Higher Relative Yield Research Articles

Wider spectrum of fruit traits in invasive than native floras may increase the vulnerability of oceanic islands to plant invasions

Plant–animal mutualisms such as seed dispersal can play an important role in enabling some species to become invasive. For example, an introduced species could become invasive because birds prefer its fruits to those of native plants. To investigate this possibility, we compared various measures of fruit quality of 22 of the most common native and invasive woody species on the oceanic island Mahé (Seychelles, Indian Ocean).Individual measures of food quality tended to vary much more amongst invasive species than amongst native species; thus, whereas for particular traits the fruits of some invasive species had higher values than any native species, others had relatively low values. However, invasive species consistently produced fruits with a lower water content, resulting in a higher relative yield (i.e. dry pulp weight to total wet fruit weight ratio), and a higher energy content. The fruits of the most abundant invasive tree Cinnamomum verum (Lauraceae) were of particularly high nutritional quality, with individual berries containing 3.5 times more protein and 55 times more lipid than the median values of the native species.We suggest that our results may reflect a general tendency for island plants to produce fruits of low energy content, perhaps reflecting reduced competition for dispersal agents on isolated islands. In addition, we argue that inconsistent results on the relevance of fruit quality for plant invasions reported in the literature may be resolved by comparing the widths of trait spectra for native and alien floras rather than average values. Gaps in the native fruit trait spectrum may provide opportunities for particular invasive species, and weaken the resistance of regional floras to invasions. Such empty niche opportunities may occur for several reasons, including generally broader trait spectra in globally assembled alien than regional native floras (especially on oceanic islands), or the loss of native species due to human activities. More generally, a focus on trait variation rather than average trends may help to advance generalisation in invasion biology.

Photodissociation mechanism of methyl nitrate. A study with the multistate second-order multiconfigurational perturbation theory

The photodissociation reactions of methyl nitrate CH(3)ONO(2) starting at the 193 and 248 nm photolytic wavelengths have been studied with the second-order multiconfigurational perturbation theory (CASPT2) by computation of numerical energy gradients for stationary points. In addition, energy profiles of reaction paths and vertical excitations have been investigated with the multistate extension of the multiconfigurational second-order perturbation theory (MS-CASPT2). It is found that excitation at 193 nm yields three reaction paths: (i) the so-called slow channel CH(3)ONO(2)--> CH(3)O + NO(2)--> CH(3)O + NO + O; (ii) the fast channel CH(3)ONO(2)--> CH(3)O + NO(2); and (iii) CH(3)ONO(2)--> CH(3)ONO + O. The slow channel starts at the S(4) surface, in contrast, the population of the S(3) state can lead to the fast channel or to direct atomic oxygen extrusion. The rather high relative yield of the channel leading to oxygen extrusion from methyl nitrate is explained on the basis of an S(3)/S(2) conical intersection that transfers the initial excitation localized in the npi* S(3) state to the sigmapi* S(2) state with a consequent weakening of the N-O bond. With respect to photolysis at 248 nm, it was not possible to unambiguously distinguish between S(1) and S(2) as the populated state, however, the S(2) state is suggested as mainly responsible for dissociation at this excitation energy.

Photophysical properties of PPP and PPV derivatives bearing polystyrene or polycaprolactone as side groups

This contribution reports on detailed photophysical investigations of poly( p-phenylene) PPP and poly( p-phenylene-vinylene) (PPV) derivatives laterally decorated with polystyrene ( PPV-PSt) or poly(ε-caprolactone) ( PPP-PCL, PPP- alt PCL, PPV-PCL and PPV-PCL-Br). The polymers emit blue and exhibit very high relative and absolute photoluminescence quantum yield, Φ f, in dilute solution, thin film (spin-coated and inkjet-printed) and bulk state. This is ascribed to the presence of the lateral macromolecules, which suppress the strong π–π interactions and consequently excimers formation. Lower Φ f value was obtained for the bromine containing polymer and its corresponding model compound dibromodistyrylbenzene Br 2-DSB , which was ascribed to heavy atom effect enabling intersystem crossing from S 1 to T 1. However, studies at 77 K did not reveal phosphorescence, in contrast an enhancement of the fluorescence intensity with respect to room temperature measurement was observed.

