Colonisation by arbuscular mycorrhizal and fine endophytic fungi in four woodland grasses – variation in relation to pH and aluminium

Acidic soils are harsh environments for plants. One of the major problems is the potential toxicity of aluminium (Al) and hydrogen ions at a pH below 5; another is the shortage of nutrients usually accompanying soil acidity. The aim of this study was to elucidate the relationship between arbuscular mycorrhizal (AM) colonisation and soil acidity (measured by pH and Al concentration) in order to evaluate the possibility that AM fungi facilitate the existence of plants on acidic soils. We sampled tussocks of four grass species, Elymus caninus, Poa nemoralis, Deschampsia cespitosa and Deschampsia flexuosa, together with samples of the surrounding soil, in oak forests of varying soil pH in southern Sweden. We determined pH, easily reacting Al (Al_r), extractable Al (Al_BaCl2) and phosphate in the soil samples, analysed the shoots for Al and phosphorous and quantified the degree of AM and fine endophyte (FE) colonisation in the roots. E. caninus was found on the least acidic soils and had the highest AM colonisation of all the species studied, while D. flexuosa, which was found on the most acidic soils, had the lowest AM colonisation. P. nemoralis and D. cespitosa were intermediate with respect to pH and AM colonisation. The colonisation of AM fungi exceeded FE colonisation for E. caninus and P. nemoralis, while the opposite was true for the two Deschampsia species. Our results indicated a negative relationship between Al_r and the degree of AM colonisation at the within-species level. The low colonisation of AM fungi on acidic soils may to some extent be explained by a sensitivity of AM fungi to Al_r: this parameter showed a stronger negative association with AM colonisation than did pH and Al_BaCl2. We hypothesize that Al toxicity is a critical factor for plant nutrition in forest soils through the impact on symbiotic fungi.     

A simple method to obtain endophytic microorganisms from field-collected roots

We describe a simple technique for obtaining endophytic microorganisms from field-collected roots. Roots of plant species were surfaced-sterilized, cut into pieces, and then each root piece was transferred to drops of Gel-Gro medium. The number of segments with bacteria and fungi was quantified and those with bacteria and dark septate endophytic (DSE) fungi were plated onto tryptic soy agar (TSA) and malt extract agar (MEA), respectively. When arbuscular mycorrhizal fungi (AMF) grew from root segments, they were inoculated into Ri T-DNA-transformed carrot root cultures. Eight different species of bacteria and five dark septate endophytes were isolated. Thirty AMF isolates were identified and continuous pure cultures established. This easy and inexpensive approach allowed us to culture various endophytic microorganisms in an in vitro system saving time and space.     

Seasonal patterns of cadmium accumulation in Arrhenatherum elatius (Poaceae): Influence of mycorrhizal and endophytic fungal colonisation

We investigated the influence of arbuscular mycorrhizae (AM) and dark septate fungi (DSF) colonisation on cadmium (Cd) accumulation in Arrhenatherum elatius from heavy metal-contaminated sites. AM colonisation disappeared when Cd concentrations in soil increased, while DSF infection was weak but constant throughout the experiment indicating that soil heavy metals are toxic to AM but not to DSF. AM colonisation was greatest when plant Cd concentrations were highest providing evidence that AM colonisation may influence Cd accumulation. In addition, the disappearance of AM and the concomitant reduction of Cd in shoots during seed maturation result in our suggestion that seasonal variation in AM may play a role in protecting developing seeds from soil pollution.     

Comparison of arbuscular mycorrhizal and dark septate endophyte fungal associations in soils irrigated with pulp and paper mill effluent and well-water

We compared arbuscular mycorrhizal (AM) and dark septate endophyte (DSE) fungal associations in 2 crops and 31 weeds commonly occurring in pulp and paper mill effluent irrigated and well-water irrigated soils. Soil pH, organic C, N, P and K, were higher in pulp and paper mill effluent irrigated than in well-water irrigated soils. In contrast, the average AM fungal colonization, root length with AM fungal hyphae/hyphal coils, spore numbers and diversity were lower in pulp and paper mill effluent irrigated soils compared to well-water irrigated soils. However, no significant variation was found in DSE fungal colonization nor root length with AM fungal arbuscules/arbusculate coils and vesicles between pulp and paper mill effluent irrigated and well-water irrigated soils. A significant negative correlation existed between AM and DSE fungal colonization in both effluent and well-water irrigated soils. Twelve AM fungal spore morphotypes belonging to Acaulospora, Dentiscutata, Glomus, Racocetra and Scutellospora were isolated from the well-water irrigated soils, whereas spores of six morphotypes were isolated from effluent irrigated soils. AM fungal spore numbers were correlated significantly and positively to AM fungal colonization in effluent and well-water irrigated soils.     

