Host plant recognition by the root feeding clover weevil, Sitona lepidus (Coleoptera: Curculionidae)

This study investigated the ability of neonatal larvae of the root-feeding weevil, Sitona lepidus Gyllenhal, to locate white clover Trifolium repens L. (Fabaceae) roots growing in soil and to distinguish them from the roots of other species of clover and a co-occurring grass species. Choice experiments used a combination of invasive techniques and the novel technique of high resolution X-ray microtomography to non-invasively track larval movement in the soil towards plant roots. Burrowing distances towards roots of different plant species were also examined. Newly hatched S. lepidus recognized T. repens roots and moved preferentially towards them when given a choice of roots of subterranean clover, Trifolium subterraneum L. (Fabaceae), strawberry clover Trifolium fragiferum L. (Fabaceae), or perennial ryegrass Lolium perenneL. (Poaceae). Larvae recognized T. repens roots, whether released in groups of five or singly, when released 25 mm (meso-scale recognition) or 60 mm (macro-scale recognition) away from plant roots. There was no statistically significant difference in movement rates of larvae

The growth and activity of wheat root systems

A knowledge of root growth and the activity of separate members of the root system is necessary before a comprehensive understanding of plant water and nutrient uptake is possible. The literature describing the developmental characteristics of wheat root systems is first reviewed. Methods of examining root systems in the field are compared, and studies of the contribution of seminal and nodal roots, and the effects of soil environment are discussed. Finally, nutrient and water uptake are considered mainly from the literature concerned with soil processes supplying nutrients to the root surface. The literature survey highlights the scarcity of field studies of water and nutrient uptake compared to laboratory studies and the poor understanding of the ways in which soil water status affects root growth and activity. An experiment in which spring wheat was grown in soil columns in a controlled environment is reported. Water was withheld during growth and the consequences for root growth and nutrient and water uptake followed. Nodal root growth was also restricted but this treatment was largely inconclusive because of the limited time during which conditions comparable to those in the field could be maintained. It was decided from these experiments to work with a field crop; a major study of the micro-climate and growth of winter wheat was in progress, so it was appropriate to examine in detail the growth and functioning of the crop's root system. A number of experiments were set up but this thesis mainly describes the root growth, and associated nutrient and water uptake of the normal field-grown crop. Measurements of root dry weight and length, plant nutrient content and water use are reported in early sections, with subsequent calculations of nutrient and water inflow; the possible contribution of mass-flow to plant nutrient is considered. A pattern of nutrient inflow not previously reported was found and possible explanations are discussed. The influence of soil properties, root distribution and atmospheric conditions on water inflow are also examined. The work shows the importance of field studies in understanding root growth and activity, and puts forward a number of suggestions for future progress

The growth and activity of wheat root systems

A knowledge of root growth and the activity of separate members of the root system is necessary before a comprehensive understanding of plant water and nutrient uptake is possible. The literature describing the developmental characteristics of wheat root systems is first reviewed. Methods of examining root systems in the field are compared, and studies of the contribution of seminal and nodal roots, and the effects of soil environment are discussed. Finally, nutrient and water uptake are considered mainly from the literature concerned with soil processes supplying nutrients to the root surface. The literature survey highlights the scarcity of field studies of water and nutrient uptake compared to laboratory studies and the poor understanding of the ways in which soil water status affects root growth and activity. An experiment in which spring wheat was grown in soil columns in a controlled environment is reported. Water was withheld during growth and the consequences for root growth and nutrient and water uptake followed. Nodal root growth was also restricted but this treatment was largely inconclusive because of the limited time during which conditions comparable to those in the field could be maintained. It was decided from these experiments to work with a field crop; a major study of the micro-climate and growth of winter wheat was in progress, so it was appropriate to examine in detail the growth and functioning of the crop's root system. A number of experiments were set up but this thesis mainly describes the root growth, and associated nutrient and water uptake of the normal field-grown crop. Measurements of root dry weight and length, plant nutrient content and water use are reported in early sections, with subsequent calculations of nutrient and water inflow; the possible contribution of mass-flow to plant nutrient is considered. A pattern of nutrient inflow not previously reported was found and possible explanations are discussed. The influence of soil properties, root distribution and atmospheric conditions on water inflow are also examined. The work shows the importance of field studies in understanding root growth and activity, and puts forward a number of suggestions for future progress

