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Highlights: [•] We detected two pathways through which glyphosate can affect grassland mycorrhiza. [•] Application on the soil, even at low doses, reduced directly spore viability. [•] Arbuscules were more affected indirectly, when glyphosate was applied to plant tissue. [•] Mycorrhizal root colonization was similarly reduced by both pathways. [•] Glyphosate application affects AMF functionality regardless of the pathway involved. [ABSTRACT FROM AUTHOR]

Summary: Soil biota such as earthworms, arbuscular mycorrhizal fungi (AMF) and plant roots are known to play a major role in engineering the belowground part of the terrestrial ecosystems, thus strongly influencing the water budget and quality on earth. However, the effect of soil organisms and their interactions on the numerous soil physical properties to be considered are still poorly understood. Shrinkage analysis allows quantifying a large spectrum of soil properties in a single experiment, with small standard errors. The objectives of the present study were, therefore, to assess the ability of the method to quantify changes in soil properties as induced by single or combined effects of leek roots (Allium porrum), AMF (Glomus intraradices) and earthworms (Allolobophora chlorotica). The study was performed on homogenised soil microcosms and the experiments lasted 35weeks. The volume of the root network and the external fungal hyphae was measured at the end, and undisturbed soil cores were collected. Shrinkage analysis allowed calculating the changes in soil hydro-structural stability, soil plasma and structural pore volumes, soil bulk density and plant available water, and structural pore size distributions. Data analysis revealed different impacts of the experimented soil biota on the soil physical properties. At any water content, the presence of A. chlorotica resulted in a decrease of the specific bulk volume and the hydro-structural stability around 25%, and in a significant increase in the bulk soil density. These changes went with a decrease of the structural pore volumes at any pore size, a disappearing of the thinnest structural pores, a decrease in plant available water, and a hardening of the plasma. On the contrary, leek roots decreased the bulk soil density up to 1.23gcm−3 despite an initial bulk density of 1.15gcm−3. This increase in volume was accompanied with a enhanced hydro-structural stability, a larger structural pore volume at any pore size, smaller structural pore radii and an increase in plant available water. Interestingly, a synergistic effect of leek roots and AMF in the absence of the earthworms was highlighted, and this synergistic effect was not observed in presence of earthworms. The structural pore volume generated by root and AMF growth was several orders of magnitude larger than the volume of the organisms. Root exudates as well as other AMF secretion have served as carbon source for bacteria that in turn would enhance soil aggregation and porosity, thus supporting the idea of a self-organization of the soil–plant–microbe complex previously described. [Copyright &y& Elsevier]

Abstract: The effects of an arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) on atrazine dissipation, soil phosphatase and dehydrogenase activities and soil microbial community structure were investigated. A compartmented side-arm (‘cross-pot’) system was used for plant cultivation. Maize was cultivated in the main root compartment and atrazine-contaminated soil was added to the side-arms and between them 650 or 37μm nylon mesh was inserted which allowed mycorrhizal roots or extraradical mycelium to access atrazine in soil in the side-arms. Mycorrhizal roots and extraradical mycelium increased the degradation of atrazine in soil and modified the soil enzyme activities and total soil phospholipid fatty acids (PLFAs). Atrazine declined more and there was greater stimulation of phosphatase and dehydrogenase activities and total PLFAs in soil in the extraradical mycelium compartment than in the mycorrhizal root compartment when the atrazine addition rate to soil was 5.0mg kg−1. Mycelium had a more important influence than mycorrhizal roots on atrazine degradation. However, when the atrazine addition rate was 50.0mg kg−1, atrazine declined more in the mycorrhizal root compartment than in the extraradical mycelium compartment, perhaps due to inhibition of bacterial activity and higher toxicity to AM mycelium by atrazine at higher concentration. Soil PLFA profiles indicated that the AM fungus exerted a pronounced effect on soil microbial community structure. [Copyright &y& Elsevier]

The formation of a common mycorrhizal network among roots of different plant species growing close to each other can influence plant community dynamics, regulating plant relationships through the differential transfer of nutrients from one plant to another. However, knowledge of the mechanisms that regulate this process is poor. Here we quantify the contribution of arbuscular mycorrhizae to the transfer of N among heterospecific plants growing adjacent to each other and examine whether the differential transfer of N within the plant community via mycorrhizae can alter competitive relationships among plant species. Plants of four species (wheat, pea, flax, and chicory) were grown in four-compartment pots (one species per compartment) under three conditions: no belowground interaction permitted among the compartments (Clo-sys); belowground interaction limited to soil microorganisms (including arbuscular mycorrhizal [AM] fungi) and soil solution (Res-sys); and belowground interaction permitted, so the crossing of roots, soil microorganisms, and soil solution was allowed (Ope-sys). Each condition was tested in both the absence (−myc) and presence (+myc) of AM symbiosis. The transfer of N from pea to the three non-legume companion species (assessed via direct 15N labelling) was greater in Ope-sys than Res-sys for wheat and chicory but not for flax. In general, N transfer was greater in +myc than –myc in all species. In wheat the positive effects of AM symbiosis on N transfer were pronounced in Ope-sys but not in Res-sys, whereas in flax and chicory mycorrhization had similar effects in both Ope-sys and Res-sys. In Res-sys and in the absence of AM symbiosis, wheat intercepted about 50% of the total N transferred from pea, chicory about 40%, and flax about 10%. Mycorrhization altered these ratios, reducing the proportion of N transferred to wheat while increasing the proportion transferred to the other two species (especially to chicory), thus favouring the weakest components of the mixture. Similar effects of AM symbiosis were observed in Ope-sys. Our study shows that AM symbiosis affects the distribution of N and as a consequence the competitive relationships among adjacent plants of different species. • Arbuscular mycorrhizae increased N-transfer from the legume to the neighbouring plants • AM symbiosis differentially affected the distribution of N to the neighbouring plants • N-transfer was mostly due to the uptake of N released from the legume into the substrate • AM symbiosis differentially affected the growth of the associated plant species • CMNs altered the competitive relationships among associated plant species [ABSTRACT FROM AUTHOR]