Understanding Arbuscular Mycorrhizal Colonization in Walnut Plantations: The Contribution of Cover Crops and Soil Microbial Communities

Babacar Thioye,François Hirissou,Isabelle Trinsoutrot-Gattin,Lisa Castel,Marc Legras,Naouel Chaftar

doi:10.3390/agriculture12010001

Babacar Thioye, François Hirissou + Show 4 more

Open Access

https://doi.org/10.3390/agriculture12010001

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Journal: Agriculture	Publication Date: Dec 21, 2021
Citations: 9	License type: CC BY 4.0

Affiliation: UNiLaSalle, University of Rouen

Abstract

Soil microorganisms play a central role in biological soil functioning. One of the beneficial microbiota that has a symbiotic association with most of the plants is arbuscular mycorrhizal fungi (AMF). Nevertheless, little is known about the impact of cover crops—widely used in conservation agriculture or organic farming—on native mycorrhizal fungi. This study was conducted in Southern France, in 20-year-old walnut orchards, where faba bean (Vicia faba Roth) was intercropped. To find whether the native AM fungal community associated with walnut trees was influenced by cover crops and soil microbial communities, analyses of soil physicochemical and microbiological indicators were carried out with roots and soil samples collected from four modalities (walnut in conventional farming with and without cover crops, and walnut in organic farming with and without cover crops). Our results showed that the presence of cover crops mainly influenced the soil microbial abundance and activities in conventional plots. In contrast, cover crops stimulated AM fungal colonization of walnut roots in organic plots, reaching 35% and 54% for arbuscule abundance and mycorrhizal intensity, respectively. In conventional plots, ergosterol and mineral nitrogen contents were mainly correlated with mycorrhizal colonization, while only acid phosphatase activity in soil was positively correlated with mycorrhizal colonization in organic plots. The use of the faba bean showed the great role played by cover crops in the enhancement of walnut trees’ mycorrhizal colonization. Identification of the functional traits of AM fungi sensitive to walnut trees is required to inform decisions in specific agricultural practices.

Highlights

Walnut tree (Juglans regia L., Fam.: Juglandaceae) is the most widespread nut tree in the world and the predominant tree species in current European agroforestry systems [1]
The objective of this study is to evaluate the effect of cover crops and soil microbial communities on AM fungal colonization in walnut plantations under organic and conventional farming systems
Bacterial and fungal abundance as well as the total biomass follow the organic status of the soil, where SOM, soil organic carbon (SOC) and mineral nitrogen contents are higher in the plots with cover crops

Summary

Introduction

Walnut tree (Juglans regia L., Fam.: Juglandaceae) is the most widespread nut tree in the world and the predominant tree species in current European agroforestry systems [1]. That is why good organic matter mineralization by soil microorganisms as well as the optimal use of mineral and water resources by the plant is a real challenge for walnut orchards. The use of beneficial soil microorganisms is a promising strategy for optimizing plant growth and agricultural sustainability. It should be noted that studies on AMF colonization in an agroforestry system, and not just with a single tree species, are rare [13,14] These studies already show us that this association allows an increase in AMF spore abundance as well as colonization of plant roots. The community assembly of AMF species is often limited in intensively managed agricultural systems [15]

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