C. Roumet | Centre National de la Recherche Scientifique / French National Centre for Scientific Research (original) (raw)

Papers by C. Roumet

Ecological Engineering

The influence of vegetation on slope stability is well understood at the slope level but scaling ... more The influence of vegetation on slope stability is well understood at the slope level but scaling up to the catchment level is still a challenge, partially because of a lack of suitable data to validate models. We tested the physical landslide model, LAPSUS_LS, which models slope stability at the catchment scale. LAPSUS_LS combines a hydrological model with a Limit Equilibrium Method model, and calculates the factor of safety of individual cells based on their hydrological and geomorphological characteristics. We tested two types of vegetation on slope stability: (i) coffee monoculture (Coffea arabica) and (ii) a mixed plantation of coffee and deep rooting Erythrina (Erythrina poeppigiana) trees. Using soil and root data from Costa Rica, we performed simulations to test the response of LAPSUS_LS to root reinforcement, soil bulk density, transmissivity, internal friction angle and depth of shear plane. Furthermore, we modified the model to include biomass surcharge effect in the calculations. Results show that LAPSUS_LS was most sensitive to changes in additional cohesion from roots. When the depth of the shear plane was fixed at 1.0 m, slopes were not unstable. However, when the shear plane was fixed to 1.5 m, the mixed plantation of coffee and trees stabilized slopes, but the coffee monoculture was highly unstable, because root reinforcement was low at a depth of 1.5 m. Soil transmissivity had a limited impact on the results compared to bulk density and internal friction angle. Biomass surcharge did not have any significant effect on the simulations. In conclusion, LAPSUS_LS responded well to the soil and vegetation input data, and is a suitable candidate for modeling the stability of vegetated slopes at the catchment level. (Resume d'auteur)

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Plant and Soil, 2003

Interspecific variations in carbon (C) allocation and partitioning in the rhizosphere were invest... more Interspecific variations in carbon (C) allocation and partitioning in the rhizosphere were investigated on 12 Mediterranean species belonging to different family groups (grasses, legumes, non-legume forbs) and having different life cycles. Plants grown individually in artificial soil, in a greenhouse and inoculated with rhizosphere microflora were labelled with 14CO2 for 3 h at the vegetative stage. Rhizosphere respiration was measured

New Phytologist, 1996

ABSTRACT

New phytologist, 1996

... Navas ML, Guillerm JL, Fabreguettes J, Roy J. 1995. The influence of elevated CO2 on communit... more ... Navas ML, Guillerm JL, Fabreguettes J, Roy J. 1995. The influence of elevated CO2 on community structure, biomass and carbon balance of mediterranean old-field microcosms. Global Change Biology 1: 325-335. Nelson CJ, Sleper DA, Coutts JH. 1985. ...

Summary • Specific leaf area (leaf area to dry mass ratio), leaf dry matter content (leaf dry mas... more Summary • Specific leaf area (leaf area to dry mass ratio), leaf dry matter content (leaf dry mass to saturated fresh mass ratio) and leaf nitrogen concentration (LNC) have been proposed as indicators of plant resource use in data bases of plant functional traits. • We tested whether species ranking based on these traits was repeatable by studying spatio-temporal variations

Intraspecific variability of total phenolic compound concentrations and their responses to elevat... more Intraspecific variability of total phenolic compound concentrations and their responses to elevated CO 2 were studied in two wild Mediterranean perennial grasses, Dactylis glomerata and Bromus erectus. Ten and nine genotypes of each species were grown in climate-controlled naturally-lit glasshouses under plant intergenotypic and interspecific competition for water, light and nutrients. Carbon source-sink balance hypotheses of resource allocation were also tested. Elevated CO 2 induced changes in dry shoot biomass (DM), leaf total non-structural carbohydrate concentrations [TNC] and leaf nitrogen concentrations [N] found in a previous study (New Phytol. 143 (1999) 73) were related to changes in phenolic compound concentrations. Phenolic compound concentrations increased to 15.2% DM in D. glomerata and 86.9% DM in B. erectus under elevated CO 2. These changes were more pronounced when expressed on a structural dry mass basis (DM st). Increases in DM st and [TNC st ] and decreases in [N st ] were also found according to current resource allocation hypotheses. However, there were no proportional changes between phenolic responses to elevated CO 2 and DM st , [TNC st ] and [N st ] responses. Phenolic concentrations were highly determined by genetics in both species, but all studied genotypes responded in a similar way to elevated CO 2. Considering the present experimental conditions with plants growing in intraspecific and interspecific competition, the absence of CO 2 × genotype interaction would lead to little changes of fitness in terms of antiherbivore chemical defence, and, therefore, to low evolutionary consequences in CBSC under the increasing atmospheric CO 2 concentrations of the next decades.

