Arbuscular Mycorrhiza Colonization Research Articles

Native arbuscular mycorrhiza colonization in seedling root of dogfruit (Archidendron pauciflorum) planted as seed-ball in field

Arbuscular mycorrhiza (AM) is a mutualistic symbiosis between soil fungi and plants, including dogfruit (Archidendron pauciflorum). Archidendron pauciflorum is a local plant from Southeast Asia, including Indonesia that is used for food and animal forest feed. Planting A. pauciflorum seedlings on revegetation land with a sharp slope is difficult and dangerous to workers. Therefore, seed-ball planting technique is required for revegetation of post-mining sharp slope areas. This research aimed to study the ability of the native AM fungi to colonize A. pauciflorum seedlings grown as a seed-ball in the field for revegetation purposes. The seed-ball was made using three types of fungal inoculum sources, namely control without AM fungi, natural forest, and stockpile inoculum. All colonization structures, such as entry points, coils, arbuscules, and vesicles, were observed. All seedlings were colonized by AM fungi, with root colonization ranging from 2% to 16%. Stockpile inoculum had a higher AM colonization than the natural forest inoculum. Both sources of native AM fungi tended to improve the growth of the seedling. There were two types of AM spores found in all treatments, Glomus sp. 1 and Glomus sp. 2. Glomus sp. 2 is the dominant species of AM fungi in all treatments.

Cover crop identity determines root fungal community and arbuscular mycorrhiza colonization in following main crops

AbstractCover crops (CC) can promote nutrient retention and recycling for main crops yet may also promote soilborne pathogens or suppress beneficial root symbionts such as arbuscular mycorrhizal fungi (AMF). We investigated how root fungal communities of main crop are affected by preceding CC monocultures and mixtures and by main crop identity. We expected that AMF abundance and diversity in main crops are promoted by AM‐host CC, and suppressed by non‐AM‐host CC, and that mixtures of CC species can promote beneficial and suppress pathogenic root fungi. Our full‐factorial field experiment comprised crop rotation in sand soil with different CC treatments (monocultures of radish [AM non‐host], ryegrass, clover, vetch [AM hosts], mixtures of radish + vetch, ryegrass + clover and fallow) and two main crops (oat and endive). At peak crop growth, we investigated the root fungal communities in the main crops using microscopy and high throughput sequencing (Illumina MiSeq). Cover crop identity was of prime importance and CC legacy overruled main crop identity in determining root fungal communities in main crops. Compared with fallow, CC with ryegrass increased AMF colonization and richness in both main crops and of non‐AMF in oat. Legacies of ryegrass, ryegrass + clover and vetch resulted in distinct root fungal communities in the main crops, while the legacy of CC with radish were similar to the legacy of fallow. Root fungal community in crops after clover had highest abundance of representative fungal pathogens in contrast with the other CC treatments that resulted in fungal communities where pathogens were scarce. Oppositely to expected, CC mixtures did not enhance fungal symbionts or suppressed pathogens. Overall, fungal communities in roots of the main crops in our field experiment were determined by the preceding CC species in monoculture, rather than by the CC AMF preference or functional group. This research highlights that the choice of CC determines the root fungal community in main crop which may influence crop quality.

Effects of different fertilizer applications on citrus rhizosphere soil quality and arbuscular mycorrhizae colonization

To understand the effects of different fertilizer applications on soil quality and arbuscular mycorrhizal colonization, we examined the changes in soil physical and chemical properties, mycorrhizal colonization and propagules, and their relationships in citrus under inorganic fertilization (IF), organic fertilization (OF), combined organic and inorganic fertilization (CF), and no fertilization (CK) treatments. Results showed that all fertilization treatments improved the content of rhizospheric soil organic carbon (SOC), nutrient contents, and electrical conductivity (EC). Both CF and OF significantly increased soil pH, soil aggregate stability, activities of urease, catalase, and sucrase, and the colonization and reproduction of arbuscular mycorrhizae fungi (AMF) in citrus rhizosphere. However, IF treatment significantly decreased soil pH and the colonization and reproduction of AMF in citrus rhizosphere. The number of mycorrhizal colonization and propagation was positively correlated with soil aggregate stability, SOC content, total nitrogen content, total phosphorus content, urease activity, and soil pH. Combined with the principal component analysis, we concluded that application of inorganic fertilizer alone could cause soil acidification and inhibit AMF colonization in citrus orchards. In contrast, organic fertilizer combined with inorganic fertilizer in citrus could improve the soil quality and AMF colonization.

