Arbuscular Mycorrhizal Symbionts Research Articles

Effects of the synergistic treatments of arbuscular mycorrhizal fungi and trehalose on adaptability to salt stress in tomato seedlings.

AMF improve the plant adaptability to salt resistance by increasing mineral absorption and reducing the damage of saline soil. Trehalose plays an important role in plant response to salt damage by regulating osmotic pressure. Together, the use of AMF and trehalose in tomato seedlings proved efficient in regulating host substance synthesis, osmosis, and antioxidant enzymes. These synergistic effects significantly improved seedling adaptability to salt stress by enhancing cell osmotic protection and cell antioxidant capacity, ultimately reducing losses to crops grown on land where salinization has occurred.

Mycorrhiza Diversity in Some Intercropping Systems of Potato (Solanum tuberosum L) and Faba Bean (Vicia faba L)

Arbuscular mycorrhizal fungi (AMF) is the most widely distributed mycorrhizal fungi in the soil and can make a symbiosis with the roots of host plants to form arbuscular mycorrhizal symbionts. Intercropping is a practice of polyculture cropping where two or more plant species are simultaneously cultivated in the same field. The objective of this study was to define the effect of intercropping on the density and diversity of mycorrhizal spores. In this study, potatoes and faba beans, both of which have the ability to symbiosis with mycorrhizae, were intercropped. A randomized group design with 5 planting system treatments was employed in this study with 5 replications. The results concluded that density of mycorrhizal spores in the intercropping planting pattern was not statistically different from the density of mycorrhiza in the monoculture cultivation pattern. The types of mycorrhiza found included the genus of Glomus, Funneliformis, Scutellospora, Cetraspora, Septoglomus, and Entrophospora Keywords: pH; Root exudate; Spore density, Spore identification; Spore diversity.

The Perspective of Arbuscular Mycorrhizal Symbiosis in Rice Domestication and Breeding.

In nature, symbiosis with arbuscular mycorrhizal (AM) fungi contributes to sustainable acquisition of phosphorus and other elements in over 80% of plant species; improving interactions with AM symbionts may mitigate some of the environmental problems associated with fertilizer application in grain crops such as rice. Recent developments of high-throughput genome sequencing projects of thousands of rice cultivars and the discovery of the molecular mechanisms underlying AM symbiosis suggest that interactions with AM fungi might have been an overlooked critical trait in rice domestication and breeding. In this review, we discuss genetic variation in the ability of rice to form AM symbioses and how this might have affected rice domestication. Finally, we discuss potential applications of AM symbiosis in rice breeding for more sustainable agriculture.

Zinc and Iron Biofortification and Accumulation of Health-Promoting Compounds in Mycorrhizal Cichorium intybus L.

The positive impact of arbuscular mycorrhizal symbionts on plant growth and health has been reported for many species, and supports their use as biofertilizers and bioenhancers. Here, the potential role of the arbuscular mycorrhizal symbiont Funneliformis mosseae in the improvement of chicory (Cichorium intybus L.) nutritional value, in terms of nutrient uptake and accumulation of health-promoting compounds, was studied using an in vivo whole-plant system, allowing both plant and fungal tissue collection. Biomass and nutrient distribution were determined in plant and extraradical mycelium, and photosynthetic pigments and fructooligosaccharide concentrations were evaluated in chicory shoots and roots. Zinc shoot concentration of mycorrhizal chicory was significantly increased, as well as the whole-plant Fe uptake, while root Cu concentration was decreased, compared with uninoculated controls. F. mosseae extraradical mycelium accumulated Cu, Zn, Mn, and Fe at high concentrations, compared with those of the host plant tissues, suggesting that it plays a double functional “scavenging-filtering” role, by its ability to balance the uptake of microelements or to limit their translocation depending on plant-soil concentrations. The higher Zn and Fe uptake by mycorrhizal plants was significantly correlated with higher carotenoid, inulin, and fructose levels, suggesting a relationship among the modulation of micronutrient uptake by mycorrhizal symbionts and the biosynthesis of health-promoting molecules by the host. Overall, data from this work may boost the implementation of arbuscular mycorrhizal fungal inoculation aimed at inducing plant biofortification and enhancement of nutritional value of plant-derived food.

