Soil test measures of available P (Colwell, resin and DGT) compared with plant P uptake using isotope dilution

Background and aims

Recent research has demonstrated the high accuracy of a new method for assessment of plant available P in soil called diffusive gradients in thin-films (DGT). The process of P released by additions of bicarbonate to soil samples simulating common soil P tests is yet to be assessed by the new method (DGT). The aim of this study was to identify the pools of soil P extracted by soil test methods (DGT, Colwell and resin) by comparing, in ³²P–labelled soils, the specific activity (SA) of phosphorus extracted by common soil test extracts with the SA of wheat plants grown in a range of agricultural soils from southern Australia.

Methods

Wheat (cv. Frame) was grown for 4 weeks in 14 soils that were labelled uniformly with carrier-free ³²P. The specific activity (SA) of P (MBq ³²P kg ³¹P^?1) in each soil test extract was compared to the SA of P in the wheat plants.

Results

The SA of P in plants were similar to P extracted by the Colwell extractant in only 4 of the 14 soils; while SA in plants and extractants corresponded in 10 of the soils for the resin method and in 12 of the soils for the DGT method. Phosphorus in the Colwell and resin extract solutions had significantly lower SAs compared to P in the plants for 10 and 4 of the soils, respectively, indicating greater extraction of non-labile P sources (unlabelled ³¹P). Phosphorus in the DGT extractant had significantly lower SA than the plants for 1 soil and in 1 soil the SA was higher. Overall, across all soils, 25 % of P extracted by the Colwell method was non labile compared to 9 % and 2 % for the resin and DGT methods, respectively.

Conclusion

The new DGT method for extraction of soil P has the potential to accurately predict occurrences of P deficiency because it generally extracts the same pool of labile soil P accessed by wheat plants, while methods using bicarbonate solution (e.g. Colwell, Olsen) or water (resin) at wide soil:solution ratios are more likely to measure more non-labile forms of P in soil.     

Economic activity in the South-Asian population in Britain: the impact of ethnicity,religion, and class

This paper expands the existing literature on ethnicity and economic activity in Britain by studying the impact of religion and class. It argues that while the class location of the different South-Asian groups is important in determining their labour market outcomes, it does not operate independently from ethnicity; rather it is highly influenced by ethnicity in the process of determining the labour market participation of these groups. We use data obtained from the 2001 UK Census on Indian, Pakistani, and Bangladeshi men and women aged between twenty and twenty nine. Our findings confirm that class structure of the South-Asian groups is highly ethnicized, in that the ethno-religious background and class are interwoven to the extent that the separation between them is not easy, if not impossible.     

Species traits explain variation in detectability of UK birds

Capsule Heterogeneous detectability amongst species may impact multi-species bird surveys and if not accounted for, may bias community level conclusions. Estimates of detectability were produced for 195 UK bird species, and detectability was significantly affected by bird size, diet and habitat specialization.

Aims To estimate detectability and understand which species traits may impact detectability.

Methods We estimated the detectability of 195 species of birds in the UK using distance sampling methods and examined the average detectability of genetically related groups. We tested the significance of species traits in describing variation in detectability, whilst controlling for phylogenetic relationships.

Results Passeriformes had the lowest median detectability of 0.37 and Charadriiformes the highest median detectability of 0.65, of the seven largest orders considered. Species most associated with closed habitats such as woodland and urban areas had the lowest detectability. Smaller species had lower detectability than larger species.

Conclusion Heterogeneity in species detectability could lead to biased conclusions, particularly when calculating multi-species indices such as species richness or diversity. Accounting for detectability will be most important in studies that cover a wide range of habitat types or a diverse spread of taxa.     

