Arbuscular Mycorrhizal Fungi Root Colonization Research Articles

Drought neutralizes positive effects of long‐term grazing on grassland productivity through altering plant–soil interactions

Abstract Livestock grazing is among the most intensive land‐use activities in grasslands, and can affect plant communities directly or indirectly via grazing‐induced soil legacies. Under climate change, grasslands are threatened globally by recurrent drought. However, the extent to which drought influences grazing‐induced soil legacy effects on plant biomass production and community composition remains largely unexplored. We grew five naturally co‐occurring plant species (three dominants and two subordinates) in mixed communities in a glasshouse experiment in live and sterilized soil that had or had not been subjected to 19 years of grazing; these plant communities were then exposed to a subsequent drought. We tested the treatment effects on plant community biomass, proportional above‐ground biomass of individual species, arbuscular mycorrhizal (AM) fungal root colonization, and soil nutrient availability. Under drought‐free conditions, soils from grazed plots produced significantly higher plant above‐ground and total community biomass compared to soils from ungrazed plots. In contrast, plant above‐ground and total community biomass were similar between grazed and ungrazed soils under drought conditions. Similarly, soils from grazed plots increased the proportional biomass of dominant species but decreased the proportion of subordinate species; however, the proportional biomass of dominant and subordinate species was similar between grazed and ungrazed soils under drought conditions. Soil NO3−‐N in grazed soil was significantly higher compared to ungrazed soil. Drought dramatically increased soil NO3−‐N in sterilized soil and had a more pronounced increase in grazed soil than in ungrazed soil. Arbuscular mycorrhizal fungal root colonization from grazed soil was lower compared to ungrazed soil. Drought significantly increased the soil available phosphorus concentration, as well as plant community AM fungal root colonization. Synthesis. Our study suggests that drought can neutralize positive grazing effects on plant community biomass production via altered plant–soil interactions. Also, we found that drought can alleviate the negative effects of grazing legacies on subordinate species by reducing competitiveness of dominant species. Our study provides new insights for understanding the underlying mechanisms of grazing effects on grassland productivity under climate change. Read the free Plain Language Summary for this article on the Journal blog.

Impact of Water Shortage on Soil and Plant Attributes in the Presence of Arbuscular Mycorrhizal Fungi from a Harsh Environment.

Arbuscular mycorrhizal fungi (AMF) play a crucial role in plant health due to their ability to improve tolerance to biotic and abiotic stresses. Our aim was to evaluate the effectiveness of a pool of native AMF from a harsh environment on plant performance and changes in soil attributes under different levels of drought. An experiment using maize was established, varying the soil water content to simulate severe drought (30% of the water-holding capacity [WHC]), moderate (50% of the WHC) and no drought (80% of the WHC, control treatment). Soil and plant attributes were measured (enzyme activity, microbial biomass, AMF root colonisation and plant biomass and nutrient uptake). There was a two-fold increase in plant biomass under moderate drought when compared to no drought treatment, but there was no difference in nutrient uptake. Under severe drought, there were the highest enzyme activities related to phosphorus (P) cycling and P microbial biomass, indicating higher P microbial immobilization. The increase in AMF root colonisation was observed in plants under moderate and no drought. Our findings demonstrated that the better use of the AMF inoculum varied according to drought levels, with better performance under moderate drought due to the increase in plant biomass.

Arbuscular mycorrhizas amplify the risk of heavy metal transfer to human food chain from fly ash ameliorated agricultural soils

