Arbuscular Mycorrhizal Fungi Activity Research Articles

Agricultural Managements Influence the Diversity of Arbuscular Mycorrhizal Fungi in Vineyards from Chilean Mediterranean Climate Ecosystems

Abstract Purpose Grapevine (Vitis vinifera L.) is a relevant crop, which is associated to arbuscular mycorrhizal fungi (AMF) that are influenced by agricultural practices. The hypothesis of this study is that organic/biodynamic management stimulates grapevine mycorrhizal colonisation and increases AMF diversity in Chilean vineyards. The aim of this study was to determine the influence of agricultural management on AMF association and AMF diversity in Chilean vineyards. Methods Mycorrhizal colonisation of grapevine roots from organic/biodynamic and conventional vineyards in Northern (Elqui Valley), Central (Casablanca and Cachapoal Valleys), and Southern Chile (Maule and Itata Valleys), was determined under a microscope. AMF diversity was analysed by morphological, and molecular characterisation of spores through SSU-ITS-LSU rRNA region sequence analyses. Results AMF colonisation of grapevine roots was influenced by vineyard management independent of the season. Higher mycorrhizal colonisation was detected in organic/biodynamic grapevine soils (20 − 35%), compared with conventional soils (6 − 31%). Twelve AMF species were identified in vineyards, belonging to five Glomeromycota families. Interestingly, organic/biodynamic vineyards showed higher AMF diversity. The three predominant morphotypes were Funneliformis verruculosum (GL1), Septoglomus sp. (GL4) and Septoglomus constrictum (GL5). Molecular analyses of AMF spores highlighted the occurrence of Septoglomus, Acaulospora, Pacispora and Cetraspora genera in vineyards. Conclusions In this study, AMF diversity in Chilean vineyards is described for the first time. The diversity of AMF in vineyards in Chile was higher than the diversity reported in other wine-producing ecosystems. The understanding of agricultural practices on AMF activity and diversity may be crucial to improve the vineyard management.

Seasonality and Activity of Arbuscular Mycorrhizal Fungi in the Rhizosphere of Endemic Tree Species.

This study analyzed arbuscular mycorrhizal fungi(AMF) activity and soil chemical properties in Aspidosperma pyrifolium, Bauhinia ungulata, Caesalpinia pyramidalis, and Caesalpinia ferrea. AMF spores, root colonization, total glomalin-related soil protein (T-GRSP), easily extracted GRSP(EE-GRSP), and soil chemical properties were measured four times (July 2019, 2020 and December 2019, 2020). Significant differences were observed in AMF spores, root colonization, T-GRSP, and EE-GRSP among the plant species and across seasons. For soil chemical properties, we observed differences among plant species. During the dry season, B. ungulata and C. pyramidalis had the highest AMF spores and root colonization (57.3 ± 0.27 spores 50 g soil-1and 48.8 ± 1.05, respectively), whereas during the rainy season, C. pyramidalis and C. ferrea showed the highest AMF spores and root colonization (36.6 ± 0.13 spores 50 g soil-1and 62.2 ± 1.17, respectively). A. pyrifolium showed the highest T-GRSP in both seasons. On the basis of the soil chemical properties, we found that (i) A. pyrifolium, B. ungulata, and C. ferrea showed the highest soil organic carbon (1.32 ± 0.03 g kg-1), phosphorus(7.01 ± 0.26 mg kg-1), and soil pH (5.85 ± 0.23)and (ii) C. pyramidalis showed the highest Ca2+, Mg2+, Na+, H+ + Al3+, K+, and soil total nitrogen (1.36 ± 0.04, 0.73 ± 0.01, 3.72 ± 0.85, 4.56 ± 0.12 cmolc kg-1, 15.43 ± 1.53 mg kg-1, and 0.16 ± 0.01 g kg-1, respectively). Our results highlight the advantage of AMF spores as perennating structures over other AM fungal propagules in seasonal vegetation like Caatinga.

