# Unexpected impact of N availability on the interaction between Quercus and Deschampsia

Antoine Vernay, Philippe Malagoli, Marine Fernandez, Thomas Perot, Thierry

Ameglio, Philippe Balandier

► To cite this version:

Antoine Vernay, Philippe Malagoli, Marine Fernandez, Thomas Perot, Thierry Ameglio, et al. Unexpected impact of N availability on the interaction between Quercus and Deschampsia. Conférence Ecologie fonctionnelle et environnement, Jul 2017, Castanet Tolosan, France. 10.13140/RG.2.2.12352.84489 . hal-01603184

HAL Id: hal-01603184

https://hal.science/hal-01603184

Submitted on 5 Jun 2020

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<figure><img src="image_1.png" /></figure>
# Unexpected impact of N availability on the interaction between *Quercus petraea* and *Deschampsia cespitosa*

VERNAY Antoine¹, MALAGOLI Philippe¹, FERNANDEZ Marine¹, PEROT Thomas², AMEGLIO Thierry¹, BALANDIER Philippe²

¹PIAF, INRA, Univ. Clermont-Auvergne, 63100 Clermont-Ferrand, France

²Irstea, Research Unit on Forest Ecosystems (EFNO), Domaine des Barres, F-45290 Nogent-sur-Vernisson, France

## Introduction :

The influence of resource quantity on plant - plant interactions has not led to a consensus. This study aimed to understand how oak tree seedlings and tussock grass interaction evolve among different N×L availability combinations.

## Objectives :

* Determine how were early oak / *D. cespitosa* responses affected by abiotic environment

* Assess importance and intensity of the interactions, either competition or facilitation

* Highlight plant strategy to face interactions with other species

## Materials & Methods

* Nitrogen (N) : no N supply ($N_0$) or 89 kg.ha⁻¹ ($N_{89}$)

* Light (L) : pot under light shelter (27%iPAR, $L_{27}$) or well lit (~59%iPAR, $L_{59}$)

* Competition (C) : oak alone, with 3 *D. cespitosa* tufts in mixture or 3 *D. cespitosa* tufts alone

$$1 \text{ pot} = N \times L \times C$$

* ¹⁵N supply 17d before harvesting. Oak and *D. cespitosa* organs were separated for allocation analyse.

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** Relationship between importance ($I_{imp}$) and intensity ($I_{int}$) of interaction by *D. cespitosa* on oak (Fig 1A) and by oak on *D. cespitosa* (Fig 1B).</figcaption></figure>

## Results:

* Fig 1A: In $N_{89}$ treatment, positive $I_{int}$ and $I_{imp}$ → oak seedlings facilitated *D. cespitosa*.

* Fig 1B: $I_{int}$ and $I_{imp}$ < 0 for all oaks organ → *D. cespitosa* competed with oak seedlings. Competition was the highest in $L_{59}$ compared to $L_{27}$. N supply increased competition inside each L treatment.

<figure><img src="image_3.png" /><figcaption>**Fig 2:** Relative allocation of ¹⁵N among leaves, stems, coarse (CR) and fine roots (FR) in oak seedlings and *D. cespitosa* (above ground biomass (AG) and below ground biomass (BG)) when sole- (SSp) or mixed-grown (MSp)</figcaption></figure>

## Results:

* More ¹⁵N allocated to oak storage organs, and particularly coarse roots, when mixed with *D. cespitosa* (Fig 2)

* *D. cespitosa* preferentially allocated ¹⁵N resource to aboveground organs (Fig 2)

## Conclusion:

* When N-fertilised oak seedlings facilitate *D. cespitosa* growth. We hypothesize that oaks seedling would produce more exudates available for fast capture by *D. cespitosa*.

* In every cases interaction is negative (competition) for oak. Higher resource availability (L or N) increased competition.

* The two species display different strategies, capture strategy for grass and conservative strategy for oak.

## Perspective:

* Integrate other resources as water or phosphorus.

* Assess a potential impact of allelopathic compounds

* Determine role of tree seedling reserve to face competition with grass.