Physiological and transcriptomic response of Medicago truncatula to colonization by high- or low-benefit arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal (AM) fungi form a root endosymbiosis with many agronomically important crop species. They enhance the ability of their host to obtain nutrients from the soil and increase the tolerance to biotic and abiotic stressors. However, AM fungal species can differ in the benefits they provide to their host plants. Here, we examined the putative molecular mechanisms involved in the regulation of the physiological response of Medicago truncatula to colonization by Rhizophagus irregularis or Glomus aggregatum, which have previously been characterized as high- and low-benefit AM fungal species, respectively. Colonization with R. irregularis led to greater growth and nutrient uptake than colonization with G. aggregatum. These benefits were linked to an elevated expression in the roots of strigolactone biosynthesis genes (NSP1, NSP2, CCD7, and MAX1a), mycorrhiza-induced phosphate (PT8), ammonium (AMT2;3), and nitrate (NPF4.12) transporters and the putative ammonium transporter NIP1;5. R. irregularis also stimulated the expression of photosynthesis-related genes in the shoot and the upregulation of the sugar transporters SWEET1.2, SWEET3.3, and SWEET 12 and the lipid biosynthesis gene RAM2 in the roots. In contrast, G. aggregatum induced the expression of biotic stress defense response genes in the shoots, and several genes associated with abiotic stress in the roots. This suggests that either the host perceives colonization by G. aggregatum as pathogen attack or that G. aggregatum can prime host defense responses. Our findings highlight molecular mechanisms that host plants may use to regulate their association with high- and low-benefit arbuscular mycorrhizal symbionts.

Unraveling the Interaction between Arbuscular Mycorrhizal Fungi and Camellia Plants

Camellia is a genus of evergreen shrubs or trees, such as C. japonica, C. sinensis, C. oleifera, etc. A group of beneficial soil microorganisms, arbuscular mycorrhizal fungi (AMF), inhabit the rhizosphere of these Camellia spp. A total of eight genera of Acaulospora, Entrophospora, Funneliformis, Gigaspora, Glomus, Pacispora, Scutellospora, and Sclerocystis were found to be associated with Camellia plants with Glomus and/or Acaulospora being most abundant. These mycorrhizal fungi can colonize the roots of Camellia spp. and thus form arbuscular mycorrhizal symbionts. AMF is an important partner of Camellia spp. in the field of physiological activities. Studies indicated that AMF inoculation has been shown to promote plant growth, improve nutrient acquisition and nutritional quality, and increase resistance to drought, salinity and heavy metal contamination in potted Camellia. This review thus provides a comprehensive overview of AMF species occurring in the rhizosphere of Camellia spp. and summarizes the variation in root AMF colonization rate as well as the environmental factors and soil nutrients affecting root colonization. The paper also reviews the effects of AMF on plant growth response, nutrient acquisition, food quality, and stress tolerance of Camellia spp.

Arsenic transformation and volatilization by arbuscular mycorrhizal symbiosis under axenic conditions

It is well known that arbuscular mycorrhizal (AM) fungi can enhance plant arsenic (As) resistance by influencing As uptake, translocation, and speciation; however, As transformation and volatilization by an entire plant inoculated with AM fungus remains uninvestigated. In the present study, AM symbiosis of Rhizophagus irregularis with unbroken Medicago sativa was successfully established in vitro. Afterwards, five concentrations of arsenate were applied to the culture media. The results showed that AM inoculation could methylate inorganic As into dimethylarsinic acid (DMA), dimethylarsine (DMAsH), and trimethylarsine (TMAs), which were detected in the plants, media, or air. Volatile As, accounting for a small proportion of total organic As, appeared under high arsenate exposure, accompanied by remarkable upregulation of root RiMT-11, an arsenite methyltransferase gene in R. irregularis. In addition, AM colonization significantly increased arsenite percentages in plant tissues and external media. Regardless of As species, AM inoculation tended to release the transformed As into the environment rather than transfer them to plant tissues. Our present study, for the first time, comprehensively verified As methylation, volatilization, and reduction by AM fungus associated with the entire plant under absolute axenic conditions and gained a deeper insight into As metabolism in AM symbionts.

