Glyphosate reduces spore viability and root colonization of arbuscular mycorrhizal fungi

Glyphosate is the most widely used herbicide in the world, but its effects on non-target organisms, such as arbuscular mycorrhizal fungi (AMF), are unclear. No studies have been found that made reference to effects of glyphosate on AMF spore viability despite its importance as a source of propagules for the perpetuation and spread of AMF in the system. The objective of this study was to evaluate the effect of glyphosate application on AMF spore viability, and their ability to colonize roots. Soil samples were collected from a grassland area located in the Flooding Pampa region (Argentina). We evaluated three herbicide rates: 0, 0.26 and 1× recommended field rate, 10 and 30 days after application. Part of the soil from each tray was used to estimate the spore viability, and the remainder was used as substrate for growing Lolium multiflorum Lam. One month after sowing, total root colonization and percentage of arbuscules and vesicles were determined. The spore viability in herbicide untreated soils was between 5.8- and 7.7-fold higher than in treated soils. This reduction was detected even when the lower rate was applied. Root colonization was significantly lower in plants grown in glyphosate treated soil than in untreated ones. A decrease in arbuscular colonization (but not in vesicles) was found in plants grown in soils treated with the highest herbicide rate. That would indicate that symbiosis functionality was affected, given that arbuscules are the main site for host–fungus nutrient exchange. The results indicate that soil residence time of glyphosate and/or its degradation products was enough to reduce AMF spore viability and their ability to colonize roots. This decrease in propagules viability may affect plant diversity, taking into account the different degrees of mycorrhizal dependency between plant species that may coexist in grassland communities.     

Plant growth-promoting rhizobacteria alter rooting patterns and arbuscular mycorrhizal fungi colonization of field-grown spring wheat

The impact of plant growth-promoting rhizobacteria (PGPR) inoculants on the growth, yield and interactions of spring wheat with arbuscular mycorrhizal fungi (AMF) was assessed in field studies. The pseudomonad inoculants P. cepacia R55, R85, P. aeruginosa R80, P. fluorescens R92 and P. putida R104, which enhance growth and yield of winter wheat, were applied at a rate of ca. 10⁷–10⁸ cfu seed^-1 and plots established on pea stubble or summer fallow at two different sites in Saskatchewan. Plant shoot and root biomass, yield and AMF colonization were determined at four intervals. Plant growth responses were variable and dependent on the inoculant strain, harvest date and growth parameter evaluated. Significant increases or decreases were measured at different intervals but these were usually transient and final seed yield was not significantly affected. Harvest index was consistently increased by all pseudomonad inoculants; responses to strain R55 and R104 were significant. Root biomass to 60 cm depth was not significantly affected by inoculants except strain R104, which significantly reduced root dry weight. However, root distribution, root length and AMF colonization of roots within the soil profile to 60 cm were significantly altered by inoculants. Most of these responses were reductions in the assessed parameter and occurred at depths below 15 cm; however, strains R85 and R92 significantly increased root dry weight in the 0- to 15-cm zone. These results indicate that some PGPR inoculants may adversely affect mutualistic associations between plants and indigenous soil microorganisms, and suggest a possible reason as to why spring wheat growth was not consistently enhanced by these pseudomonad PGPR.     

The influence of arbuscular mycorrhizal colonization and environment on root development in soil