Occurrence of dark septate endophytes in Phragmites australis in the Baiyang Lake and their resistance to Cd stress

Heavy metal pollution poses a serious hazard to human health, and microbial remediation of heavy metals in soil has been widely studied. A group of ascomycetes classified as dark septate endophytes (DSEs) colonize plant roots and benefit host plants under abiotic stress conditions. In this study, Phragmites australis, a common remediation plant in the Baiyang Lake in North China, was investigated. Soils and roots of P. australis were collected in typical heavy metal-contaminated sites, and the species diversity and community structure of DSEs in P. australis roots were studied. In addition, DSE strains were isolated, cultured, and tested for their tolerance to Cd stress. The results showed that DSEs occurred extensively in P. australis roots, forming typical dark septate hyphae, with a total colonization rate of 19.7%-83.1%. Morphological and internal transcribed spacer sequencing analyses were used to identify 10 species within 9 genera of DSE fungi. Among these fungi, 6 strains with considerable resistance to Cd stress were identified. The biomasses of Poaceascoma helicoides, Alternaria doliconidium, and Acrocalymma vagum strains increased as the Cd levels increased. These results can not only help to understand plant-DSE interactions in wetland environments, but also provide a theoretical basis for making full use of DSE fungi to alleviate heavy metal contamination in soil.     

Patterns of endorhizal fungal associations in fruit crops of southern India

A survey on the endorhizal status of 39 fruit crops of 25 families, indicated that 22 fruit crops had arbuscular mycorrhizal (AM)–, four had dark septate endophyte (DSE)–fungal association, and 13 had dual colonization of AM and DSE fungi. Fruit crops were capable of forming Arum‐, Paris‐, or intermediate‐types of AM morphologies of which intermediate‐type was common. To our knowledge, we report for the first time AM in 10 fruit crops and DSE‐fungal association in 17 fruit crops. The extent of AM‐ and DSE‐fungal colonization ranged from 41% to 98% and < 1% to 89.9%, respectively, in different fruit crops. Arbuscular mycorrhizal–fungal spore numbers in the rhizosphere ranged from 6 to 61 spores per 25 g of soil. Arbuscular mycorrhizal–fungal spores belonging to Acaulospora, Glomus, and Scutellospora were isolated from the rhizosphere soil.     

Diversity of halophytes and identification of arbuscular mycorrhizal fungi colonising their roots in an abandoned and sustained part of Sečovlje salterns

Sečovlje salterns are an important protected area of biotic diversity in the Mediterranean. They represent an extreme environment with high salinity and drought that severely influence the growth of organisms. In the present study, diversity of plant halophytes and their mycorrhizal status were screened at eight different locations, which were mostly dikes and salt ponds, and which were deliberately selected for their distinct properties (e.g. soil salinity ranging from 105 to 2627 μS cm⁻¹, vegetation type and management practice of the salterns).Twelve different halophytic plant species were recorded, of which eleven are designated as vulnerable. With few exceptions, they were found at the abandoned (Fontanigge) and sustained (Lera) locations of the Sečovlje salterns, distributed according to their tolerance to the salinity and waterlogging. The highest diversity of halophytes was listed at Fontanigge, in the abandoned, periodically flooded and gradually overgrown salt ponds. All of the examined species were colonised with either arbuscular mycorrhizal fungi (AMF) and/or dark septate endophytes (DSEs). High levels of colonisation were however detected only for species belonging to the Asteraceae and Plantaginaceae families. Higher root colonisation frequencies were generally seen for plants growing in the abandoned parts, when compared to the managed parts, whereas there was little correlation of the colonisation parameters with physicochemical parameters of rhizospheric soil properties.Molecular analysis by temporal temperature gradient gel electrophoresis (TTGE) of roots of halophytic plant species with confirmed AMF colonisation (arbuscules present) revealed the occurrence of at least six different AMF species, related to Glomus geosporum, Glomus caledonium and Glomus intraradices, and to different Glomus sp. clades and the Diversispora clade. This is to the best of our knowledge the first report of AMF and DSE mycorrhizal status of most of the halophyte plant species examined and of the brother scale identification of AMF species based on molecular analyses of roots of diverse halophytes from high saline environments.     