Dual Irrigation Technology (DIT) Under Surface Irrigation System

In the dual irrigation technology (DIT), irrigation process is divided into two stages. In the first stage saline water is added as a part of irrigation water requirements , then good quality irrigation water is supplied in the second stage to complete irrigation water requirements. Piston flow may accurse in the soil because the time interval between two stages as short as possible , so the water content is greater than field capacity . Piston flow leaches the saline water that used in the firs stage of (DIT) under the root zone depth, so it is minimize the salinity effects of that water. Drainage water of 6 ds/m and Euphrates river water (1ds/m) are used to irrigate corn under furrow irrigation system with (DIT) at Ramady city in Iraq. Advance face in the furrow completes from drainage water , then second stage of (DIT) using river water . The experiment results summarized in the high relative yield (more than 95%) and saving about third quantity of fresh irrigation water. No significant differences in the salinity effects at the upper two thirds of the root zone depth compared with some furrows irrigated by river water only . Salinity effects at the lower third decrease as the distance from the upstream of the furrow increase, logarithmic relation between salinity effect and furrow length is proposed Key words: Dual Irrigation , saline irrigation water , water quality

Genetic dissection of grain yield in bread wheat. I. QTL analysis

Grain yield forms one of the key economic drivers behind a successful wheat (Triticum aestivum L.) cropping enterprise and is consequently a major target for wheat breeding programmes. However, due to its complex nature, little is known regarding the genetic control of grain yield. A doubled-haploid population, comprising 182 individuals, produced from a cross between two cultivars 'Trident' and 'Molineux', was used to construct a linkage map based largely on microsatellite molecular makers. 'Trident' represents a lineage of wheat varieties from southern Australia that has achieved consistently high relative grain yield across a range of environments. In comparison, 'Molineux' would be rated as a variety with low to moderate grain yield. The doubled-haploid population was grown from 2002 to 2005 in replicated field experiments at a range of environments across the southern Australian wheat belt. In total, grain yield data were recorded for the population at 18 site-year combinations. Grain yield components were also measured at three of these environments. Many loci previously found to be involved in the control of plant height, rust resistance and ear-emergence were found to influence grain yield and grain yield components in this population. An additional nine QTL, apparently unrelated to these traits, were also associated with grain yield. A QTL associated with grain yield on chromosome 1B, with no significant relationship with plant height, ear-emergence or rust resistance, was detected (LOD > or =2) at eight of the 18 environments. The mean yield, across 18 environments, of individuals carrying the 'Molineux' allele at the 1B locus was 4.8% higher than the mean grain yield of those lines carrying the 'Trident' allele at this locus. Another QTL identified on chromosome 4D was also associated with overall gain yield at six of the 18 environments. Of the nine grain yield QTL not shown to be associated with plant height, phenology or rust resistance, two were located near QTL associated with grain yield components. A third QTL, associated with grain yield components at each of the environments used for testing, was located on chromosome 7D. However, this QTL was not associated with grain yield at any of the environments. The implications of these findings on marker-assisted selection for grain yield are discussed.

A new approach towards improving the quality and yield of arc-generated carbon nanotubes

The paper reports the deterministic effects of a focusing electric field in improving the purity and yield of the arc-generated carbon nanotubes (CNTs). The method utilizes a focusing electrostatic field, which was superimposed on the arc symmetrically. The focusing voltage was varied from 0 to 1200 V at steps of 200 V and a number of cathode deposits, thus generated, were collected and thoroughly analysed in their totality with the help of weight balance, Raman spectroscopy, transmission electron microscopy and thermogravimetry. With the optimally configured focusing electric field, the arc generator is found to utilize nearly 85% of the consumed anode material, for converting into cathode deposit consisting of CNTs, as compared with about 35% in the conventional arc plasma method. The sample prepared under optimized conditions exhibited high oxidation temperature (851 °C) in the thermogravimetric analysis, negligible D band intensity along with a reduced G band line-width (14 cm−1) in the Raman spectrum, confirming the presence of high purity CNTs with a high relative yield.

