[PhD defence] 07/04/2025 - Émile Melloul: "The effects of irrigation on biodiversity in Mediterranean wine-growing ecosystems" (UMR IMBE)

Mr Emile MELLOUL will publicly defend his thesis entitled "Effects of irrigation on biodiversity in Mediterranean wine-growing ecosystems" on Monday 7 April 2025.

Laboratory

UMR 7263 IMBE - Mediterranean Institute of Biodiversity and Ecology EECAR

Composition of the jury

MR ARMIN BISCHOFF	Avignon University	Thesis supervisor
Mr Olivier BLIGHT	Avignon University	Thesis co-director
Mr Raphaël GROS	Aix-Marseille university	Thesis co-director
Mickaël HEDDE	INRAE, the French National Research Institute for Agriculture, Food and the Environment	Rapporteur
Mr Sébastien BAROT	Institute of Ecology and Environmental Sciences-Paris	Rapporteur
Ms Apolline AUCLERC	University of Lorraine	Examiner
Ms Estelle FOREY	University of Rouen Normandy	Examiner

Summary

Irrigation is a common practice in agriculture, helping to stabilise water supplies and improve crop yields. It is also one of the main ways in which farmers are responding to climate change, which is expected to lead to changes in rainfall patterns and higher temperatures. These changes will be particularly pronounced in the Mediterranean region, where higher temperatures and more frequent and intense droughts are expected. In the vineyards, irrigation is booming. It is used to stabilise production and regulate sugar levels in the wine. It is mainly used by drip irrigation during periods of drought, to simulate the effects of summer storms. Although beneficial for production in a context of water stress, increased humidity could affect the biodiversity of the agroecosystem by modifying its composition, structure and interaction networks.

This could affect key ecological functions and have repercussions for crops. It is therefore vital to gain a better understanding of the effects and processes associated with irrigation, which is becoming increasingly frequent and intense. This is the context for my thesis work, which aims to gain a better understanding of the effects of irrigation on biodiversity in Mediterranean wine-growing agroecosystems. This led to three main research questions: (1) What effects does irrigation have on vegetation and epigeous arthropods in vine inter-rows? (2) What effects does irrigation have on vegetation and soil organisms in the short and medium term under the vine row? (3) How do the effects of irrigation evolve in the short term during the summer period? In the first area (1), we showed a reduction in floral cover in the irrigated vineyards, although no difference was observed in terms of species richness. The abundance of several beneficial arthropods was directly affected by irrigation. These direct effects were amplified by the negative impact of irrigation on floral cover. Predation rates were also lower in irrigated vineyards, but only during the day.

In the second axis (2), no clear effect of irrigation was observed on the vegetation under the vine row. However, an increase in soil fauna was noted during the summer period, at the time of irrigation, with an increase in predatory mite populations and a change in the structure of mite and springtail communities. Irrigation appears to mitigate the effects of drought, which have a negative impact on springtails and mites. Springtails, which are more sensitive to drought, were absent from the surveys carried out in August.

In the third axis (3), the addition of water to the vines during the drought period had a 'priming' effect on bacteria, but did not alter the composition of the microbial community. We also observed an increase in the abundance of springtails and mites, as well as an increase in biological activity in the soil. The more drought-resistant organisms were not affected by the irrigation. The effects of irrigation disappeared after just a few days. However, in the long term, there could be a potential depletion of soil organic matter due to peaks in activity during rewetting cycles. All these results highlight the importance of studying the effects of irrigation and their temporality, in a context where its use is tending to become the norm. This thesis opens up new perspectives on the potential effects of irrigation, particularly in terms of the functional traits of organisms and the specific composition of communities.

Keywords Irrigation, vine, arthropods, mesofauna, microorganisms, Mediterranean