Soil contaminants threaten global food security by posing threats to food safety through food chain pollution. Fly ash is a potential agent of soil contamination that contains heavy metals and hazardous pollutants. However, being rich in macro- and micronutrients that have direct beneficial effects on plant growth, fly ash has been recommended as a low-cost soil ameliorant in agriculture in countries of the Global South. Arbuscular mycorrhizal fungi (AMF), ubiquitous in agricultural soils, enhance efficiency of plant nutrient uptake from soils but can equally increase uptake of toxic pollutants from fly ash ameliorated soils to edible crop tissues. We investigated AMF-mediated amplification of nutrient and heavy metal uptake from fly ash amended soils to shoots, roots and grains of barley. We used a microcosm-based experiment to analyse the impacts of fly ash amendments to soil in concentrations of 0 (control), 15, 30 or 50% respectively, on root colonization by AMF Rhizophagus irregularis and AMF-mediated transfer of N, P and heavy metals: Ni, Co, Pb and Cr to barley tissues. These concentrations of fly ash are equivalent to 0, 137, 275 and 458 t ha−1 respectively, in soil. Root AMF colonization correlated negatively with fly ash concentration and was not detected at 50% fly ash amendment. Shoots, roots and grains of mycorrhizal barley grown with 15, 30 and 50% fly ash amendments had significantly higher concentrations of Ni, Co, Pb and Cr compared to the control and their respective non-mycorrhizal counterparts. Presence of heavy metals in barley plants grown with fly ash amended soil and their increased AMF-mediated translocation to edible grains may significantly enhance the volume of heavy metals entering the human food chain. We recommend careful assessment of manipulation of agricultural soils with fly ash as heavy metal accumulation in agricultural soils and human tissues may cause irreversible damage.

Changes of root AMF community structure and colonization levels under distribution pattern of geographical substitute for four Stipa species in arid steppe

The establishment of symbiotic relationship between arbuscular mycorrhizal fungi (AMF) and roots is a mutually beneficial process and plays an important role in plant succession in ecosystems. However, there is less understanding of information about the AMF community in roots under vegetation succession on a large regional scale, especially the spatial variation in the AMF community and its potential ecological functions. Here, we elucidated the spatial variations in root AMF community structure and root colonization along a distribution pattern of four zonal Stipa species in arid and semiarid grassland systems and explored key factors regulating AMF structure and mycorrhizal symbiotic interactions. Four Stipa species established a symbiosis with AMF, and annual mean temperature (MAT) and soil fertility were the main positive and negative driving factors of AM colonization, respectively. The Chao richness and Shannon diversity of AMF community in the root system of Stipa species tended to increase firstly from S. baicalensis to S. grandis and then decreased from S. grandis to S. breviflora. While evenness of root AMF and root colonization showed a trend of increasing from S. baicalensis to S. breviflora, and biodiversity was principally affected by soil total phosphorus (TP), organic phosphorus (Po) and MAT. It is emphasized that Stipa species have certain dependence on AMF, especially in a warming environment, and the root AMF community structure among the four Stipa taxa was different. Additionally, the composition and spatial distribution of root AMF in host plants varied with MAT, annual mean precipitation (MAP), TP and host plant species. These results will broaden our understanding of the relationship between plant and AMF communities and their ecological role, and provide basic information for the application of AMF in the conservation and rehabilitation of forage plants in degraded semiarid grasslands.

Individual and combined effects of arbuscular mycorrhizal fungi and phytohormones on the growth and physiobiochemical characteristics of tea cutting seedlings.

Both arbuscular mycorrhizal fungi (AMF) and phytohormones collectively regulate plant growth and root development, but their individual and combined effects on tea [Camellia sinensis (L.) O. Kuntze] cutting seedings remain unclear. This study examined the individual and combined effects of two species of AMF (Rhizophagus intraradices, RI and Funneliformis mosseae, FM) and two types of palnt hormones (strigolactones, SLs; polyamines, PAs) on tea cutting seedings, by evaluating the growth and physiobiochemical characteristics of plants treated with the AMFs and/or hormones. The results showed that inoculation with either AMF individually or hormones treatment alone could significantly enhanced mycorrhizal colonization, growth target and physiobiochemical characteristics of tea cutting seedlings. Interestingly, the addition of a combination of AMFs and hormones showed superior effects, while SL and RI exhibited the most improvements to the colonization rate, plant growth, root-morphological traits, root DHA activity, photosynthesis, chlorophyll content, soluble sugar content in leaves, and the activities of antioxidant enzymes (SOD, POD, and CAT), compared to other treatment combinations (SL + FM, PA + RI, and PA + FM). Correlation analyses revealed a significantly (p < 0.05) positive correlation of root AMF colonization with root-related traits (e.g., DHA, root total length, surface area, and volume) and leaf-related traits (e.g., leaf area, shoot biomass, total chlorophyll, and antioxidant enzyme activities). This study demonstrated that while the apllication of individual AMF or plant hormones had a certain good effects on most growth and physiobiochemical characteristics parameters of tea cutting seedings, the additive effect was from specific combined of AMF and plant hormones. These results highlight the possibility for combined of AMF and plant hormones to improve the asexual reproduction of tea plants via cuttings.

