Grazing in a megagrazer-dominated savanna does not reduce soil carbon stocks, even at high intensities

Recent studies suggest that wild animals can promote ecosystem carbon sinks through their impacts on vegetation and soils. However, livestock studies show that intense levels of grazing reduce soil organic carbon (SOC), leading to concerns that rewilding with large grazers may compromise ecosystem carbon storage. Furthermore, wild grazers can both limit and promote woody plant recruitment and survival on savanna grasslands, with both positive and negative impacts on SOC, depending on the rainfall and soil texture contexts. We used grazing lawns in one of the few African protected savannas that are still dominated by megagrazers (> 1000 kg), namely white rhinoceros Ceratotherium simum, as a model to study the impact of prolonged and intense wild grazing on SOC stocks. We contrasted SOC stocks between patches of varying grazing intensity and woody plant encroachment in sites across different rhino habitat types. We found no differences in SOC stocks between the most- and least grazed plots in any of the habitats. Intermediately grazed plots, however, had higher SOC stocks in the top 5 cm compared to most and least grazed plots, but only in the closed-canopy woodland habitat and not in the open habitats. Importantly, we found no evidence to support the hypothesis that wild grazing reduces SOC, even at high grazing intensities by the world's largest megagrazer. Compared to the non-encroached reference plots, woody encroached plots had higher SOC stocks in soils with low clay content and lower SOC stocks in soils with high clay content, although only in the top 5 cm. Accordingly, our study highlights that wild grazers may influence SOC indirectly through their impact on tree-grass ratios in grassy ecosystems. Our study thus provides important insights for future natural climate solutions that focus on wild grazer conservation and restoration. Keywords: fire, grazing impact, rewilding, soil carbon, white rhinoceros, woody encroachmen

Current use and barriers and facilitators for implementation of standardised measures in physical therapy in the Netherlands

In many countries, the need for physical therapists to use standardised measures has been recognised and is recommended in clinical practice guidelines. Research has shown a lack of clinimetric knowledge and clinical application of measurement instruments in daily practice may hamper implementation of these guidelines. The aims of this study are 1) to investigate the current use of measurement instruments by Dutch physical therapists; 2) to investigate the facilitators and barriers in using measurement instruments

Why no part on syntax in the greek school grammar ? Solecisms and Education

ABSTRACT : In this paper I argue for the view that in the Greek system of education teachers had no need of an explicit syntactic theory ; as for the Stoic theory, whether or not it may be called syntactic, it was not relevant for their purpose. The theory of solecisms and grammatical figures was strong enough to provide adequate help when a teacher had to explain seemingly grammatical mistakes in the texts of the authors read at school and to correct the mistakes of their pupils. After a survey of the scholarly opinions concerning the absence of a part on syntax in ancient grammar I shortly discuss the praxis of Aristarchus, Nicanor, and Dionysius of Halicarnassus so far as syntactic peculiarities are concerned. Finally I compare the method of ancient teachers with my own experience with the teaching of syntactic theory in my school days.RÉSUMÉ : Ma thèse dans cet article est que, dans le système d'éducation grec, les professeurs n'avaient pas besoin d'une théorie syntaxique explicite ; quant à la théorie stoïcienne, qu'il faille ou non l'appeler syntaxique, elle n'avait aucune pertinence pour leur propos. La théorie du solécisme et des figures grammaticales était assez forte pour fournir au professeur l'aide dont il avait besoin, tant pour l'explication des apparentes fautes de grammaire rencontrées dans les textes lus à l'école que pour la correction des fautes des élèves. Après avoir passé en revue les opinions des savants touchant l'absence, dans la grammaire antique, d'une partie consacrée à la syntaxe, je discute brièvement la pratique d'Aristarque, de Nicanor et de Denys d'Halicarnasse face à des problèmes de syntaxe. Pour finir, je compare la méthode des professeurs de l'Antiquité avec ma propre expérience scolaire d'apprentissage de la théorie syntaxique.Schenkeveld D. M. Why no part on syntax in the greek school grammar ? Solecisms and Education. In: Histoire Épistémologie Langage, tome 22, fascicule 1, 2000. Horizons de la grammaire alexandrine (1) pp. 11-22

Constraints to Synergistic Fe Mobilization from Calcareous Soil by a Phytosiderophore and a Reductant