Exploring an extensive dataset to establish woody vegetation cover and composition in Kruger National Park for the late 1980s

Woody plant cover and species composition play an important role in defining the type and function of savanna ecosystems. Approximately 2000 sites in the Kruger National Park (KNP) were surveyed by F.J. Venter over a period from 1985 to 1989, recording vegetation, soil and topological characteristics. At each of these sites (approximately 20 m × 20 m each), woody vegetation cover and species were recorded using a rapid, Braun-Blanquet classification for three height classes: shrub (0.75 m – 2.50 m), brush (2.50 m – 5.50 m) and tree (> 5.50 m). The objective of this study was to re-analyse the vegetation component of the field data, with a specific focus to provide a spatially explicit, height-differentiated, benchmark dataset in terms of species occurrence, species richness and structural canopy cover. Overall, 145 different woody species were recorded in the dataset out of the 458 species documented to occur in the park. The dataset describes a woody layer dominated by a relatively small number of widely occurring species, as 24 of the most common woody species accounted for all woody species found on over 80% of all sites. The less common woody species (101) were each recorded on 20 sites or less. Species richness varied from 12 to 1 species per site. Structural canopy cover averaged 9.34%, 8.16% and 2.89% for shrub, brush and tree cover, respectively. The dataset provides a useful benchmark for woody species distribution in KNP and can be used to explore woody species and height class distributions, as well as comparison with more recent or future woody vegetation surveys. Conservation implications: The results provided evidence that large-scale, woody vegetation surveys conducted along roads offer useful ecosystem level information. However, such an approach fails to pick up less common species. The data presented here provided a useful snapshot of KNP woody vegetation structure and composition and could provide excellent opportunities for spatio-temporal comparisons

Reactive inkjet printing of functional silk stirrers for enhanced mixing and sensing

Stirring small volumes of solution can reduce immunoassay readout time, homogenize cell cultures, and increase enzyme reactivity in bioreactors. However, at present many small scale stirring methods require external actuation, which can be cumbersome. To address this, here, reactive inkjet printing is shown to be able to produce autonomously rotating biocompatible silk-based microstirrers that can enhance fluid mixing. Rotary motion is generated either by release of a surface active agent (small molecular polyethylene glycol) resulting in Marangoni effect, or by catalytically powered bubble propulsion. The Marangoni driven devices do not require any chemicals to be added to the fluid as the "fuel," while the catalytically powered devices are powered by decomposing substrate molecules in solution. A comparison of Marangoni effect and enzyme powered stirrers is made. Marangoni effect driven stirrers rotate up to 600 rpm, 75-100-fold faster than enzyme driven microstirrers, however enzyme powered stirrers show increased longevity. Further to stirring applications, the sensitivity of the motion generation mechanisms to fluid properties allows the rotating devices to also be exploited for sensing applications, for example, acting as motion sensors for water pollution

A tillering inhibition gene influences root-shoot carbon partitioning and pattern of water use to improve wheat productivity in rainfed environments

Genetic modification of shoot and root morphology has potential to improve water and nutrient 19 uptake of wheat crops in rainfed environments. Near-isogenic lines (NILs) varying for a tillering 20 inhibition (tin) gene and representing multiple genetic backgrounds were investigated in contrasting 21 controlled environments for shoot and root growth. Leaf area, shoot and root biomass were similar 22 until tillering whereupon reduced tillering in tin-containing NILs produced reductions of up to 60% in 23 total leaf area and biomass, and increases in total root length of up to 120% and root biomass to 24 145%. Together, root-to-shoot ratio increased two-fold with the tin gene. The influence of tin on shoot 25 and root growth was greatest in the cv. Banks genetic background, particularly in the biculm-selected 26 NIL, and was typically strongest in cooler environments. A separate de-tillering study confirmed 27 greater root-to-shoot ratios with regular tiller removal in non-tin containing genotypes. In validating 28 these observations in a rainfed field study, the tin allele had a negligible effect on seedling growth but 29 was associated with significantly (P<0.05) reduced tiller number (-37%), leaf area index (-26%) and 30 spike number (-35%) to reduce plant biomass (-19%) at anthesis. Root biomass, root-to-shoot ratio at 31 early stem elongation and root depth at maturity were increased in tin-containing NILs. Soil water use 32 was slowed in tin-containing NILs resulting in greater water availability, greater stomatal 33 conductance, cooler canopy temperatures and maintenance of green leaf area during grain-filling. 34 Together these effects contributed to increases in harvest index and grain yield. In both the controlled 35 and field environments, the tin gene was commonly associated with increased root length and biomass 36 but the significant influence of genetic background and environment suggests careful assessment of 37 tin-containing progeny in selection for genotypic increases in root growth