Direct evidence for modulation of photosynthesis by an arbuscular mycorrhiza-induced carbon sink strength.

It has been suggested that plant carbon (C) use by symbiotic arbuscular mycorrhizal fungi (AMF) may be compensated by higher photosynthetic rates because fungal metabolism creates a strong C sink that prevents photosynthate accumulation and downregulation of photosynthesis. This mechanism remains largely unexplored and lacks experimental evidence. We report here two experiments showing that the experimental manipulation of the mycorrhizal C sink significantly affected the photosynthetic rates of cucumber host plants. We expected that a sudden reduction in sink strength would cause a significant reduction in photosynthetic rates, at least temporarily. Excision of part of the extraradical mycorrhizal mycelium from roots, and causing no disturbance to the plant, induced a sustained (10-40%) decline in photosynthetic rates that lasted from 30min to several hours in plants that were well-nourished and hydrated, and in the absence of growth or photosynthesis promotion by mycorrhizal inoculation. This effect was though minor in plants growing at high (700ppm) atmospheric CO2 . This is the first direct experimental evidence for the C sink strength effects exerted by arbuscular mycorrhizal symbionts on plant photosynthesis. It encourages further experimentation on mycorrhizal source-sink relations, and may have strong implications in large-scale assessments and modelling of plant photosynthesis.

Saffron Cultivation in Marginal Alpine Environments: How AMF Inoculation Modulates Yield and Bioactive Compounds

Arbuscular mycorrhizal fungi (AMF) establish mutualistic symbiotic associations with plant roots and act as biofertilizers by enhancing plant nutrient and water uptake. Moreover, AMF colonization may influence the biosynthesis of plant bioactive compounds in medicinal and aromatic plants. There is limited information on AMF associations with Crocus sativus L. (saffron) roots and their effect on crop performances and spice quality. In the present work we verified the efficiency of root mycorrhization in potted conditions, and then we evaluated the yield and quality of the saffron produced in two Alpine sites during two cultivation cycles with the application of AMF. Two inocula were applied, either a single-species (Rhizophagus intraradices) or a multispecies mixture (R. intraradices and Funneliformis mosseae). The trial conducted in potted conditions confirmed that both AMF commercial inocula established symbiotic relationships with saffron roots. The multispecies inoculation yielded the highest content of arbuscules in colonized portions of the root (100%), while the single-species was slightly less (82.9%) and no AMF were recorded in untreated control corms. In open-field conditions, AMF colonization of the root systems, flower production, and saffron yields were monitored, and bioactive compounds contents and antioxidant activity in the dried spice were analyzed using spectrophotometry and high performance liquid chromatography. Overall, the saffron produced was high quality (ISO category) and had high contents of bioactive compounds, with very high total polyphenol content and elevated antioxidant activity. The use of arbuscular mycorrhizal symbionts as biostimulants positively affected saffron cultivation, improving the crop performances and the content of important nutraceutical compounds. In particular, the inoculum composed by R. intraradices and F. mosseae increased flower production and the saffron yield. R. intraradices alone enhanced the spice antioxidant activity and the content of bioactive compounds such as picrocrocin, crocin II, and quercitrin. Since saffron is the world’s highest priced spice, the increases in yield and quality obtained using AMF suggests that farms in marginal areas such as alpine sites can increase profitability by inoculating saffron fields with arbuscular mycorrhiza.

The Response Patterns of Arbuscular Mycorrhizal and Ectomycorrhizal Symbionts Under Elevated CO2: A Meta-Analysis.

