Distribution of interaction networks and functions in a spatially heterogeneous system, case of agroforestry

Thanks to their perennial structures, these trees create a microclimate that varies over time, leading to changes in the associated biodiversity and the activity of organisms through habitat diversification. However, few studies have looked at the effects of agroforestry on soil organisms and the functions they perform. Trees in agricultural plots provide mosaics of specific habitats because of their perennial above- and below-ground structures. They have a strong impact on the heterogeneity of the plot microclimate, which varies from season to season depending on the phenology and morphology of the trees. As a result, they modify the associated biodiversity and the activity of other organisms. Finally, the presence of trees, and sometimes of associated herbaceous strips, leads to local concentrations of organic resources from the production of aerial and subterranean litter, and a local increase in soil organic carbon and nutrient levels. Soil structure and aggregate stability can be improved under tree lines, leading to spatial heterogeneity in soil microhabitat characteristics.

Objectives

The general aim of this project is to highlight the response of networks of ecological interactions and functions to the spatial organisation of the environment following the establishment of trees and grass strips in arable crops. The main hypothesis of the project is that modifying the spatial organisation of plots by planting trees leads to an increase in the diversity and multifunctionality of agricultural plots. The operational objectives are (A) to characterise the changes in biodiversity within taxa and by trophic group, (B) to infer the interaction networks between the organisms studied, (C) to establish the relationships between the ecological interaction networks, the physicochemical functioning of the soils and plant growth in order to understand the multifunctionality of these plots.

Approach

This study will be carried out on the Instrumented Mediterranean Agroforestry System under water stress (DIAMs), South of Montpellier, France, on an INRAE experimental station (UE Diascope, Mauguio). This is a factorial experimental set-up covering 5 ha, divided into three blocks. In each block, 3 modalities were compared: forest plantation plots, an agroforestry system and field crop plots. Within the agroforestry system, we separated several habitats: (i) the line of trees and the grassy strip at their foot, and (ii) the cultivated alley. The crops are grown using conventional, low-input farming methods. The instrumented site is used to monitor radiation reaching the soil, soil temperature and humidity at different depths, root growth and nutrient levels in the soil solution.

The growth and yields of crops and the growth and resource allocation strategies of black locust trees will be monitored. Morphological or molecular identification will be used to characterise the communities of soil engineers, surface macro-arthropods, free-living and parasitic nematodes (phytophagous and entomopathogenic), fungi and bacteria (free-living in the soil and associated with parasitic nematodes) and weeds. Interaction networks will be reconstructed using field observations, either directly, such as bipartite interactions (e.g. symbiotic bacteria of entomopathogenic nematodes or pollinators on flowers), or inferred by combining taxon co-occurrence data with a knowledge graph of trophic interactions in soils (via databases).

The intensity of the response of the various taxonomic groups studied will be analysed by comparing the values obtained with those obtained in the agricultural control and the forest control. The response of the structure/composition of the reconstructed modules will be tested in relation to the spatial organisation of the agroforestry plots.

Participants

INRAE structures

• AGROECOSYSTEM department
  • UMR Eco&Sols 
• BAP department
  • UE DIASCOPE
• SPE department
  • UMR DGIM 
• IRD
  • UMR PHIM