General and specialized metabolites in peanut roots regulate arbuscular mycorrhizal symbiosis

Arbuscular mycorrhizae (AM) fungi form symbiotic associations with plant roots, providing nutritional benefits and promoting plant growth and defenses against various stresses. Metabolic changes in the roots during AM fungal colonization are key to understanding the development and maintenance of these symbioses. Here, we investigated metabolic changes in the roots of peanut (Arachis hypogaea L.) plants during the colonization and development of AM symbiosis, and compared them to uncolonized roots. The primary changes during the initial stage of AM colonization were in the contents and compositions of phenylpropanoid and flavonoid compounds. These compounds function in signaling pathways that regulate recognition, interactions, and pre-colonization between roots and AM fungi. Flavonoid compounds decreased by 25% when the symbiosis was fully established compared to the initial colonization stage. After AM symbiosis was established, general metabolism strongly shifted toward the formation of lipids, amino acids, carboxylic acids, and carbohydrates. Lipid compounds increased by 8.5% from the pre-symbiotic stage to well-established symbiosis. Lyso-phosphatidylcholines, which are signaling compounds, were only present in AM roots, and decreased in content after the symbiosis was established. In the initial stage of AM establishment, the content of salicylic acid increased two-fold, whereas jasmonic acid and abscisic acid decreased compared to uncolonized roots. The jasmonic acid content decreased in roots after the symbiosis was well established. AM symbiosis was associated with high levels of calcium, magnesium, and D-(+)-mannose, which stimulated seedling growth. Overall, specific metabolites that favor the establishment of AM symbiosis were common in the roots, primarily during early colonization, whereas general metabolism was strongly altered when AM symbiosis was well-established. In conclusion, specialized metabolites function as signaling compounds to establish AM symbiosis. These compounds are no longer produced after the symbiosis between the roots and AM becomes fully established.

The mysterious non-arbuscular mycorrhizal status of Brassicaceae species.

The Brassicaceae family is unique in not fostering functional symbiosis with arbuscular mycorrhiza (AM). The family is also special in possessing glucosinolates, a class of secondary metabolites predominantly functioning for plant defence. We have reviewed what effect the glucosinolates of this non-symbiotic host have on AM or vice versa. Isothiocyanates, the toxic degradation product of the glucosinolates, particularly the indolic and benzenic glucosinolates, are known to be involved in the inhibition of AM. Interestingly, AM colonization enhances glucosinolate production in two AM-host in the Brassicales family- Moringa oleifera and Tropaeolum spp. PHOSPHATE STARVATION RESPONSE 1 (PHR1), a central transcription factor that controls phosphate starvation response also activates the glucosinolate biosynthesis in AM non-host Arabidopsis thaliana. Recently, the advances in whole-genome sequencing, enabling extensive ecological microbiome studies have helped unravel the Brassicaceae microbiome, identifying new mutualists that compensate for the loss of AM symbiosis, and reporting cues for some influence of glucosinolates on the microbiome structure. We advocate that glucosinolate is an important candidate in determining the mycorrhizal status of Brassicaceae and has played a major role in its symbiosis-defence trade-off. We also identify key open questions in this area that remain to be addressed in the future.

Weeds: An Insidious Enemy or a Tool to Boost Mycorrhization in Cropping Systems?

Weeds have always been considered an insidious enemy, capable of reducing crop production. Conversely, the agroecological vision attributes a key role to the spontaneous flora in promoting plant diversity and belowground interactions, which may improve the ecological performance of agroecosystems. We summarized the literature on the weeds' arbuscular-mycorrhizae (AM) interaction and we analyzed evidence on the: (i) AM suppressive/selective effect on weed communities; (ii) effect of weeds on AM colonization, and (iii) positive role of AM-supporting weeds on forming shared mycorrhizal hyphal connections in agroecosystems. While some authors conceptualized AM as a weed control tool, others underlined their selective effect on weed communities. Recent studies suggest that AM-host weeds can participate in the development of a common mycorrhizal mycelial network (MMN) among different plants species. Nevertheless, direct evidence of the actual exchange of nutrients and C between coexisting plants through MMN in agroecosystems is missing. Although the effect of agricultural practices on plant community-AM interactions are complex, more conservative farming management seems to foster AM populations. Future studies should focus on: (i) field studies, (ii) weed communities and their traits, rather than on the most abundant species, and (iii) the use of advanced analytical techniques, able to monitor MMN development and functionality.