Anaerobically mineralized nitrogen as a potential indicator of the activity and abundance of mycorrhizal fungi in Mollisols

Anaerobically mineralized nitrogen (AN) is a suitable soil health indicator. The AN is sensitive to soil use changes and is related to soil and particulate organic carbon and aggregate stability. This work aims to evaluate the relationship between AN and 1) easily extractable glomalin-related soil proteins; 2) abundance of arbuscular mycorrhizal fungi measured by the number of arbuscular mycorrhizal fungi spores, and 3) arbuscular mycorrhizal fungi activity (root colonization). Soil samples were taken at depths of 0-5 and 5-20 cm from cultivated and uncultivated plots throughout the southeastern province of Buenos Aires. Anaerobically mineralized nitrogen, soil organic carbon, particulate organic carbon, aggregate stability, easily extracted glomalin-related soil proteins and the logarithm of the number of arbuscular mycorrhizal fungi spores (log spores) at 0-5, 5-20 and 0-20 cm depths were determined. In wheat roots, the percentages of total infection and arbuscules at 0-20 cm were measured. At all depths, AN was positively correlated to easily extractable glomalin-related soil proteins (r=0.34-0.65), which is an indicator of arbuscular mycorrhizal fungi activity and abundance. Likewise, AN was positively related to log-spores (r=0.58-0.78), which is an indicator of arbuscular mycorrhizal fungi abundance. However, AN was not related to root colonization (the percentages of total infection and arbuscules) that manifests the activity of arbuscular mycorrhizal fungi at a specific moment. Thus, anaerobically mineralized nitrogen would be an indicator of mid- to long-term changes in arbuscular mycorrhizal fungi abundance and activity (easily extractable glomalin-related soil proteins and log-spores) resulting from soil use. Consequently, the AN would allow monitoring an important aspect of soil microbiological health associated with arbuscular mycorrhizal fungi. However, it is necessary to evaluate the relationships studied in this work in a wider range of soil situations.

Long-Term Monitoring Studies of the Mycorrhizal Colonization of Aesculus hippocastanum L. Roots and the Vitality of Soil Microorganisms in Urban and Non-Urban Environments

Stress factors typical in urban environments adversely affect the productivity and vigor of trees and may limit the development of tree roots with associated soil fungi and bacteria. Studies on mycorrhizal symbiosis and the activity of soil microorganisms are important in monitoring the adaptation of trees to urban conditions. We compared the symbiotic activity of arbuscular mycorrhizal fungi (AMF) living in the rhizosphere of mature white chestnut trees (Aesculus hippocastanum L.) in an urban ecosystem at sites with varying degrees of anthropopressure and in a rural area. We used two methods: (1) direct analysis of the root samples, (2) assessment of the colonization of trap plants grown in the soil taken from under selected white horse chestnut trees. The seasonality of mycorrhizal colonization and soil microbial respiration based on the enzyme activity of nonspecific dehydrogenase (DHA) was studied over several growing seasons. The concentrations of macronutrients in the soil from all study sites were in the ranges accepted as normal for the upper soil layer. However, the C/N ratio indicated carbon limitation in the soil at urban and rural study sites. The results showed that arbuscular mycorrhizal fungi indigenous in the rhizosphere of A. hippocastanum developed a functioning mycorrhizal symbiosis at all research sites, including at highly disturbed urban locations, and that the mycorrhizal colonization varied between the study sites and the research term. The trap culture method confirmed the high biological potential of the soil microbial community, including AMF in urban ecosystems, which was comparable to that at the reference site in the rural environment. Soil moisture strongly affected the overall soil microbial vitality. This research showed that the mycorrhizal status of A. hippocastanum is more strongly influenced by climatic conditions and seasonal rhythms of trees than by urban/non-urban locations.

Arbuscular Mycorrhizal Fungi Associated with Maize (Zea mays L.) in the Formation and Stability of Aggregates in Two Types of Soil.