Rhizobium tropici and Riboflavin Amendment Condition Arbuscular Mycorrhiza Colonization in Phaseolus vulgaris L.

Phaseolus vulgaris L. (Fabaceae) forms symbioses with arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing rhizobia (NFB). The tripartite relationship uses molecular singals to establish intracellular symbioses in roots. The goal of this study was to determine if Rhizobium tropici CIAT 899 and exogenous riboflavin (vitamin B2) have an effect on AMF species selection and root colonization of P. vulgaris. Using SSU rRNA fragment amplification of DNA extracted from P. vulgaris roots, we found that the presence of R. tropici altered the relative distribution of AMF species. Dominikia bernensis (Ohel) was the most abundant AMF species in P. vulgaris roots but when R. tropici was co-inoculated, Glomus species dominated. Rhizobacteria such as R. tropici, secrete riboflavin and could affect AMF symbiosis. Addition of 50 μM riboflavin to P. vulgaris, increased plant growth (28%), dry nodule weight (18%), AMF colonization (248%) and mycorrhizal vesicle frequency (56%) in bean roots. 3.12 and 12.5 µM riboflavin favored the presence of Glomus macrocarpum in P. vulgaris roots. This work provides the basis to further study of rhizobial and mycorrhizal co-inoculation of Phaseolus vulgaris bean.

Can arbuscular mycorrhizal fungi and rhizobacteria facilitate 33P uptake in maize plants under water stress?

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) are able to provide key ecosystem services, protecting plants against biotic and abiotic stresses. Here, we hypothesized that a combination of AMF (Rhizophagus clarus) and PGPR (Bacillus sp.) could enhance 33P uptake in maize plants under soil water stress. A microcosm experiment using mesh exclusion and a radiolabeled phosphorus tracer (33P) was installed using three types of inoculation: i) only AMF, ii) only PGPR, and iii) a consortium of AMF and PGPR, alongside a control treatment without inoculation. For all treatments, a gradient of three water-holding capacities (WHC) was considered i) 30% (severe drought), ii) 50% (moderate drought), and iii) 80% (optimal condition, no water stress). In severe drought conditions, AMF root colonization of dual-inoculated plants was significantly lower compared to individual inoculation of the AMF, whilst 33P uptake by dual-inoculated plants or plants inoculated with bacteria was 2.4-fold greater than the uninoculated treatment. Under moderate drought conditions the use of AMF promoted the highest 33P uptake by plants, increasing it by 2.1-fold, when compared to the uninoculated treatment. Without drought stress, AMF showed the lowest 33P uptake and, overall, plant P acquisition was lower for all inoculation types when compared to the severe and moderate drought treatments. The total shoot P content was modulated by the water-holding capacity and inoculation type, with the lowest values observed under severe drought and the highest values under moderate drought. The highest soil electrical conductivity (EC) values were found under severe drought in AMF-inoculated plants and the lowest EC for no drought in single or dual-inoculated plants. Furthermore, water-holding capacity influenced the total soil bacterial and mycorrhizal abundance over time, with the highest abundances being found under severe and moderate drought. This study demonstrates that the positive influence of microbial inoculation on 33P uptake by plants varied with soil water gradient. Furthermore, under severe stress conditions, AMF invested more in the production of hyphae, vesicles and spore production, indicating a significant carbon drain from the host plant as evidenced by the lack of translation of increased 33P uptake into biomass. Therefore, under severe drought the use of bacteria or dual-inoculation seems to be more effective than individual AMF inoculation in terms of 33P uptake by plants, while under moderate drought, the use of AMF stood out.

Cover Crops Modulate the Response of Arbuscular Mycorrhizal Fungi to Water Supply: A Field Study in Corn.