Spirobenzopyran-based photochromic nanohybrids with photoswitchable fluorescence

The preparation and performance characterization of about 40nm spirobenzopyran-based photochromic nanohybrids with photoswitchable fluorescence are presented. The nanohybrids were fabricated by means of a modified miniemulsion polymerization process, in which hydrophobic spirobenzopyran and the matched fluorescent dyes are intermolecularly hybridized and embedded in the nanoscale crosslinked polymeric matrix. The obtained nanohybrids with high relative fluorescence quantum yield (Q) exhibited superior fluorescent photoswitchable performance due to the effective photoinduced intermolecular energy transfer, and also the thermal stability of photomerocyanine was improved.

Functional and performance comparisons of invasive Hieracium lepidulum and co‐occurring species in New Zealand

Abstract One of the key environmental factors affecting plant species abundance, including that of invasive exotics, is nutrient resource availability. Plant functional response to nutrient availability, and what this tells us about plant interactions with associated species, may therefore give us clues about underlying processes related to plant abundance and invasion. Patterns of abundance of Hieracium lepidulum, a European herbaceous invader of subalpine New Zealand, appear to be related to soil fertility/nutrient availability, however, abundance may be influenced by other factors including disturbance. In this study we compare H. lepidulum and field co‐occurring species for growth performance across artificial nutrient concentration gradients, for relative competitiveness and for response to disturbance, to construct a functional profile of the species. Hieracium lepidulum was found to be significantly different in its functional response to nutrient concentration gradients. Hieracium lepidulum had high relative growth rate, high yield and root plasticity in response to nutrient concentration dilution, relatively low absolute yield, low competitive yield and a positive response to clipping disturbance relative to other species. Based on overall functional response to nutrient concentration gradients, compared with other species found at the same field sites, we hypothesize that H. lepidulum invasion is not related to competitive domination. Relatively low tolerance of nutrient dilution leads us to predict that H. lepidulum is likely to be restricted from invading low fertility sites, including sites within alpine vegetation or where intact high biomass plant communities are found. Positive response to clipping disturbance and relatively high nutrient requirement, despite poor competitive performance, leads us to predict that H. lepidulum may respond to selective grazing disturbance of associated vegetation. These results are discussed in relation to published observations of H. lepidulum in New Zealand and possible tests for the hypotheses raised here.

Effect of a focusing electric field on the formation of arc generated carbon nanotubes

The effect of a focusing electric field on the formation of carbon nanotubes in adirect current arc-plasma is investigated. The hard deposits on the surface of thecathode are the main products, rich in multi-walled carbon nanotubes. It is seenthat the focusing electric field has a distinct influence on the yield, purity andmorphology of the nanotubes. The yield of the carbon nanotubes under the ‘focusedfield condition’ has been found to be higher than that derived from the normalelectrode configuration. It has been observed that the deposition of carbonaceoussoot on the reactor wall is considerably reduced on application of the focusingelectric field. Transmission electron microscopy has been used to determine themorphology of the nanotubes. In addition, Raman spectroscopy has helped indistinguishing the graphene-like structures from the disordered carbon networksand helped in analysing the morphology of the tubes. Thermal analysis gave aqualitative estimation of the relative yield of carbon nanotubes within the cathodedeposits and their thermal stabilities. The crystalline nature of the samples hasbeen confirmed by x-ray diffraction analysis. The results clearly indicate that thefocusing electric field confines the positively charged carbon precursors within thecathode–anode space causing high relative yield and purity and has a distincteffect on controlling the inner diameter of the as-synthesized carbon nanotubes.