Diversity and seasonal variations of mycorrhiza and rhizosphere bacteria in three common plant species at the Slovenian Ljubljana Marsh

Interactions between plants and microorganisms can significantly affect plant health and productivity as well as ecosystem functioning. Detailed knowledge of the tripartite relationships between plants, fungi, and bacteria, and their environment is still limited. In the present study, the soils adjacent to three plant species (Cruciata laevipes, Mentha piperita, Equisetum arvense) in the Ljubljana Marsh and the bulk, plant-free soil were analyzed for their bacterial community structure in June and October 2006. The terminal restriction fragment length polymorphism analysis indicated a different bacterial community structure in the rhizosphere and in bulk soil, however, with almost no seasonal changes between late spring and autumn samples and no apparent impact of the three plant species. In addition, root colonization of the three plant species by arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) was microscopically assessed monthly from May until October 2006. A presumably accidental correlation between monthly precipitation and the degree of arbuscule formation, with the latter lagging 1 month, was noted for M. piperita, the most heavily colonized of the three plant species. With all three plants, the phosphorus content in roots correlated positively with most AMF structures. Microsclerotia of DSE were mainly abundant in autumn samples. Fungal diversity in roots was estimated using temporal temperature gradient gel electrophoresis separation of the fungal polymerase chain reaction products obtained for both 18S-rDNA and the 5.8S-ITS2-28S rDNA segments. No specific effects of either plant species or seasonal changes on mycorrhizal community structure were discernible.     

Root Exudation of Organic Acids of Herbaceous Pioneer Plants and Their Growth in Sterile and Non-Sterile Nutrient-Poor, Sandy Soils from Post-Mining Sites

Nutrient-poor, sandy soils form the prevailing substrate at post-mining sites of the Lusatian region(Brandenburg, Germany) and present a challenge for vegetation development. We studied the organic acid quantity and composition of three commonly occurring pioneer plant species, the legumes Lotus corniculatus L. and Trifolium arvense L. and the grass Calamagrostis epigeios(L.) Roth, to determine if plant growth and exudation differed with(non-sterilized soil) and without(sterilized soil) an indigenous soil microbial community. We investigated whether organic acids were found in the rhizosphere and surrounding soil and whether this influenced nutrient mobilization. This study consists of linked field investigations and a greenhouse experiment. Plants were grown in the greenhouse in either sterilized or non-sterilized sandy soil from a reclamation site in the Lusatian mining landscape(Welzow Su¨d, East Germany). After seven months, the plant biomass, root morphology, organic acids, and water-soluble nutrients and root colonization with arbuscular mycorrhizal fungi(AMF) and dark septate endophytes(DSE) were analyzed. Roots of all three plants in the field and greenhouse experiments were highly colonized with AMF. Calamagrostis epigeios and T. arvense had a significantly higher colonization frequency with DSE than L. corniculatus. The quantity and composition of organic acids strongly differed among plant species, with the highest number of organic acids found for L. corniculatus and lowest for C. epigeios. The quantity of organic acids was greatly reduced in all plants under sterilized soil conditions. However, the composition of organic acids and plant growth in sterilized soil were reduced for both legumes, but not for C. epigeios, which had a higher biomass under sterilized conditions. Changes in nutrient concentrations in the field rhizosphere soil relative to those in the control were measurable after seven months. While the spectrum of organic acids and the growth of legumes seemed to be dependent on a highly diverse soil microbial community and a symbiotic partner, the grass C. epigeios appeared capable of mobilizing enough nutrients without an indigenous microbial community, and might be more competitive on sites where soil microbial diversity and activity are low.     

Ergosterol content in ericaceous hair roots correlates with dark septate endophytes but not with ericoid mycorrhizal colonization

The relationship between ergosterol content in ericaceous hair roots and ericoid mycorrhizal (ErM) colonization versus dark septate endophytic (DSE) hyphal colonization was examined in a dwarf shrub-dominated subarctic mire in Northern Sweden. Ergosterol content in hair roots did not correlate with ErM colonization in corresponding root samples. However, a significant positive relationship was found between hair root DSE hyphal colonization and ergosterol content. This is the first study to demonstrate that ergosterol cannot be used as a colonization indicator for ErM in hair roots growing under natural conditions. It also suggests the possibility of using ergosterol as an estimate of DSE hyphal colonization in ericaceous dwarf shrubs. This study has implications for the interpretation of results in field studies where ergosterol was used as a sole proxy for ErM colonization.     