Functional ecology, 2001

... I: initial treatment (value measured immediately upon return to the lab, no further hydration... more ... I: initial treatment (value measured immediately upon return to the lab, no further hydration); PR: storage of leaves in moist paper in a cool chest until return to the lab, where the stem wasre-cut under water; PN: same as PR, but stem not re-cut under water; TR: stems placed ...

This study investigated the relationships between root structure and anatomy and whole-plant func... more This study investigated the relationships between root structure and anatomy and whole-plant functioning in herbaceous species. Fourteen annual and perennial species representative of a Mediterranean old-field succession were grown in monocultures in a common-garden experiment. Whole-plant functioning was assessed by inherent relative growth rate (RGR(max)), measured in standardized conditions, and maximum height (H(max)). Root tissue density (TMD(r)), considered as a major component of root structure, was measured on roots harvested within in-growth cores. Anatomical characteristics were analysed on cross-sectional areas (CSA). TMD(r) was correlated positively with H(max) and negatively with RGR(max). Root CSA explained interspecific variation in H(max) but not that in TMD(r) and RGR(max). Root xylem CSA and xylem proportion in root CSA were positively correlated with TMD(r) and H(max) and negatively with RGR(max). Mean xylem vessel CSA did not account for variations in TMD(r), H(max) and RGR(max). These results suggested that RGR(max) and H(max) are constrained by opposite root structural and anatomical traits, which have potential links with hydraulic conductance, support and longevity.

New Phytologist, 2006

Here, we tested whether root traits associated with resource acquisition and conservation differe... more Here, we tested whether root traits associated with resource acquisition and conservation differed between life histories (annuals, perennials) and families (Fabaceae, Asteraceae and Poaceae). Root topology, morphology, chemistry and mycorrhizal colonization were measured on whole root systems of 18 field-grown herbaceous species grown and harvested in central Argentina. Annuals differed from perennials in several root traits important in resource uptake and conservation. They exhibited higher specific root length (SRL), root nitrogen concentration (RNC) and mycorrhizal colonization but had lower root tissue density (RTD) than perennials. They did not differ in topology or construction cost. These differences were consistent among families. Families differed only in a few root traits known to be strongly associated with certain lineages such as topology and nitrogen concentration. There was a strong parallel between root traits and analogous leaf traits described in the literature for annuals and perennials. Our results suggest the existence at the root level of an acquisitive vs conservative syndrome consistent among families similar to that previously reported for above-ground traits.

Plant and Soil, 1989

The process of symbiotic nitrogen fixation, though of obvious advantage to legumes in situations ... more The process of symbiotic nitrogen fixation, though of obvious advantage to legumes in situations in which nitrogen is limiting, results in substantial penalty to the host plant in terms of cost of maintenance, synthesis and nitrogen reduction. Accurate estimates of costs are difficult to obtain because of the lack of simple methods to measure N2 fixation and associated energy consumption. In relation to these difficulties, a multiple-step approach involving isotopes (~4CO2-~5N2) methodologies is described. The estimation of net respiratory cost associated with the N2 reduction activity in near-natural conditions was achieved using simultaneous ~4CO2 and ~5N 2 labelling. It gives a minimum value of 2.5 mg C/mg N fixed. This value was corrected by the estimation of the amount of carbon saved through the process of CO2 fixation by the PEP carboxylase of the nodules, using ~4CO2 in the soil atmosphere. This gives a real respiratory cost of 4 mg C/mg N fixed.

Journal of Ecology, Nov 1, 2007

Summary 1. Increasing functional diversity often leads to an increase in ecosystem productivity i... more Summary 1. Increasing functional diversity often leads to an increase in ecosystem productivity in the form of overyielding. While the mechanisms (ie complementarity or facilitation) that underlie overyielding provide strong insights into species coexistence and community assembly, they are rarely tested. In subalpine grasslands, traditional management through manuring and hay-making results in intermediate productivity that is associated with high functional diversity. This functional diversity results from the ...