Claire Jouany

ABSTRACT Exchange isotherms were prepared for Na+ in Na+—» Ca2+ and Na+^ Mg2+ exchange reactions, and for Mg2+ in Ca2+—» Mg2+ exchange reactions, at 298 K on Wyoming bentonite suspended in a 0.05 M perchlorate background. These isotherms ...

Predicting the response of plant communities to variation in resources and disturbance is still a challenge, because findings depend on how ecological gradients are characterized and how grassland functional composition is assessed. Focusing on leaf dry matter content (LDMC), the efficacy of different methods for evaluating the best response of plant communities to either environmental or disturbance change is examined. Data were collected on 69 grasslands located at four sites in the Pyrenees and Massif Central. N-Ellenberg indices and plant nutrient content (Ni) were compared to assess fertility, and either LDMC (meas) measured or calculated from a trait database for which traits were measured under the same environmental conditions (db). Management regime (MR) was characterized in terms of categories (grazing, cutting) and plant height. LDMCdb was positively correlated to LDMCmeas, but depended significantly on site temperature. N-Ellenberg and Ni were significantly correlated, a...

ABSTRACT Soil acidification due to N supplied from fertilizer or aerial deposition in grasslands is well recognized and documented; however, little is known about its consequences on soil P availability. This question was addressed on a long-term field experiment done on grassland in Erce (Central Pyrenees, France), where plots were treated for 6 yr with a factorial combination of mineral N added as NH(4)NO(3) (0 and 190 kg ha(-1) yr(-1)) and P (0 and 50 kg ha(-1) yr(-1)) and managed with a frequent defoliation regime (3 cuts yr(-1)). Diffusive PO(4) ion dynamics at the soil-solution interface was determined by coupling sorption studies with (32)P labeling of PO(4) ions (Pi) and dilution analysis. Results showed that the soil pH did not change in zero-N treatments (5.9 +/- 0.1) in comparison with the initial soil (5.9 +/- 0.1), whereas it decreased to 5.3 +/- 0.1 on N-treated soils. Meanwhile the cation exchange capacity and exchangeable Ca(2+) and Mg(2+) contents decreased significantly and the saturation percentage of the adsorption complex by Al(3+) increased from 2 to 15; no changes were observed for untreated soils. Furthermore, the gross amount of diffusive Pi (Pr) was accurately described as a function of the concentration of PO(4) ions in the solution (Cp) and time (t) by a Freundlich kinetic equation; these dynamics were significantly modified by N supply but not by P.

... Research Articles. Using Leaf Traits to Rank Native Grasses According to Their Nutritive Value. Raouda Al Haj Khaled 1 a , Michel Duru b , Virginie Decruyenaere c , Claire Jouany d , and Pablo Cruz e ... Al Haj Khaled, R. , M. Duru , JP Theau , S. Plantureux , and P. Cruz . 2005. ...

ABSTRACT The link between species’ functional traits and competitive abilities has been described as a major factor structuring plant communities. However, two diverging hypotheses have been proposed to explain this process: competition-trait similarity and competition-trait hierarchy.We performed a greenhouse experiment to determine whether grasses’ root foraging strategies, from acquisitive or conservative functional groups, are linked to plant competitive ability and to test which hypothesis better explains interactions during the early stage of grass establishment under contrasting growth conditions.Two grass species of each functional group were grown with and without a neighbour under two levels of water and phosphorus supplies. Three functional traits related to plant competitive ability were measured on all plants grown without neighbours: specific root length (SRL), root phosphorus use efficiency and root length density. Aboveground biomass was measured on plants grown with and without neighbours to evaluate the intensity of plant interaction.We demonstrated that for the three traits the intensity of interaction is driven mainly by hierarchical trait distance, i.e. trait distance between target and neighbour, and not by trait similarity. Growth conditions strongly affected the significance of the relation between hierarchical distances and competition intensity. For the SRL hierarchical distance, this effect may be due to the most competitive species (with high SRL) being strongly impacted by water shortage, which modified the competitive hierarchy. Trait plasticity in response to stresses also appeared an important factor influencing the competitive ability of species, i.e. species with the most plastic SRL in response to P stress were also the most competitive under P stress.A strong hierarchy exists among grasses’ competitive abilities in non-limiting growth conditions that is linked to their root functional traits and investment in the root system. Consequently, our results support the trait-hierarchy hypothesis in its ability to describe competitive interaction among grasses during early stages of establishment.Our study provides evidence that root functional hierarchical trait distance and plasticity explain how grasses interact with their neighbours. This distance enables species to be ranked according to their competitive ability; however, this ranking may be influenced by the growth conditions and traits considered. This article is protected by copyright. All rights reserved.

The phosphorus nutrition index (PNI) method proved to be suitable for diagnosing P nutrition level over a wide range of grass swards. It is based on relative nutrient concentrations and relies on a critical curve for optimum P concentration which is a function of sward N concentration. The objectives of this paper were to verify to what extent this method

A long-term field experiment was conducted near Toulouse (south-west France) to verify to what extent increasing fertilizer dressings would increase yields on calcareous soils in a cereals-oilseeds-legumes rotation. Over a 25-year period, withholding K significantly depressed yield once; K inputs affected the total amount of K absorbed at flowering, without subsequent effects on yields.Exchangeable K content on non-fertilized plots declined slightly over the experimental period, but without reaching levels expected from nutrient balance estimates. Annual applications of K equal to average offtake in grain were adequate to maintain available soil K content at its initial value.Potassium release kinetics for the exchangeable fraction, evaluated from Ca-resin extraction, clearly discriminated between fertilized and non-fertilized treatments. Both soils exhibited similar patterns for diffusion-controlled K release. These results highlight the role of K reserves readily available in illite-rich calcareous soils and demonstrate the importance of cultural residues in K fertility management.

Fertiliser recommendation systems should aim at a finer tuning of non-renewable P inputs for agronomic, environmental and economic reasons. Modern decision support systems should take into account the relevant soil characteristics, the P recycling capabilities of the cropping system, and crop requirements for attainable production in a range of soil/weather conditions. Unfortunately, information is still lacking for low input cropping

... Morard a , Guillaume Piva b , Claire Jouany b & Patrick Petitbon b ... Ten maize plants were sampled at the 8–10 leaf stage between 10 and 12 am On each plot, soil P concentration was analyzed by the Olsen method.[8]8. Olsen, SR, Cole, CV, Watanabe, FS and Dean, LA 1954. ...