Elevated carbon dioxide (eCO2), a much-discussed topic in global warming, influences development and functions of mycorrhizal fungi and plants. However, due to the inconsistent results reported in various publications, the response patterns of symbionts associated with the arbuscular mycorrhizal (AM) or with ectomycorrhizal (ECM) fungi to eCO2 remains still unclear. Therefore, we performed a meta-analysis to identify how eCO2 affected mycorrhizal fungi and if there is a significant different response between AM and ECM symbionts. Our results demonstrated that eCO2 increased mycorrhizal plants biomass (+26.20%), nutrient contents [+2.45% in nitrogen (N), and +10.66% in phosphorus (P)] and mycorrhizal fungal growth (+22.87% in extraradical hyphal length and +21.77% in mycorrhizal fungal biomass), whereas plant nutrient concentrations decreased (−11.86% in N and −12.01% in P) because the increase in plant biomass was greater than that in nutrient content. The AM plants exhibited larger increases in their biomass (+33.90%) and in their N (+21.99%) and P contents (+19.48%) than did the ECM plants (+20.57% in biomass, −4.28% in N content and −13.35% in P content). However, ECM fungi demonstrated increased responses of mycorrhizal fungal biomass (+29.98%) under eCO2 compared with AM fungi (+6.61%). These data indicate different patterns in the growth of AM and ECM symbionts under eCO2: AM symbionts contributed more to plant growth, while ECM symbionts were more favorable to mycorrhizal fungal growth. In addition, the responses of plant biomass to eCO2 showed no significant difference between short-term and long-term groups, whereas a significant difference in the responses of mycorrhizal fungal growth was found between the two groups. The addition of N increased plant growth but decreased mycorrhizal fungal abundance, and P addition increased total plant biomass and extraradical hyphal length, but shoot biomass largely increased in low P conditions. Mixtures of mycorrhizal fungi affected the total plant and root biomasses more than a single mycorrhizal fungus. Clarifying the different patterns in AM and ECM symbionts under eCO2 would contribute to a better understanding of the interactions between mycorrhizal fungi and plant symbionts under the conditions of global climate change as well as of the coevolution of flora with Earth's environment.

Local diversity of native arbuscular mycorrhizal symbionts differentially affects growth and nutrition of three crop plant species

Intact whole native AMF communities occurring across a 100-m-long field were used for the evaluation of plant performance, as determined by the actual fungal species colonizing host roots. The soil from distinct plots within a “hot spot” field was collected to set up 54 experimental units where three different plant species were grown, in order to test whether the whole native AMF communities were able to differentially affect plant growth, to assess the genetic identity of the AMF actually colonizing the tested plants and to analyse their community composition in the different hosts. Molecular analyses revealed that plant growth and nutrition of the crop plants were differentially affected by the diverse native arbuscular mycorrhizal communities colonizing the roots of the three plants, whose performance varied depending on the identity of plant hosts and fungal symbionts, more than on a rich and diversified AMF community. Such results, improving our understanding of AMF distribution at the local scale, represent a starting point allowing the selection, isolation and characterization of the most efficient AMF assemblages to be used as inoculants in sustainable food production systems.

Responses of arbuscular mycorrhizal symbionts to contrasting environments: field evidence along a Tibetan elevation gradient.

Plant adaptation to alpine ecosystems is not fully explained by plant physiological and morphological traits. Arbuscular mycorrhizal (AM) associations may be involved in mediating plant performance in response to environmental differences. Little is known, however, as to whether or not a close relationship exists between plant performance and arbuscular mycorrhizal fungus status across environmental gradients. We conducted a field investigation of the performance of six plant species and their associated AM fungi along higher and lower elevation gradients on Mount Segrila in Tibet. In most of our species, we observed higher shoot and inflorescence biomass production and a lower root-to-shoot ratio in the populations at those sites where the species was dominant (intermediate elevation sites) than in populations sampled at the limits of the distribution. The elevation pattern of root colonization differed with plant species on both gradients, and the extraradical hypha development of most species showed a unimodal pattern as did plant growth. The relationship between plant and fungus traits shows that AM fungus development generally matched host plant performance on the lower elevation gradient but not on the higher elevation gradient. This study provides evidence that plant distribution and productivity were significantly related to root and soil colonization by AM fungi, especially under less physically stressful conditions.