Cover crops (CCs) were found to improve soil health by increasing plant diversity and ground cover. They may also improve water supply for cash crops by reducing evaporation and increasing soil water storage capacity. However, their influence on plant-associated microbial communities, including symbiotic arbuscular mycorrhizal fungi (AMF), is less well understood. In a corn field trial, we studied the response of AMF to a four-species winter CC, relative to a no-CC control, as well as to two contrasting water supply levels (i.e., drought and irrigated). We measured AMF colonization of corn roots and used Illumina MiSeq sequencing to study the composition and diversity of soil AMF communities at two depths (i.e., 0-10 and 10-20 cm). In this trial, AMF colonization was high (61-97%), and soil AMF communities were represented by 249 amplicon sequence variants (ASVs) belonging to 5 genera and 33 virtual taxa. Glomus, followed by Claroideoglomus and Diversispora (class Glomeromycetes), were the dominant genera. Our results showed interacting effects between CC treatments and water supply levels for most of the measured variables. The percentage of AMF colonization, arbuscules, and vesicles tended to be lower in irrigated than drought sites, with significant differences detected only under no-CC. Similarly, soil AMF phylogenetic composition was affected by water supply only in the no-CC treatment. Changes in the abundance of individual virtual taxa also showed strong interacting effects between CCs, irrigation, and sometimes soil depth, although CC effects were clearer than irrigation effects. An exception to these interactions was soil AMF evenness, which was higher in CC than no-CC, and higher under drought than irrigation. Soil AMF richness was not affected by the applied treatments. Our results suggest that CCs can affect the structure of soil AMF communities and modulate their response to water availability levels, although soil heterogeneity could influence the final outcome.

Effects of Arbuscular Mycorrhizal Fungi on the Growth and Root Cell Ultrastructure of Eucalyptus grandis under Cadmium Stress

Eucalyptus grandis (E. grandis) has been reported to form a symbiosis with arbuscular mycorrhizal fungi (AMF), which plays an important role in improving plant tolerance of heavy metal. However, the mechanism of how AMF intercept and transport cadmium (Cd) at the subcellular level in E. grandis still remains to be researched. In this study, a pot experiment was conducted to investigate the growth performance of E. grandis under Cd stress and Cd absorption resistance of AMF and explored the Cd localization in the root by using transmission electron microscopy and energy dispersive X-ray spectroscopy. The results showed that AMF colonization could enhance plant growth and photosynthetic efficiency of E. grandis and reduce the translocation factor of Cd under Cd stress. After being treated with 50, 150, 300, and 500 μM Cd, the translocation factor of Cd in E. grandis with AMF colonization decreased by 56.41%, 62.89%, 66.67%, and 42.79%, respectively. However, the mycorrhizal efficiency was significant only at low Cd concentrations (50, 150, and 300 μM). Under 500 μM Cd concentration condition, the colonization of AMF in roots decreased, and the alleviating effect of AMF was not significant. Ultrastructural observations showed that Cd is abundant in regular lumps and strips in the cross-section of E. grandis root cell. AMF protected plant cells by retaining Cd in the fungal structure. Our results suggested that AMF alleviated Cd toxicity by regulating plant physiology and altering the distribution of Cd in different cell sites.

Grassland ecosystem type drives AM fungal diversity and functional guild distribution in North American grasslands.

Nutrient exchange forms the basis of the ancient symbiotic relationship that occurs between most land plants and arbuscular mycorrhizal (AM) fungi. Plants provide carbon (C) to AM fungi and fungi provide the plant with nutrients such as nitrogen (N) and phosphorous (P). Nutrient addition can alter this symbiotic coupling in key ways, such as reducing AM fungal root colonization and changing the AM fungal community composition. However, environmental parameters that differentiate ecosystems and drive plant distribution patterns (e.g., pH, moisture), are also known to impact AM fungal communities. Identifying the relative contribution of environmental factors impacting AM fungal distribution patterns is important for predicting biogeochemical cycling patterns and plant-microbe relationships across ecosystems. To evaluate the relative impacts of local environmental conditions and long-term nutrient addition on AM fungal abundance and composition across grasslands, we studied experimental plots amended for 10 years with N, P, or N and P fertilizer in different grassland ecosystem types, including tallgrass prairie, montane, shortgrass prairie, and desert grasslands. Contrary to our hypothesis, we found ecosystem type, not nutrient treatment, was the main driver of AM fungal root colonization, diversity, and community composition, even when accounting for site-specific nutrient limitations. We identified several important environmental drivers of grassland ecosystem AM fungal distribution patterns, including aridity, mean annual temperature, root moisture, and soil pH. This work provides empirical evidence for niche partitioning strategies of AM fungal functional guilds and emphasizes the importance of long-term, large scale research projects to provide ecologically relevant context to nutrient addition studies.

