaltered mantle clinopyroxene, and olivine and clinopyroxene show an inverse Li partitioning compared to literature data. These findings along with textural observations and major element composition obtained from microprobe analysis suggest reaction of the peridotites with a mafic silicate melt before serpentinization. Serpentine minerals are enriched in B (most values between 10 and 100 mu g g(-1)), depleted in Li (most values below I mu g g(-1)) compared to the primary phases, with considerable variation within and between samples. Be is at the detection limit. Analysis of whole rock samples by prompt gamma activation shows that serpentinization tends to increase B (10.4-65.0 mu g g(-1)), H2O and Cl contents and to lower Li contents (0.07-3.37 mu g g(-1)) of peridotites, implying that-contrary to alteration of oceanic crust-B is fractionated from Li and that the B and Li inventory should depend essentially on rock-water ratios. Based on our results and on literature data, we calculate the inventory of B and Li contained in the oceanic lithosphere, and its partitioning between crust and mantle as a function of plate characteristics. We model four cases, an ODP Leg 209-type lithosphere with almost no igneous crust, and a Semail-type lithosphere with a thick igneous crust, both at I and 75 Ma, respectively. The results show that the Li contents of the oceanic lithosphere are highly variable (17-307 kg in a column of I m x I m x thickness of the lithosphere (kg/col)). They are controlled by the primary mantle phases and by altered crust, whereas the B contents (25-904 kg/col) depend entirely on serpentinization. In all cases, large quantities of B reside in the uppermost part of the plate and could hence be easily liberated during slab dehydration. The most prominent input of Li into subduction zones is to be expected from Semail-type lithosphere because most of the Li is stored at shallow levels in the plate. Subducting an ODP Leg 209-type lithosphere would mean only very little Li contribution from the slab. Serpentinized mantle thus plays an important role in B recycling in subduction zones, but it is of lesser importance for Li. (C) 2008 Elsevier Ltd. All rights reserved.

Microstructure of highly oriented, hexagonal, boron nitride thin films grown on crystalline silicon by radio frequency plasma-assisted chemical vapor deposition

We present a high‐resolution electron microscopy study of the microstructure of boron nitride thin films grown on silicon (100) by radio‐frequency plasma‐assisted chemical vapor deposition using B2H6 (1% in H2) and NH3 gases. Well‐adhered boron nitride films grown on the grounded electrode show a highly oriented hexagonal structure with the c‐axis parallel to the substrate surface throughout the film, without any interfacial amorphous layer. We ascribed this textured growth to an etching effect of atomic hydrogen present in the gas discharge. In contrast, films grown on the powered electrode, with compressive stress induced by ion bombardment, show a multilayered structure as observed by other authors, composed of an amorphous layer, a hexagonal layer with the c‐axis parallel to the substrate surface and another layer oriented at random

Plasma-enhanced chemical vapor deposition of boron nitride thin films from B2H6-H2-NH3 and B2H6-N2 gas mixtures

Highly transparent and stoichiometric boron nitride (BN) films were deposited on both electrodes (anode and cathode) of a radio-frequency parallel-plate plasma reactor by the glow discharge decomposition of two gas mixtures: B2H6-H2-NH3 and B2H6-N2. The chemical, optical, and structural properties of the films, as well as their stability under long exposition to humid atmosphere, were analyzed by x-ray photoelectron, infrared, and Raman spectroscopies; scanning and transmission electron microscopies; and optical transmittance spectrophotometry. It was found that the BN films grown on the anode using the B2H6-H2-NH3 mixture were smooth, dense, adhered well to substrates, and had a textured hexagonal structure with the basal planes perpendicular to the film surface. These films were chemically stable to moisture, even after an exposition period of two years. In contrast, the films grown on the anode from the B2H6-N2 mixture showed tensile stress failure and were very unstable in the presence of moisture. However, the films grown on the cathode from B2H6-H2-NH3 gases suffered from compressive stress failure on exposure to air; whereas with B2H6-N2 gases, adherent and stable cathodic BN films were obtained with the same crystallographic texture as anodic films prepared from the B2H6-H2-NH3 mixture. These results are discussed in terms of the origin of film stress, the effects of ion bombardment on the growing films, and the surface chemical effects of hydrogen atoms present in the gas discharge.