The production of fine roots is one of the principal means by which carbon, fixed during photosynthesis, enters the soil, and quantifying the production for particular combinations of environmental and biotic factors is important for predicting the sequestration of carbon in the soils of grassland ecosystems. Arbuscular mycorrhizal fungi (AMF) can have a major effect on the production of roots, and we studied how colonization by AMF affects the lifespan of roots. Twenty per cent of control roots of Trifolium repens survived for longer than 42 days whereas 37% survived that long in AMF‐colonized plants. The overall survival of the roots of Lolium perenne was less than in T. repens: around 10% of roots survived beyond 42 days and this was not affected by AMF colonization. Previous studies have shown that lifespans of roots can be affected by temperature. We tested the hypothesis that these observations are linked to a change in the morphology of the root system caused by temperature and also by AMF. We found that inoculation with AMF in a microcosm study using Plantago lanceolata grown at various temperatures, with and without AMF, showed no clear effect of AMF on branching patterns. Temperature had a significant effect on total lengths, numbers and branching rates of some higher orders of roots. Total lengths of both secondary and tertiary roots grown at 27°C were about double those of plants grown at 15°C. Colonization by AMF tended to reduce this effect. Evidently the effect of colonization by AMF on root lifespan depends on the species. Increased branching, and thus a greater proportion of ephemeral roots, was responsible for shortening the lives of the roots at increased temperature, which suggests a strong link between lifespan and morphology.     

N,P Contribution and soil adaptability of four arbuscular mycorrhizal fungi

Abstract

A glasshouse study was conducted to investigate the symbiotic efficiency and soil adaptability of four AMF using glass-bead cultivation systems. The results showed that efficiency and adaptability of four fungi varied among three soils. Particularly, efficiency of BEG167 shifted from positive in Beijing soil to negative in Guangdong soil. Furthermore, BEG167 had high adaptability in all three soils. Intraspecific differences of BRG168 and BEG221 were found in efficiency and adaptability in three soils. Taking efficiency and adaptabilty into consideration, it was concluded that BEG167, BEG168 and BEG221 in Beijing soil, BEG151 in Hubei soil, and BEG151 and BEG168 in Guangdong soil were effective AMF for maize.     

The inconsistent effect of soil disturbance on colonization of roots by arbuscular mycorrhizal fungi: a test of the inoculum density hypothesis

Reducing the tillage of agricultural soils can increase early-season crop-P uptake. Consistent increases in plant-P have been found in both field- and laboratory-systems with undisturbed (U) compared to disturbed (D) soil. A concomitant stimulatory effect on colonization of roots in U soil by arbuscular mycorrhizal (AM) fungi has been found in some cases, but in others the colonization has been similar in U and D treatments. Disruption of the extraradical mycelium that remains from the previous crop is the mechanism by which soil disturbance restricts mycorrhizally mediated P uptake for the subsequent crop, with a tandem change in colonization not necessary, but sometimes seen. Nonetheless, a complete account of these processes will need an understanding of the conditions under which the extent of colonization is affected. Soil-P does not explain when a difference in colonization will appear. Among ecosystems in Western Australia, high inoculum density in a pasture was reported previously to preclude the appearance of a difference in colonization in response to soil disturbance, whereas for other ecosystems with lower inoculum densities a difference in colonization was seen. Here, we determined if a similar mechanism operates for an agricultural soil collected mid-season during the growth of a maize (Zea mays L.) crop in Ontario, Canada. Blending various proportions of pasteurized and non-pasteurized soil gave a range of inoculum densities. Maize was taken through two 3-week growth cycles in pots, and for the D treatment the soil was passed through a 5 mm sieve between cycles. All plants became colonized with AM fungi. Reducing the inoculum density served to limit colonization to similar low levels in both U and D soils. Stimulation of colonization and of shoot-P uptake in the U-compared with the D-treatment was greater for plants under the higher inoculum conditions tested. We conclude that the inoculum density during crop growth of the soil studied here is moderate, and that this density makes it possible, if other conditions are met, for a reduction of colonization of roots in response to soil disturbance. Whether or not a difference in colonization will appear following disturbance of a soil such as the one studied here probably depends on the interaction between the environment and the plant. Possible interactions are discussed. The high inoculum density of ecosystems such as the pasture studied in Australia likely overrides any effect of soil disturbance and ensures roots of all plants become well-colonized by AM fungi.     