Brassicaceae, Chenopodiaceae ve Urticaceae Familyalarına Ait Bazı Bitki Türlerinin Arbusküler Mikorhizal Fungus (AMF) ve Rhizobacteria Arasındaki İlişki

This study was conducted to investigate the effects of some plant growth-promoting rhizobacteria (PGPR) on the arbuscular mycorrhizal fungi (AMF) formation on [Brassica oleracea (cauliflower), Spinacia oleracea (spinach) ,and Urtica urens (stinging nettle)] belonging to Brassicaceae, Chenopodiaceae and Urticaceae families, which are known to have a negative influence on the symbiotic life formation with AMF. Two PGPR isolates that contributed to the plant's growth and served as a “mycorrhizal helper” in various hosts were predetermined at the initial stage; then they were applied to three plant species with AMF species [Gigaspora margarita and commercial AMF (ERS)]. The obtained results revealed that combined AMF x PGPR treatments improved the growth and morphological development parameters of cauliflower, spinach, and nettle plants. PGPR bacteria had different effects on AMF root colonization depending on the plant species. The highest root colonization rate was achieved in spinach plants with the commercial AMF treatments. Commercial AMF isolate, alone or in combination with PGPR strains, was also found to increase AMF spore density and mycorrhizal dependency in cauliflower and spinach plants. There was no significant difference in total phosphorus content in cauliflower and nettle compared to the control group, and only one application group (G. margarita x PGPR) in spinach plants had an increase in phosphorus content.

Assessment of Community Dynamics of Arbuscular Mycorrhizal Fungi in the Rice (Oryza sativa L.) Rhizosphere and Potential Application as Biofertilizer

Arbuscular mycorrhizal fungi (AMF) have the potential to maintain the sustainability of rice cultivation via maintaining soil health. The objective of this study was to produce an AMF-based biofertilizer for the rice variety Bg350 using indigenous dominant species of AMF that are adapted to paddy wetland soil conditions in dry, wet, and intermediate zones in Sri Lanka and are co-inoculated with the bacterium Azospirillum. A pot experiment was carried out to evaluate the effectiveness of the produced biofertilizer using the rice variety Bg350. Treatments were inorganic fertilizer, compost, biochar, produced AMF-biofertilizer [1 kg of ground carrier material inoculated with 50 g of AMF propagules and 20 mL of 1.5 × 108 (CFU/mL) of Azospirillum], and the control. A two-factor factorial, completely randomized design was used under sterilized and non-sterilized soil conditions with four replicates. The genera Glomus, Claroideoglomus, and Aculospora were identified as the most common AMFs in paddy soil in all investigated sites. In the 9th week of sampling, AMF root colonization was positively correlated (p = 0.028) with spore density. In Sri Lanka, for the first time, the highest AMF colonization rates in rice were recorded at 36.40% in the roots of the Bg350 from the Gampaha district. AMF root colonization increased over sampling time and was different according to the interactive effect of fertilizer application and soil condition. The biometric parameters and yield-attributing characteristics were significantly higher in the rice plants grown in sterilized soil, independent of the tested treatments. The number of grains per panicle was significantly similar (p ≤ 0.05) in the compost, AMF-biofertilizer, and inorganic fertilizer added treatments. It can be concluded that application of paddy soil adapted AMF species as a biofertilizer increased rice plant growth, productivity, and yield.

