Mycorrhiza‐mediated interference between cover crop and weed in organic winter cereal agroecosystems: The mycorrhizal colonization intensity indicator

Abstract

The mycorrhizal fungi are symbiotic organisms able to provide many benefits to crop production by supplying a set of ecosystem functions. A recent ecological approach based on the ability of the fungi community to influence plant–plant interactions by extraradical mycelium development may be applied to diversified, herbaceous agroecosystems. Our hypothesis is that the introduction of a winter cereal cover crop (CC) as arbuscular mycorrhizal fungi (AMF)–host plant in an organic rotation can boosts the AMF colonization of the other plants, influencing crop–weed interference. In a 4‐years organic rotation, the effect of two winter cereal CC, rye and spelt, on weed density and AMF colonization was evaluated. The AMF extraradical mycelium on CC and weeds roots was observed by scanning electron microscopy analysis. By joining data of plant density and mycorrhization, we built the mycorrhizal colonization intensity of the Agroecosystem indicator (MA%). Both the CC were colonized by soil AMF, being the mycorrhizal colonization intensity (M%) affected by environmental conditions. Under CC, the weed density was reduced, due to the increase of the reciprocal competition in favor of CC, which benefited from mycorrhizal colonization and promoted the development of AMF extraradical mycelium. Even though non‐host plants, some weed species showed an increased mycorrhizal colonization in presence of CC respect to the control. Under intense rainfall, the MA% was less sensitive to the CC introduction. On the opposite, under highly competitive conditions, both the CC boosted significantly the mycorrhization of coexistent plants in the agroecosystem. The proposed indicator measured the agroecological service provided by the considered CCs in promoting or inhibiting the overall AMF colonization of the studied agroecosystems, as affected by weed selection and growth: It informs about agroecosystem resilience and may be profitably applied to indicate the extent of the linkage of specific crop traits to agroecosystem services, contributing to further develop the functional biodiversity theory.

Agroecological Service Crops Drive Plant Mycorrhization in Organic Horticultural Systems

“…In 2014, Moora [ 30 ] proposed to consider the weighted means of plant community mycorrhizal traits by defining the mycorrhization index (MI). More recently, the mycorrhization index of the agroecosystem (MA) was developed, based on a ponderal weight of each plant species within the plant community and its in-field mycorrhizal colonization intensity [ 14 ]. The present research proposes an intermediate approach, where the plant mycorrhization measured in field is related to the mycorrhizal functional trait of weeds selected by the different ASC, aiming at verifying the ecological role played by ASC at improving the mycorrhization and yield and/or quality of the cash crop.…”

“…To verify the presence of AMF extra-hyphal ( hyp ) mycelium development on melon and orange tree roots, selected fresh root fragments were observed at increasing magnifications by Scanning Electron Microscopy (Microscope EVO MA10—Zeiss) under variable pressure, equipped with a LaB 6 electron sources by using the back-scattered electrons detector (SEM-BSE). The applied variable pressure mode (at 20–25 kV EHT/10 Pa chamber pressure) prevented surface damage of such biological and non-conductive samples, giving a high-resolution image without any sample pretreatment [ 14 ].…”

“…If this ability to interconnect different individuals is widely recognized in arboreal systems, it is much less so in herbaceous systems, where endomycorrhizas do not always develop external mycelium capable of spreading, connecting plants of different species. However, in diversified agricultural systems, the role played by the mycorrhizal network among coexisting plants, such as the yield crops and the spontaneous flora (i.e., the weeds), has been observed [ 14 ], although it is only understood partly so far.…”

“…In an artichoke organic production, a selected intercropped living mulch, compared to the same no mulched system, was able not only to contain weeds, but also to promote artichoke mycorrhization [ 10 , 23 ]. In a no-till, Mediterranean organic rotation, the introduction of rye and spelt ASCs as winter-cereal cover crops inhibited or boosted the spontaneous mycorrhization of coexistent plants, respectively [ 14 ]. In fact, due to their allelopathic properties, the rye exudates were able to inhibit the radicle development of the curly dock, thus hindering the mycorrhizal colonization at the beginning of the seedling, preventing the AMF intra-hyphal invagination in cortex cells of the weed rootlet [ 24 ].…”

Weed Functional Diversity as Affected by Agroecological Service Crops and No-Till in a Mediterranean Organic Vegetable System

“…Species occurrence relies on a suite of response ‘traits’ able to guarantee their survival in a given ecosystem [ 26 ] and it is mainly related to strategies to overcome weed control practices in agroecosystems. Each species is characterized by several functional traits that can be related to production (e.g., attraction of beneficials, hosting mychorriza) or to non-production agroecosystem services (e.g., bird or arthropod population [ 26 , 27 ]).Moreover, the potential additive effect of ASC mixture on weed suppression has been reported [ 23 ] but, to the best of our knowledge, no work has focused on the effect of different ASC species of the same botanical family.…”