Spatial and temporal stability of weed patches in cereal fields under direct drilling and harrow tillage

The adoption of conservation agriculture (CA) techniques by farmers is changing the dynamics of weed communities in cereal fields and so potentially their spatial distribution. These changes can challenge the use of site-specific weed control, which is based on the accurate location of weed patches for spraying. We studied the effect of two types of CA (direct drilling and harrow-tilled to 20 cm) on weed patches in a three-year survey in four direct-drilled and three harrow-tilled commercial fields in Catalonia (North-eastern Spain). The area of the ground covered by weeds (hereafter called “weed cover”) was estimated at 96 to 122 points measured in each year in each field, in 50 cm × 50 cm quadrats placed in a 10 m × 10 m grid in spring. Bromus diandrus, Lolium rigidum, and Papaver rhoeas were the main weed species. The weed cover and degree of aggregation for all species varied both between and within fields, regardless of the kind of tillage. Under both forms of soil management all three were aggregated in elongated patterns in the direction of traffic. Bromus was generally more aggregated than Lolium, and both were more aggregated than Papaver. Patches were stable over time for only two harrow-tilled fields with Lolium and one direct-drilled field with Bromus, but not in the other fields. Spatial stability of the weeds was more pronounced in the direction of traffic. Herbicide applications, crop rotation, and traffic seem to affect weed populations strongly within fields, regardless of the soil management. We conclude that site-specific herbicides can be applied to control these species because they are aggregated, although the patches would have to be identified afresh in each season.This research was funded by the Spanish National Program (project: AGL2010-22084-C02-0). A.E.M. was funded by the Institute Strategic Programme (ISP) grants, “Soils to Nutrition” (S2N) grant number BBS/E/C/000I0330, and the joint Natural Environment Research Council (NERC) and Biotechnology and Biological Sciences Research Council (BBSRC) ISP grant “Achieving Sustainable Agricultural Systems” (ASSIST) grant number BBS/E/C/000I0100, using facilities funded by the BBSRC

X-ray generation using carbon nanotubes

Since the discovery of X-rays over a century ago the techniques applied to the engineering of X-ray sources have remained relatively unchanged. From the inception of thermionic electron sources, which, due to simplicity of fabrication, remain central to almost all X-ray applications, there have been few fundamental technological advances. However, with the emergence of ever more demanding medical and inspection techniques, including computed tomography and tomosynthesis, security inspection, high throughput manufacturing and radiotherapy, has resulted in a considerable level of interest in the development of new fabrication methods. The use of conventional thermionic sources is limited by their slow temporal response and large physical size. In response, field electron emission has emerged as a promising alternative means of deriving a highly controllable electron beam of a well-defined distribution. When coupled to the burgeoning field of nanomaterials, and in particular, carbon nanotubes, such systems present a unique technological opportunity. This review provides a summary of the current state-of-the-art in carbon nanotube-based field emission X-ray sources. We detail the various fabrication techniques and functional advantages associated with their use, including the ability to produce ever smaller electron beam assembles, shaped cathodes, enhanced temporal stability and emergent fast-switching pulsed sources. We conclude with an overview of some of the commercial progress made towards the realisation of an innovative and disruptive technology.Clare Collins is studying for the MRes in Ultra Precision, funded by the EPSRC, at the University of Cambridge.This is the final published version. It first appeared at http://www.nanoconvergencejournal.com/content/2/1/1

Species Delimitation and Lineage Separation History of a Species Complex of Aspens in China

Species delimitation in tree species is notoriously challenging due to shared polymorphisms among species. An integrative survey that considers multiple operational criteria is a possible solution, and we aimed to test it in a species complex of aspens in China. Genetic [four chloroplast DNA (cpDNA) fragments and 14 nuclear microsatellite loci (nSSR)] and morphological variations were collected for 76 populations and 53 populations, respectively, covering the major geographic distribution of the Populus davidiana-rotundifoliacomplex. Bayesian clustering, analysis of molecular variance (AMOVA), Principle Coordinate Analysis (PCoA), ecological niche modeling (ENM), and gene flow (migrants per generation), were employed to detect and test genetic clustering, morphological and habitat differentiation, and gene flow between/among putative species. The nSSR data and ENM suggested that there are two separately evolving meta-population lineages that correspond to P. davidiana (pd) and P. rotundifolia (pr). Furthermore, several lines of evidence supported a subdivision of P. davidiana into Northeastern (NEC) and Central-North (CNC) groups, yet they are still functioning as one species. CpDNA data revealed that five haplotype clades formed a pattern of [pdNEC, ((pdCNC, pr), (pdCNC, pr))], but most haplotypes are species-specific. Meanwhile, PCA based on morphology suggested a closer relationship between the CNC group (P. davidiana) and P. rontundifolia. Discrepancy of nSSR and ENM vs. cpDNA and morphology could have reflected a complex lineage divergence and convergence history. P. davidiana and P. rotundifolia can be regarded as a recently diverged species pair that experienced parapatric speciation due to ecological differentiation in the face of gene flow. Our findings highlight the importance of integrative surveys at population level, as we have undertaken, is an important approach to detect the boundary of a group of species that have experienced complex evolutionary history

Conservation genomics of an Australian cycad, cycas calcicola and the absence of key genotypes in botanic gardens

Understanding the genetic diversity of wild populations is fundamental to conserving species in-situ and ex-situ. To aid conservation plans and to inform ex-situ conservation, we examined the genetic diversity of the cycad Cycas calcicola (Cycadaceae). Samples were collected from wild populations in the Litchfield National Park and Katherine regions in the Northern Territory, Australia. Additional samples were obtained from botanic garden plants that were originally collected in the Katherine region, Daly River and Spirit Hills in the Northern Territory, Australia. Using RADseq we recovered 2271 informative genome-wide SNPs, revealing low to moderate levels of gene diversity (uHe = 0.037 to 0.135), very low levels of gene flow, and significant levels of inbreeding (mean FIS = 0.491). Population structure and multivariate analysis showed that populations fall into two genetic groups (Katherine vs Litchfield + Daly River + Spirit Hills). Genetic differentiation was twice as high between populations of the Katherine and Litchfield regions (FST ~ 0.1) compared to within these two regions (FST ~ 0.05). Increasing population fragmentation together with high levels of inbreeding and very little gene flow are concerning for the future adaptability of this species. The results indicated that the ex-situ collections (1) had significantly lower genetic diversity than the wild populations, and (2) only partly capture the genetic diversity present, particularly because the Litchfield National Park populations are not represented. We recommend that ex-situ collections be expanded to incorporate the genetic diversity found in Litchfield National Park and to increase the number of representatives from Daly River/Spirit Hills, and that in-situ populations from the Katherine and Greater Litchfield regions be conserved as separate management units