丛枝菌根真菌参与下植物-土壤系统的养分交流及调控

丛枝菌根真菌参与下植物-土壤系统的养分交流及调控

Effects of soil tillage and planting grass on arbuscular mycorrhizal fungal propagules and soil properties in citrus orchards in southeast China

Arbuscular mycorrhizal (AM) fungi play important roles in plant nutrition and soil conservation. AM fungal activity and amount of glomalin (a glycoprotein derived from AM fungi) are influenced by a series of abiotic and biotic factors associated with changes in soil management. However, the informations concerning AM fungal activity, amount of glomalin-related soil protein (GRSP), and its relationship with soil fertility and enzyme activities are scarce in citrus orchards under different soil management systems. Accordingly, this paper reports the effects of tilling soil and planting grass on AM colonization; AM fungal propagules; the amount of GRSP and its relationship with soil chemicals including organic carbon, available nitrogen, Olsen phosphorus, and available potassium; the activity levels of soil enzymes like catalase, invertase, urease, and acid phosphatase in citrus (Citrus unshiu Marc. grafted on Poncirus trifoliata L. Raf.) orchards in southeast China. Measurements were conducted in the fifth year of an ongoing tillage and grass planting experiment on an Acrisol soil under one of three treatments: natural grass cover, sod culture with white clover, and clean tillage. Soils and roots were sampled in March, July, and November 2013, during the vigorous growth period of citrus trees. AM colonization, AM fungal propagules, and GRSP were significantly higher in both no-tillage and grass-planted orchards than in clean tillage orchards. Soil organic carbon, available nitrogen, and soil enzyme activities showed a similar trend. Principal component analysis revealed that tillage and grass planting dramatically affected soil conditions in citrus orchards. However, sod culture promoted citrus mycorrhizal colonization and available nitrogen in soil more effectively than did grass cover, whereas natural grass cover enhanced AM fungal propagules, soil organic carbon, and soil enzyme activities more effectively than did sod culture. Soil organic carbon, available nitrogen, and soil enzymes activities were significantly (P<0.05) correlated with AM fungal propagules or GRSP, suggesting that plentiful AM symbionts may help preserve soil quality, especially in grass-planted orchards.

AM真菌在植物病虫害生物防治中的作用机制

丛枝菌根(Arbuscular Mycorrhizae,AM)真菌是一类广泛分布于土壤生态系统中的有益微生物,能与大约80%的陆生高等植物形成共生体。由土传病原物侵染引起的土传病害被植物病理学界认定为最难防治的病害之一。研究表明,AM真菌能够拮抗由真菌、线虫、细菌等病原体引起的土传性植物病害,诱导宿主植物增强对病虫害的耐/抗病性。当前,利用AM真菌开展病虫害的生物防治已经引起生态学家和植物病理学家的广泛关注。基于此,围绕AM真菌在植物病虫害生物防治中的最新研究进展,从AM真菌改变植物根系形态结构、调节次生代谢产物的合成、改善植物根际微环境、与病原微生物直接竞争入侵位点和营养分配、诱导植株体内抗病防御体系的形成等角度,探究AM真菌在植物病虫害防治中的作用机理,以期为利用AM真菌开展植物病虫害的生物防治提供理论依据,并对本领域未来的发展方向和应用前景进行展望。;Arbuscular mycorrhizal (AM) fungi are one of the widely spread micro-organisms, which could form symbionts with more than 80% of the vascular plants in natural ecosystems. It has been showed that AM symbionts could improve plant nutrients and water absorption; increase the resistance ability to stress conditions, thus AM fungi could enhance the host plant growth. The plant soil-borne diseases caused by soil-borne pathogens, including fungi, nematodes and bacteria, are considered as one of the most difficult controlling diseases in agriculture ecosystem. Previous studies have been demonstrated that AM symbionts could increase plant resistance to diseases, and to antagonize soil-borne pathogens. Thus, using AM fungi as a biological control method to antagonize soil-borne pathogens has received increasing interests by phytopathologists and ecologists. On the basis of this, the mechanisms of resistance to diseases induced by AM fungi were summarized in this paper. Mechanisms covered in this review include root morphology alteration, regulation of secondary metabolite production, improvement of rhizosphere environments, competition with pathogenic microorganisms on invasive sites and on nutrition distribution in host plants, and formation of defense systems in plants. Firstly, the characteristics of root morphology alterations were explained, including how AM fungi influence their structures and functions. Secondly, the regulation of AM fungi to secondary metabolites was illustrated. Several types of products, including phytoalexin, callose, alkaloid and phenols were reviewed. Thirdly, AM fungi could improve the rhizosphere environments by influence soil physical and chemical proprieties, and enhance the growth of other beneficial microorganism in rhizosphere soil. Fourth, AM fungi could compete with pathogenic microorganisms. The two kinds of microorganisms maybe compete for the same invasive sites in root systems, and thus they could regulate the nutrition distribution. Fifth, AM fungi could induced the host plant to form the defense systems in plants, including improvement the concentrations of phytohormone, induced the production of signal substrates, regulation of genes expression and enhanced the proteins production, thus AM fungi could enhance the resistance ability of host plant to pathogenic microorganisms. The aim of this paper was to enhance the potential use of AM fungi as a biological control method for preventing plant diseases in future.