Knowledge of native Arbuscular Mycorrhizal Fungi (AMF) and their relationship with the edaphic characteristics where they live is important to establish the influence of allochthonous AMF, which were inoculated, on the development and stability of soil aggregates. The objectives of this research were to know the composition of native AMF species from two contrasting soils, and to establish the development and stability of aggregates in those soils with corn plants after inoculating them with allochthonous AMF. The experiment had three factors: Soil (two levels [S1 and S2]), HMA (three levels: without application [A0], with the application of Claroideoglomus claroideum [A1] and with the application of a consortium [A2]) and Fertilization (two levels (without fertilization [f0] and with fertilization [f1])). Twelve treatments were generated, with five replicates (60 experimental units [EU]). The EU consisted of a pot with a corn plant and the distribution was completely random. The results demonstrated that the Typic Ustifluvent presented nine species of native AMF, while the Typic Dystrustert had three; the native AMF in each soil influenced the activity of allochthonous AMF, such as their colonization and sporulation. Likewise, differences were found in the stability of macro-sized aggregates (0.5 to 2.0 mm).

Enhancing Vicia faba’s immunity against Rhizoctonia solani root rot diseases by arbuscular mycorrhizal fungi and nano chitosan

BackgroundThe spreading of root rot disease of faba bean plant (Vichia faba L, VF) in Egypt is still of great challenge faced researchers since VF is an important legume in Egypt, because their seeds are used for human feeding. Fungicides are used for treatment of either seeds or soil; unfortunately they cause environmental pollution. Therefore, there is a need to continue research to find out safe natural solutions. In this regard, Arbuscular mycorrhizal fungi (AMF) and chitosan (micro or nanoform) were used as an inhibitory product against Rhizoctonia solani OM918223 (R.solani) either singly or in combinations.ResultsThe results employed herein have exhibited that R.solani caused root rot disease of VF plants in more than 80% of the plants under investigation. Chitosan nanoparticles (Chitosan NPs) were prepared by ionic gelatin method and characterized by using dynamic light scattering (DLS), transmission electron microscopy (TEM) imaging and Fourier transform infra-red (FTIR). Chitosan NPs are spherical with a diameter of 78.5 nm and exhibited the presence of different functional groups. The inhibitory natural products against R.solani were arranged according to their ability to inhibit the pathogen used in the following descending manner; combination of AMF with Chitosan NPs, AMF with micro chitosan and single AMF, respectively. Where, Chitosan NPs showed a potent influence on R.solani pathogen and reduced the pre-and post-emergence of R. solani. In addition, Chitosan NPs reduced Disease Incidence (DI %) and Disease Severity (DS %) of root rot disease and are widely functional through mixing with AMF by about 88% and 89%. Further, Chitosan NPs and micro chitosan were proved to increase the growth parameters of VF plants such as nutritional status (mineral, soluble sugar, and pigment content), and defense mechanisms including total phenol, peroxidase, and polyphenol oxidase in mycorrhizal plants more than non-mycorrhizal one either in infected or healthy plants. Moreover, activity of AMF as an inhibitory against R.solani and improvement natural agent for VF growth parameters was enhanced through its fusing with Chitosan NPs.ConclusionsThe use of AMF and Chitosan NPs increased faba bean plant resistance against the infection of root rot R. solani, with both prevention and cure together. Therefore, this research opens the door to choose natural and environmental friendly treatments with different mechanisms of plant resistance to disease.

Durum wheat-lentil relay intercropping enhances soil mycorrhizal activity but does not alter structure of arbuscular mycorrhizal fungal community within roots

