Dual-labelled (13C/15N) green manure to differentiate between plant uptake of organic and inorganic N

Experimental data is still lacking for determining whether plant uptake of organic nitrogen in agricultural soils contributes substantially to the total N uptake. Pulseinjection studies with dual-labelled amino acids have confirmed that non-mycorrhizal crops possess the capacity to take up organic N but failed to quantify the uptake relative to total N uptake

Organic Agriculture: A New Field of International Development Policy

This paper reviews strategically selected global policy documents and development literature and analyse perspectives on the role of organic agriculture (OA) as a possible vehicle for sustainable development in developing countries. It shows that not only has compliance assessed organics made entry in terms of projects and programmes in many LICs. OA is also gaining position in formal policies and strategies of international donor agencies and organisations. If agriculture is generally “back” in development business, organic farming has certainly “arrived”

Axioms for infinite matroids

We give axiomatic foundations for non-finitary infinite matroids with duality, in terms of independent sets, bases, circuits, closure and rank. This completes the solution to a problem of Rado of 1966.Comment: 33 pp., 2 fig

Lieber, Francis (1798-1872), Author and Professor.

The debate about the origin of the vertebrate dentition has been given fresh fuel by new fossil discoveries and developmental studies of extant animals. Odontodes (teeth or tooth-like structures) can be found in two distinct regions, the 'internal' oropharyngeal cavity and the 'external' skin. A recent hypothesis argues that regularly patterned odontodes is a specific oropharyngeal feature, whereas odontodes in the external skeleton lack this organization. However, this argument relies on the skeletal system of modern chondrichthyans (sharks and their relatives), which differ from other gnathostome (jawed vertebrate) groups in not having dermal bones associated with the odontodes. Their external skeleton is also composed of monoodontode 'placoid scales', whereas the scales of most early fossil gnathostomes are polyodontode, i.e. constructed from several odontodes on a shared bony base. Propagation phase contrast X-ray Synchrotron microtomography (PPC-SRmCT) is used to study the polyodontode scales of the early bony fish Andreolepis hedei. The odontodes constructing a single scale are reconstructed in 3D, and a linear and regular growth mechanism similar to that in a gnathostome dentition is confirmed, together with a second, gap-filling growth mechanism. Acanthodian tooth whorls are described, which show that ossification of the whorl base preceded and probably patterned the development of the dental lamina, in contrast to the condition in sharks where the dental lamina develops early and patterns the dentition. The new findings reveal, for the first time, how polyodontode scales grow in 3D in an extinct bony fish. They show that dentition-like odontode patterning occurs on scales and that the primary patterning unit of a tooth whorl may be the bony base rather than the odontodes it carries. These results contradict the hypothesis that oropharyngeal and external odontode skeletons are fundamentally separate and suggest that the importance of dermal bone interactions to odontode patterning has been underestimated

Collembola’s role in regulating mass fluxes in soil and the effects of contrasting life histories

The study determined metabolic rates and elemental pools for two Collembola species with contrasting life histories. The fittest of the two species, P. minuta, excreted the equivalent of 10–12% of the elemental body content per day, and P. armata 7–10%. Most elements are lost to excretion (CO2 and N-waste). These figures in combination with stoichiometry and life histories indicate that the cost of P. minuta’s better fitness is a requirement for a higher quality diet than P. armata. The data produced in this study can be used to estimate the collembolan contribution to C and N fluxes in the soil

Nutrient allocations and metabolism in two collembolans with contrasting reproduction and growth strategies