AM真菌对重金属污染土壤生物修复的应用与机理

土壤重金属污染威胁人类健康和整个生态系统,而高效、低耗、安全的生物修复技术显示出了极大的应用潜力,特别是利用植物-微生物共生体增强生物修复效应的应用。丛枝菌根(Arbuscular Mycorrhizae,AM)真菌是一类广泛分布于土壤生态系统中的有益微生物,能与90%以上的陆生高等植物形成共生体。研究发现,AM真菌能够增强宿主植物对土壤中重金属胁迫的耐受性。当前,利用AM真菌开展重金属污染土壤的生物修复已经引起环境学家和生态学家的广泛关注。基于此,围绕AM真菌在重金属污染土壤生物修复作用中的最新研究进展,从物理性防御体系的形成、对植物生理代谢的调控、生化拮抗物质的产生、基因表达的调控等角度探究AM真菌在重金属污染土壤生物修复中的作用机理,以期为利用AM真菌开展重金属污染的生物修复提供理论依据,并对本领域未来的发展和应用前景进行了展望。;Heavy-metal pollution in soil is a major threat to human health and the whole ecosystem, while bioremediation has become a promising option to recover the contaminated soils for its effective, non-intrusive and inexpensive. In particular, the application of symbiotic micro-organisms such as mycorrhizal fungi to enhance bioremediation efficiency has been paid more and more attention. Arbuscular mycorrhizal (AM) fungi are one of the widely spread micro-organisms, which could form symbionts with most of the vascular plants in natural or artificial ecosystem. It has demonstrated that AM symbionts could increase the stressed ability of host plants in heavy metal polluted soil. Nowadays, using bioremediation methods to recovery heavy metal polluted soils with AM fungi has been one of the hotspots in environmental and ecological science. In order to review the physiological and molecular mechanism of heavy metals tolerance induced by AM fungi, four strategies were discussed in this paper: 1) the physical defense system formation, 2) the regulation to physiological metabolism of plants, 3) the production of biochemical antagonist material and 4) the regulation of gene expression. On the basis of this, this paper indicated that the possibility of using the system of AM-soil microbiology-host plant for remediation of heavy metals polluted soil in the future. For this purpose, to enhance the studies below would be necessary: 1) molecular mechanisms that AM fungi regulate heavy metal uptake and translocation; 2) phytoremediation of polymetal-contaminated soils through selection of heavy metal tolerant AM fungi strains by genetic engineering; 3) the combination of other remediation techniques and AM-assisted bioremediation.

A model that explains diversity patterns of arbuscular mycorrhizas

Worldwide arbuscular mycorrhizal (AM) plants in grassland ecosystems associate with multiple AM symbionts; the literature suggests that the typical range varies from 7 to 11 AM symbionts. Using a model based on group selection, we examine the evolutionary traits that could be responsible for maintaining this situation. We assumed that from a pool of 160 potential symbionts some of them would deliver a profit for the plant while the others (“defectors”) would deliver comparable damage. The plant could control the number of simultaneous fungi it associated with but not their identities. Plants admitting higher numbers of symbionts can gain greater benefits but run a greater risk of associating with defectors. Based on simulation results we can demonstrate convergence toward an optimal number of fungal symbionts which occurs faster for plants that experience low survivorship and higher selection pressure. Additionally, for seedling survivorship rates close to those experienced in grassland biomes (i.e. around 50%) there appears to be a steady plateau with an optimum of 7 symbionts over a wide range of defection probabilities. This does not hold for other biomes with higher plant mortality such as woodlands in which there is an unsteady situation with highly likely modification of the number of simultaneous symbionts. This may hold important clues about to the origin of the ectomycorrhizal associations where only one symbiont is optimum.