In intercropping systems, crop species select host-adapted microorganisms and influence the associated plant-microbial interactions like in the case of arbuscular mycorrhizal fungi (AMF). Attempts to assess the impact of intercropping on the activity, diversity, and community composition of AMF remain inconclusive, more so in intercropping systems involving traditional Mediterranean crops such as durum wheat and lentils. We carried out field experiments in Central Italy to assess the impact of relay intercropping durum wheat (Triticum durum Desf. cv. Minosse) and lentil (Lens culinaris Medik. cv. Elsa) on soil mycorrhizal inoculum potential (MIP) (2019 and 2020), AMF root colonization (2019, 2020, and 2021), and root AMF diversity and community composition (2020 and 2021), compared to the respective sole crops. Results showed that relay intercropping enhanced lentil grain yield and durum wheat grain protein concentration but marginally reduced durum wheat grain yield and lentil grain protein concentration. In addition, relay intercropping enhanced soil mycorrhizal activity but differentially influenced mycorrhizal root colonization compared to sole cropping. Sequencing analyses generated a total of 234 amplicon sequence variants belonging to Glomeromycota, which were assigned to 31 virtual taxa using the MaarjAM reference database. Glomeraceae and Claroideoglomeraceae were the most abundant taxa but had contrasting abundances in 2020 and 2021. The overall changes in AMF species diversity and community structure were affected by the interaction between crop species and year, and not by intercropping. Claroideoglomus and Septoglomus showed a strong association with lentil roots while Rhizophagus and Paraglomus were associated with durum wheat roots in 2020, affirming host genotype-AMF preferences. The principal component analysis showed that grain protein concentration was associated with selected mycorrhizal parameters such as community richness and AMF root colonization. Further studies on the functional analysis of the different AMF communities selected by the crop genotype and year may reveal the importance of intercropping in maintaining soil functionality and productivity under low-input systems.

Arbuscular mycorrhizal fungi activity in the rhizosphere of tree seedlings subjected to residual herbicides.

Trees occurring on the margins of agricultural areas can mitigate damage from residual herbicides. Rhizospheric microbial activity associated with trees is one of the main remedial capacity indicators. The objective of this study was to evaluate the rhizospheric microbiological activity in tree species subjected to the herbicides atrazine and sulfentrazone via the rhizosphere. The experiment was designed in four blocks and a 6 × 3 factorial scheme. The first factor consisted of six tree species from Brazil and the second of atrazine, sulfentrazone, and water solutions. Four herbicide applications were performed via irrigation. The total dry mass of the plants, mycorrhizal colonization, number of spores, basal respiration of the rhizospheric soil, and survival rate of bioindicator plants after phytoremediation were determined. Trichilia hirta had higher biomass when treated with atrazine and sulfentrazone. Herbicides decreased the microbial activity in Triplaris americana and did not affect the microbiological indicators of Myrsine gardneriana, Schizolobium parahyba, and Toona ciliata. Fewer bioindicator plants survived in soil with Triplaris americana and sulfentrazone. Microbiological indicators were influenced in different ways between species by the presence of herbicides in the rhizosphere.

Responses of arbuscular mycorrhizal fungi to elevated atmospheric CO2 concentration and warming: A review

Global changes have profound impacts on biodiversity and ecological functioning of terrestrial ecosystems. Arbuscular mycorrhizal (AM) fungi can form symbiotic associations with most terrestrial plant species and play an important role in nutrient acquisition of host plants, promotion of plant growth, and maintenance of plant diversity. In this review, we primarily focused on the responses and feedbacks of AM fungal community and functioning to elevated atmospheric CO2(eCO2) and warming in forest and grassland ecosystems. eCO2 influenced AM fungi mainly through indirectly impacting host plants and soil carbon inputs. A majority of previous studies reported that eCO2 could enhance the abundance and activity of AM fungi, and influence their diversity and community composition. Warming could have direct and indirect (via plant and/or soil pathways) impacts on AM fungi. Warming significantly altered the community compositions of AM fungi in forest soils. But the results from grassland were not consistent. We identified some outstanding problems in current studies and proposed future research topics which deserve more attentions. Our aim was to elucidate the AM fungal responses and adaptation to eCO2 and warming and to improve our understanding of AM fungal functioning in soil ecological processes. This review could provide insights into the implications of AM fungi to mitigate global change and improve the resilience of soil functions, as well as climate change adaptation of ecosystems.