Delayed response to ring nematode (Mesocriconema xenoplax) feeding on grape roots linked to vine carbohydrate reserves and nematode feeding pressure

The chronic impact of ring nematode (Mesocriconema xenoplax) feeding on grapevine (Vitis vinifera) was studied under controlled conditions. ‘Pinot noir’ grapevines were exposed to ring nematode or kept nematode-free for three growing seasons and vines were either grown in full sunlight, 15% of full sun, or partially defoliated to manipulate vine carbohydrate status. Whole plants were destructively sampled to assess the impact of ring nematode on whole plant biomass, carbohydrate, and mineral nutrient accumulation. Vine shoot growth and total biomass was unaffected by ring nematode in the first growing season, although reserves of nonstructural carbohydrates (NSC), P, K, and Ca in the roots and wood were reduced in all canopy management treatments. Vine shoot growth and total biomass were reduced by ring nematode in Year 2, and greater declines in reserve NSC and most mineral nutrients had occurred. Reserves of NSC were affected more than biomass or nutrients during the second year. During the third year of exposure to ring nematode, vines in the 15% sun treatment were dying (prompting an earlier destructive harvest), even though these vines had similar biomass and NSC reserves as the partially defoliated vines at the end of the second year. The demise of the 15% sun vines was associated with higher ring nematodes per unit of root mass, as compared to either full sun or defoliated vines. Therefore, predicting plant response to this nematode requires an understanding of nematode density per quantity of roots, not nematodes per unit of soil which is how plant parasitic nematodes are currently enumerated.     

Effects of hexachlorocyclohexane on rhizosphere fungal propagules and root colonization by arbuscular mycorrhizal fungi in Plantago lanceolata

Lindane ( γ‐hexachlorocyclohexane or γ‐HCH) is an organochlorine insecticide previously used extensively for the control of agricultural pests. We studied the effects of soil HCH contamination on vegetation and its associated arbuscular mycorrhizas (AM). The polluted and unpolluted plots had similar plant cover, with the same species richness and abundance. Plantago lanceolata plants were selected for mycorrhizal analysis because of their presence in both plots and known mycotrophy. The presence of HCH appeared to have no significant effect on the extent of colonization of Plantago roots by AM, suggesting a similar functionality of the fungal symbionts. However, infective AM propagules, the density of AM spores and viable AM hyphae in the rhizosphere were much less in the HCH‐polluted soil than in the unpolluted plot. Pre‐inoculation of four plant species with an isolate of Glomus deserticola obtained from the HCH‐contaminated soil resulted in increased growth and fungal colonization of roots compared with plants pre‐inoculated with the introduced fungus G. macrocarpum or colonized by the consortium of indigenous AM fungal species, when those plants were transplanted to an HCH‐contaminated soil. This suggests that the fungus increases the tolerance of plants to the toxic soil environment. We conclude that herbaceous and woody plants can grow in soil with little P contaminated with <100 mg HCH kg^?1 with the help of tolerant AM, despite the detrimental effect of HCH on AM fungal propagules in soil. The effects of AM fungi on plant growth and soil microbial community structure in HCH‐polluted sites could be important for remediation of the pollutant through the microbial activity in the rhizosphere.     

Changing soil characteristics alter the arbuscular mycorrhizal fungi communities of Arabica coffee (Coffea arabica) in Ethiopia across a management intensity gradient

Coffee is the most important tropical agricultural commodity worldwide, cultivated in more than 70 countries. Despite the plant's huge economic importance, there is very limited knowledge on the association of arbuscular mycorrhizal fungi (AMF) with coffee roots. We investigated the environmental drivers affecting the diversity and community composition of AMF on Arabica coffee in its Ethiopian center of origin. We used 454 amplicon pyrosequencing to describe AMF communities in the roots of Arabica coffee plants that were sampled along a large management intensity gradient, covering the major Ethiopian coffee production systems. We identified AMF genera that have not been reported before in Arabica coffee production regions elsewhere in the world and show that high soil phosphorus availability decreases AMF diversity and that soil pH, nitrogen and phosphorus availability strongly affect AMF community composition. At the scale of our study (max. 82 km distance between sampling points, and 770 m altitude difference), no effect was found of spatial location or altitude on AMF communities. This is the first study analyzing the drivers of naturally occurring AMF in the roots of a globally important tropical crop, providing preliminary data to improve coffee production in its native and introduced range, through targeted intervention in coffee AMF communities.     

