Ecophysiology of Grasslands: Dynamic Aspects of Forage Plant Populations in Grazed Swards

The aim of this paper is to review knowledge of the ecophysiological mechanisms influencing the dynamics of plant populations in grazed swards. Such an objective requires some definitions. Firstly, it is necessary to define “ecophysiology” as the study of the interactions between biological individuals (plants) with their own environment: how individuals perceive and react to any constraint and change of their environment, and how the functioning of plants as a population can modify their own environment. Such a definition implies a dynamic approach to pant population functioning as resulting from constant plant-plant interactions mediated by micro-environment modifications. In a grazed plant community, these plant to plant interactions are perturbed by spatially explicit defoliation events which have a direct effect on the functioning of defoliated plants and also an indirect effect via the modification of the micro-environment of the neighbour plants. Secondly, it is necessary to define more precisely what we mean by “dynamics of plant population”. Because this paper is restricted to “ecophysiology of grasslands” plant population dynamics are not entirely taken into account in the sense that invasion or recruitment processes of new plants through seed dispersion and seed banks in the soil are not explicitly included in our approach. So the dynamic aspects of plant population discussed in this paper are restricted to competition between individual plants, including ability for clonal reproduction, survival ability, and morphological adaptation to defoliation and neighbourhood interactions. These determine the dynamic evolution of both sward structure for a short term and botanical composition for a longer term in a sward subjected to a given management. The analysis will focus on three main concepts of ecophysiology: (i) the mechanisms of competition among individual plants within a plant community and their consequences to sward structure dynamics, (ii) the adaptive morphogenetic mechanisms of plants to defoliation and the consequence to plant morphology and sward structure dynamics, and (iii) the interactions between these two types of mechanism for an overall understanding of the vegetation dynamics of a grazed plant community and its consequence for sustainable pasture management

DC-conductivity of a suspension of insulating particles with internal rotation

We analyse the consequences of Quincke rotation on the conductivity of a suspension. Quincke rotation refers to the spontaneous rotation of insulating particles dispersed in a slightly conducting liquid and subject to a high DC electric field: above a critical field, each particle rotates continuously around itself with an axis pointing in any direction perpendicular to the DC field. When the suspension is subject to an electric field lower than the threshold one, the presence of insulating particles in the host liquid decreases the bulk conductivity since the particles form obstacles to ion migration. But for electric fields higher than the critical one, the particles rotate and facilitate ion migration: the effective conductivity of the suspension is increased. We provide a theoretical analysis of the impact of Quincke rotation on the apparent conductivity of a suspension and we present experimental results obtained with a suspension of PMMA particles dispersed in weakly conducting liquids

Room temperature soft ferromagnetism in the nanocrystalline form of YCo2 - a well-known bulk Pauli paramagnet

The Laves phase compound, YCo2, is a well-known exchange-enahnced Pauli paramagnet. We report here that, in the nanocrystalline form, this compound interestingly is an itinerant ferromagnet at room temperature with a low coercive-field. The magnitude of the saturation moment (about 1 Bohr-magneton per formula unit) is large enough to infer that the ferromagnetism is not a surface phenomenon in these nanocrystallites. Since these ferromagnetic nanocrystallines are easy to synthesize with a stable form in air, one can explore applications, particularly where hysteresis is a disadvantage

A review of stakeholders and interventions in Nigeria's electricity sector

In this paper, we explored the interplay between the electricity market structure, methods of electricity trading and different stakeholder dynamics within the Nigerian Electricity Supply Industry (NESI) with a view to understanding how these interplays impact on various forms of interventions in the Nigerian electricity sector. We started off by exploring the market structure and electricity trading system within the Nigerian electricity sector and reviewed the various stakeholder groups within centralized and decentralized electricity systems in Nigeria's electricity sector by highlighting their core responsibilities and the dynamics at play in satisfying their interests. This study revealed that: (1) external stakeholder groups (such as donor agencies and multi-lateral organizations) exert more influence in Nigeria's electricity sector through financial interventions; (2) lack of coordination and engagement among various stakeholder groups pose a challenge to effective electricity infrastructure interventions that address the needs of people in society. The study concludes by highlighting the implications of these challenges and the need to address the rising complexities and uncertainties for better stakeholder involvement in addressing the salient challenges in the sector

Change in Grassland Science: Implications for Training, Research and Grassland Societies

In most of the world the priority for production-oriented research has been succeeded by the need for grassland research to focus on systems which satisfy requirements relating to the stability and protection of land, water and atmospheric resources and to biodiversity, in addition to production efficiency. This dictates not only a new approach to research, but also new approaches for the organisation of research, the training and development of research scientists and the activities of Grassland Societies and associated organisations

Distribution of phytoplankton pigments in nine European estuaries and implications for an estuarine typology