Mycorrhizal fungi arbuscular in forage grasses cultivated in Cerrado soil

The Cerrado is one of the most important regions for agricultural development in the world and is the main productive breadbasket of the Americas. One of the main agricultural activities in the region is high-tech livestock. Cerrado soils are predominantly low in fertility, and arbuscular mycorrhizal fungi play a fundamental role in plant nutrition in this biome. Understanding the behavior of mycorrhizal fungi in the soil under pasture is essential for the development of more efficient and sustainable management practices. Thus, this work aims to verify the activity of arbuscular mycorrhizal fungi in different species of forage grasses cultivated in cerrado soil. To measure mycorrhizal activity, soil spore density factors and mycorrhizal colonization rates in roots of 14 forage grass genotypes were investigated. No significant differences were identified in spore density values between the investigated genotypes. Panicum maximum cv and Mombasa showed the lowest values of mycorrhizal colonization, and the highest values were found in the roots of Brachiaria decumbens. Among the identified genera associated with the rhizosphere of the genotypes studied, Gigaspora, Scutelospora and Sclerocysts are less frequent, which indicates that the association with these fungal genera is less recurrent than with the others.

Elucidating the Mechanisms Underlying Enhanced Drought Tolerance in Plants Mediated by Arbuscular Mycorrhizal Fungi.

Plants are often subjected to various environmental stresses during their life cycle, among which drought stress is perhaps the most significant abiotic stress limiting plant growth and development. Arbuscular mycorrhizal (AM) fungi, a group of beneficial soil fungi, can enhance the adaptability and tolerance of their host plants to drought stress after infecting plant roots and establishing a symbiotic association with their host plant. Therefore, AM fungi represent an eco-friendly strategy in sustainable agricultural systems. There is still a need, however, to better understand the complex mechanisms underlying AM fungi-mediated enhancement of plant drought tolerance to ensure their effective use. AM fungi establish well-developed, extraradical hyphae on root surfaces, and function in water absorption and the uptake and transfer of nutrients into host cells. Thus, they participate in the physiology of host plants through the function of specific genes encoded in their genome. AM fungi also modulate morphological adaptations and various physiological processes in host plants, that help to mitigate drought-induced injury and enhance drought tolerance. Several AM-specific host genes have been identified and reported to be responsible for conferring enhanced drought tolerance. This review provides an overview of the effect of drought stress on the diversity and activity of AM fungi, the symbiotic relationship that exists between AM fungi and host plants under drought stress conditions, elucidates the morphological, physiological, and molecular mechanisms underlying AM fungi-mediated enhanced drought tolerance in plants, and provides an outlook for future research.

Effects of biochar amendment on wheat production, mycorrhizal status, soil microbial community, and properties of an Andisol in Southern Chile

Biochar (BC) production from agroforestry wastes and mycorrhizal fungi are potentially important agricultural practices for improving crops yields and increasing phosphorus (P) in volcanic soils. This study aimed to test the effect of BC application on wheat biomass and grain yield production, indigenous arbuscular mycorrhizal (AM) fungi propagules and soil microbial community and related to soil quality properties of an Andisol in Southern Chile. Biochars (BCs) were produced from oat hulls (OBC) and pine bark (PBC). Doses of 0, 5, 10, and 20 Mg ha−1 of BCs were applied on soil using wheat as the test crop. Wheat biomass (root and shoot portion) and grain yield, AM root colonization, spore, mycelium density, and glomalin content (glomalin related soil protein, EE-GRSP) were measured and related with soil quality properties such as bulk density, water-stable aggregates (WSA), and water holding capacity (WHC). The OBC had a significantly higher macronutrients content (N, P, K) than PBC. The highest dose of both BCs significantly improved shoot and root biomass and wheat grain yield. Application of 20 Mg ha−1 of OBC and PBC increased AM spore density and root colonization relative to control treatment. In the same way, the BC application significantly affects the AM mycelium density. The results showed that the application of higher BC dose changed the soil microbial community. The use of BCs in this volcanic soil is an effective strategy to increase wheat biomass, increase grain yield production, stimulate the indigenous AM fungi activity, enhance soil quality properties, and increase the sustainability levels of agricultural systems.