Soil microbial and plant responses to the absence of plant cover and monoculturing in low arctic meadows

Arctic ecosystems are sensitive to disturbance yet there is little information on the fate and recovery of soil microbial communities after disturbance and persistence in the absence of plants. Neighbouring plants may facilitate seedling establishment through amelioration of the physical environment and maintenance of arbuscular fungal community in soil. The inoculum of arbuscular mycorrhizal symbionts is critical for the establishment of low-latitude arctic herbs that are obligately mycorrhizal. In the present work, we investigated plant–soil and plant–plant interactions in low arctic meadow habitat. Plant cover was experimentally removed and field plots were left without plant cover, or a monoculture of the common local herb, Solidago virgaurea, was planted on the plots or the plant cover was left intact. After two years, three herb species were sown on the plots and their growth, mycorrhizal colonization and soil microbial communities were measured. Relative fungal abundance decreased in the soil community in the treatments where the soil had been disturbed. Soil microbial community structure by functional group was maintained in the soil two years after no plant cover and microbial biomass per organic matter was not reduced. Mycorrhizal colonization potential was not impaired after two years of absence of host plants and thus it is concluded that symbiotic propagules are able to persist for two years in the absence of host plants. The Solidago monoculture did not facilitate seedling establishment nor change soil microbial community markedly in short-term. Overall, the low arctic soil microbial community was markedly resistant to disturbance.

Simulated mammal browsing and host gender effects on dual mycorrhizal Salix repens

We studied effects of simulated browsing and host plant gender on mycorrhizal status of dioecious Salix repens, forming both ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) symbioses. Owing to their lower biomass production, AM fungi may require less carbon from the host and have a competitive advantage over ECM fungi when carbon availability is reduced. Further, in dioecious plants, females have generally higher reproduction costs than males. Hence, herbivory may be especially detrimental to female plants and their ECM symbionts in favour of AM symbionts. Fifty percent shoot clipping increased the number of vegetative shoots but reduced the proportion of flowering shoots equally in male and female hosts. Despite clipping, ECM and AM colonization remained unchanged. However, slightly reduced soil fungal biomass was found in clipped patches of male S. repens. Our novel finding of AM spores occurring in the ECM fungal mantle of S. repens roots suggests that both mycorrhizal partners may coexist in the same root segment. Since no interaction between gender and clipping in fungal parameters was detected, we conclude that female and male S. repens are equally preferable hosts for fungal symbionts, even when carbohydrate availability has been decreased because of herbivory.

Interrelationships between mycorrhizal symbiosis, soil pH and plant sex modify the performance of Antennaria dioica

AM symbiosis is usually beneficial for plants, but the benefits gained may depend on the soil abiotic factors. In dioecious plants, female and male individuals have different resource demands and allocation patterns. As a consequence of these differences, it is logical to assume that female and male plants differ in their relationship with arbuscular mycorrhizal (AM) fungi, although this has rarely been examined. We used a factorial greenhouse experiment to investigate whether female and male plants in the dioecious model species Antennaria dioica have a different relationship with their AM symbionts under two soil pH levels. In particular, we asked: (1) Do the sexes in A. dioica have sex-specific benefits from AM symbiosis? (2) If so, which sex gains the highest benefit? (3) How does soil pH affect the sex – AM fungal relationship? Our results indicate that the sexes responded similarly to AM symbiosis and pH when mycorrhizal benefit was examined as growth and phosphorus accumulation. However, the sexes differed in response to AM symbiosis in terms of survival, as mortality was increased due to AM symbiosis in female plants whilst the opposite effect was detected in males. The plant–AM fungus relationship was significantly affected by soil pH as lowering the soil pH decreased the benefits gained by the plants from the mycorrhizal fungus. Taken together, our findings indicate that AM symbiosis is beneficial for plants depending on the life history trait considered. In addition, interactions between plants and their AM symbionts are modified by soil factors and the sex of the plant.