Intensity Of Mycorrhizal Colonization Research Articles

Rock fragment content in soils shift root foraging behavior in xerophytic species

Root traits associated with resource foraging, including fine-root branching intensity, root hair, and mycorrhiza, may change in soils that vary in rock fragment content (RFC), while how these traits covary at the level of individual root branching order is largely unknown. We subjected two xerophytic species, Artemisia vestita (subshrub) and Bauhinia brachycarpa (shrub), to increasing RFC gradients (0%, 25%, 50%, and 75%, v v− 1) in an arid environment and measured fine-root traits related to resource foraging. Root hair density and mycorrhizal colonization of both species decreased with increasing root order, but increased in third- or fourth-order roots at high RFCs (50% or 75%) compared to low RFCs. The two species tend to produce more root hairs than mycorrhizas under the high RFCs. For both species, root hair density and mycorrhizal colonization intensity were negatively correlated with root length and root diameter across root order and RFCs. Rockiness reduced root branching intensity in both species comparing with rock-free soil. At the same level of RFC, A. vestita had thicker roots and lower branching intensity than B. brachycarpa and tended to produce more root hairs. Our results suggest the high RFC soil conditions stimulated greater foraging functions in higher root orders. We found evidence for a greater investment in root hairs and mycorrhizal symbioses as opposed to building an extensive root system in rocky soils. The two species studied, A. vestita and B. brachycarpa, took different approaches to foraging in the rocky soil through distinctive trait syndromes of fine-root components.

Mycorrhiza helper bacterium Bacillus pumilus HR10 improves growth and nutritional status of Pinus thunbergii by promoting mycorrhizal proliferation.

Mycorrhizal helper bacteria (MHB) play an important role in mediating mycorrhizal symbiosis, which improves the growth and nutrient uptake of plants. This study examined the growth-promoting effects and mechanisms of pine growth after inoculation with the MHB Bacillus pumilus HR10 and/or Hymenochaete sp. Rl. The effect of B. pumilus HR10 on Hymenochaete sp. Rl growth, enzyme activity and gene expression related to mycorrhiza formation were determined. The growth, root activity, nitrogen, phosphorus, and potassium content and chlorophyll fluorescence activity of Pinus thunbergii and the mycorrhizal colonization intensity of Hymenochaete sp. Rl-inoculated pine seedlings after inoculation with B. pumilus HR10 were also evaluated. The results showed that B. pumilus HR10 promoted growth, regulated the expression of mycorrhizal-related genes and affected the β-1,3-glucanase activity of Hymenochaete sp. Rl. The mycorrhizal colonization intensity of pine seedlings co-inoculated with B. pumilus HR10 and Hymenochaete sp. Rl was 1.58-fold higher than seedlings inoculated with only Hymenochaete sp. Rl. Inoculation with B. pumilus HR10 and/or Hymenochaete sp. Rl increased lateral root number and root activity of pine seedlings and chlorophyll fluorescence activity of pine needles compared with the control. Bacillus pumilus HR10 facilitated nutrient uptake by enhancing the mycorrhizal proliferation of pine and induced greater photosynthesis and root activity of pine seedlings, which confirms its role as an outstanding plant-growth-promoting rhizobacterium. These findings improve our understanding of the mechanism of B. pumilus HR10 promotion of mycorrhizal symbiosis.

