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

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.

Arbuscular mycorrhiza induces low oxidative burst in drought-stressed walnut through activating antioxidant defense systems and heat shock transcription factor expression

“…Behrooz et al (2019) reported that AMF (G. mosseae and G. etunicatum) significantly increased contents of some metabolites (e.g., total phenols and proline) in walnut plants under DS. Moreover, AMF also promoted plant growth and nutrient acquisition in walnut plants (Thioye et al, 2022), and thereby improved the adaption of walnut plants in response to DS. The study of Liu et al (2021) showed the an endophytic fungus (Serendipita indica) triggered the enhancement in superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities in walnut plants under soil water deficit, accompanied by the reduction of superoxide anion free radical (O 2…”

“…Combining AMF ( Glomus fasciculatus ) inoculation with foliar fertilization would increase plant growth as well as the survival of walnuts ( Ponder, 1984 ). In addition, AMF ( Diversispora spurca ) inoculation accelerated nutrient uptake of walnuts such as P and K ( Huang et al., 2020 ; Thioye et al., 2022 ). Potted studies had shown the role of AMF in drought tolerance of walnut plants.…”

“…mosseae and G. etunicatum ) significantly increased contents of some metabolites (e.g., total phenols and proline) in walnut plants under DS. Moreover, AMF also promoted plant growth and nutrient acquisition in walnut plants ( Thioye et al., 2022 ), and thereby improved the adaption of walnut plants in response to DS. The study of Liu et al.…”

Biodynamic compost effects on soil parameters in a 27-year long-term field experiment

“…occurring between soil functions and soil-based ecosystem services [41]. Therefore, the evaluation of biological indicators of soil quality is necessary to link the microbial community composition and activity to the changes in the soil abiotic properties [39]. Multi-substrate induced respiration (multi-SIR) is a sensitive method used to determine the catabolic fingerprint of microbial communities [42].…”

“…Microbial biomass indices reflect the availability of C, N, S, and P in soil [36,37]. Consequently, they are key components for assessing soil fertility and quality [38,39] in different agricultural management systems [13,28,38,40]. Soil quality is defined as the capacity of a soil to function within ecosystem to maintain key biological functions, environmental quality, and promote plant and animal health [38,41].…”