Can multi-cropping affect soil microbial stoichiometry and functional diversity, decreasing potential soil-borne pathogens? A study on European organic vegetable cropping systems

Abstract

Crop diversification in spatial and temporal patterns can optimize the synchronization of nutrients plant demand and availability in soils, as plant diversity and soil microbial communities are the main drivers of biogeochemical C and nutrient cycling. The introduction of multi-cropping in organic vegetable production can represent a key strategy to ensure efficient complementation mediated by soil microbiota, including beneficial mycorrhizal fungi. This study shows the effect of the introduction of multi-cropping in five European organic vegetable systems (South-West: Italy; North-West: Denmark and Belgium; North-East: Finland and Latvia) on: (i) soil physicochemical parameters; (ii) soil microbial biomass stoichiometry; (iii) crop root mycorrhization; (iv) bacterial and fungal diversity and composition in crop rhizosphere; (v) relative abundance of selected fungal pathogens species. In each site, three cropping systems were considered: (1) crop 1—monocropping; (2) crop 2—monocropping; (3) crop 1—crop 2—intercropping or strip cropping. Results showed that, just before harvest, multi-cropping can increase soil microbial biomass amount and shape microbial community toward a predominance of some bacteria or fungi phyla, in the function of soil nutrient availability. We mainly observed a selection effect of crop type on rhizosphere microbiota. Particularly, Bacteroidetes and Mortierellomycota relative abundances in rhizosphere soil resulted in suitable ecological indicators of the positive effect of plant diversity in field, the first ones attesting an improved C and P cycles in soil and the second ones a reduced soil pathogens' pressure. Plant diversity also increased the root mycorrhizal colonization between the intercropped crops that, when properly selected, can also reduce the relative abundance of potential soil-borne pathogens, with a positive effect on crop productivity in long term.

Weeds: An Insidious Enemy or a Tool to Boost Mycorrhization in Cropping Systems?

“…However, it was found that mycorrhizal extra-radical mycelium can cover also roots of weed species belonging to the Brassicaceae family: on these roots, morphological types of arbuscular and coiled hyphae were observed, which are the most common in grasses [ 61 ]. Similar results were obtained in an organic beetroot intercropping system: here, an extra-radical mycelium was found on beetroot roots surfaces as a result of the presence of SAM weeds (namely, Capsella bursa-pastoris L., Senecio vulgaris L., Spergula arvensis L., and Plantago maior L.) in intercropping, while the external hyphal mycelium was missed in the monocropping system, where SAM species were not recorded [ 62 ].…”

“…Evidently, weeding practices can strongly impact native seedbanks’ diversity, potentially affecting the abundance of SAM weeds in the field and, consequently, limiting the fungal mycelium development and the ecosystem services provided by mycorrhizae. On the contrary, the introduction of SAM cover crops, such as the winter cereals [ 59 ], or the intercropping with legumes (e.g., faba bean, [ 62 ]) can promote the AM colonization of SAM weeds and, thus, of the whole cropping system.…”

Why Do We Need Alternative Methods for Fungal Disease Management in Plants?

“…Similar to crop rotations, the inter-cropping of different species can serve to reduce pathogen pressures [56]. In this respect, the examination of soil microbiomes as a result of multi-cropping in five organic vegetable farming systems revealed that inter-cropping was associated with a decrease in the abundance of soil-borne pathogens [57]. Thus, determining the ideal combinations for inter-cropping for each species may serve as an effective form of disease control.…”

Insights into the Belowground Biodiversity and Soil Nutrient Status of an Organic Apple Orchard as Affected by Living Mulches

“…The soil microbiome is recognized as having a crucial role in soil health and fertility. Microbial communities are involved in direct and indirect interactions with plants, which depend on environmental and agronomic factors [23,24]. However, the soil microbiome is also interconnected with the major nematode trophic groups (bacteria and fungi feeders).…”