Demonstrational gardens with EDTA-washed soil. Part II: Soil quality assessment using biological indicators

In this study, we evaluated the impact of washing of Pb, Zn and Cd contaminated soil using EDTA-based technology (ReSoil®) on soil biological properties by measuring some of the most commonly used/sensitive biological indicators of soil perturbation. We estimated the temporal dynamics of the soil respiration, the activities of soil enzymes (dehydrogenase, β-glucosidase, urease, acid and alkaline phosphatase), and the effect of the remediation process on arbuscular mycorrhizal (AM) fungi in original (Orig), remediated (Rem) and remediated vitalized (Rem+V) soils during a more than one-year garden experiment. ReSoil® technology initially affected the activity level of soil microbial respiration and all enzyme activities except urease and reduced AM fungal potential in the soil. However, after one year of vegetable cultivation and standard gardening practices, soil microbial respiration, acid and alkaline phosphatase in the Rem and Rem+V reached similar activities as in the Orig. Only the activities of dehydrogenase and β-glucosidase remained lower in the remediated soil compared to the Orig. The frequency of arbuscular mycorrhiza in the root system, arbuscular density in the colonized root fragment, and the intensity of mycorrhizal colonization in the colonized root fragments in the remediated treatments increased with time; at the end of the experiment, no consistent differences in these parameters of mycorrhizal colonization were found among the treatments. Our results suggest a restored biological functioning of the remediated soil after one year of vegetable cultivation. In general, no differences were found between the Rem and Rem+V treatments, indicating that simple common garden practices are sufficient to restore soil functioning after remediation.

Impact of Mycorrhization on Phosphorus Utilization Efficiency of Acacia gummifera and Retama monosperma under Salt Stress

The impact of salt stress on the growth and phosphorus utilization efficiency (PUE) of two leguminous species: Retama monosperma and Acacia gummifera was studied. The effectiveness of arbuscular mycorrhizal fungi (AMF) to mitigate salt stress was furthermore assessed. Growth, N and P tissue concentrations, mycorrhizal root colonization frequency and intensity, and P utilization efficiency (PUE) in the absence or presence of AMF were evaluated under no salt (0 mM L−1) and three salt (NaCl) concentrations of (25, 50 and 100 mM L−1) using a natural sterilized soil. A significant difference in mycorrhizal colonization intensity, root-to-shoot ratio, P uptake, PUE, and N uptake was observed between the legume species. Salt stress inhibited the shoot and root growth, and reduced P and N uptake by the legume species. Mycorrhizal inoculation aided to mitigate the effects of salt stress with an average increase of shoot and root growth responses by 35% and 32% in the inoculated than in the non-inoculated A. gummifera treatments. The average shoot and root growth responses were 37% and 45% higher in the inoculated compared to the non-inoculated treatments of R. monosperma. Average mycorrhizal shoot and root P uptake responses were 66% and 68% under A. gummifera, and 40% and 95% under R. monosperma, respectively. Mycorrhizal inoculated treatments consistently maintained lower PUE in the roots. The results provide insights for further investigations on the AMF conferred mechanisms to salt stress tolerance response by A. gummifera and R. monosperma, to enable the development of effective technologies for sustainable afforestation and reforestation programs in the Atlantic coast of Morocco.

Respuesta del pasto Yacaré (Urochloa híbrido cv. CIAT BR02/1752) a la biofertilización con hongos micorrízicos arbusculares

With the aim to evaluate the biofertilization effectiveness with arbuscular mycorrhizal fungi in Yacare pasture ( Urochloa hybrid) cultivated in Lixiviated Ferrallitic Red soil, an experiment was carried out at Nina Bonita Genetic Cattle Enterprise. Four treatments were evaluated: three species of arbuscular mycorrhizal fungi (AMF), Glomus cubense , Funneliformis mosseae , and Rizhophagus irregularis , in addition to a control without inoculating, distributed in a Latin square design. Different species inoculation of AMF was carried out at sowing time. The indicators evaluated were the frequency and intensity of mycorrhizal colonization, AMF spore number in the rhizosphere, the NPK biomass concentrations, the dry mass yield of the pasture and its nutritive value, as well as the efficiency index and AMF strains influence in pasture nutrition. All the strains produced significant increases in the evaluated variables; nevertheless, when G. cubense was inoculated, increases in the efficiency index and in pasture nutrition were obtained. It is concluded that biofertilization with G. cubense can be an effective agronomic practice to improve the yield and nutritive value of the Yacare pasture cultivated in Lixiviated Ferrallitic Red soil.