Boron Leaching Decreases withIncreases on Soil pH

ABSTRACT Management of boron fertilization depends on the magnitude of B leaching in the soil profile, which varies proportionally with the concentration of B in the soil solution, which, in turn, decreases as the soil pH increases due to the higher sorption of B on soil solid surfaces. The objective of this study was to quantify the effect of liming and rates of B applied to the soil on B leaching. The experiment was carried out in the laboratory in 2012, and treatments consisted of a factorial combination of two rates of liming (without and with lime to raise the soil pH to 6.0) and five rates of B (0, 10, 20, 50 and 100 mg kg-1, as boric acid). A Typic Rhodudalf was used, containing 790 g kg-1 clay and 23 g kg-1 organic matter; the pH(H2O) was 4.6. Experimental units were composed of PVC leaching columns (0.10 m in diameter) containing 1.42 kg of soil (dry base). Boron was manually mixed with the top 0.15 m of the soil. After that, every seven days for 15 weeks, 300 mL of distilled water were added to the top of each column. In the percolated solution, both the volume and concentration of B were measured. Leaching of B decreased with increased soil pH and, averaged across the B rates applied, was 58 % higher from unlimed (pH 4.6) than from limed (pH 6.6) samples as a result of the increase in B sorption with higher soil pH. In spite of its high vertical mobility, the residual effect of B was high in this oxisol, mainly in the limed samples where 80 % of B applied at the two highest rates remained in the soil, even after 15 water percolations. Total recovery of applied B, including leached B plus B extracted from the soil after all percolations, was less than 50 %, showing that not all sorbed B was quantified by the hot water extraction method.

Mineralization of the recalcitrant oxalic and oxamic acids by electrochemical advanced oxidation processes using a boron-doped diamond anode

Oxalic and oxamic acids are the ultimate and more persistent by-products of the degradation of N-aromatics by electrochemical advanced oxidation processes (EAOPs). In this paper, the kinetics and oxidative paths of these acids have been studied for several EAOPs using a boron-doped diamond (BDD) anode and a stainless steel or an air-diffusion cathode. Anodic oxidation (AO-BDD) in the presence of Fe2+ (AO-BDD-Fe2+) and under UVA irradiation (AO-BDD-Fe2+-UVA), along with electro-Fenton (EF-BDD), was tested. The oxidation of both acids and their iron complexes on BDD was clarified by cyclic voltammetry. AO-BDD allowed the overall mineralization of oxalic acid, but oxamic acid was removed much more slowly. Each acid underwent a similar decay in AO-BDD-Fe2+ and EFBDD, as expected if its iron complexes were not attacked by hydroxyl radicals in the bulk. The faster and total mineralization of both acids was achieved in AO-BDD-Fe2+-UVA due to the high photoactivity of their Fe(III) complexes that were continuously regenerated by oxidation of their Fe(II) complexes. Oxamic acid always released a larger proportion of NH4 + than NO3- ion, as well as volatile NOx species. Both acids were independently oxidized at the anode in AO-BDD, but in AO-BDD-Fe2+-UVA oxamic acid was more slowlydegraded as its content decreased, without significant effect on oxalic acid decay. The increase in current density enhanced the oxidation power of the latter method, with loss of efficiency. High Fe2+ contents inhibited the oxidation of Fe(II) complexes by the competitive oxidation of Fe2+ to Fe3+. Low current densities and Fe2+ contents are preferable to remove more efficiently these acids by the most potent AO-BDD-Fe2+-UVA method.

Shallow-platform palaeoenvironmental conditions recorded in deep-shelf sediments: C and stable isotopes in Upper Jurassic sections of southern Germany (Oxfordian-Kimmeridgian)

A high-resolution carbon and oxygen isotope analysis of Late Oxfordian-Early Kimmeridgian deep-shelf sediments of southern Germany is combined with investigation of nannofossil assemblage composition and sedimentological interpretations in order to evaluate the impact of regional palaeoenvironmental conditions on isotopic composition of carbonates. This study suggests that carbonate mud was essentially derived from the Jura shallow platform environments and also that the isotopic signature of carbonates deposited in the Swabian Alb deep shelf indirectly expresses the palaeoenvironmental evolution of the platform. Short-term fluctuations in delta(13) C and delta(18)O are probably controlled by changes in salinity (fresh-water input versus evaporation) in platform environments. Long-term fluctuations in carbon and oxygen isotope record throughout the Late Oxfordian-Early Kimmeridgian result from the interplay of increasing temperature and decreasing humidity, which both control the trophic level. Changes from mesotrophic to oligotrophic conditions in platform environments and in the deep-shelf surface waters are inferred. During the Late Oxfordian (Bimammatum Subzone to Planula Zone), the delta(13)C curve displays a positive shift of about 1 parts per thousand, which is comparable in intensity to global perturbations of the carbon cycle. This evident isotopic shift has not been documented yet in other basinal settings. It can be reasonably explained by local palaeoenvironmental changes on the Jura platform (salinity, temperature, and nutrient availability) that controlled platform carbonate production, and the geochemistry of overlying waters. However, increasing carbonate production on the Jura platform and related positive delta(13)C shifts recorded in the Swabian Alb deep shelf are the regional signatures of climatic changes affecting other palaeogeographical domains of Europe in which the carbonate production increased throughout the Late Oxfordian. (C) 2002 Elsevier Science B.V. All rights reserved.