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Mont-Saint-Aignan, France

Trap J.,IRD Montpellier | Hattenschwiler S.,CNRS Center of Evolutionary and Functional Ecology | Gattin I.,Laboratoire Biosol | Aubert M.,CNRS Biodiversity Studies Laboratory
Forest Ecology and Management | Year: 2013

The role of forest age as a potential driver of intraspecific variation in leaf litter quality, that is a key plant trait determining ecosystem functioning, has largely been neglected. Using a set of fully replicated pure beech (Fagus sylvatica) forest stands differing in age (15, 65, 95 and 130. years), we quantified the forest stand age related variability of twelve leaf litter quality traits. Litter Mg, N and K showed significantly higher concentrations in litter from 15-yrs-old stands and decreased with increasing stand age. Mn was the only nutrient analyzed that was highest in the oldest stands. Hemicellulose and cellulose were lowest, and lignin and lignin/N ratio were highest in stands of intermediate age. The amount of N within the litter lignin fraction was highest in the 95-yrs-old stands (51% of total N) and lowest in the oldest stands (34% of total N). The amount of N associated within the hemicellulose fraction (<3%) showed the opposite pattern along the forest stand age gradient compared to lignin. Using Partial Least Squares regressions, we showed that litter N, C/N, lignin/N, K, Mn and Mg were the most important predictors of litter decomposition along the chronosequence. In contrast the proportions of C fractions and the amount of N within these C fractions were the most significant variables explaining the variation in final litter N content after one year of decomposition. N mineralization in ground litter was highly related to the proportion of total N within lignin and humus N mineralization was mostly explained by Mn and the lignin/N ratio. We showed that forest age is an important driver of litter quality variation and contributed considerably to the overall variation of F. sylvatica leaf litter quality traits observed from a reviewed data of published studies conducted at the continental scale. Furthermore, intraspecific litter quality variation greatly impacted belowground processes. Accounting for forest age related litter trait variation, and for the crucial role of the distribution of N within different litter C fractions, may improve the mechanistic understanding of ecosystem functioning. © 2013 Elsevier B.V.

Niepceron M.,CNRS Laboratory of Microbiology Signals and Microenvironment | Niepceron M.,University of Rouen | Martin-Laurent F.,CNRS Agroecology Lab | Martin-Laurent F.,French National Institute for Agricultural Research | And 8 more authors.
Environmental Pollution | Year: 2013

The impact of a multiple contamination by polycyclic aromatic hydrocarbons (PAHs) was studied on permanent grassland soil, historically presenting low contamination (i.e. less than 1 mg kg-1). Soil microcosms were spiked at 300 mg kg-1 with either single or a mixture of seven PAHs. While total dissipation of the phenanthrene was reached in under 90 days, only 60% of the PAH mixture were dissipated after 90 days. Interestingly, after 30 days, the abundance of the GammaProteobacteria class (assessed by qPCR) become significantly higher in microcosms spiked with the PAH mixture. In addition, the specific abundance of the cultivable Pseudomonas spp., which belong to the GammaProteobacteria class, increased earlier and transiently (after 8 days) in the microcosms spiked with the PAH mixture. Consequently, we propose to use the GammaProteobacteria as a bioindicator to detect the impact on the bacterial community of a multiple contamination by PAHs in agricultural soils. © 2013 Elsevier Ltd. All rights reserved.

Trap J.,Laboratoire Biosol | Trap J.,Institute Of Recherche Pour Le Daveloppement | Bureau F.,CNRS Biodiversity Studies Laboratory | Perez G.,CNRS Biodiversity Studies Laboratory | Aubert M.,CNRS Biodiversity Studies Laboratory
Soil Biology and Biochemistry | Year: 2013

Using Partial Least Squares regression, we ranked the ability of leaf litter and topsoil properties to predict humus form shift along a 130-yr-old pure beech forest chronosequence. Three models were tested, including only litter properties (model 1), only topsoil properties (model 2) and both litter and topsoil properties (model 3). The first model was highly significant and explained more than 91% of the humus form variability with N-based variables, Mn, Mg and K as the best predictors. The second model showed lower goodness of fit (75%) with Ca and Mg contents, pHKCl and ΔpH as good predictors. The last model showed that litter traits were better predictors compared to topsoil variables, suggesting that beech trees may impact humus form along forest development mainly through aboveground pathways. © 2012 Elsevier Ltd.

Cannesan M.A.,University of Rouen | Durand C.,University of Rouen | Burel C.,University of Rouen | Gangneux C.,Laboratoire Biosol | And 6 more authors.
Plant Physiology | Year: 2012

Root tips of many plant species release a number of border, or border-like, cells that are thought to play a major role in the protection of root meristem. However, little is currently known on the structure and function of the cell wall components of such root cells. Here, we investigate the sugar composition of the cell wall of the root cap in two species: pea (Pisum sativum), which makes border cells, and Brassica napus, which makes border-like cells. We find that the cell walls are highly enriched in arabinose and galactose, two major residues of arabinogalactan proteins. We confirm the presence of arabinogalactan protein epitopes on root cap cell walls using immunofluorescence microscopy. We then focused on these proteoglycans by analyzing their carbohydrate moieties, linkages, and electrophoretic characteristics. The data reveal (1) significant structural differences between B. napus and pea root cap arabinogalactan proteins and (2) a cross-link between these proteoglycans and pectic polysaccharides. Finally, we assessed the impact of root cap arabinogalactan proteins on the behavior of zoospores of Aphanomyces euteiches, an oomycetous pathogen of pea roots. We find that although the arabinogalactan proteins of both species induce encystment and prevent germination, the effects of both species are similar. However, the arabinogalactan protein fraction from pea attracts zoospores far more effectively than that from B. napus. This suggests that root arabinogalactan proteins are involved in the control of early infection of roots and highlights a novel role for these proteoglycans in root-microbe interactions. © 2012 American Society of Plant Biologists. All Rights Reserved.

Cannesan M.A.,University of Rouen | Gangneux C.,Laboratoire Biosol | Lanoue A.,CNRS Biomolecule and Plant Biotechnology Laboratory | Giron D.,CNRS Research Institute of Insect Biology | And 4 more authors.
Annals of Botany | Year: 2011

•Background and Aims: The oomycete Aphanomyces euteiches causes up to 80% crop loss in pea (Pisum sativum). Aphanomyces euteiches invades the root system leading to a complete arrest of root growth and ultimately to plant death. To date, disease control measures are limited to crop rotation and no resistant pea lines are available. The present study aims to get a deeper understanding of the early oomyceteplant interaction at the tissue and cellular levels. •Methods: Here, the process of root infection by A. euteiches on pea is investigated using flow cytometry and microscopic techniques. Dynamic changes in secondary metabolism are analysed with high-performance liquid chromatography with diode-array detection. •Key Results: Root infection is initiated in the elongation zone but not in the root cap and border cells. Border-cell production is significantly enhanced in response to root inoculation with changes in their size and morphology. The stimulatory effect of A. euteiches on border-cell production is dependent on the number of oospores inoculated. Interestingly, border cells respond to pathogen challenge by increasing the synthesis of the phytoalexin pisatin. •Conclusions: Distinctive responses to A. euteiches inoculation occur at the root tissue level. The findings suggest that root border cells in pea are involved in local defence of the root tip against A. euteiches. Root border cells constitute a convenient quantitative model to measure the molecular and cellular basis of plantmicrobe interactions. © The Author 2011. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.

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