Synergistic effects between ligand- and reductant-based Fe acquisition strategies can enhance the mobilization of Fe, but also of competing metals from soil. For phytosiderophores, this may alter the time and concentration window of Fe uptake during which plants can benefit from elevated Fe concentrations. We examined how the size of this window is affected by the ligand and reductant concentration and by non-simultaneous addition. To this end, a series of kinetic batch experiments was conducted with a calcareous clay soil to which the phytosiderophore 2′-deoxymugineic acid (DMA) and the reductant ascorbate were added at various concentrations, either simultaneously or with a one- or two-day lag time. Both simultaneous and non-simultaneous addition of the reductant and the phytosiderophore induced synergistic Fe mobilization. Furthermore, initial Fe mobilization rates increased with increasing reductant and phytosiderophore concentrations. However, the duration of the synergistic effect and the window of Fe uptake decreased with increasing reductant concentration due to enhanced competitive mobilization of other metals. Rate laws accurately describing synergistic mobilization of Fe and other metals from soil were parameterized. Synergistic Fe mobilization may be vital for the survival of plants and microorganisms in soils of low Fe availability. However, in order to optimally benefit from these synergistic effects, exudation of ligands and reductants in the rhizosphere need to be carefully matched

Constraints to Synergistic Fe Mobilization from Calcareous Soil by a Phytosiderophore and a Reductant

Synergistic effects between ligand- and reductant-based Fe acquisition strategies can enhance the mobilization of Fe, but also of competing metals from soil. For phytosiderophores, this may alter the time and concentration window of Fe uptake during which plants can benefit from elevated Fe concentrations. We examined how the size of this window is affected by the ligand and reductant concentration and by non-simultaneous addition. To this end, a series of kinetic batch experiments was conducted with a calcareous clay soil to which the phytosiderophore 2′-deoxymugineic acid (DMA) and the reductant ascorbate were added at various concentrations, either simultaneously or with a one- or two-day lag time. Both simultaneous and non-simultaneous addition of the reductant and the phytosiderophore induced synergistic Fe mobilization. Furthermore, initial Fe mobilization rates increased with increasing reductant and phytosiderophore concentrations. However, the duration of the synergistic effect and the window of Fe uptake decreased with increasing reductant concentration due to enhanced competitive mobilization of other metals. Rate laws accurately describing synergistic mobilization of Fe and other metals from soil were parameterized. Synergistic Fe mobilization may be vital for the survival of plants and microorganisms in soils of low Fe availability. However, in order to optimally benefit from these synergistic effects, exudation of ligands and reductants in the rhizosphere need to be carefully matched

The Effect of pH and Biogenic Ligands on the Weathering of Chrysotile Asbestos : The Pivotal Role of Tetrahedral Fe in Dissolution Kinetics and Radical Formation

Abstract Chrysotile asbestos is a soil pollutant in many countries. It is a carcinogenic mineral, partly due to its surface chemistry. In chrysotile, FeII and FeIII substitute Mg octahedra (Fe[6]), and FeIII substitutes Si tetrahedra (Fe[4]). Fe on fiber surfaces can generate hydroxyl radicals (HO.) in Fenton reactions, which damage biomolecules. To better understand chrysotile weathering in soils, net Mg and Si dissolution rates over the pH range 3.0?11.5 were determined in the presence and absence of biogenic ligands. Also, HO. generation and Fe bulk speciation of pristine and weathered fibers were examined by EPR and Mössbauer spectroscopy. Dissolution rates were increased by ligands and inversely related to pH with complete inhibition at cement pH (11.5). Surface-exposed Mg layers readily dissolved at low pH, but only after days at neutral pH. On longer timescales, the slow dissolution of Si layers became rate-determining. In the absence of ligands, Fe[6] precipitated as Fenton-inactive Fe phases, whereas Fe[4] (7?% of bulk Fe) remained redox-active throughout two-week experiments and at pH?7.5 generated 50±10?% of the HO. yield of Fe[6] at pristine fiber surfaces. Ligand-promoted dissolution of Fe[4] (and potentially Al[4]) labilized exposed Si layers. This increased Si and Mg dissolution rates and lowered HO. generation to near-background level. It is concluded that Fe[4] surface species control long-term HO. generation and dissolution rates of chrysotile at natural soil pH