Long-lasting impact of chito-oligosaccharide application on strigolactone biosynthesis and fungal accommodation promotes arbuscular mycorrhiza in Medicago truncatula.

• The establishment of arbuscular mycorrhiza (AM) between plants and Glomeromycotina fungi is preceded by the exchange of chemical signals: fungal released Myc-factors, including chitoligosaccharides (CO) and lipo-chitooligosaccharides (LCO), activate plant symbiotic responses, while root exuded strigolactones stimulate hyphal branching and boost CO release. Furthermore, fungal signaling reinforcement through CO application was shown to promote AM development in Medicago truncatula, but the cellular and molecular bases of this effect remained unclear. • Here we focused on long-term M. truncatula responses to CO treatment, demonstrating its impact on the transcriptome of both mycorrhizal and non-mycorrhizal roots over several weeks and providing an insight into the mechanistic bases of the CO-dependent promotion of AM colonization. • CO treatment caused the long-lasting regulation of strigolactone biosynthesis and fungal accommodation related genes. This was mirrored by an increase in root didehydro-orobanchol content, and the promotion of accommodation responses to AM fungi in root epidermal cells. Lastly, an advanced down-regulation of AM symbiosis marker genes was observed at the latest time point in CO-treated plants, in line with an increased number of senescent arbuscules. • Overall, CO treatment triggered molecular, metabolic and cellular responses underpinning a protracted acceleration of AM development.

Ascomycetous isolates promote soil biological and nutritional attributes in corn and soybeans in sandy and clayey soils

Biological inputs are environmentally friendly agriculture practices for conserving natural resources in the face of the world's increasing demand for food, fiber and biofuels. The effects of beneficial non-mycorrhizal fungi on soil and plants are multifactorial and mostly unknown. In this regard, we aimed to assess the effects of five ascomycetous isolates, namely Beauveria bassiana, Metarhizium anisopliae, Pochonia chlamydosporia, Purpureocillium lilacinum and Trichoderma asperellum, on the biology and fertility of sandy and clayey soils from the Cerrado biome under corn and soybeans grown in a greenhouse. The fungal treatments produced some differences in soil microbial biomass, enzyme activity and fertility and consistently promoted arbuscular mycorrhiza (AM) colonization in both soils under corn and soybeans. Fungal applications significantly increased colonization efficacy of arbuscular mycorrhiza fungi (AMF) by 28%–72% in corn and from 57% to 105% in soybeans, relative to a control. A combination of principal component analysis and correlation analysis showed that applications of any of the five ascomycetous fungi increased AM colonization, and shoot concentrations of P, K, S and Cu in the corn assays, and shoot concentrations of K and phosphatase and fluorescein diacetate hydrolysis activity in the soil of the soybean assays. Thus, the application of fungal isolates, with the stimulation of root colonization, nutrient absorption and soil biological activity, may have effects on soil function and quality in the medium and long term. These findings can contribute to the development and adoption of more sustainable agricultural practices.

Identification of microRNAs responsive to arbuscular mycorrhizal fungi in Panicum virgatum (switchgrass)