Potency of GABA at human recombinant GABAA receptors expressed in Xenopus oocytes: a mini review

GABA_A receptors are members of the ligand-gated ion channel superfamily that mediate inhibitory neurotransmission in the central nervous system. They are thought to be composed of 2 alpha (α), 2 beta (β) subunits and one other such as a gamma (γ) or delta (δ) subunit. The potency of GABA is influenced by the subunit composition. However, there are no reported systematic studies that evaluate GABA potency on a comprehensive number of subunit combinations expressed in Xenopus oocytes, despite the wide use of this heterologous expression system in structure–function studies and drug discovery. Thus, the aim of this study was to conduct a systematic characterization of the potency of GABA at 43 human recombinant GABA_A receptor combinations expressed in Xenopus oocytes using the two-electrode voltage clamp technique. The results show that the α-subunits and to a lesser extent, the β-subunits influence GABA potency. Of the binary and ternary combinations with and without the γ2L subunit, the α6/γ2L-containing receptors were the most sensitive to GABA, while the β2- or β3-subunit conferred higher sensitivity to GABA than receptors containing the β1-subunit with the exception of the α2β1γ2L and α6β1γ2L subtypes. Of the δ-subunit containing GABA_A receptors, α4/δ-containing GABA_A receptors displayed highest GABA sensitivity, with mid-nanomolar concentrations activating α4β1δ and α4β3δ receptors. At α4β2δ, GABA had low micromolar activity.     

A novel hearing specialization in the New Zealand bigeye,Pempheris adspersa

The New Zealand bigeye, Pempheris adspersa, is a nocturnal planktivore and has recently been found to be an active sound producer. The rostral end of the swim bladder lies adjacent to Baudelot''s ligament which spans between the bulla and the cleithrum bone of the pectoral girdle. The aim of this study was to use the auditory evoked potential technique to physiologically test the possibility that this structure provides an enhanced sensitivity to sound pressure in the bigeye. At 100 Hz, bigeye had hearing sensitivity similar to that of goldfish (species with a mechanical connection between the swim bladder and the inner ear mediated by the Weberian ossicles) and were much more sensitive than other teleosts without ancillary hearing structures. Severing Baudelot''s ligament bilaterally resulted in a marked decrease in hearing sensitivity, as did swim bladder puncture or lateral line blockage. These results show that bigeye have an enhanced sensitivity to sound pressure and provide experimental evidence that the functional basis of this sensitivity represents a novel hearing specialization in fish involving the swim bladder, Baudelot''s ligament and the lateral line.     

A Technology for Developing Synbodies with Antibacterial Activity

The rise in antibiotic resistance has led to an increased research focus on discovery of new antibacterial candidates. While broad-spectrum antibiotics are widely pursued, there is evidence that resistance arises in part from the wide spread use of these antibiotics. Our group has developed a system to produce protein affinity agents, called synbodies, which have high affinity and specificity for their target. In this report, we describe the adaptation of this system to produce new antibacterial candidates towards a target bacterium. The system functions by screening target bacteria against an array of 10,000 random sequence peptides and, using a combination of membrane labeling and intracellular dyes, we identified peptides with target specific binding or killing functions. Binding and lytic peptides were identified in this manner and in vitro tests confirmed the activity of the lead peptides. A peptide with antibacterial activity was linked to a peptide specifically binding Staphylococcus aureus to create a synbody with increased antibacterial activity. Subsequent tests showed that this peptide could block S. aureus induced killing of HEK293 cells in a co-culture experiment. These results demonstrate the feasibility of using the synbody system to discover new antibacterial candidate agents.     

Testing Rare-Variant Association without Calling Genotypes Allows for Systematic Differences in Sequencing between Cases and Controls

Next-generation sequencing of DNA provides an unprecedented opportunity to discover rare genetic variants associated with complex diseases and traits. However, the common practice of first calling underlying genotypes and then treating the called values as known is prone to false positive findings, especially when genotyping errors are systematically different between cases and controls. This happens whenever cases and controls are sequenced at different depths, on different platforms, or in different batches. In this article, we provide a likelihood-based approach to testing rare variant associations that directly models sequencing reads without calling genotypes. We consider the (weighted) burden test statistic, which is the (weighted) sum of the score statistic for assessing effects of individual variants on the trait of interest. Because variant locations are unknown, we develop a simple, computationally efficient screening algorithm to estimate the loci that are variants. Because our burden statistic may not have mean zero after screening, we develop a novel bootstrap procedure for assessing the significance of the burden statistic. We demonstrate through extensive simulation studies that the proposed tests are robust to a wide range of differential sequencing qualities between cases and controls, and are at least as powerful as the standard genotype calling approach when the latter controls type I error. An application to the UK10K data reveals novel rare variants in gene BTBD18 associated with childhood onset obesity. The relevant software is freely available.