Agricultural management affects communities of culturable root-endophytic fungi in temperate grasslands

Three grassland sites of similar physical characteristics but differing management histories were chosen to test the hypothesis that agricultural disturbance has a deleterious effect on the diversity of culturable root-endophytic fungi and favours potentially pathogenic species. Species abundance data were collected for fungi isolated from surface sterilised root samples. Brillouin index of diversity, Twinspan and detrended correspondence analysis were applied to the community data. Quantitative ordination separated the samples by site showing that the communities differed in fields of contrasting management and this was supported by data from a microcosm experiment. Species presence and absence appeared to be affected seasonally; site differences were manifested in relative abundance. Diversity did not appear to vary by site, but a methodological explanation for this is proposed. Sterile dark septate endophytes were shown to be among the most abundant groups at all sites.     

Ectomycorrhizal fungi and dark septate endophyte inoculation improve growth and tolerance of Pinus tabulaeformis under cadmium stress

Forest trees can establish symbiotic associations with dark septate endophytes (DSEs) and ectomycorrhizal fungi (ECMF) simultaneously. However, the combined effects of these two fungi on the growth and cadmium (Cd) tolerance of host plants remain largely unexplored. To address this knowledge gap, a pot experiment was conducted to examine the effects of the interaction between an ECMF strain (Suillus granulatus) and a DSE strain (Pseudopyrenochaeta sp.) on Pinus tabulaeformis under Cd stress, by assessing plant growth and physiological parameters, nutrient uptake, and soil properties. Notably, the colonization rates of both fungal strains were found to increase in response to Cd stress, with the extent of this increase being influenced by the specific fungal species and the Cd level in the soil. Compared to the non-inoculation treatment, single inoculation with fungal strain resulted in enhanced biomass, root development, and nutrient contents in P. tabulaeformis seedlings under Cd stress. Furthermore, a synergistic effect was observed when these seedlings were co-inoculated with S. granulatus and Pseudopyrenochaeta sp., as indicated by significantly greater measurements in various indicators compared to both the single and non-inoculation treatments. Fungal inoculation effectively regulated the antioxidant defense responses and photosynthesis of P. tabulaeformis seedlings subjected to Cd stress, particularly in the co-inoculation treatment. In addition, fungal inoculation facilitated the Cd accumulation in P. tabulaeformis, suggesting a promising potential for the implementation of bioremediation strategies in the areas contaminated with heavy metals. The findings from this study indicate that the utilization of root symbiotic fungi obtained from stress environments could potentially enhance the growth performance and tolerance of P. tabulaeformis towards heavy metals, and co-inoculation of both fungal groups may result in even more pronounced synergistic effects on the overall fitness of the plant.     

Colonisation of seminal roots of wheat and barley by egg-parasitic nematophagous fungi and their effects on Gaeumannomyces graminis var. tritici and development of root-rot

This study provides evidence that egg-parasitic nematophagous fungi, Pochonia chlamydosporia, Pochonia rubescens and Lecanicillium lecanii, can also reduce root colonisation and root damage by a fungal pathogen. Interactions of nematophagous fungi with the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt), and their influence on severity of the root disease it causes were studied in laboratory and pot experiments. In Petri dish experiments the three nematophagous fungi reduced colonisation of barley roots by Ggt and also reduced necrotic symptoms. On the contrary, root colonisation by nematophagous fungi was unaffected by Ggt. In growth tube experiments, the three nematophagous fungi again reduced Ggt root colonisation and increased effective root length of barley seedlings. This was true for both simultaneous and sequential inoculation of nematophagous fungi versus Ggt. In the pot experiments the inoculum of the tested fungi in soil was applied in the same pot, as a mixture or in layers, or in coupled pots used for wheat grown with a split-root system. The nematophagous fungi P. chlamydosporia (isolate 4624) and L. lecanii (isolate 4629), mixed with Ggt or in split root systems with the pathogen, promoted growth of wheat (i.e. increased shoot weight), although no disease reduction was found. In split root systems, lower levels of peroxidase activity were found in seedlings inoculated with Ggt in combination with the nematophagous isolates 4624 and 4629 than when the take-all fungus was applied alone.Our results show that nematophagous fungi reduce root colonisation by Ggt, root damage and stress induced senescence in Ggt-inoculated plants.     