BackgroundMicroRNAs (miRNAs) are important post-transcriptional regulators involved in the control of a range of processes, including symbiotic interactions in plants. MiRNA involvement in arbuscular mycorrhizae (AM) symbiosis has been mainly studied in model species, and our study is the first to analyze global miRNA expression in the roots of AM colonized switchgrass (Panicum virgatum), an emerging biofuel feedstock. AM symbiosis helps plants gain mineral nutrition from the soil and may enhance switchgrass biomass production on marginal lands. Our goals were to identify miRNAs and their corresponding target genes that are controlling AM symbiosis in switchgrass.ResultsThrough genome-wide analysis of next-generation miRNA sequencing reads generated from switchgrass roots, we identified 122 mature miRNAs, including 28 novel miRNAs. By comparing miRNA expression profiles of AM-inoculated and control switchgrass roots, we identified 15 AM-responsive miRNAs across lowland accession “Alamo”, upland accession “Dacotah”, and two upland/lowland F1 hybrids. We used degradome sequencing to identify target genes of the AM-responsive miRNAs revealing targets of miRNAs residing on both K and N subgenomes. Notably, genes involved in copper ion binding were targeted by downregulated miRNAs, while upregulated miRNAs mainly targeted GRAS family transcription factors.ConclusionThrough miRNA analysis and degradome sequencing, we revealed that both upland and lowland switchgrass genotypes as well as upland-lowland hybrids respond to AM by altering miRNA expression. We demonstrated complex GRAS transcription factor regulation by the miR171 family, with some miR171 family members being AM responsive while others remained static. Copper miRNA downregulation was common amongst the genotypes tested and we identified superoxide dismutases and laccases as targets, suggesting that these Cu-miRNAs are likely involved in ROS detoxification and lignin deposition, respectively. Other prominent targets of the Cu miRNAs were blue copper proteins. Overall, the potential effect of AM colonization on lignin deposition pathways in this biofuel crop highlights the importance of considering AM and miRNA in future biofuel crop development strategies.

SlSPX1-SlPHR complexes mediate the suppression of arbuscular mycorrhizal symbiosis by phosphate repletion in tomato.

Forming mutualistic symbioses with arbuscular mycorrhizae (AMs) improves the acquisition of mineral nutrients for most terrestrial plants. However, the formation of AM symbiosis usually occurs under phosphate (Pi)-deficient conditions. Here, we identify SlSPX1 (SYG1 (suppressor of yeast GPA1)/Pho81(phosphate 81)/XPR1 (xenotropic and polytropic retrovirus receptor 1) as the major repressor of the AM symbiosis in tomato (Solanum lycopersicum) under phosphate-replete conditions. Loss of SlSPX1 function promotes direct Pi uptake and enhances AM colonization under phosphate-replete conditions. We determine that SlSPX1 integrates Pi signaling and AM symbiosis by directly interacting with a set of arbuscule-induced SlPHR proteins (SlPHR1, SlPHR4, SlPHR10, SlPHR11, and SlPHR12). The association with SlSPX1 represses the ability of SlPHR proteins to activate AM marker genes required for the arbuscular mycorrhizal symbiosis. SlPHR proteins exhibit functional redundancy, and no defective AM symbiosis was detected in the single mutant of SlPHR proteins. However, silencing SlPHR4 in the Slphr1 mutant background led to reduced AM colonization. Therefore, our results support the conclusion that SlSPX1-SlPHRs form a Pi-sensing module to coordinate the AM symbiosis under different Pi-availability conditions.

The Gastrodia menghaiensis (Orchidaceae) genome provides new insights of orchid mycorrhizal interactions

BackgroundTo illustrate the molecular mechanism of mycoheterotrophic interactions between orchids and fungi, we assembled chromosome-level reference genome of Gastrodia menghaiensis (Orchidaceae) and analyzed the genomes of two species of Gastrodia.ResultsOur analyses indicated that the genomes of Gastrodia are globally diminished in comparison to autotrophic orchids, even compared to Cuscuta (a plant parasite). Genes involved in arbuscular mycorrhizae colonization were found in genomes of Gastrodia, and many of the genes involved biological interaction between Gatrodia and symbiotic microbionts are more numerous than in photosynthetic orchids. The highly expressed genes for fatty acid and ammonium root transporters suggest that fungi receive material from orchids, although most raw materials flow from the fungi. Many nuclear genes (e.g. biosynthesis of aromatic amino acid L-tryptophan) supporting plastid functions are expanded compared to photosynthetic orchids, an indication of the importance of plastids even in totally mycoheterotrophic species.ConclusionGastrodia menghaiensis has the smallest proteome thus far among angiosperms. Many of the genes involved biological interaction between Gatrodia and symbiotic microbionts are more numerous than in photosynthetic orchids.