Contrasting effects of long term phosphorus fertilization on glomalin-related soil protein (GRSP)

Glomalin-related soil protein (GRSP) is believed to be produced by arbuscular mycorrhizal fungi (AMF). However, this fraction of organic matter is influenced by various soil and land-use parameters and its link with AMF has been questioned. The aim of this study was to advance the understanding of the origin of GRSP and its value as a marker of AMF activity by focusing on the effects of soil P status. Archived soils from two phosphorus fertilization field trials on sandy soils under maize cultivation in the south-west of France were studied. Trends in GRSP and soil organic carbon (SOC) were compared. Grain yield and available P (Olsen-P) were monitored and compared to assess P sufficiency/limitation. The time trends of GRSP for each site were not significant. No significant P-fertilization effect on GRSP was observed for the P-sufficient continuously cropped soil, for which the crop yield increase was small. For the P-deficient, former forest soil, P fertilization led to a marked increase in crop production and a significantly larger GRSP content. These trends are coherent with GRSP input linked to crop C-inputs, including the incorporation of crop residue.

Native arbuscular mycorrhizal fungi respond to rehabilitation in iron ore mining areas from the Eastern Brazilian Amazon

Rehabilitation of mining areas is a relevant and current subject, in which the response of microbial communities is an important evaluation tool regarding their progress. In this context, our study had the objective of evaluating the effect of rehabilitation on the community composition and activity of arbuscular mycorrhizal fungi, and their relation with main soil properties, in three iron ore mining sites from Serra Norte of Carajás in the Eastern Brazilian Amazon. For that, non-rehabilitated, rehabilitated, and reference areas within each site were evaluated for spore density and diversity, mycorrhizal colonization, glomalin contents, as well as soil chemical and physical attributes. In general, all mycorrhizal variables responded positively to the rehabilitation processes in the three mining sites. Over time, an increase of similarity of the mycorrhizal communities between rehabilitated and reference areas from each site was observed, as well as, a decrease of the easily extractable glomalin/total extractable glomalin ratio. High ratios of easily extractable glomalin/total extractable glomalin indicated high degree of disturbance and/or disequilibrium of ecosystems, whereas low ratios indicated their equilibrium and/or recovery. This relation can be an interesting parameter, easy to interpret and compare for assessing the degree of disturbance, equilibrium and/or recovery of environments, regardless of absolute values of these variables. Main soil properties related to mycorrhizal response were pH, texture, organic matter content, and cation exchange capacity. Briefly, our results showed the resilience of native mycorrhizal communities and the success of the rehabilitation actions carried out in this Amazonian region.

Soil N2O emissions are more sensitive to phosphorus addition and plant presence than to nitrogen addition and arbuscular mycorrhizal fungal inoculation

Although phosphorus (P) addition and arbuscular mycorrhizal fungal (AMF) colonization have potential for mitigating soil N2O emission, the effects and mechanisms remain unresolved. We conducted a pot experiment with ryegrass (Lolium perenne) growing in a growth chamber for 80 days with three factors: Plant and AMF presence (unplanted, with plants, with plants colonized by AMF), two nitrogen (N) addition levels (0 and 50 mg N kg−1 soil) and two P addition levels (0 and 20 mg P kg−1 soil). Our results showed that N addition and AMF colonization had insignificant effects on soil N2O emission. However, the presence of plants decreased soil N2O emission by 90%–99% (planted vs. unplanted) under P addition. Moreover, P addition increased (+134%) N2O emission from unplanted soil, but decreased (74%–98%) it from planted soil. Further analysis showed that soil N2O emission was controlled by soil available P, soil NO3−-N, plant biomass P and N across all treatments. The lower N2O emissions from planted soils were mainly due to the lower soil NO3−-N content which might be immobilized by plant biomass, while the higher N2O emissions from unplanted soils under P addition were attributed to the increased soil available P content. Furthermore, we found an antagonistic effect between AMF inoculation and P addition on soil N2O emission because sufficient soil P may inhibit AMF colonization and activity. Taken together, we conclude that plant presence combined with P addition can effectively reduce N2O emission from P-limited soils.