Contribution to study of evaluation of the quality of pig carcasses according to method recommended by EU with focus on withers fat thickness

The quality traits of Swedish landrace pig carcasses were investigated. According to short procedure of the method pf partial dissection described in detail by Walstra and Merkus (1996) the highest relative yield of muscle tissue in leg/ham, shoulder, back-loin section and belly-rib fat in carcasses of pigs with thinner withers fat - I group ( 65,76; 66,32; 50,70 and 53,95%). The highest relative share of intermuscular fat in shoulder, back-loin section and belly-rib fat was established in pigs with thicker withers fat - II group (3,16; 5,63 and 7,96%). Differences were significant at the level of 5%. Higher yield of muscle tissue in carcasses was determined in fatteners with thinner withers fat - I group (57,83%) and differences between I and II research groups weren?t significant (p>0,05).

Supercritical CO2 Extraction of β-Carotene from a Marine Strain of the Cyanobacterium Synechococcus Species

Dynamic extraction of carotenoids from a marine strain of Synechococcus sp. (Cyanophyceae) with supercritical CO2 (SC-CO2) was investigated with regard to operation pressure and temperature effects on extraction efficiency. Extraction yield (milligrams of pigment per gram of dry weight) for SC-CO2) was compared with the extraction yield for dimethylformamide (DMF). Carotenoids extracted with SC-CO2 were beta-carotene (Ct), zeaxanthin (Z), beta-cryptoxanthin (Cr), and equinenone; chlorophyll a was poorly extracted, whereas myxoxanthophyll, another major carotenoid, was not extracted under any experimental condition. The highest relative yield, which is defined here as y(r) = [(mg of pigment(SC-CO2)/mg of pigment(DMF))] x 100, was 76.1 +/- 8.6% for Ct, but it rose to 87.0 +/- 3.4% when 15% ethanol was used as cosolvent. The pressure effect on y(r) was found to be significant (p < 0.05) for both Cr and Z, along with total carotenoids, whereas the effect of square T (TT) was significant for only Ct. From empirical correlations, pairwise pressure (bar) and temperature (degrees C), respectively, for optimal extraction were determined to be (358, 50) for Ct, (454, 59) for Cr, and (500, 60) for Z. Cell disruption by sonication or detergent treatment of the biomass did not improve the extraction efficiency. Matrix structure together with material state could explain the low carotenoid extraction yield obtained with SC-CO2 as compared to DMF in Synechococcus sp. However, the process can be applied to selective extraction of different carotenoids.

Competition between Artemisia frigida and Cleistogenes squarrosa under different clipping intensities in replacement series mixtures at different nitrogen levels

AbstractThe relative competitive ability of Artemisia frigida Willd. (C3, semi‐shrub) and Cleistogenes squarrosa (Trin.) Keng (C4, perennial bunchgrass), grown in a greenhouse, was studied under three nitrogen fertilizer levels, three defoliation intensities and five competitive replacement series in a factorial arrangement. Relative yield total and the respective crowding coefficients for each species were calculated with reference to aboveground, below‐ground and total biomass. The index of aggressivity was also determined relative to total biomass. Cleistogenes squarrosa was a consistently weak competitor at all nitrogen fertilizer and clipping levels compared with A. frigida. Artemesia frigida had a higher relative yield when grown in mixtures with C. squarrosa than in monocultures, whereas the yield of C. squarrosa was lower in mixtures with A. frigida than in monocultures. The relative competitive ability of A. frigida over C. squarrosa declined significantly at different clipping intensities with increasing nitrogen fertilizer. The interaction of nitrogen fertilizer with clipping was significant, although the clipping effect on aggressivity was not significant.