Karakteristik Mikoriza Arbuskula Tanaman Serai Wangi (Cymbopogon nardus L.) di Lapangan Ternaungi dan Tidak Ternaungi

Arbuscular mycorrhiza (AM) characteristics of citronella grass in the field have not been reported. This research aimed to study the AM characteristics of citronella grass grown in unshaded and shaded fields. The roots of citronella grass were collected from citronella grass plantations in Cianjur, West Java. The root samples were analyzed for AM structures, namely entry points, intercellular hyphae, arbuscules, and vesicles. The results showed that the citronella grass form AM colonization. The quality of root colonization differed between the two cultivation systems. The unshaded citronella grass had higher root colonization compared to shaded citronella grass. In the unshaded citronella grass, the number of arbuscules was 7 per cm of root length, whereas in the shaded citronella grass was 4 per cm of root length. The types of arbuscules observed were arum and intermediate. There were no differences in the number of entry points in the two cultivated systems, which was 3,5 entry points per cm of root length. The numbers of vesicles and internal hyphae in unshaded citronella grass were lower than that of in the shaded citronella grass. In the unshaded citronella grass, the number of vesicles and intracellular hyphae were 1,5 and 8,5 per cm root length, whereas in the shaded citronella grass were 3,5 and 11 per cm root length, respectively. Shading plants grown in the field were bamboo, banana, coffee, tea, and sugar palm. All the shading plants formed AM symbiosis with a colonization value of 7 to 30%. This research indicates that arbuscular mycorrhiza is an important component in the citronella grass cultivation in unshaded and shaded fields.
 
 Keywords: Arbuscule, entry point, intercellular hyphae, root colonization, vesicle

The Effect of Microbial Fertilizer on the Growth, Rhizospheric Environment and Medicinal Quality of Fritillaria taipaiensis

Fritillaria taipaiensis is a valuable traditional Chinese medicinal plant affected by germplasm degradation during cultivation. To find a suitable solution for this problem, F. taipaiensis was inoculated with exogenous arbuscular mycorrhiza (AM) fungi, potassium-solubilizing bacteria, and phosphorus-solubilizing bacteria in pot experiments. The effects of inoculation on the AM colonization, photosynthetic pigment, and superoxide dismutase contents, rhizospheric enzyme activities, alkaloid, and nucleotide content of F. taipaiensis were studied. The results showed that the inoculation increased mycorrhizal infection intensity of F. taipaiensis. Compared to the control group, the photosynthetic pigment contents in the leaf of the inoculation groups were increased; the content of soluble protein, the activities of the superoxide dismutase, catalase, and peroxidase in leaves were all significantly increased, and the content of malondialdehyde was decreased. The microbial inoculum also increased the content of active ingredients in F. taipaiensis bulbs and increased the enzyme activities, total microorganism number, bacteria/fungi, and actinomycetes/fungi ratios in the rhizosphere. To sum up, microbial fertilizer can significantly improve the rhizospheric environment and medicinal quality of F. taipaiensis. This research provides a theoretical basis and experimental evidence for the sustainable development of an F. taipaiensis industry.

Bioprospecting aerobic rice (Oryza sativa) and mycorrhizal interaction for nutrient uptake and plant growth

With the growing concern of water scarcity in agriculture, aerobic rice (Oryza sativa L.) is a promising mode of cultivation for reducing water use, although the reduced optimal plant growth and yield are major constraints. Arbuscular mycorrhiza (AM) are known to readily colonize rice roots under aerobic conditions, however, the response of upland and lowland rice genotypes has not been investigated. This study was carried out during 2018-19 at ICAR-IARI, New Delhi, using a mycorrhizal consortium and percent colonization was observed to be higher by 58% in upland rice genotypes. AM- upland plants also showed 20% higher plant biomass. AM colonization significantly enhanced rice growth under aerobic conditions, with the upland rice genotypes. Pyari and Satyabhama showed higher response upon AM inoculation. AM colonization increased the total chlorophyll by 54% and the upland rice genotypes showed 51% enhanced nitrogenase activity in their root zones, with highest recorded for Satyabhama. The AM plants showed enhanced activities of nitrate reductase (NR) and glutamine synthetase (GS), and interestingly, the rice genotypes with higher NR and GS (Pyari, Satyabhama) also exhibited more (20%) biomass production and plant N content (36%). Significant varietal differences were recorded in terms of accumulation of antioxidant compounds such as ascorbate, glutathione and proline in AM inoculated plants, which helped to alleviate negative effects of water stress in rice plants under aerobic cultivation.