The effect of nitrogen-modified lignite granules on mycorrhization and root and shoot growth of Secale cereale (winter rye) in a nutrient-deficient, sandy soil

ABSTRACT Organic soil amendments such as modified lignite and biostimulants like arbuscular mycorrhizal fungi (AMF) may have the potential to improve soil biological conditions of agricultural soils. The aim of the study was to test if nitrogen-modified lignite granules (NH) are beneficial for mycorrhization, root and shoot development compared to common mineral nitrogen (Nmin) in a nitrogen and phosphorus limited soil. A greenhouse experiment with Secale cereale L. was carried out using non-sterilized and sterilized sand substrate treated with NH, AMF or Nmin and AMF+NH and AMF+Nmin and was compared to an untreated substrate (control). 7.5 t ha−1 NH and 120 kg Nmin ha−1 led to a similar increase of AMF colonization compared to the control; however, Nmin had a more positive influence on biomass development. Significantly highest mycorrhizal colonization intensity was found for AMF+NH. The co-application of AMF+NH revealed that shoot and root development and shoot nutrient concentrations were significantly higher or were among the significantly highest values, when compared to the other treatments. AMF+NH may be a suitable soil amendment for nutrient-limited soils and may be more sustainable than Nmin due to a combined increase of nitrogen, AMF and carbon/humic acids in the soil that comes with the NH.

Rhizophagus irregularis MUCL 41,833 Association with Green Cuttings of Prunus sp. Rootstocks

Sour cherry ‘Latvijas Zemais’ (Prunus cerasus) is a promising dwarfing rootstock for sweet cherries in Latvia, but low growing rate of newly propagated sour cherry plants limits their use. Plum rootstock PU 20651 was selected from hybrids of P. cerasifera and P. salicina ssp. usuriensis recently. The aim of our study was to estimate the effect of arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis MUCL 41833 (Ri) on the growth and P content of rooted green cuttings of sour cherry ‘Latvijas Zemais’ 52, cherry rootstock Gisela 5 (P. cerasus x P. canescens), and plum rootstock PU 20651. The cuttings were planted in peat substrate and grown in plastic tunnel equipped with automatic air moistening system and controllable floor heating. We determined growth parameters and P content in shoots and roots, intensity of mycorrhizal colonization, and frequency of mycorrhiza in root system. In all three Prunus sp. genotypes, the inoculation with Ri resulted in the root colonization. PU 20651 had highest level of colonization at all arbuscular mycorrhiza (AM) estimation parameters. A common effect of colonization was increased diameter of root collar and positive correlation between the leaf number and AM parameters. The effect of Ri on plant biomass and P content depended on the genotype. Beneficial effect of AM on root mass and root P content was detected in ‘Latvijas Zemais’ 52. However, no AM effects on P content were found in Gisela 5, but little negative impact of AM on shoot mass and shoot P content—in PU 20651.

