Papers by Christian Dupraz
La Revue Du Praticien, 2009
Agroforestry is a land use type where crops and trees are grown together in the same place and at... more Agroforestry is a land use type where crops and trees are grown together in the same place and at the same time. Agroforestry systems have the advantage of providing multiple products (e.g. wood, fruits) or services (e.g. biodiversity enhancement, erosion control) whilst maintaining agricultural production. If they are known to store carbon into the biomass of the trees, they could also increase soil organic carbon (SOC) stocks. However their impact has rarely been studied under temperate conditions and has mostly concerned superficial soil layers. Our objectives were (i) to quantify and spatialize SOC stocks in an agroforestry system and in an adjacent agricultural plot, (ii) to assess what SOC fractions are responsible for possible additional carbon storage, and (iii) to quantify all organic inputs entering the soil. The trial was established in 1995 in southern France. Hybrid walnut trees are intercropped with durum wheat. SOC stocks were measured on 200 soil cores down to 2 m so...
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La Revue du praticien, Jan 20, 2009
The recommendations of the French consensus (Lille 1990) advise the stop of the tracking by cervi... more The recommendations of the French consensus (Lille 1990) advise the stop of the tracking by cervical smears of cancer at 65-years-old, if the former follow-up were regular and if the last two smears were normal. 33% cervical cancers are after 65-years-old. How many pathological smears are after 65 years? Descriptive, retrospective study analyzing the results of 12339 smears of women of more than 65 years, carried out during one year in the same laboratory of anatomo-pathology. They were analysed with Bethesda's system. 2.67% of smears are of insufficient quality (CI 95%: 2, 46%; 3%); 2.43% of smears are pathological (CI 95%: 2, 2%; 2, 7%). That pathological smear's rate is comparable to the one found among women of less than 65-years-old (2 to 3%). The squamous cell carcinoma's rate is more important in this group. This work encourages us to continue smear's practice among women of more than 65 years.
Nature, Jan 31, 2000
For three billion years, before the Cambrian diversification of life, laminated carbonate build-u... more For three billion years, before the Cambrian diversification of life, laminated carbonate build-ups called stromatolites were widespread in shallow marine seas. These ancient structures are generally thought to be microbial in origin and potentially preserve evidence of the Earth's earliest biosphere. Despite their evolutionary significance, little is known about stromatolite formation, especially the relative roles of microbial and environmental factors in stromatolite accretion. Here we show that growth of modern marine stromatolites represents a dynamic balance between sedimentation and intermittent lithification of cyanobacterial mats. Periods of rapid sediment accretion, during which stromatolite surfaces are dominated by pioneer communities of gliding filamentous cyanobacteria, alternate with hiatal intervals. These discontinuities in sedimentation are characterized by development of surface films of exopolymer and subsequent heterotrophic bacterial decomposition, forming ...
Le stock de carbone (C) des sols est extrêmement sensible au changement d'usage des terres, et pe... more Le stock de carbone (C) des sols est extrêmement sensible au changement d'usage des terres, et peut à la fois être une source ou un puits de CO 2 atmosphérique. Les systèmes
ABSTRACT According to the FAO (2012), agriculture is responsible for 14 percent of global greenho... more ABSTRACT According to the FAO (2012), agriculture is responsible for 14 percent of global greenhouse gas emissions. Agriculture suffers the impacts of climate change, but “agriculture has the potential to be an important part of the solution, through mitigation” as recognizes IPCC. Agroforestry (AGF) systems are known to sequester C into aerial biomass, but also play an important role by enhancing C inputs into deep soil horizons. AGF trees have often a deep rooting system, due to the competition with the annual crop (Mulia and Dupraz 2006). C inputs from roots (turnover and exudates) may constitute an important part of SOC as they are easily stabilized through different processes (Oelbermann et al. 2004; Rasse et al. 2005; Peichl et al. 2006). ECOSFIX project aims at studying ecosystem services of shallow and deep roots such as hydraulic redistribution, C sequestration and soil fixation in different ecosystem structures and climates (Costa Rica, Laos, France). This work focusses on the experimental device that was implemented in an intercropping system at Restinclières, France in 1995 (durum wheat and walnut (13x8m)). A huge pit (5m long, 4m deep) was dug into the soil, perpendicularly to a tree row. Fine root impacts (< 2mm diameter) were counted on each trench walls, cubes of soil (1 dm3) were sampled at different depth and a model of root length density (RLD) from root intercept counts was established (Maurice et al. 2010). It well fitted (R2=0.59). This method allowed estimating root density through the profile, which was surprisingly homogeneous, down to a depth of 4 m and across the cropped alley. Soil cylinders were collected to measure C content, bulk density, penetrometry and soil C fractionation. Roots were sampled at different depths to be chemically analysed and study root traits. 16 minirhizotrons and Tª sensors were implemented in the pit at different depths and distances from the trees, to estimate fine root turnover of walnut trees. Images are collected every three weeks. 3 other 1.5 m deep pits were dug (in AGF, agriculture control and forestry control), and litterbags containing fine roots were installed at different depths before the pits were filled up. Chemical composition changes and mass loss will be analyzed after one year to determine the decomposition rate. Root C input into the soil was also modeled with the Hi-sAFe model.