Season of year effect on response of orchardgrass to N fertilizer in a maritime climate

This study compared the response of harvests taken in May, June, August and September-October in terms of crop responses (yield, N uptake, and concentrations of crude protein and nitrate) to N fertilizer and residual soil nitrate and ammonium. Three trials were conducted in south coastal British Columbia in 1990–1992 to evaluate the response of an established sward of orchardgrass (Dactylis glomerata L.) to a range of N fertilizer rates. Both yields and daily crop growth rates were highest in cut 1, lowest in cut 4 and intermediate in cuts 2 and 3. For all four cuts, 95 and 90% of maximum yield was attained at about 136 and 82 kg ha-1 of applied N, respectively. Crop N supply from non-fertilizer sources ranged from 36 to 90 kg N ha-1, of which about 52% was attributed to nitrate present in the soil prior to growth and about 48% was N released from the soil, translocated from roots or deposited from the atmosphere. At 95% of maximum yield, crude protein concentrations ranged from 147 g kg-1 in the higher yielding cut 1 to 189 g kg-1 in cuts 2 and 4, while at 90% of maximum yield concentrations were 10 g kg-1 lower in each cut. Plant nitrate concentrations were close to levels that are toxic to cattle for the 95% target yield, but relatively safe at the 90% yield. The crop removed about 50 kg ha-1 more N when fertilized for 95% of maximum yield than for 90%, which translates to over 300 kg ha-1 more crude protein. High relative yield leaves behind more soil nitrate after harvest. The results suggest that the first cut should be managed for 95% of maximum yield with about 130 kg N ha-1. Cuts 2 and 3 should be managed for 90% of maximum yield, to avoid high plant nitrate concentrations, with 100–110 kg N ha-1. Cut 4 should be given no more than 50 kg N ha-1 for less than 90% of maximum yield because of the risk of residual soil nitrates. This study shows for the first time the benefits and disadvantages of applying N at different rates for each harvest over the growing season. Key words: Plant nitrate, nitrogen use efficiency, nitrogen recovery, Dactylis glomerata, relative yield, maximum economic yield

PHOTOSYNTHATE DISTRIBUTION IN WHEAT VARIETIES DIFFERING IN PHOSPHORUS EFFICIENCY

The distribution of phosphorus (P), photosynthates, and the amount of assimilated 14C secreted as root exudate were measured in wheat genotypes differing in phosphorus efficiency. Two wheat genotypes, one P-efficient (Triticum aestivum L., cv. Xiaoyan 54) and the other inefficient (Triticum aestivum L., cv. Jing 411) were used in this study. The plants were cultivated in solution culture for 4 weeks under controlled conditions. Xiaoyan 54 had higher relative yield, higher P concentration in roots and higher root/shoot ratio than Jing 411 under P-deficient condition. Xiaoyan 54 distributed more P and assimilated carbon to the roots than Jing 411 under P deficiency and also released a higher percentage of assimilated 14C as root exudates. The percentage released was 3.98% for Xiaoyan 54 and 2.47% for Jing 411 under P deficiency, and 2.95% and 3.28%, respectively, under P-sufficiency. However, P deficiency led to more assimilated 14C being partitioned to roots by both wheat genotypes. Regardless of genotypes, the 14C distributed to roots of P-deficient plants was 5 to 6 times that of P-sufficient plants. The P-efficient genotype translocated more assimilated 14C to roots than the P-inefficient genotype under P deficiency and the difference between the two genotypes were smaller under P sufficiency. It is concluded that Xiaoyan 54 has higher relative biomass and better root system under P limited condition, which main reasons are that Xiaoyan 54 can maintain a higher P concentration, release more root exudate, and distribute P to roots.