ОЦЕНКА ВЛИЯНИЯ АРБУСКУЛЯРНО-МИКОРИЗНЫХ ГРИБОВ НА ХОЗЯЙСТВЕННО ЦЕННЫЕ ПОКАЗАТЕЛИ ЛУКА РЕПЧАТОГО

Allium cepa L. is one of the main vegetable crops. It is actively used in food industry and medicine. The biochemical composition of plants, both bulbs and green leaves, in different periods of growth changes depending on the variety, environmental and agrotechnical conditions of plant cultivation. Representatives of the genus Allium are highly sensitive to the presence of arbuscular mycorrhiza (AM) in soil due to root development features. The aim of our work was to identify effective associations of AM fungi to increase the productivity and quality of onions in the conditions of southern chernozem. Pot and field experiments were carried out with associations of AM fungi and onion varieties from the collection of the Research Institute of Agriculture of Crimea. The initial assessment of the AM fungi collection was conducted in the pot with a sterile substrate under artificial lighting conditions according to the intensity of mycorrhizal colonization and the accumulation of phytomass of the storage plant. Field studies were carried out on southern carbonate chernozem in 2019. It is established that the AM fungi association M9 significantly exceeds the referent in the arbuscules abundance by 13.3 %. Association 1–16 showed the most considerable abundance of vesicles, which was 11.1–13.3 % higher than other variants of this experiment. The dry mass of onion shoots had a significant increase of 11.719.7 mg per plant (38.865.8 %) from inoculation by associations AM S1-4, 1-16 and M9. The positive effect of the AM fungi association 1-16 on the accumulation of phytomass in the onset phase of bulb formation and onion productivity of the onion variety Yaltinskiy plus and line 11A with an increase by 0.690.8 g / plant (31.351.7 %) and 1.11.3 t / ha (14.114.9 %), respectively, and an increase in the content of ascorbic acid by 18.524.4 % to the variant without treatment are shown.

Belowground responses of woody plants to nitrogen addition in a phosphorus-rich region of northeast China

Nitrogen addition leads to large increases in shoot growth but limited increases in root growth and reductions in mycorrhizal colonization of Sorbus pohuashanensis and Acanthopanax sessiliflorus. Soil in the cultivated fields of Changbai Mountain region of China is rich in phosphorus (P) and deficient in nitrogen (N) for most woody plants. However, currently N deposition is increasing and reducing its limitation on plant growth. How N addition shifts carbon investment among shoots, roots and arbuscular mycorrhizal (AM) fungi is not well understood, especially in woody plants growing in the field. We examine the responses of the growth, biomass partitioning and AM colonization of Sorbus pohuashanensis Hedl. and Acanthopanax sessiliflorus Seem. to low and high N fertilization in northeastern China on high-P soil over 3 years. With N addition, both plants increased shoot biomass by 20–45%, and N and P content by 13–30%, while root biomass increased only by 2.1–5.4%. The slower increase in root growth relative to shoot growth resulted in lower root mass fraction. After plant size (ontogeny) was accounted for, root mass fraction still decreased significantly with high N fertilization in both species. Mycorrhizal colonization intensity and AM-colonized root length decreased with an increase in N addition. In this P-rich site, the limited increase in root biomass and large decrease in AM colonization with N addition presumably promoted plant growth and nutrient uptake. Our results imply that the growth of these two species may be improved by increased carbon allocation to shoots, as N addition permitted sufficient nutrient uptake by roots and AM fungi to meet shoot nutrient demand without additional belowground carbon expenditure.

Mycorrhiza-mediated interference between cover crop and weed in organic winter cereal agroecosystems: The mycorrhizal colonization intensity indicator.

The mycorrhizal fungi are symbiotic organisms able to provide many benefits to crop production by supplying a set of ecosystem functions. A recent ecological approach based on the ability of the fungi community to influence plant–plant interactions by extraradical mycelium development may be applied to diversified, herbaceous agroecosystems. Our hypothesis is that the introduction of a winter cereal cover crop (CC) as arbuscular mycorrhizal fungi (AMF)–host plant in an organic rotation can boosts the AMF colonization of the other plants, influencing crop–weed interference. In a 4‐years organic rotation, the effect of two winter cereal CC, rye and spelt, on weed density and AMF colonization was evaluated. The AMF extraradical mycelium on CC and weeds roots was observed by scanning electron microscopy analysis. By joining data of plant density and mycorrhization, we built the mycorrhizal colonization intensity of the Agroecosystem indicator (MA%). Both the CC were colonized by soil AMF, being the mycorrhizal colonization intensity (M%) affected by environmental conditions. Under CC, the weed density was reduced, due to the increase of the reciprocal competition in favor of CC, which benefited from mycorrhizal colonization and promoted the development of AMF extraradical mycelium. Even though non‐host plants, some weed species showed an increased mycorrhizal colonization in presence of CC respect to the control. Under intense rainfall, the MA% was less sensitive to the CC introduction. On the opposite, under highly competitive conditions, both the CC boosted significantly the mycorrhization of coexistent plants in the agroecosystem. The proposed indicator measured the agroecological service provided by the considered CCs in promoting or inhibiting the overall AMF colonization of the studied agroecosystems, as affected by weed selection and growth: It informs about agroecosystem resilience and may be profitably applied to indicate the extent of the linkage of specific crop traits to agroecosystem services, contributing to further develop the functional biodiversity theory.