Plant and Soil, 2005
A Dehesa is a structurally complex agro-silvo-pastoral system where at least two strata of vegeta... more A Dehesa is a structurally complex agro-silvo-pastoral system where at least two strata of vegetation, trees and herbaceous plants coexist. We studied the root distribution of trees (Quercus ilex L.) and herbaceous plants, in order to evaluate tree and crops competition and complementarity in Dehesas of Central Western Spain. 72 soil cores of 10 cm diameter (one to two metre deep) were taken out around 13 trees. Seven trees were intercropped with Avena sativa L. and six trees were in a grazed pasture dominated by native grasses. Soil coring was performed at four distances from the tree trunks, from 2.5 (beneath canopy) till 20 m (out of the canopy). Root length density (RLD) of herbaceous plants and trees was measured using the soil core-break method. Additionally, we mapped tree roots in 51 profiles of 7 recently opened road cuts, located between 4 and 26 m of distance from the nearest tree. The depth of the road cuts varied between 2.5 and 5.5 m. Herbaceous plant roots were located mostly in the upper 30 cm, above a clayey, dense soil layer. RLD of herbaceous plants decreased exponentially with depth until 100 cm depth. Holm-oak showed a much lower RLD than herbs (on average, 2.4 versus 23.7 km m )3 , respectively, in the first 10 cm of the soil depth). Tree RLD was surprisingly almost uniform with depth and distance to trees. We estimated a 5.2 m maximum depth and a 33 m maximum horizontal extension for tree roots. The huge surface of soil explored by tree roots (even 7 times the projection of the canopy) could allow trees to meet their water needs during the dry Mediterranean summers. The limited vertical overlap of the two root profiles suggests that competition for soil resources between trees and the herbaceous understorey in the Dehesa is probably not as strong as usually assumed.
European Journal of General Practice, 2014
Several studies have shown that vitamin D supplementation could be useful for treating diffuse mu... more Several studies have shown that vitamin D supplementation could be useful for treating diffuse musculoskeletal (DMS) pain in adults. The aim of this study was to evaluate the effects of correcting a vitamin D deficiency (≤ 50 nmol/l) on DMS pain and quality of life in adults. A pragmatic prospective study was conducted in a general practice setting in the Rhone-Alps area between 1 February and 30 April 2009. Patients between the ages of 18 and 50 years old who consulted their general practitioner (GP) for DMS pain or chronic unexplained asthenia and had a deficient serum 25 (OH) D level with no signs of any other disease were enrolled in this study. The patients received high doses of vitamin D supplements (400 000 to 600 000 units). Mean pain evaluation scores were evaluated before and after vitamin D supplementation using mixed models and accounting for repeated measures. Before vitamin D supplementation, the adult study cohort (n = 49) had an adjusted mean serum 25 (OH) D level of 23.7 nmol/l, a mean pain evaluation score of 5.07 and a mean quality of life score of 3.55. After vitamin D supplementation, the adjusted mean serum 25 (OH) D level increased to 118.8 nmol/l (P < 0.001), the mean quality of life score increased to 2.8 nmol/l (P < 0.001) and the mean pain evaluation score decreased to 2.8 (P < 0.001). In this small before-and-after study, vitamin D supplementation decreased pain scores in adult patients with diffuse musculoskeletal pain and vitamin D deficiency. These results must be confirmed by further studies.
The precipitation of calcium carbonate in microbial mat systems such as stromatolites creates a g... more The precipitation of calcium carbonate in microbial mat systems such as stromatolites creates a geological record of life. We cannot read that record, however, without understanding the mechanism of precipitation and lithification (the consolidation of loose sediment grains into solid rock). Several different groups of mat bacteria have been implicated in the precipitation and dissolution of calcium carbonate, most notably
Modern microbialites are formed through microbially mediated alkalinity changes, exopolymer produ... more Modern microbialites are formed through microbially mediated alkalinity changes, exopolymer production and microbial communication. Here, we present an overview of field and laboratory observations and emerging models of how these systems may form.
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Papers by Christian Dupraz