Crop Interactions in Broccoli Intercropping

ABSTRACT The research goals were to evaluate crop suitability to intercropping systems, to evaluate a population density limit to successful intercropping and to study the main factors responsible for crop performance when intercropped. Three experiments were carried out during 1995 and 1996 by intercropping broccoli either with contrast crops (pea, beans, potato or oats) or with similar crops (cauliflower or cabbage) in additive and substitutive designs at different intercropping rates. The overall intercrop characteristics as leaf area index, soil coverage and biomass yield were not related to a higher yield, and similar results were due to different factors. Land Equivalent Ratios (LER) similar to 1.0 were due either to a high and constant Relative Yield (RY) of the main crop associated with low RY of the secondary crop, or to trade-off between the RY of both associated crops. Similarly, a LER of 1.34 resulted from a reasonable performance of the dominated crop (beans) in the second experiment at the 50% additive design, whereas in the third experiment there was no dominating crop in the broccoli-potato intercropping but the LER reached 1.27. The mechanisms involved in the overyielding were the bean canopy plasticity and its temporal deployment asynchrony when compared with broccoli, allowing reduction of the competition for light, and the crop development temporal asynchrony between broccoli and potato, reducing the competition for production factors.

Fertilizer nitrogen recommendations for silage corn in high-fertility environment based on pre-sidedress soil nitrate test

The purpose of this study was to measure corn response to nitrogen (N), to evaluate the feasibility of using the pre-sidedress soil nitrate test (PSNT) for making fertilizer N recommendations for silage corn, and to evaluate the environmental and economic implications of adopting fertilizer N recommendations based on the PSNT in south coastal British Columbia, Canada, a region of high soil N fertility. Eighty-seven trials were conducted from 1994–1996 with corn or forage grass as a preceding crop on fields having a history of manure application. Non-manured trials received no spring manure application whereas manured trials received a spring application typical of that farm field. In 1994, treatments included sidedress N rates of 0, 30, 60, 90, 120, and 150 kg N ha−1 replicated twice. In 1995 and 1996, trials with less than 30 mg NO3-N kg−1 soil to 30 cm depth prior to sidedress received the same treatments as in 1994, whereas trials with concentrations above this value received two treatments, 0 and 150 kg N ha−1, replicated four times. Trials received less than 50 kg N ha−1 at planting. Yield response to sidedress N was limited, with 71, 87, and 55% of trials with 90% or higher relative yield (yield at 0 kg N ha−1 divided by yield at 150 kg N ha−1) in 1994, 1995 and 1996, respectively. The limited yield response was attributed to high soil N mineralization, which averaged 166 and 146 kg N ha−1 for non-manured trials in 1995 and 1996, respectively. The critical PSNT value (above which no yield response to sidedress N is expected) was predicted to be 19 and 23 mg NO3-N kg−1 soil using the Cate-Nelson procedure and a linear-plateau regression procedure, respectively. A critical PSNT test value of 32 mg NO3-N kg−1 soil was predicted using a linear-plateau regression of the estimated N rate which would maximize economic return (NMER) against PSNT test value. In addition, a model designed to minimize the risk of yield loss was developed with a critical PSNT test value of 30 mg NO3-N kg−1 soil. Average soil NO3 content at harvest was slightly higher for sidedress N rates based on the minimum risk model (70 kg N ha−1) than at NMER (64 kg N ha−1). Based on a survey of farm fields, the potential to reduce fertilizer N application in south coastal BC was estimated to be about 90 kg N ha−1 yr−1.

Tillage Effect on Soil Water Content and Corn Yield in a Strip Intercropping System