Associations of root-inhabiting fungi with herbaceous plant species of temperate forests in relation to soil chemical properties

The overwhelming majority of research on fungal interactions with plants in the forest ecosystems of the temperate climate zone focuses on ectomycorrhizal associations and no studies so far have compared the occurrence of root-inhabiting fungi in herbaceous plant species. We thus studied arbuscular mycorrhizal fungi (AMF) and fungal root endophyte colonization rates as well as AMF species richness and composition under 19 herbaceous plant species in temperate forests (southeast Poland) in relation to soil chemical properties. Seventeen species formed arbuscular mycorrhiza (AM), while 2 were non-mycorrhizal. The intensity of AMF colonization varied between species. Relative mycorrhizal root length (MAMF%) ranged from 0% to 100%. AMF spore abundance ranged from 0 to 11.4 in 1 g of soils. Sixteen AMF species were recorded, both widespread (e.g. Funneliformis constrictum, Claroideoglomus claroideum) and rare (Acaulospora cavernata, Entrophospora infrequens). The composition of AMF species related to the plants differed. Fungal root endophytes were recorded only in some plants; dark septate endophytes (DSE) in 13 species, while Olpidium spp. in 6 species. Moreover, DSE mycelia and Olpidium spp. sporangia were observed with low abundance, and their occurrence differed between particular plant species. Among soil chemical properties, only the concentration of available phosphorus was significantly negatively correlated with the MAMF% parameter. In conclusion, several groups of root-inhabiting fungi were related to herbaceous plants; however, they occurred with varied frequency. AMF spore abundance and species richness differed as well; however, they persisted at a low level compared to other ecosystems. Nonetheless, we detected significant negative correlation between available P contents in soils and the intensity of mycorrhizal colonization, which suggests the importance of AM for the plants in sites with low P concentration.

Is intensity of plant root mycorrhizal colonization a good proxy for plant growth rate, dominance and decomposition in nutrient poor conditions?

AbstractQuestionsMycorrhizae may be a key element of plant nutritional strategies and of carbon and nutrient cycling. Recent research suggests that in natural conditions, intensity of mycorrhizal colonization should be considered an important plant feature. How are inter‐specific variations in mycorrhizal colonization rate, plant relative growth rate (RGR) and leaf litter decomposability related? Is (arbuscular) mycorrhizal colonization linked to the dominance of plant species in nutrient‐stressed ecosystems?LocationTeberda State Biosphere Reserve, northwest Caucasus, Russia.MethodsWe measured plant RGR under mycorrhizal limitation and under natural nutrition conditions, together with leaf litter decomposability and field intensity of mycorrhizal colonization across a wide range of plant species, typical for alpine communities of European mountains. We applied regression analysis to test whether the intensity of mycorrhizal colonization is a good predictor of RGR and decomposition rate, and tested how these traits predict plant dominance in communities.ResultsForb species with a high level of field mycorrhizal colonization had lower RGR under nutritional and mycorrhizal limitation, while grasses were unaffected. Litter decomposition rate was not related to the intensity of mycorrhizal colonization. Dominant species mostly had a higher level of mycorrhizal colonization and lower RGR without mycorrhizal colonization than subordinate species, implying that they were more dependent on mycorrhizal symbionts. There were no differences in litter decomposability.ConclusionsIn alpine herbaceous plant communities dominated by arbuscular mycorrhizae, nutrient dynamics are to a large extent controlled by mycorrhizal symbiosis. Intensity of mycorrhizal colonization is a negative predictor for whole plant RGR. Our study highlights the importance of mycorrhizal colonization as a key trait underpinning the role of plant species in carbon and nutrient dynamics in nutrient‐limited herbaceous plant communities.