Physiological mechanisms such as allocation and release of nutrients are keys to understanding an animal\u27s adaptation to a particular habitat. This study investigated how two detrivores with contrasting life‐history traits allocated carbon (C) and nitrogen (N) to growth, reproduction and metabolism. As model organisms we used the collembolans, Proisotoma minuta (Tullberg 1871) and Protaphorura fimata (Gisin 1952). To estimate allocations of C and N in tissue, we changed the isotopic composition of the animal\u27s yeast diets when they became sexually mature and followed isotope turnover in tissue, growth and reproduction for 28 days. In addition, we measured the composition of C, N and phosphorus (P) to gain complementary information on the stoichiometry underlying life‐history traits and nutrient allocation. For P. minuta, the smallest and most fecund of the two species, the tissue turnover of C and N were 13% and 11% day−1, respectively. For P. fimata, the equivalent rates were 5% and 4% d−1, respectively. Protaphorura fimata had the lowest metabolic rate relative to total body mass but the highest metabolic rates relative to reproductive investment. Adult P. fimata retained approximately 17% of the nutrient reserves acquired while a juvenile and adult P. minuta about 11%. N and P contents of total tissue were significantly higher in P. minuta than in P. fimata, suggesting that tissue turnover was correlated with high protein‐N and RNA‐P. Our results suggest that the lower metabolism and nutritional requirements by P. fimata than P. minuta is an adaptation to the generally low availability and quality of food in its natural habitat. The methodological approach we implemented tracking mass balance, isotope turnover and elemental composition is promising for linking nutrient budgets and life‐history traits in small invertebrates such as Collembola

Finite connectivity in infinite matroids

We introduce a connectivity function for infinite matroids with properties similar to the connectivity function of a finite matroid, such as submodularity and invariance under duality. As an application we use it to extend Tutte's linking theorem to finitary and to co-finitary matroids.Comment: 16 page

Model atmospheres of irradiated exoplanets: The influence of stellar parameters, metallicity, and the C/O ratio

Many parameters constraining the spectral appearance of exoplanets are still poorly understood. We therefore study the properties of irradiated exoplanet atmospheres over a wide parameter range including metallicity, C/O ratio and host spectral type. We calculate a grid of 1-d radiative-convective atmospheres and emission spectra. We perform the calculations with our new Pressure-Temperature Iterator and Spectral Emission Calculator for Planetary Atmospheres (PETIT) code, assuming chemical equilibrium. The atmospheric structures and spectra are made available online. We find that atmospheres of planets with C/O ratios $\sim$ 1 and $T_{\rm eff}$ $\gtrsim$ 1500 K can exhibit inversions due to heating by the alkalis because the main coolants CH$_4$, H$_2$O and HCN are depleted. Therefore, temperature inversions possibly occur without the presence of additional absorbers like TiO and VO. At low temperatures we find that the pressure level of the photosphere strongly influences whether the atmospheric opacity is dominated by either water (for low C/O) or methane (for high C/O), or both (regardless of the C/O). For hot, carbon-rich objects this pressure level governs whether the atmosphere is dominated by methane or HCN. Further we find that host stars of late spectral type lead to planetary atmospheres which have shallower, more isothermal temperature profiles. In agreement with prior work we find that for planets with $T_{\rm eff}$ $<$ 1750 K the transition between water or methane dominated spectra occurs at C/O $\sim$ 0.7, instead of $\sim$ 1, because condensation preferentially removes oxygen.Comment: 30 pages, 20 figures. Accepted for publication in Ap

Perceptions of legitimacy, attitudes and buy-in among athlete groups: a cross-national qualitative investigation providing practical solutions

First paragraph: In order to achieve its stated purpose, anti-doping relies on athlete buy-in to its overall goals and methods and their compliance with anti-doping policies. Previous research on athlete behavior focused on ways to induce athletes into compliance. However, the authors of the Sport Drug Control Model hypothesized that athletes views of anti-doping and their resultant behaviors resulted from their first hand experiences with anti-doping (Donovan et al, 2002). These and similar findings supported the hypothesis that the greater the levels of perceived legitimacy of antidoping organizations among athletes, the greater the likelihood athletes would comply with anti-doping policies. A better understanding of which experiences at the policy, agency, and individual levels are viewed positively or negatively can provide a path for improving perceptions of legitimacy among athletes. The purpose of this study is to investigate perceived legitimacy, athletes' attitudes, and buy-in towards anti-doping policies in a selection of national contexts and sports. The overall objective is to provide clear, practical guidance as to how to improve the athlete experience to increase levels of perceived legitimacy of anti-doping organizations and regulations among athletes