Disentangling the abiotic and biotic components of AMF suppressive soils

Arbuscular mycorrhizal fungi (AMF) are important in plant nutrient uptake, but their function is prone to environmental constraints including soil factors that may suppress AMF transfer of phosphorus (P) from the soil to the plant. The objective of this study was to disentangle the biotic and abiotic components of AMF-suppressive soils. Suppression was measured in terms of AMF-mediated plant uptake of 33P mixed into a patch of soil and treatments included soil sterilization, soil mixing, pH manipulation and inoculation with isolated soil fungi. The degree of suppression was compared to volatile organic compound (VOC) production by isolated fungi and to multi-element analysis of soils. For a selected suppressive soil, sterilization and soil mixing experiments confirmed a biotic component of suppression. A Fusarium isolate from that soil suppressed the AMF activity and produced greater amounts than other fungal isolates of the antimicrobial VOC trichodiene (a trichothecene toxin precursor), beta-chamigrene, alpha-cuprenene and p-xylene. These metabolites deserve further attention when unravelling the chemical background behind the suppression of AMF activity by soil microorganisms. For the abiotic component of suppression, soil liming and acidification experiments confirmed that suppression was strongest at low pH. The pH effect might be associated with changed availability of specific suppressive elements. Indeed 33P uptake from the soil patches correlated negatively to Al levels and Al toxicity seems to play a major role in the AMF suppressiveness at pH below 5.0–5.2. However, the documentation of a biotic component of suppression for both low and high pH soils leads to the conclusion that biotic and abiotic components of suppression may act in parallel in some soils. The current insight into the components of soil suppressiveness of the AMF activity aids to develop management practices that allow for optimization of AMF functionality.

The Effects of Biochar on Indigenous Arbuscular Mycorrhizae Fungi from Agroenvironments.

The effects of biochar on soil–plant–microorganisms systems are currently being extensively investigated. Considering that arbuscular mycorrhizal fungi (AMF) play an essential role in nutrient dynamics, the present study aims at understanding vine shoot-derived biochar effects on AMF activity and the impact of their multiplication in soils on water-stress resistance of plants. Three agronomic tests were performed in greenhouse pots. The first experiment evaluated the effects of three factors: final pyrolysis temperature for biochar production (400 °C and 600 °C), application rate (0 weight-wt.- % as a control, 1.5 wt. %, and 3.0 wt. %) and texture of the growing media (sandy-loam and clay-loam origin) on AMF, microbial communities and phosphatase activity. In the second experiment, an indigenous consortium of AMF was multiplied through the solid substrate method and sorghum as a trap plant with biochar addition. This process was compared to a control treatment without biochar. Obtained inocula were tested in a third experiment with lettuce plants under different water irrigation conditions. Results from the first experiment showed a general increase in AMF activity with the addition of the biochar produced at 400 °C in the sandy-loam texture substrate. Results of the second experiment showed that the biochar addition increased AMF root colonization, the number of AMF spores and AMF infective potential. Results of the third experiment showed that biochar-derived AMF inoculum increased AMF root colonization, AMF spores, dry biomass and the SPAD index in a lettuce crop under low-water irrigation conditions.

Species-specific trade-offs between regrowth and mycorrhizas in the face of defoliation and phosphorus addition

Arbuscular mycorrhizal fungi (AMF) enhance nutrient provision in exchange for carbon. However, a shift from nutrient to carbon limitation, induced by repeated or intense defoliation, can represent a trade-off between plant regrowth and the maintenance of mycorrhiza. The combined effects of AMF, phosphorus and defoliation on growth of A gropyron elongatum (C 3 grass, low mycorrhizal responsiveness) and B rachiaria brizantha (C 4 grass, high mycorrhizal responsiveness) were explored. Each species was subjected to a manipulative experiment with AMF inoculation (non-inoculated, inoculated), soluble P supply (low, high) and defoliation (non-defoliated, 60% defoliated). In A. elongatum , at low P supply, mycorrhizal plants showed increased growth rates following defoliation without substantial changes in AMF colonization. At high P supply instead, we found a clear trade-off between regrowth and the maintenance of mycorrhiza evidenced by growth depression (biomass and tillers) and lower AMF activity (reduction of arbuscules). In contrast, in B. brizantha , defoliation effects on plant regrowth were independent from AMF at any P supply (no trade-off). This indicates that cost-benefit relationship in defoliated plants is highly context-dependent and may vary with mycorrhizal responsiveness of species. This variation of responses can play a decisive role on plant recovery in pastures and natural grasslands subjected to herbivory. • First comparative study of AMF, defoliation and P supply in C 3 and C 4 grasses. • In the C 3 grass, AMF promoted recovery from defoliation at low P supply. • Mycorrhiza and defoliation trade off in the C 3 grass at high P supply. • In the C 4 grass, mycorrhizae were beneficial at all environmental contexts. • AMF effects on the recovery from defoliation depend on P supply and plant identity.