Spatiotemporal variation of arbuscular mycorrhizal fungal colonization in olive (Olea europaea L.) roots across a broad mesic-xeric climatic gradient in North Africa.

This study aims to determine the spatiotemporal dynamics of root colonization and spore density of arbuscular mycorrhizal fungi (AMF) in the rhizosphere of olive trees (Olea europaea) with different plantation ages and under different climatic areas in Algeria. Soil and root samples were seasonally collected from three olive plantations of different ages. Other samples were carried out in productive olive orchards cultivated under a climatic gradient (desertic, semi-arid, subhumid, and humid). The olive varieties analysed in this study were Blanquette, Rougette, Chemlel and the wild-olive. Spore density, mycorrhization intensity (M%), spore diversity and the most probable number (MPN) were determined. Both the intensity of mycorrhizal colonization and spore density increased with the increase of seasonal precipitation and decreased with the increase of air temperature regardless of the climatic region or olive variety. The variety Rougette had the highest mycorrhizal levels in all plantation ages and climates. Spore community was composed of the genera Rhizophagus, Funneliformis, Glomus, Septoglomus, Gigaspora, Scutellospora and Entrophospora. The genus Glomus, with four species, predominated in all climate regions. Spores of Gigaspora sp. and Scutellospora sp. were the most abundant in desertic plantations. Statistical models indicated a positive relationship between spore density and M% during spring and winter in young seedlings and old plantations. A significant positive relationship was found between MPN and spore density under different climates. For a mycotrophic species, the rhizosphere of olive trees proved to be poor in mycorrhiza in terms of mycorrhizal colonization and numbers of the infective AMF propagules.

Mycorrhizal status of selected herbaceous plants in Molinia meadows of Folusz, near Szubin (Poland)

This preliminary study examined the arbuscular mycorrhizal (AM) status of native plant species in the Molinia meadows of Folusz in the Kujawy region, Poland. Root samples from ten plant species characteristic of Molinia meadows ( Betonica officinalis , Dianthus superbus , Galium boreale , Inula salicina , Ostericum palustre , Sanguisorba officinalis , Selinum carvifolia , Serratula tinctoria , Silaum silaus , and Succisa pratensis ) were collected in August 2014. Root colonization by AM fungi was considered an indicator of symbiosis development. AM was found in all plant species examined. The frequency of mycorrhizal structures ranged between 68% and 99%. The intensity of mycorrhizal colonization in roots varied with the plant species, ranging between 3.9% ( O. palustre ) and 40.1% ( B. officinalis ). To our knowledge, this is the first study to examine the mycorrhizal status of three species: D. superbus , O. palustre , S. carvifolia . Because AM colonization depends on plant genotype and environmental factors, further studies should examine seasonal variability in plant root colonization and the compositions of AM fungal communities, which may serve as indicators of site conditions

Application of Mycorrhizal Technology for Improving Yield Production of Common Bean Plants