De adviserende rol van commissarissen in het licht van de code Tabaksblat: Minder overlappende commissariaten meer interne verantwoordelijkheden

Van oudsher bestaan de hoofdverantwoordelijkheden van de raad van commissarissen uit het houden van toezicht op het beleid van de raad van bestuur en het bijstaan van de raad van bestuur door het geven van advies en het dienen als klankbord. Op het eerste gezicht lijken deze beide hoofdverantwoordelijkhedenmet elkaar te conflicteren: voor toezicht is namelijk onafhankelijkheid noodzakelijk, terwijl voor advisering een zekere mate van betrokkenheid noodzakelijk is (VanManen enVan der Reijden, 2005;Huse, 2007). In de praktijk worstelen commissarissen dan ookmet dit vraagstuk. Temeer doordat het wettelijk raamwerk in Nederland geen duidelijke oplossing aandraagt

Caged Black Holes: Black Holes in Compactified Spacetimes II - 5d Numerical Implementation

We describe the first convergent numerical method to determine static black hole solutions (with S^3 horizon) in 5d compactified spacetime. We obtain a family of solutions parametrized by the ratio of the black hole size and the size of the compact extra dimension. The solutions satisfy the demanding integrated first law. For small black holes our solutions approach the 5d Schwarzschild solution and agree very well with new theoretical predictions for the small corrections to thermodynamics and geometry. The existence of such black holes is thus established. We report on thermodynamical (temperature, entropy, mass and tension along the compact dimension) and geometrical measurements. Most interestingly, for large masses (close to the Gregory-Laflamme critical mass) the scheme destabilizes. We interpret this as evidence for an approach to a physical tachyonic instability. Using extrapolation we speculate that the system undergoes a first order phase transition.Comment: 42 pages, 19 eps figures; v2: 3 references added, version to appear in Phys.Rev.

Weak-field approximation of effective gravitational theory with local Galilean invariance

We examine the weak-field approximation of locally Galilean invariant gravitational theories with general covariance in a $(4+1)$-dimensional Galilean framework. The additional degrees of freedom allow us to obtain Poisson, diffusion, and Schr\"odinger equations for the fluctuation field. An advantage of this approach over the usual $(3+1)$-dimensional General Relativity is that it allows us to choose an ansatz for the fluctuation field that can accommodate the field equations of the Lagrangian approach to MOdified Newtonian Dynamics (MOND) known as AQUAdratic Lagrangian (AQUAL). We investigate a wave solution for the Schr\"odinger equations.Comment: 15 page

Caged Black Holes: Black Holes in Compactified Spacetimes I -- Theory

In backgrounds with compact dimensions there may exist several phases of black objects including the black-hole and the black-string. The phase transition between them raises puzzles and touches fundamental issues such as topology change, uniqueness and Cosmic Censorship. No analytic solution is known for the black hole, and moreover, one can expect approximate solutions only for very small black holes, while the phase transition physics happens when the black hole is large. Hence we turn to numerical solutions. Here some theoretical background to the numerical analysis is given, while the results will appear in a forthcoming paper. Goals for a numerical analysis are set. The scalar charge and tension along the compact dimension are defined and used as improved order parameters which put both the black hole and the black string at finite values on the phase diagram. Predictions for small black holes are presented. The differential and the integrated forms of the first law are derived, and the latter (Smarr's formula) can be used to estimate the ``overall numerical error''. Field asymptotics and expressions for physical quantities in terms of the numerical ones are supplied. Techniques include ``method of equivalent charges'', free energy, dimensional reduction, and analytic perturbation for small black holes.Comment: 23 pages. v3: version to be published in PRD, 3 references adde