Acidic soil inhibits the functionality of arbuscular mycorrhizal fungi by reducing arbuscule formation in tomato roots

ABSTRACT

Acidic soil is widely distributed in terrestrial ecosystems, which causes large challenges to crop production. Arbuscular mycorrhizal fungi (AMF) can increase plant tolerance to acidic soil; however, the effects of acidic soil on the functionality of AMF and arbuscule formation are far from being thoroughly understood. In this study, we inoculated tomato plants with Rhizophagus irregularis at pH 4.5 (original acidic soil) or pH 6.5 (limed soil), and monitored the mycorrhizal colonization, alkaline phosphatase (ALP) activity, and expression of SlPTs (which encode phosphate transporters) and EXO70s (which encode subunits of exocysts) in the roots. We aimed to characterize the arbuscule development in colonized roots in response to acidic soil and to investigate how acidic soil affects the functionality of AMF. Our results revealed that acidic soil sharply reduced arbuscule abundance by approximately 90%, and greatly impeded arbuscule development such that no mature arbuscules were observed. The negative effect of acidic soil on arbuscule formation was supported by EXO70A1-like expression. The functionality of AMF, e.g., ALP activity in arbuscules and the expression of SlPT4 and SlPT5, was simultaneously greatly inhibited in acidic soil in the same manner as that of arbuscule formation. The close relationship between the functionality of AMF and arbuscule abundance in this study indicates that acidic soil strongly inhibits AMF function mainly via a reduction in arbuscule formation. Considering the coupling of arbuscule formation and periarbuscular membrane construction, the fine-tuning of both processes in response to acidic soil merits additional in-depth investigations.     

Differential effects of soil disturbance and plant residue retention on function of arbuscular mycorrhizal (AM) symbiosis are not reflected in colonization of roots or hyphal development in soil

The effects of soil disturbance and residue retention on the functionality of the symbiosis between medic (Medicago truncatula L.) and arbuscular mycorrhizal fungi (AMF) were assessed in a two-stage experiment simulating a crop rotation of wheat (Triticum aestivum L.) followed by medic. Plants were inoculated or not with the AMF, Glomus intraradices and Gigaspora margarita, separately or together. The contribution of the arbuscular mycorrhizal (AM) pathway for P uptake was determined using ³²P-labeled soil in a small hyphal compartment accessible only to hyphae of AMF. In general AM colonization was not affected by soil disturbance or residue application and disturbance did not affect hyphal length densities (HLDs) in soil. At 4 weeks disturbance had a negative effect on growth and phosphorus (P) uptake of plants inoculated with G. margarita, but not G. intraradices. By 7 weeks disturbance reduced growth of plants inoculated with G. margarita or AMF mix and total P uptake in all inoculated plants. With the exception of plants inoculated with G. margarita in disturbed soil at 4 weeks, the AM pathway made a significant contribution to P uptake in all AM plants at both harvests. Inoculation with both AMF together eliminated the negative effects of disturbance on AM P uptake and growth, showing that a fungus insensitive to disturbance can compensate for loss of contribution of a sensitive one. Application of residue increased growth and total P uptake of plants but decreased ³²P in plants inoculated with the AMF mix in disturbed soil, compared with plants receiving no residue. The AMF responded differently to disturbance and G. intraradices, which was insensitive to disturbance, compensated for lack of contribution by the sensitive G. margarita when they were inoculated together. Colonization of roots and HLDs in soil were not good predictors of the outcomes of AM symbioses on plant growth, P uptake or P delivery via the AM pathway.     

