New article accepted!!!

Hierarchy of root functional trait values and plasticity drive early-stage competition for water and phosphorus among grasses

Florian Fort*, Pablo Cruz, Claire Jouany

Functional Ecology


1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

Keywords: specific root length, root phosphorus use efficiency, root length density, plant competition, trait similarity, trait hierarchy

Lay summary

Thesis defence « Grassland species root functional strategies to face abiotic and biotic stresses »

In order to optimise grassland ecosystem services we need to improve our understanding of root system functioning. As a result, we decided to characterise strategies of species coming from grassland’ Fabaceae and Poaceae families, by root functional traits measurement.
The main result of this work is the establishment of several axes of root strategies differentiation. The main axis is the trade-off between resources capture and conservation
strategies. Species with capture strategies appear to be adapted to non-water stressful habitat and are barely impacted by phosphorus shortage; they also happen to be strong competitors.
On the opposite, species with conservation strategies are adapted to water stressful continental climates, but are strongly impacted by phosphorus shortage and happen to be weak competitors. The kind of relation between above-ground and below-ground strategies also appears to be a marker of the plants adaptation to stress.
We showed that the root system study is a good way to predict grassland species comportment to face abiotic and biotic constraints. The present work widens interesting perspectives for the sowing of mixed grassland species better adapted to their environments.

SUMMER SCHOOL Facilitation process for nutrients acquisition in pluri-specific plant populatings


• Master the theories and the concepts of the ecology applied to the functioning of the pluri-specific plant populatings.
• Distinguish the advantages and the limits of  models and experimental approach susceptible to be mobilized for quantifying the sharing of the  nutriments in these populatings.
• Elaborate a research strategy  to test the validity of various process of interaction (facilitation / competition, etc.) within this kind of populatings, in diverse kind of agro-systemic contexts.

Flyer   /   Form

Language of the summer school : FRENCH

The interested persons have to make a request with Mrs H. Guillemain ( ) before April 30th, 2012.

ISRR 2012: « Roots to the Future »

26-29 June 2012 Dundee, Scotland

The eighth symposium of the International Society of Root Research (ISRR), to be held in summer of 2012 in Dundee, UK, will mark the 30th anniversary of the Society’s founding and its first meeting in the UK.