English

The main residue of iron and nickel mining is slag, a solid residue of low solubility and rich in magnesium silicate. A residue with potential use as a soil conditioner, however, it is still necessary to investigate whether its use brings impacts to the environment. Microorganisms are extremely sensitive to environmental changes, changes that can be used as environmental quality indicators. Among the organisms that act as microbiological indicators of soil quality, the activity of arbuscular mycorrhizal fungi stands out. With this, this study aimed to verify the mycorrhizal activity as a quality indicator under application of nickel iron mining slag as soil conditioner. The experiment was carried out in the greenhouses of the agronomy course and in the laboratory of agricultural microbiology of the Evangelical College of Goianésia. Magnesium silicate was supplied by Anglo American Mining Company, located in Barro Alto, Goiás. Agronomic and microbiological analyses were performed at the Evangelical College of Goianésia, Goiás. The experimental design used was completely randomized, arranged with five treatments and with five replications, where the treatments were composed of four doses of magnesium silicate: 9, 12, 15, and 18 g dm-3 of soil in addition to the control without application. Ten golden saw rice seeds were planted in 10-L pots. Soil analysis used in the experiment was performed to determine soil nutritional parameters. The application of iron and nickel mining slag does not influence the development of rice in the first application. The application of 9 dm³g-1 of iron and nickel mining slag soil positively influences mycorrhizal activity on roots and soil.   Key words: Mycorrhiza, magnesium silicate, stress, cerrado.

Effect of mixed substrate with different mycorrhizal fungi concentrations on the physiological and productive response of three varieties of tomato

The application of arbuscular mycorrhizal fungi (AMF) in a mixed substrate is a vegetable production practice capable of improving plant productivity and sustainability of agricultural ecosystems. This study was conducted to determine the effect of a mixed substrate (agricultural soil with coconut fiber substrate) not enriched (S0) and enriched with 100 and 300 g m−3 of the fungus Glomus iranicum var. Tenuihypharum (S100 and S300) in water relations, photosynthetic and nutritional capacity, as well as production and fruit quality in three tomato varieties “H4”, “H3” (susceptible to mycorrhization) and “Jacaranda” not susceptible to mycorrhization). Plants irrigated with moderately saline water (EC: 2.35 dS m-1) in a commercial greenhouse in Mediterranean climate conditions were used for this study. Results showed that plants grown in substrate S100 showed an increase of AMF colonization, leaf phosphorus concentration, leaf total carbon and total nitrogen content compared with those grown in S0 and S300, which induced an increase in photosynthesis and stomatal conductance. This positive response was less evident by the application of substrate S300. Variety “H3” had a decrease in leaf sodium content, as well as higher photosynthesis values. There were no differences in stem water potential between factors. The lowest fruit production was observed in the “H4” variety, while fruit firmness decreased by AMF concentration and in variety “Jacaranda”. Root and aerial biomass increased in plants grown in S100 and S300, with respect to S0. Therefore, the improvements in the physiological and nutritional behaviour of these plants resulted in increased vegetative growth, but not in increased production. Varieties susceptible to AMF infection were more colonized than “Jacaranda”, but there were not improvements in yield and fruit quality. These results suggest that aspects related to the composition of the selected substrate, enzymatic AMF activity, fruit nutrition, as well as molecular mechanisms that control the plant-AMF interaction should be studied in depth.