Organic acid exudation by mycorrhizal Andropogon virginicus L. (broomsedge) roots in response to aluminum

Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments.     

Effects of arbuscular mycorrhizal inoculation on cadmium accumulation by different tobacco (Nicotiana tabacum L.) types

The effect of arbuscular mycorrhiza (AM) on cadmium (Cd) uptake by tobacco (Nicotiana tabacum L.) was studied in a pot experiment. Three commercial varieties, Basma BEK, K326 and TN90, representing three distinct tobacco types, were each grown in a different soil with nutritional conditions matching as closely as possible their requirements for field production. Cd concentrations in these soils were within the background range. Each variety was either non-mycorrhizal or inoculated with one of five AM fungal isolates. Cd concentration in leaves was decreased by inoculation with selected isolates in the K326 and TN90 variety grown in acidic soils. In contrast, it was increased by inoculation with most isolates in the Basma BEK variety grown in a basic soil with low Cd availability. Besides, plants of all three varieties had significantly higher leaf concentrations of phosphorus and nitrogen in some inoculated treatments. The percentage of root colonisation was mostly low in the inoculated treatments. In the Basma BEK and TN90 variety, the tested AM fungal isolates differed in their ability to colonise roots, but no correlation was found between the root colonisation of an isolate and its effects on the Cd concentrations in tobacco leaves. One isolate influenced most pronouncedly Cd concentrations and improved mineral nutrition in all the three combinations of variety and soil despite its low colonisation levels. AM symbiosis probably affected Cd uptake of tobacco by indirect mechanisms such as stimulation of root growth or mycorrhizal plant mediated changes in chemical or biological soil properties.     

Effects of avocado (Persea americana Mill.) scion on arbuscular mycorrhizal and root hair development in rootstock

Grafting is an important process to propagate horticulture plants; however, the mechanism through which the scion affects the absorption of rootstock remains poorly understood. The effects of the scion on AM fungi types in the rhizosphere soil of rootstock and the absorption of mycorrhizal root were determined in this study. Composition of arbuscular mycorrhizal (AM) fungi, soil assessment, spore density, hyphal length density, glomalin-related soil protein (GRSP) content in rhizosphere soil, root hair morphology and AM colonisation rate were measured among ‘Kampong’ avocado rootstocks grafted with five scions and ‘Kampong’ seedling trees. Results showed the main types of AM fungi in avocado seedling trees and trees grafted with five scions were nearly identical. However, the proportion of main genera exhibited differences. In addition, alkali-hydrolysable N, alkali-hydrolysable P and available K in rhizosphere soil, root hair density, AM colonization, spore density, hyphal length and GRSP content suggested the absorption of ‘Kampong’ rootstocks grafted with ‘Monroe’, ‘Wilson seedless’, ‘Hass’ and ‘Tonnage’ possessed stronger absorption than ‘Kampong’ seedling trees because of high AM colonisation and root hair density. This study suggested scions regulated both the AM and root hair development systematically and laid the foundation for future research of AM-enhancing avocado production.     

Effects of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal fungus (Glomus intraradices) on enzyme activities of a sterilized soil–sand mixture and nutrient uptake by maize

A pot experiment was conducted to investigate the effect of epigeic earthworm (Eisenia fetida) and arbuscular mycorrhizal (AM) fungi (Glomus intraradices) on soil enzyme activities and nutrient uptake by maize, which was grown on a mixture of sterilized soil and sand. Maize plants were grown in pots inoculated or not inoculated with AMF, treated or not treated with earthworms. Wheat straw was added as a feed source for earthworms. Mycorrhizal colonization of maize was markedly increased in AM fungi inoculated pots and further increased by addition of epigeic earthworms. AM fungi and epigeic earthworms increased maize shoot and root biomass, respectively. Soil acid phosphatase activity was increased by both earthworms and mycorrhiza, while urease and cellulase activities were only affected by earthworms. Inoculation with AM fungi significantly (p?<?0.001) increased the activity of soil acid phosphatase but decreased soil available phosphorus (P) and potassium (K) concentrations at harvest. Addition of earthworms alone significantly (p?<?0.05) increased soil ammonium-N content, but decreased soil available P and K contents. AM fungi increased maize shoot weight and root P content, while earthworms improved N, P, and K contents in shoots. AM fungi and earthworm interactively increased maize shoot and root biomass through their regulation of soil enzyme activities and on the content of available soil N, P, and K.     

