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The development of the mining industry and the overuse of inorganic fertilizers have led to an excess of manganese (Mn) in the soil, thereby, contaminating the soil environment and people's health. On heavy metal-contaminated soils, the combined arbuscular mycorrhizal fungi (AMF)-phytoremediation technique becomes a hotspot because of its environmentally friendly, in situ remediation. AMF inoculation often leads to a decrease in host Mn acquisition, which provides a basis for its application in phytoremediation of contaminated soils. Moreover, the utilization value of native AMF is greater than that of exotic AMF, because native AMF can adapt better to Mn-contaminated soils. In addition to the fact that AMF enhance plant Mn tolerance responses such as regionalization, organic matter chelation, limiting uptake and efflux, and so on, AMF also develop plant-independent fungal pathways such as direct biosorption of Mn by mycorrhizal hyphae, fungal Mn transporter genes, and sequestration of Mn by mycorrhizal hyphae, glomalin, and arbuscule-containing root cortical cells, which together mitigate excessive Mn toxicity to plants. Clarifying AMF-plant interactions under Mn stress will provide support for utilizing AMF as a phytoremediation in Mn-contaminated soils. The review reveals in detail how AMF develop its own mechanisms for responding to excess Mn and how AMF enhance plant Mn tolerance, accompanied by perspectives for future research. [Display omitted] • AMF inoculation diversely affects host Mn levels, dominated by reduced Mn uptake. • Mn-contaminated soils reduce AMF diversity, along with Glomus as the dominant genus and native AMF more tolerant. • AMF enhances plant Mn tolerance such as regionalization and chelation. • AMF hyphae have direct biosorption and sequestration of Mn. • Fungal Mn transporters, glomalin, and arbuscule-contained cortical cells mitigate Mn. [ABSTRACT FROM AUTHOR]

Soil water stress (WS) affects the decomposition of soil organic carbon (SOC) and carbon (C) emissions. Glomalin, released by arbuscular mycorrhizal fungi into soil that has been defined as glomalin-related soil protein (GRSP), is an important pool of SOC, with hydrophobic characteristics. We hypothesized that mycorrhizal fungi have a positive effect on SOC pools under soil WS for C sequestration in GRSP secreted by extraradical mycorrhizal hyphae. A microsystem was used to establish a root chamber (co-existence of roots and extraradical mycorrhizal hyphae) and a hyphal chamber (the presence of extraradical mycorrhizal hyphae) to study changes in plant growth, leaf water potential, soil aggregate stability, SOC, GRSP, C concentrations in GRSP (CGRSP), and the contribution of CGRSP to SOC after inoculating Rhizophagus intraradices with trifoliate orange (Poncirus trifoliata) in the root chamber under adequate water (AW) and WS. Inoculation with R. intraradices alleviated negative effects on leaf water potential and plant growth after 7 weeks of WS. Soil WS decreased SOC and mean weight diameter (MWD), while AMF inoculation led to an increase in SOC and MWD in both chambers, with the most prominent increase in the hyphal chamber under WS. The C concentration in easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) was 7.32 − 12.57 and 24.90 − 32.60 mg C/g GRSP, respectively. WS reduced CGRSP, while AMF mitigated the reduction. Extraradical mycorrhizal hyphae increased GRSP production and CGRSP, along with a more prominent increase in DE-GRSP under WS than under AW. Extraradical mycorrhizal hyphae increased the contribution of CDE-GRSP to SOC only under WS. CEE-GRSP and CDE-GRSP were significantly positively correlated with SOC and MWD. It is concluded that extraradical mycorrhizal hyphae prominently promoted C sequestration of recalcitrant DE-GRSP under soil WS, thus contributing more organic C accumulation and preservation in aggregates and soil C pool. [ABSTRACT FROM AUTHOR]

Either arbuscular mycorrhizal (AM) fungi or earthworms as soil organisms promote plant growth, while their interaction on nitrogen (N) content in plants, soil, and glomalin-related soil protein (GRSP) is not known. In this study, an AM fungus (Funneliformis mosseae) and an earthworm (Pheretima guillelmi), either in single or in combination, were introduced into soil growing white clover to analyze their effects on plant growth, chlorophyll, soluble protein, N contents in leaves, roots, GRSP, and soil, and the contribution of N in purified GRSP to soil total N. The four-week introduction of earthworms significantly increased root mycorrhizal colonization rate, and accelerated an improved AM effect on chlorophyll and plant growth. The single introduction of earthworms significantly increased root N and soil total N contents, while the single introduction of AM fungi distinctly elevated N contents in leaves, roots, easily extractable GRSP, and soil (nitrate N and total N). The N in total GRSP was 5.78–7.70 mg g−1, accounting for 3.46 %–5.45 % of the soil total N, of which the contribution of N from easily extractable GRSP and difficult-to-extract GRSP was 1.84 %–3.07 % and 1.34 %–2.39 %, respectively. AM fungi, but not earthworms, significantly increased the contribution of N in GRSP to soil total N, and the introduction of earthworms further accelerated the increased effect of mycorrhizas on the contribution of N in easily extractable and total GRSP to soil total N. These results demonstrated that the introduction of earthworms into mycorrhizosphere can facilitate N storage in GRSP and thus a contribution to soil total N. • Effects of earthworms and AMF on N content of soil and plants were studied. • Dual earthworms and AMF addition recorded higher plant growth and chlorophyll than single addition. • Earthworms increased root N and soil total N, while AMF elevated N in plants, EE-GRSP, and soil NO 3 −−N and total N. • Dual addition recorded higher N contents in GRSPs than single addition. • Earthworm accelerated the AMF effect on the contribution of N in EE-GRSP and T-GRSP to soil total N. [ABSTRACT FROM AUTHOR]

Earthworms and arbuscular mycorrhizal fungi (AMF) are beneficial organisms in the soil and play an important role in improving soil fertility and plant growth. The objective of this study was to analyze the response of single versus dual inoculation of earthworms (Pheretima guillelmi) and AMF (Funneliformis mosseae) on mycorrhizal growth, root morphology, and rhizosphere properties of white clover (Trifolium repens). Addition of earthworms significantly increased the degree of root AMF colonization, while decreased hyphal length and spore number in the soil. Single or dual inoculation of F. mosseae and P. guillelmi significantly increased root traits (total length, area, volume, and average diameter), soil phosphatase activities (acid, neutral, and alkaline), easily extractable and total glomalin-related soil protein content, the percentage of soil water-stable aggregates at the size of 2–4 mm, 1–2 mm and 0.5–1 mm, aggregate stability, Bray-P, and soil organic carbon (SOC) contents. Among them, the dual inoculation further amplified the effect on glomalin production, phosphatase activity, and aggregate stability, but did not show a superposition effect on root improvement, Bray-P, and SOC. Our study, hence, suggested that AMF and earthworms have synergistic roles in elevating rhizosphere properties vis-à-vis agronomic responses of white clover. • Effects of earthworm-AMF (singly and in combination) on rhizosphere environment and crop response were studied. • Earthworms increased root AMF colonization, but reduced hyphae and spores in soils. • AMF or earthworms singly improved root traits, Bray-P, and soil organic carbon contents, but dual application of AMF and earthworms did not show a major effect than single application. • Single AMF or earthworms increased aggregation, phosphatase, GRSP, and dual addition amplified these responses. [ABSTRACT FROM AUTHOR]