Occurrence and Sustenance of Arbuscular Mycorrhizae in Selected Dry Zone Agricultural Lands in Sri Lanka

Arbuscular mycorrhizae (AM) are one of the important symbiotic micro-organisms that provide a primary natural pathway for soil/plant nutrient transfer. The prevalence of AM on Reddish Brown Earth soils in the dry zone was determined under three agronomic management regimes: least-, moderate- and well-managed at Kiralogama, Puliyankulama, and Medawachchiya, respectively, in the Anuradhapura District. Arbuscular mycorrhizae interactions were evaluated with varieties each; sesame (Sesamum indicum L.), bitter gourd (Momordica charantia L.), cowpea (Vigna unguiculata (L) Walp.), chilli pepper (Capsicum annuum L.) and tomato (Solanum lycopersicum L.), and locally-common four weed/non-crop species; akmella (Synedrella nodiflora (L.) Gaertn.), balathana (Eleusine indica (L.) Gaertn.), kurakkan (Eleusine coracana (L.) Gaertn.), and wal-rubber (Euphorbia heterophylla L.) in pot experiments. Rhizosphere soils at the well-managed Medawachchiya site recorded the highest number of average live (1312) and dead (2637) spores per 100 g of soil retained on 125 μm sieve compared to the lowest live (459) spores at the least-managed site at Kiralogama. At both Kiralogama and Puliyankulama, live spore counts significantly increased with the progress of Maha rainy season. Increases in plant P and Zn concentrations showed strong positive correlations with AM colonisation. Significant differences of both AM colonisation and spore counts were observed in pot experiments depending on the weed/non-crop species and the variety of crops. Akmella (51.2 %), bitter gourd (var. Black - 69.1 %), Sesame (var. Mali - 76.7 %) and wal-rubber (76.8 %) were associated with high levels of AM colonisation as well as soil spore counts.

Arbuscular mycorrhizae colonization dynamic in Iris pseudacorus L. during second year after inoculation and planting in field

In the last few years was observed an unprecedented market expansion of microbial inoculants for agriculture and environmental applications. Fungi from the phylum Glomeromycota can establish symbiosis with roots of more than 70% vascular plant species, ensuring enhanced nutrient uptake. Aim of this study was to assess functional integration of inoculated arbuscular mycorrhiza and implications for success of symbiose in field conditions and host fitness. Iris pseudacorus was used as perennial model plant for study of seasonal continuity and persisting effects in second year after inoculation. During 2019 was conducted Trouvelot microscopic evaluation for 1080 stained root samples and parameters were obtained using Mycocalc. Results showed that colonization was significantly influenced by phenophase. Inoculated plants presented values with 1.56-14.49% higher. Plant height correlated significantly positive with inoculation (r=0.336*). Results showed that colonization parameters are useful indicators in tracking symbiose across a temporal gradient.

PENINGKATAN PERTUMBUHAN SEMAI SENGON MENGGUNAKAN FUNGI MIKORIZA ARBUSKULA ASLI GAMBUT TROPIS

The research aimed to determine the effect of arbuscular mycorrhizal isolates from Central Kalimantan peat swamp forest on the growth of sengon (Falcataria moluccana (Miq) Barneby & Grimes). Arbuscular mycorrhizal isolates consisted of Glomus sp.2 (blackish brown) & Glomus sp.3 (dark brown) isolated from the peatland of Central Kalimantan. The mycorrhizal colonization was observed and plant growth parameters were measured for five months. The design used in this research was a complete randomized design and there were 6 treatments including Glo1S2 (Glomus sp.2, 2 spores), Glo1S4 (Glomus sp.2, 4 spores), Glo2S2 (Glomus sp.3, 2 spores), Glo2S4 (Glomus sp.3, 4 spores), control I and control II. The result showed that arbuscular mycorrhiza colonization significantly different between the treatments of inoculation compared with control. Glo2S4 treatment gave a significant effect on the growth of sengon in terms of plant height, stem diameter, number of leaves, root length and total biomass. Keywords: AMF, spore, Glomus, Kalimantan

Seasonal arbuscular mycorrhiza colonization dynamic displays genotype-specific pattern in Iris sibirica L.