Change in soil properties and the soil microbial community following land spreading of olive mill wastewater affects olive trees key physiological parameters and the abundance of arbuscular mycorrhizal fungi

Olive mill wastewater (OMW) constitutes a major environmental problem for Mediterranean countries, where most of the world olive oil production takes place. The recycling of the OMW and its use as water for irrigation in agriculture, provided that its impact on soil and plant is established, is an attractive possibility for the Mediterranean countries. Investigations were performed on the influence of agronomic application of OMW (amount applied: 30, 60, 100 and 150 m³ ha^?1) in a field of olive trees on trees characters (photosynthesis, root-soluble carbohydrate and root colonisation), soil properties, and soil microbial community structure. Specific attention was paid to arbuscular mycorrhizal (AM) fungi. The soil fatty acid methyl ester (FAME) 16:1ω5 was used to quantify biomass of AM fungi and the root FAME 16:1ω5 analysis was used as index for the development of colonisation in the olive trees roots. A significant increase in organic C, C/N ratio, extractable phosphorus and exchangeable potassium was found after one year of agronomic application of OMW. The development of saprophytic fungi was significantly higher in the OMW amended soils, whereas the abundance of the soil FAME 16:1ω5, root FAME 16:1ω5, photosynthetic rates and the amount of the total root-soluble carbohydrate were decreased significantly after agronomic application of OMW. A principal component analysis (PCA) of the trees characteristics profiles showed discrimination between the nonirrigated and the OMW irrigated olive trees. These findings suggest that the altering functioning of arbuscular mycorrhizas should be considered as potential factors mediating olive trees responses to agronomic application of OMW when the OMW dose applied is higher than 30 m³ ha^?1. To our knowledge, this is the first report of alterations in the soil FAME 16:1ω5 and root FAME 16:1ω5 due to land spreading of OMW.     

Humus-Rich Compost Increases Lettuce Growth, Nutrient Uptake, Mycorrhizal Colonisation, and Soil Fertility

Sandy soils, typical of Australia's west, either have little or no habitat protection for microbes including arbuscular mycorrhizal (AM) fungi, which are essential for nutrient cycling. To minimize this problem, the application of organic matter, such as humus-rich composts, is necessary during vegetable crop production. This study aimed at determining the effects of humus-rich composts on either indigenous or inoculated AM fungal colonisation in roots, lettuce (Lactuca sativa L. var. Quechua) growth, and soil fertility improvement. Four different humus-rich composts with varying humus contents were applied at the same standard rate to lettuce grown under glasshouse conditions for 10 weeks after sowing and compared with two low-humus composts and non-amended soil (control). Humus-rich composts significantly increased lettuce shoot growth, root growth, and AM fungal colonisation in roots. Humus contents in the composts were also correlated with lettuce shoot and root growth. Soil dissolved organic carbon, microbial biomass carbon, and fertility were increased with the application of humus-rich composts. These humus-rich composts, especially the compost of higher humic acid with and without AM inoculation, might have a significant role in sustainable vegetable production, for example lettuce growth. Overall, the results indicate that supplementation with humus-rich compost is highly beneficial to enhance soil fertility and potentially maintain the sustainability of vegetable production.     

Exudates of dark septate endophyte (DSE) modulate the development of the arbuscular mycorrhizal fungus (AMF) Gigaspora rosea

Exudates of a dark septate endophyte (DSE) identified as Dreschlera sp., a common endophyte isolated by the inner cortical cells of the grass Lolium multiflorum, were put in contact with the arbuscular mycorrhizal fungus (AMF) Gigaspora rosea. These exudates stimulated the hyphal length and the hyphal branching of the AMF. A negative effect on the extramatrical phase of the AMF was detected. This is the first report to show how exudates of DSE can affect the development of AMF. These results show that DSE could be modifying the mycorrhizal status of the plants, modulating a different symbiosis in the rhizosphere.