Exploration and Assessment on the Agronomic Requirement of Taverniera abyssinica A. Rich: A Critically Endangered Medicinal Plant of Ethiopia

We determined the distribution and abundance of Taverniera abyssinica A. Rich in the Shewa floristic region, Ethiopia. We also carried out a mesh-house experiment to know whether T. abyssinica is able to survive and grow in any soil. From the nine potential locations we made exploration, T. abyssinca populations were found only in the two, Lemen and Mojo. The abundance of mature individuals was estimated to be more than 600/hectare. The one-way ANOVA results indicated that soil does not have a significant (p&gt;0.05) effect on seedlings survival rate. However, it was found to have significant (p&lt;0.05) effects on seedlings growth, root nodulation, and root arbuscular mycorrhizal fungi colonization. Seedlings grown on the soil collected from Lemen and Mojo produced significantly (p&lt;0.05) more number of leaves and grew better than those grown on Addis Ababa (where the species was never reported to grow) soil. The root fresh weight of seedlings grown on Addis Ababa soil was found to be significantly (p&lt;0.05) and 38.89% and 54.17% lower than the root fresh weight of seedlings grown on Lemen and Mojo soils respectively. We report that T. abyssinica is N-fixer and arbuscular mycorrhizal. Seedlings grown on the Addis Ababa soil were not colonized by arbuscular mycorrhizal fungi while those grown on Lemen and Mojo soils were. Although the estimated abundance of mature T. abyssinica individuals was high, there is continued exploitation of the species and habitat loss is imminent. Therefore, integrated conservation program by way of ex situ conservation, in situ conservation, and cultivation should be implemented. Taverniera abyssinica could be cultivated in areas with leptosol and degraded vertisol soils with slightly acidic to basic pH. Arbuscular mycorrhizal fungi could play key role in future conservation and cultivation efforts of the species.

Biostimulatory effect of vermicompost extract enhances soil mycorrhizal activity and selectively improves crop productivity

PurposeCommercial production and the use of liquid vermicompost extract (LVE) is gaining attention as a technique that supports integrated soil-microbial-crop management for sustainable agriculture. However, the interaction effects of LVE, arbuscular mycorrhizal fungi (AMF), and host plants on the delivery of agroecosystem services in alkaline soil have been less studied.MethodsWe carried out a 3-year field experiment in Central Italy, to investigate the short-term effect of LVE on soil mycorrhizal inoculum potential (MIP), AMF root colonization, and productivity of berseem clover, lentil, and sunflower. LVE produced in different years were screened for microbial properties using Illumina Miseq sequencing. LVE was applied at seeding, crop stem elongation and flowering stages. Control crops received water as a placebo.ResultsLVE bacterial communities were more diverse and showed a higher turnover between 2019 and 2020 than fungal communities. Diverse microbial groups, the majority of which belonged to phyla Proteobacteria, Bacteroidetes, Firmicutes, and Mucoromycota, were detected, including N-fixers (Flavobacterium, Malikia, and Citrobacter), P-solubilizers (Pseudomonas), and C-degraders (Tolumonas, Arcobacter, and Mucor). Notably, LVE treatment enhanced soil MIP and AMF root colonization in most crops, but selectively improved shoot biomass of berseem clover (+ 32%) and sunflower (+ 34%), and grain yield (+ 37%) and oil concentration (+ 5%) in sunflower, compared to the corresponding non-treated controls.ConclusionsLVE had diverse groups of bacteria and a few fungal taxa, and its application enhanced mycorrhizal properties and selected growth- and yield-related variables in lentil, berseem clover, and sunflower. This could be due to LVE’s biostimulating effect arising from the vermicompost-associated microbiome and biomolecules.