Arbuscular mycorrhiza (AM) is a widespread symbiotic association between plants and Glomeromycota fungi, that brings nutritional-derived benefits for phytobiont. Influence of plant breeding on arbuscular mycorrhiza susceptibility is a topic of current interest that can have many practical implications. Insights into whether new cultivars have a lower mycorrhizal potential, are critical for optimization of AM use. Aim of this research was to conduct a comparative assessment of AM colonization across a phenophase gradient in two Iris sibirica genotypes: one displaying the wild traits versus a modern reblooming cultivar with double flowers. Analysis showed that both Iris sibirica genotypes developed Paris-morphotype. Results indicated that on average the genotype with simple flowers had a higher AM colonization frequency (84.44±2.15) compared to the new cultivar with double flowers (52.22±6.09). Significant influence was exercised both by genotype (p<0.001) as well as by phenophase (p=0.0013), over colonization frequency. The genotypes displayed contrasting colonization dynamics: highest AM frequency level occurred in spring for the genotype with simple flowers, and in autumn for the one with double flowers. Results suggest that host metabolic state has regulating role over functionality of established AM-symbiotic association according to plant nutritional requirements, while fungi might also respond to increased or decreased carbon flux in the plant, associated with geophyte phenology.

The role of CLAVATA signalling in the negative regulation of mycorrhizal colonization and nitrogen response of tomato.

Plants form mutualistic nutrient-acquiring symbioses with microbes, including arbuscular mycorrhizal fungi. The formation of these symbioses is costly, and plants employ a negative feedback loop termed autoregulation of mycorrhizae (AOM) to limit formation of arbuscular mycorrhizae (AM). We provide evidence for the role of one leucine-rich repeat receptor-like kinase (FAB), a hydroxyproline O-arabinosyltransferase enzyme (FIN), and additional evidence for one receptor-like protein (SlCLV2) in the negative regulation of AM formation in tomato. Reciprocal grafting experiments suggest that the FAB gene acts locally in the root, while the SlCLV2 gene may act in both the root and the shoot. External nutrients including phosphate and nitrate can also strongly suppress AM formation. We found that FAB and FIN are required for nitrate suppression of AM but are not required for the powerful suppression of AM colonization by phosphate. This parallels some of the roles of legume homologues in the autoregulation of the more recently evolved symbioses with nitrogen-fixing bacteria leading to nodulation. This deep homology in the symbiotic role of these genes suggests that in addition to the early signalling events that lead to the establishment of AM and nodulation, the autoregulation pathway might also be considered part of the common symbiotic toolkit that enabled plants to form beneficial symbioses.

Influence of fine root traits on in situ exudation rates in four conifers from different mycorrhizal associations.

Plant roots can exude organic compounds into the soil that are useful for plant survival because they can degrade microorganisms around the roots and enhance allelopathy against other plant invasions. We developed a method to collect carbon (C) exudation on a small scale from tree fine roots by C-free filter traps. We quantified total C through root exudation in four conifers from different microbial symbiotic groups (ectomycorrhiza (ECM) and arbuscular mycorrhiza (AM)) in a cool-temperate forest in Japan. We determined the relationship of mass-based exudation rate from three diameter classes (<0.5, 0.5-1.0, and 1.0-2.5mm) of the intact root system with root traits such as morphological traits including root diameter, specific root length (SRL), specific root area (SRA), root tissue density (RTD) and chemical traits including root nitrogen (N) content and C/N. Across species, the mass-based root exudation rate was found to correlate with diameter, SRA, RTD, N and C/N. When comparing mycorrhizal types, there were significant relationships between the exudation and diameter, SRL, SRA, root N and C/N in ECM species; however, these were not significant in AM species. Our results show that relationships between in situ root exudation and every measured trait of morphology and chemistry were strongly driven by ECM roots and not by AM roots. These differences might explain the fact that ECM roots in this study potentially covaried by optimizing the exudation and root morphology in forest trees, while exudation in AM roots did not change with changes in root morphology. In addition, the contrasting results may be attributable to the effect of degree and position of ECM and AM colonization in fine root system. Differences in fine root exudation relationships to root morphology for the two types of mycorrhizae will help us better understand the underlying mechanisms of belowground C allocation in forest ecosystems.