Impact of plant species grown as monocultures on sporulation and root colonization by native arbuscular mycorrhizal fungi in potato

Rhizosphere soils from 12 different plant species grown as monocultures at a field site of biodiversity and ecological processes in terrestrial herbaceous ecosystems (BIODEPTH) in northern Sweden were used as inoculum on potato to investigate mycorrhizal traits. Potato roots showed significantly higher mycorrhizal colonization when inoculated with soil samples from Festuca ovina and Leucanthemum vulgare compared to soil samples from other plants. The soil samples of F. ovina, L. vulgare, Phalaris arundinacea and Trifolium pratense rhizospheres were chosen for arbuscular mycorrhizal fungi identification based on spore morphology and large subunit (LSU) ribosomal DNA sequences amplified from single spores and roots. Spore morphological identification showed that Glomus mosseae and Glomus intraradices were found in F. ovina and L. vulgare soils at the site as well as in our potato trap experiment. Also, Glomus geosporum spores were present in all four plants’ soils in the potato trap experiment. LSU rDNA sequences were obtained from AM fungal spores from the collection site or potato trap experiment and colonized potato roots inoculated with L. vulgare soil. Sequences showed highest similarity to G. mosseae. Our results suggest that the host F. ovina and L. vulgare could be considered in crop rotation to enhance AM fungal inocula for potatoes.     

High colonization by native arbuscular mycorrhizal fungi (AMF) of rubber trees in small-holder plantations on low fertility soils in North East Thailand

Rubber tree is a very important crop in Thailand, representing an essential source of income for farmers. In the past two decades, rubber tree plantations have been greatly expanding in unfavorable areas, where climate conditions are difficult and soil fertility is very poor. To optimize latex yields, mineral fertilizers have been widely used. A better understanding of the roles of the biological compartment in soil fertility is essential to determine alternative management practices to sustain soil fertility and optimize latex yields. Arbuscular mycorrhizal fungi (AMF) are widely recognized as beneficial for plants, mainly through their role in improving plant nutrient uptake. The objective of this study was to assess the AMF populations in rubber tree plantations and the impact of both soil characteristics and plantation age on these communities. Our results showed that all rubber trees were highly colonized, regardless of the soil structure and nutrient contents. AMF colonization was not affected by the age of the trees, suggesting that maintaining the symbiosis is likely to be beneficial at all stages. A better understanding and management of the microbial communities would contribute to maintaining or restoring soil fertility, leading to a better tree growth and optimized latex yield.     

An improved method for bright-field imaging of arbuscular mycorrhizal fungi in plant roots

Easy observation methods to assess the colonization levels of arbuscular mycorrhizal (AM) fungi in plant roots are crucial for studying the biology of AM symbiosis and for considering agricultural use. Many AM studies employ Trypan Blue (TB) coupled with lactic acid to stain AM fungal structures as bright-field images; however, TB staining can be difficult to use owing to its noxiousness and high viscosity. Here, we report the development of an easy method for visualizing AM fungal structures as bright-field images using 3,3′-diaminobenzidine (DAB). Wheat germ agglutinin (WGA)-conjugated horseradish peroxidase (HRP), which specifically targets N-acetylglucosamine polymers and detects AM fungal cell walls, penetrated the cortical layers of 10% potassium hydroxide (KOH)-treated soybean roots and stained AM fungal mycelia in the presence of DAB and hydrogen peroxide (H₂O₂). Comparison between DAB and TB staining of soybean (Glycine max L.) roots suggested that the intactness of root systems and image contrast using DAB staining were superior. Background signals in stele observed by DAB staining were negligible as compared with those observed by WGA-fluorescein isothiocyanate staining. DAB staining, which combines the advantages of TB (easy bright-field imaging) and WGA-fluorophore (specific and high-quality) staining, provides a robust imaging method for macro- and micro-level analyses of AM roots and is applicable to at least six crops: soybean, onion (Alium cepa L.), potato (Solanum tuberosum L.), maize (Zea mays L.), rice (Oryza sativa L.), and sunflower (Helianthus annuus L.).     