Soil Application of Sewage Sludge Treated with Clay Minerals or Biochar and Its Effect on Soil Properties and White Clover’s (Trifolium repens L.) Growth and Arbuscular Mycorrhizal Fungal Root Colonization

From the perspective of finding new, more environmental-friendly methods for the stabilization of sewage sludge to be used in agriculture, sludge treated with 15% bentonite, vermiculite or biochar was investigated as a soil amendment for white clover (Trifolium repens L.) growth, by means of a pot experiment. The sludge treatments, which were applied to two soils (an acid and an alkaline soil), in three replications, were the addition of 2% (≈80 Mg ha−1) treated sludge with the clay minerals or biochar, as well as limed or untreated (air-dried) sludge (for comparison reasons). Additional treatments with inorganic fertilization or neither organic nor inorganic fertilization (control) were also included. The application of 2% sludge to both soils significantly increased salinity compared to the control, which remained below harmful levels for sensitive crops, except for the case of untreated sludge. Furthermore, it significantly increased the soil-available macronutrients N, P and K, and micronutrients Cu, Zn (several times, especially in the case of untreated sludge) and B (up to three times) compared with the control. Moreover, the pH of the acid soil was improved, except for the case of limed sludge, where an undesirable pH increase close to 8.5 was observed. Addition of the treated sludge with the clay minerals or biochar and untreated sludge to the acid and alkaline soil significantly increased the aboveground biomass yield of white clover by 117–233% and 114–153%, respectively, compared to the control, whereas limed sludge had no effect. Plant nutrient uptake increased as well. In general, the effect of sludge on soil microbiological properties and arbuscular mycorrhizal fungal root colonization was ambiguous. It was concluded that 2% soil addition of sewage sludge treated with 15% bentonite, vermiculite or biochar could improve soil fertility and enhance plant growth; however, caution is needed with respect to potential risks of soil salinization or Zn and B phytotoxicities.

Diversity and Benefits of Arbuscular Mycorrhizae in Restored Riparian Plantations

Due to the increasing use of vegetation for fuel wood, cattle, agriculture, and due to population pressure that negatively affects biodiversity values, more plantations are needed to obtain a permanent vegetal cover. Attention has been paid to microbial interactions (arbuscular mycorrhizae (AM)) for management and inoculation. To evaluate the benefits of inoculation, the root colonization of inoculated seedlings, soil aggregation, and arbuscular mycorrhizal fungi (AMF) diversity were examined by two field treatments (fertilized with organic matter (OM) vs. fertilized with natural rock phosphate (P)). The preserved and experimental areas presented higher AMF spore number and richness (nine species) than the degraded areas. The addition of OM or P did not improve root colonization by AMF; however, it was a guarantee for a successful restoration as, in the restored fields, a high soil aggregation was found, in addition to a high root colonization, spore number, and richness of AMF. However, the undisturbed site presented the more prominent values. This study showed that AMF are important components in riparian areas, and it brings information for inoculant production in ecological restoration using mixed plantations, contributing to the establishment of mycorrhizal vegetation and soil aggregation that not only benefit AM plants, but also allow non-host plants in degraded areas.

Occurrence and diversity of arbuscular mycorrhizal fungi colonising off-season and in-season weeds and their relationship with maize yield under conservation agriculture

Weeds are responsible for major crop losses worldwide but can provide beneficial agroecosystem services. This study aimed to elucidate how arbuscular mycorrhizal fungi (AMF) in weeds respond to host identity and conservation agricultural practices. The study was carried out at two locations in Southern Africa during off-season and in-season maize cultivation. Off-season AMF root colonisation, diversity indices and community composition significantly differed among weed species at both locations. Glomus sp. VTX00280 explains most of the AMF community differences. In-season, implementation of conventional tillage with mulching alone (CT + M) or together with crop rotation (CT + M + R) resulted in a 20% increase in AMF colonisation of the constantly occurring weed species, Bidens pilosa (BIDPI) and Richardia scabra (RCHSC), compared with conventional tillage plus rotations (CT + R). The diversity of AMF was highest under no-tillage plus mulching (NT + M). Off-season and in-season AMF structures of both BIDPI and RCHSC were not related, but 39% of the taxa were shared. Structural equation modelling showed a significant effect of the cropping system on weed AMF diversity parameters and weed and maize root colonisation, but no significant influence of weed root AMF traits and maize colonisation was detected on maize yield. This may be explained by the improvement in weed competitive ability, which may have offset the AMF-mediated benefits on yield. Our findings highlight that implementing M and CR to CT and NT positively affected weed AMF colonisation and diversity. The similarity between the off-season and in-season AMF composition of weeds supports the fact that weeds functionally host AMF during the non-crop period.