AbstractA three‐crop strip intercropping system including corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and oat (Avena sativa L.) interseeded with nondormant alfalfa (Medicago sativa L.), was established in south‐central Iowa on a poorly drained Haig soil (fine, smectitic, mesic Vertic Argiaquoll). In 1989 (a dry year) and 1990 (a wet year), we studied the effect of tillage treatment (conventional, CT; reduced, RT; and no‐till, NT) and row position on soil water content, canopy and air temperatures, corn grain yield, and yield components. No‐till resulted in the most favorable soil water status, plant water status, and grain yield in 1989. No‐till had the poorest performance in 1990, mainly because of excessive soil water. The opposite was true for conventional till in both years. Reduced till yield equaled that for the most productive tillage treatment in both years. Conventional and reduced tillage resulted in lower corn grain yield at the border with oat‐alfalfa than with soybean because oat depleted soil water more than soybean in both years. In contrast, for no‐till the corn grain yield at the border with oat‐alfalfa was 6% greater than corn yield bordering soybean in 1989 and 13% greater in 1990. When water was not limiting, in 1990, both corn borders outyielded the center rows by an average of 14% in NT, 27% in RT, and 28% in CT. Soil water content rankings throughout the 1989 season were NT &gt; RT &gt; CT and row position rankings were soybean border &gt; center &gt; oats‐alfalfa border. In 1990, there were no soil water content differences between tillage treatments and row positions. Reduced tillage is the most suitable soil management system for corn production with three‐crop strip intercropping on this soil, considering consistently high relative yields for both wet and dry years.

Enantioselective synthesis of several 1-O-?-D-glucoconjugates using almond ?-glucosidase (E.C. 3.2.1.21)

The almond β-glucosidase catalysed syntheses of 4-butanoic acid-N-butyl-amide-1-O-β-D-glucopyranoside (1), 3-butanoic acid ethyl ester-1-O-β-D-glucopyranoside (2) and 2-(trimethylsilyl)-ethyl-1-O-β-D-glucopyranoside (3) were done by reversed hydrolysis and by transglucosylation. The transglucosylation was much faster and resulted in higher relative yields (9.6 to 44.9%) than the reversed hydrolysis (relative yields of 1.2 to 19.1%).

Differences in aluminium tolerance of ryegrass and white clover plants grown from seed or propagated vegetatively

Abstract The effect of aluminium (Al) on the relative yield of plants grown from seeds of ryegrass (Lolium perenne L.) or white clover (Trifolium repens L.) and either tillers (ryegrass) or stolon tip cuttings (white clover) were investigated using a low ionic strength (2.7 x 10‐3 M) solution culture technique. In ryegrass, plants grown from tillers had higher relative yields than plants grown from seedlings in the tops when solution Al concentrations were greater than 16 μM and in the roots when solution Al concentrations were greater than 7 μM. In white clover, relative yields in the tops and roots plants were higher in plants grown from stolon tip cuttings than from seedlings when solution Al concentrations were greater than 10 μM. There were no significant cultivar effects. The results indicate that plants used in Al‐tolerance experiments can be grown from seed or vegetatively propagated, provided solution Al rates are adjusted to reflect differences in Al tolerance.

Wavelength effects in the photolysis of ketones: intramolecular hydrogen abstraction of o-methyl-dibenzyl ketones vs. α-cleavage in micellar solution

Abstract The chemical yields of indanols, the products of intramolecular δ-hydrogen abstraction produced in the photolysis of o -methyldibenzyl ketone ( o -MeDBK) and o , o′ -dimethyldibenzyl ketone ( o , o′ -Me 2 DBK) in SDS micelles are sensitive to the wavelength of excitation: the yields of indanols are about two times smaller for excitation at 254 nm than at ca . 320 nm. At the same time the magnitude of the secondary cage effect, arising from coupling of geminate benzyl radical pairs is increased slightly for excitation at 254 nm relative to 300 nm. In contrast to the results for micellar solution, in hexane no wavelength effect on the yields of indanols is observed. A kinetic analysis of the reaction scheme shows that the decrease in the yield of indanol in micelles for shorter wavelength excitation is caused mainly by a decrease in the recombination probability P r of the primary phenacyl/benzyl radical pair resulting from α-cleavage. This decrease in probability for recombination of the primary geminate pair causes an increase in the formation of the secondary geminate benzyl/benzyl pair and a higher relative yield of geminate cage recombination. Intramolecular hydrogen abstraction as well as further cyclization of the biradical to indanol are not wavelength dependent processes. A Salem correlation diagram for hydrogen abstraction provides theoretical support for the proposed mechanism.