Rhodotorulic acid enhances root colonization of tomato plants by arbuscular mycorrhizal (AM) fungi due to its stimulatory effect on the pre-symbiotic stages of the AM fungi

Exudates of Rhodotorula mucilaginosa, a yeast commonly found in the rhizosphere, increased hyphal length of the arbuscular mycorrhizal (AM) fungi Gigaspora rosea and Gigaspora margarita. Rhodotorulic acid (RA), a siderophore compound obtained from R. mucilaginosa exudates, increased hyphal length and branching. Thus, the increase in the number of entry points and the higher AM root colonization of tomato plants in the presence of RA can at least partially be explained by the positive effect of RA on the pre-symbiotic stages of the AM fungi.     

Suppression of other soil microorganisms by mycelium of arbuscular mycorrhizal fungi in root-free soil

The influence of mycelium of two arbuscular mycorrhizal (AM) fungi, Glomus intraradices and Glomus mosseae, on other soil microorganisms, was examined in root-free soil with and without organic substrate amendment in terms of cellulose. The AM fungi were grown in symbiosis with cucumber in a compartmented growth system, which allowed AM fungal external mycelium to grow into root-free compartments. The fungicide Benomyl was applied to the root-free compartments to create an alternative non-mycorrhizal control treatment. Whole cell biomarker fatty acids were employed to quantify different groups of soil microorganisms including the two AM fungi. Abundance of most microbial groups were reduced by external mycelium of both AM fungi, though differential effects on the microbial community composition were observed between the two AM fungi as revealed from principal component analysis. Inhibition of other soil microorganisms was more pronounced in root-free soil with mycelium of G. mosseae than with mycelium of G. intraradices. In general, cellulose increased the amount of biomarker fatty acids of most groups of soil microorganisms, but cellulose did not affect the influence of AM fungi on other soil microorganisms. Benomyl suppressed growth of the external mycelium of the two AM fungi and had limited non-target effects on other microbial groups. In conclusion, our results show differential effects of external mycelium of AM fungi on other soil microbial communities, though both AM fungi included in the study overall inhibited most microbial groups as examined using whole cell biomarker fatty acids.     

Effectiveness of native West African arbuscular mycorrhizal fungi in protecting vegetable crops against root-knot nematodes

Twenty strains of arbuscular mycorrhizal fungi (AMF), native to West Africa, and three commercial AMF, were evaluated for their protective effect against root-knot nematodes, Meloidogyne spp., in pots and field experiments in Benin. In pots, these strains were assessed in sterilized soil following inoculation of nematodes and in non-sterilized soil naturally infested with nematodes using tomato. The four strains showing greatest potential in suppressing nematode development were further assessed in the field with a relatively high natural infestation level of nematodes (155 per 100 cm³ soil) over a tomato–carrot double cropping. In the pot experiments, most native strains provided significant suppression of nematode multiplication and root galling, but in most cases the level of nematode control depends on either sterilized or non-sterilized soils. In the field experiments, application of AMF mostly resulted in significant suppression of nematode multiplication and root galling damage on both crops indicating that the AMF persists and remains protective against root-knot nematodes over two crop cycles. Field application of AMF increased tomato yields by 26% and carrot yields by over 300% compared with the non-AMF control treatments. This study demonstrates for the first time, the protective effect of indigenous West African AMF against root-knot nematodes on vegetables. The potential benefits of developing non-pesticide AMF-based pest management options for the intensive urban vegetable systems are evident.     

