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

Abstract

Weeds have always been considered an insidious enemy, capable of reducing crop production. Conversely, the agroecological vision attributes a key role to the spontaneous flora in promoting plant diversity and belowground interactions, which may improve the ecological performance of agroecosystems. We summarized the literature on the weeds’ arbuscular–mycorrhizae (AM) interaction and we analyzed evidence on the: (i) AM suppressive/selective effect on weed communities; (ii) effect of weeds on AM colonization, and (iii) positive role of AM-supporting weeds on forming shared mycorrhizal hyphal connections in agroecosystems. While some authors conceptualized AM as a weed control tool, others underlined their selective effect on weed communities. Recent studies suggest that AM-host weeds can participate in the development of a common mycorrhizal mycelial network (MMN) among different plants species. Nevertheless, direct evidence of the actual exchange of nutrients and C between coexisting plants through MMN in agroecosystems is missing. Although the effect of agricultural practices on plant community-AM interactions are complex, more conservative farming management seems to foster AM populations. Future studies should focus on: (i) field studies, (ii) weed communities and their traits, rather than on the most abundant species, and (iii) the use of advanced analytical techniques, able to monitor MMN development and functionality.

The Effects of Local Weed Species on Arbuscular Mycorrhizal Fungal Communities in an Organic Winter Wheat (Triticum durum L.) Field in Lebanon

“…Several studies have reported greater colonization and AMF proliferation in soil under controlled agroecosystems in the presence of weeds [ 24 , 25 ]. However, under real field conditions, there is no information on how the presence of weeds impacts the crop root AMF community and soil AMF abundance, by considering both biotic and abiotic factors [ 26 ].…”

“…More interestingly, the high AM propagule abundance produced in the soil in the presence of weeds had positive effects on the plant biomass and AM root colonization of M. sativa plantlets in pot culture in a greenhouse as shown by studies demonstrating the same patterns in controlled experiments [ 26 ]. It is also possible that these propagules are one of the factors responsible for the modifications in soil physico-chemical properties resulting in higher C and N contents in soil samples from blocks covered with wheat associated with weeds, as they are constituted and/or able to produce organic molecules such as chitin or glomalin, respectively [ 47 , 48 ].…”

“…While numerous studies showed that weeds can promote AMF colonization and AM proliferation in soil in controlled systems [ 24 , 25 ], their potential effects on the diversity and the composition of AM fungal communities in crop fields are not well known [ 26 ]. It is therefore important to accentuate studies in agroecosystems to understand the impact of weeds on AMFs and their consequences on crops.…”

Integration of Horse Manure Vermicompost Doses and Arbuscular Mycorrhizal Fungi to Improve Fruit Quality, and Soil Fertility in Tomato Field Facing Drought Stress

“…These helpful microorganisms develop symbiotic relationships with a diverse variety of different horticultural crops, e.g., Ocimum basilicum , Lactuca sativa , Punica granatum , and S. lycopersicum [ 19 ]. AMF regulate plant growth and development by forming extra-radical mycelium around the roots, which are inaccessible to roots or even root hairs, enabling the interchange of nutrients and water for carbon sources such as sugars and lipids [ 20 , 21 ]. Plants inoculated with AMF, such as Festuca ovina , Opuntia ficus-indica , and Zea mays , enhance plant growth and improve the absorption of nutrients, especially nitrogen (N) and phosphorus (P), demonstrating the usefulness of AMF to various plant species [ 22 , 23 , 24 ].…”

Composition and Dynamics of Plant- and Soil-Associated Microbial Communities in Forest and Agricultural Ecosystems

“…Li et al [ 12 ] examined the effects of intercropping alfalfa with mulberry on the microbial community structures and physicochemical characteristics of soil, providing a framework for the optimal management of mulberry–alfalfa intercropping. While weeds are normally considered to be a nuisance in conventional monocropping agricultural production systems, Trinchera et al [ 13 ] ask us to consider an alternative perspective in summarizing the literature on the arbuscular mycorrhizal fungi associated with weedy species. Their “agroecological” vision recognizes the role of naturally occurring plants in enhancing plant and soil microbial diversity.…”