Phytoplankton pigments were studied by LiquidChromatography (HPLC) in nine West Europeanestuaries. Three estuaries, i.e. the Rhine,Scheldt and the Gironde were sampled four timesto cover the different seasons, whereas theother six estuaries were sampled once. Pigmentdistributions in estuaries reflect bothriverine inputs as well as autochthonousblooms. Fucoxanthin was the most commonaccessory photosynthetic pigment showing thatDiatoms were the most common group in thestudied estuaries and were particularlydominant during autumn and winter. In the veryturbid Gironde estuary, degradation processeswere predominant between salinities 1 and 20,while Diatoms, Dinoflagellates and Cryptophytesbloomed above 20 salinity during spring andsummer. This contrasted with the highlyeutrophic but less turbid Scheldt, wherephytoplanktonic blooms occurred at lowsalinities close to the city of Antwerp. In theScheldt, we observed both a tenfold fluctuationof phytoplankton biomass and a fluctuatingpigment diversity index. In contrast,chlorophyll a was always low in theGironde, but we observed large variations ofpigment diversity among samplings duringdifferent seasons. Distribution of pheopigmentsshowed that the maximum turbidity zone (MTZ)was a highly reactive region for heterotrophicphytoplankton degradation. The Scheldt and theThames were the most anthropogenic influencedestuaries contrasting with the Gironde estuarythat has a less urbanised watershed. Anestuarine typology is proposed based on threeclusters emerging from a correspondenceanalysis of pigment variables and variablescharacterising the anthropogenic impact andphysical forcing

Effect of Nitrogen Fertilizer on Reproductive Tiller Development in Perennial Ryegrass

The objective of this study was to compare reproductive tiller development in two ryegrass (Lolium perenne L.) cultivars, when fertilized with nitrogen. Plots of the cultivars ‘Grasslands Ruanui’ and ‘Ellett’ ryegrass were sown in April 1996. Half of each plot received nitrogen fertilizer (30 kg N/ha) after each grazing by dairy cows from September 1996 to May 1997 and from October 1997 to April 1998. Ryegrass tiller dynamics was monitored from September 1996 to March 1998. The proportion of reproductive tillers in the total tiller population was higher, on average, over the first flowering period (October 1996 to January 1997) for ‘Ellett’ (19.5%) than for ‘Grasslands Ruanui’ (13.0%) ryegrass, and there was no response to nitrogen. Over the second flowering (September 1997 to January 1998), ‘Ellett’ ryegrass slightly increased the proportion of reproductive tillers in response to nitrogen (averaging 20%) while ‘Grasslands Ruanui’ decreased (P \u3c 0.05) the number of reproductive tillers (averaging 6%). Significant cultivar x nitrogen interactions occurred in December 1997 and January 1998 when reproductive tiller number for nitrogen treated plants averaged 24.1% for ‘Ellett’ compared with 7.8% for ‘Grasslands Ruanui’ ryegrass. This work suggests current New Zealand ryegrasses (here represented by ‘Ellett’) may produce more reproductive tillers in response to spring applied nitrogen fertilizer than do older types. To encourage vegetative tillering from the bases of dying reproductive tillers and the likelihood of improved ryegrass persistence, applications of nitrogen fertilizer in early summer are recommended

Response of male and female domestic chicks to change in the number (quantity) of imprinting objects

When facing two sets of imprinting objects of different numerousness, domestic chicks prefer to approach the larger one. Given that choice for familiar and novel stimuli in imprinting situations is known to be affected by the sex of the animals, we investigated how male and female domestic chicks divide the time spent in the proximity of a familiar versus an unfamiliar number of objects, and how animals interact (by pecking) with these objects. We confirmed that chicks discriminate among the different numerousnesses, but we also showed that females and males behave differently, depending on the degree of familiarity of the objects. When objects in the testing sets were all familiar, females equally explored both sets and pecked at all objects individually. Males instead selectively approached the familiar numerousness and pecked more at it. When both testing sets comprised familiar as well as novel objects, both males and females approached the larger numerousness of familiar objects. However, chicks directed all their pecks toward the novel object within the set. Differences in the behavior of males and females can be accounted for in terms of sex difference in the motivation to reinstate social contact with the familiar objects and to explore novel ones, likely associated with the ecology and the social structure of the species before domestication

Influence of the Convection Electric Field Models on Predicted Plasmapause Positions During Magnetic Storms

In the present work, we determine how three well documented models of the magnetospheric electric field, and two different mechanisms proposed for the formation of the plasmapause influence the radial distance, the shape and the evolution of the plasmapause during the geomagnetic storms of 28 October 2001 and of 17 April 2002. The convection electric field models considered are: Mcllwain's E51) electric field model, Volland-Stern's model and Weimer's statistical model compiled from low-Earth orbit satellite data. The mechanisms for the formation of the plasmapause to be tested are: (i) the MHD theory where the plasmapause should correspond to the last-closed- equipotential (LCE) or last-closed-streamline (LCS), if the E-field distribution is stationary or time-dependent respectively; (ii) the interchange mechanism where the plasmapause corresponds to streamlines tangent to a Zero-Parallel-Force surface where the field-aligned plasma distribution becomes convectively unstable during enhancements of the E-field intensity in the nightside local time sector. The results of the different time dependent simulations are compared with concomitant EUV observations when available. The plasmatails or plumes observed after both selected geomagnetic storms are predicted in all simulations and for all E-field models. However, their shapes are quite different depending on the E-field models and the mechanisms that are used. Despite the partial success of the simulations to reproduce plumes during magnetic storms and substorms, there remains a long way to go before the detailed structures observed in the EUV observations during periods of geomagnetic activity can be accounted for very precisely by the existing E-field models. Furthermore, it cannot be excluded that the mechanisms currently identified to explain the formation of "Carpenter's knee" during substorm events, will', have to be revised or complemented in the cases of geomagnetic storms