Field inoculation effectiveness of native and exotic arbuscular mycorrhizal fungi in a Mediterranean agricultural soil

In sustainable agriculture, arbuscular mycorrhizal (AM) fungal inoculation in agronomical management might be very important, especially when the efficiency of native inocula is poor. Here, we assessed the effect of native and exotic selected AM fungal inocula on plant growth and nutrient uptake in a low input Trifolium alexandrinum-Zea mays crop rotation. We evaluated the effects of four exotic AM fungal isolates on T. alexandrinum physiological traits in greenhouse. Then, the field performances of T. alexandrinum inoculated with the exotic AMF, both single and mixed, were compared to those obtained with a native inoculum, using a multivariate analysis approach. Finally, we tested the residual effect of AM fungal field inoculation on maize as following crop. Multivariate analysis showed that the field AM fungal inoculation increased T. alexandrinum and Z. mays productivity and quality and that the native inoculum was as effective as, or more effective than, exotic AM fungal isolates. Moreover, the beneficial effects of AMF were persistent until the second year after inoculation. The use of native AMF, produced on farm with mycotrophic plants species, may represent a convenient alternative to commercial AM fungal inocula, and may offer economically and ecologically important advantages in sustainable or organic cropping systems.     

Nitrogen capture by grapevine roots and arbuscular mycorrhizal fungi from legume cover-crop residues under low rates of mineral fertilization

The influence of mineral fertilization on root uptake and arbuscular mycorrhizal fungi-mediated ¹⁵N capture from labeled legume (Medicago polymorpha) residue was examined in winegrapes (Vitis vinifera) in the greenhouse, to evaluate compatibility of fertilization with incorporation of cover-crop residue in winegrape production. Plants grown in marginal vineyard soil were either fertilized with 0.25× Hoagland’s solution or not. This low fertilization rate represents the deficit management approach typical of winegrape production. Access to residue in a separate compartment was controlled to allow mycorrhizal roots (roots + hyphae), hyphae (hyphae-intact), or neither (hyphae-rotated) to proliferate in the residue by means of mesh core treatments. Leaves were weekly analyzed for ¹⁵N. On day 42, plants were analyzed for ¹⁵N and biomass; roots were examined for intraradical colonization; and soils were analyzed for ¹⁵N, inorganic N, Olsen-P, X-K, and extraradical colonization. As expected, extraradical colonization of soil outside the cores was unaffected by mesh core treatment, while that inside the cores varied significantly. ¹⁵N atom% excess was highest in leaves of roots + hyphae. In comparison, leaf ¹⁵N atom% excess in hyphae-intact was consistently intermediate between roots + hyphae and hyphae-rotated, the latter of which remained unchanged over time. Fertilization stimulated host and fungal growth, based on higher biomass and intraradical colonization of fertilized plants. Fertilization did not affect hyphal or root proliferation in residue but did lower %N derived from residue in leaves and stems by 50%. Our results suggest that even low fertilization rates decrease grapevine N uptake from legume crop residue by both extraradical hyphae and roots.     

Brassinosteroid (BR) and arbuscular mycorrhizal (AM) fungi alleviate salinity in wheat

This study was conducted to assess the impacts of brassinosteroide (BR), arbuscular mycorrhizal (AM) fungi, Glomus mosseae and their interactions on salt stress tolerance in Triticum aestivum L. After foliar spraying of mycorrhizal and non-mycorrhizal plants by 5 µM epibrassinolide, they were subjected to 0 and 150 mM sodium chloride (NaCl) for 2 weeks. The experiment was conducted in a randomized complete block design, replicated 4 times. Our results showed a probable potential of BR and/or AM fungi in improving salt tolerance of plants. Total phenol and proline content increased in BR and/ or AM treatments. AM fungi promoted plant growth, including leaf area, shoot and root dry weights, and lengths under saline condition. Moreover, BR improved growth parameters except root dry weights and lengths. This study indicated that BR and/or AM fungi may contribute to improve salt tolerance of the plant.