Anthocyanin pigmentation as a quantitative visual marker for arbuscular mycorrhizal fungal colonization of Medicago truncatula roots.

Visualization of root colonization by arbuscular mycorrhizal fungi (AMF) is the most elementary experiment in the field of mycorrhizal symbiosis. The most widely used approach for evaluating levels of AMF colonization is staining with trypan blue or ink, which is scored using the time-consuming grid intersection method. Here we demonstrate the use of an anthocyanin-based visual marker system for visualizing AMF colonization of Medicago truncatula roots. Expression of MtLAP1, a transcription factor which regulates the production of anthocyanins, from the AMF-induced Kunitz Protease Inhibitor 106 promoter, allowed the visualization of arbuscules in live plant tissues without microscopy or staining. This marker system allowed straightforward qualitative evaluation of the ram1, vpy and dmi3 AMF phenotypes using Agrobacterium rhizogenes hairy-root transformation. For the strigolactone biosynthesis mutant carotenoid cleavage dioxygenase 8a and a novel mutant scooby, which show quantitative AMF symbiotic phenotypes, the amount of anthocyanins in the roots estimated by spectrophotometry correlated very well with colonization levels estimated by staining and scoring using the grid intersection method. The LAP1-based marker system therefore provides a highly efficient approach for mutant screening and monitoring of AMF colonization in live tissues by eye, or for quantitative assessment using a simple and quick photometric assay.

EFFECTS OF FUNNELIFORMIS MOSSEAE INOCULATION ON CHILI PEPPER GROWTH UNDER REPEATED DROUGHT STRESS

Chili pepper (Capsicum frutescens L.) is a common commodity used as spice and pharmaceutical uses around the world. However, chili pepper cultivation failure often occurs due to drought exposure. The inoculation of arbuscular mycorrhizal fungi (AMF), such as Funneliformis mosseae, has the potential to induce defense against drought stress through symbiotic association with plant roots. The aim of this research was to investigate the effects of F. mosseae inoculation on the growth of chili pepper under repeated drought stress. Chili pepper plants were exposed to three drought regimes for two cycles, with one rewatering event between the cycles. The plant agronomic variables, physiological performance, and microorganism parameters were observed. The results showed that the plant height, fresh and dry shoot weight, along with fresh and dry root weight increased significantly with F. mosseae inoculation under repeated drought stress. The F. mosseae treatment also increased water relative content and decreased proline and lipid peroxidation significantly. Although drought exposure decreased the AMF root colonization rate, the total microbial activity and glomalin-related soil protein were still increased by the F. mosseae inoculation. However, F. mosseae inoculation was negatively correlated to the abundance of phosphate solubilizing microorganisms. The results suggested that F. mosseae gave positive effects on C. frutescens L. growth under repeated drought stress through induced morphological and physiological responses.

Contribution of arbuscular mycorrhizal fungi to nitrogen and phosphorus uptake efficiency and productivity of faba bean crop on contrasting cropping systems

The present study was focused on evaluating the effect of AMF (Arbuscular Mycorrhizal Fungi) inoculation on nitrogen and phosphorus uptake efficiency and productivity of faba bean (Vicia faba L.) crop, under different fertilization levels on organic or conventional cropping systems. The 2-year field experiment was conducted in central Greece and laid out in a split-plot design, with three replications, two main plots (AMF inoculation treatments) and five sub-plots (fertilization treatments). The results demonstrated that plants of AMF inoculated plots exhibited greater plant height, leaf area index (LAI), leading to higher biomass, and consequently higher final seed yields. Regarding the quality parameters, including nutrients (nitrogen and phosphorus) uptake and their utilization indices, similar results to those of the productivity results were found with the AMF inoculated plants presented the higher values. Finally, all the parameters of the root system, including AMF root colonization and weighted mycorrhizal dependency (WMD), were negatively affected by fertilization level, particularly in an inorganic form. As a conclusion, the current study confirmed that replacement of inorganic inputs by organic in combination with AMF inoculation, should be seriously considered as a sustainable practice of faba bean crop cultivation under Mediterranean conditions.