This study aimed to investigate the effects of arbuscular mycorrhizal (AM) fungi with different levels of NPK fertilizers on yield production of common bean plants which common bean plants were subjected to five levels of NPK fertilizers (0, 25, 50, 75, 100 %). Application of AMF significantly increased the growth and yield components of common beans with minimized the levels of NPK comparing to equivalents non-mycorrhizal ones. The results obtained revealed that inoculation with AMF and the concentrations 50% and 75% of NPK with AMF are the greater than other concentrations and non-mycorrhizal plants. Mycorrhizal Common bean plants had significantly higher number of pods, length of one pod, pods weight, 100 seeds weight, weight of seed/plant and intensity of mycorrhizal colonization(M%) . Concentrations of nutrients (N, P, K, Ca and Mg) and total carbohydrates, crude protein and mycorrhizal dependency of some yield parameters were significantly increased in mycorrhizal plants at different NPK levels when comparing to those of non-mycorrhizal plants paticularly at (50% and 75%) concentration of NPK, but lower Na concentration in mycorrhizal common bean seeds than those of non-mycorrhizal.Int J Appl Sci Biotechnol, Vol 4(2): 191-197

Impact of tree decline on spatial patterns of seedling-mycorrhiza interactions: Implications for regeneration dynamics in Mediterranean forests

In the last decades, an increasing number of forest decline events and widespread tree mortality have been reported worldwide as a consequence of different global change drivers. Such a general decrease in tree health and cover has a large potential to impact mycorrhizal communities, but this issue remains largely unexplored.We used a Bayesian framework to analyze the impact of Quercus suber decline on spatial patterns of seedling-mycorrhiza interactions in mixed Mediterranean forests in Southern Spain, and evaluate the relative importance of this symbiosis as a driver of oak seedling establishment.Our models showed that the spatial variability found in the patterns of oak seedling colonization by both arbuscular mycorrhizas and ectomycorrhizas was partially linked to the process of Q. suber decline. Moreover, seedling survival and growth was influenced by the intensity of mycorrhizal colonization, but in quite unexpected ways. Arbuscular mycorrhizas had a larger effect on seedling performance than ectomycorrhizas, and the effects of both groups were negative or neutral but never positive.We conclude that because the spatial distribution of the seedling-mycorrhiza association responded to the identity and health status of individual trees, and mycorrhizal infection did in turn affect seedling performance, tree decline might affect forest dynamics through changes in plant–soil biota feedbacks.

Assessment of arbuscular mycorrhizal fungi status and heavy metal accumulation characteristics of tree species in a lead–zinc mine area: potential applications for phytoremediation

To select suitable tree species associated with arbuscular mycorrhizal fungi (AMF) for phytoremediation of heavy metal (HM) contaminated area, we measured the AMF status and heavy metal accumulation in plant tissues in a lead-zinc mine area, Northwest China. All 15 tree species were colonized by AM fungi in our investigation. The mycorrhizal frequency (F%), mycorrhizal colonization intensity (M%) and spore density (SP) reduced concomitantly with increasing Pb and Zn levels; however, positive correlations were found between arbuscule density (A%) and soil total/DTPA-extractable Pb concentrations. The average concentrations of Pb, Zn, Cu and Cd in plant samples were 168.21, 96.61, 41.06, and 0.79mg/kg, respectively. Populus purdomii Rehd. accumulated the highest concentrations of Zn (432.08mg/kg) and Cu (140.85mg/kg) in its leaves. Considerable amount of Pb (712.37mg/kg) and Cd (3.86mg/kg) were concentrated in the roots of Robinia pseudoacacia Linn. and Populus simonii Carr., respectively. Plants developed different strategies to survive in HM stress environment: translocating more essential metals (Zn and Cu) into the aerial parts, while retaining more toxic heavy metals (Pb and Cd) in the roots to protect the above-ground parts from damage. According to the translocation factor (TF), bioconcentration factor (BCF), growth rate and biomass production, five tree species (Ailanthus altissima (Mill.) Swingle, Cotinus coggygria Scop., P. simonii, P. purdomii, and R. pseudoacacia) were considered to be the most suitable candidates for phytoextraction and/or phytostabilization purposes. Redundancy analysis (RDA) showed that the efficiency of phytoremediation was enhanced by AM symbioses, and soil pH, Pb, Zn, and Cd levels were the main factors influencing the HM accumulation characteristics of plants.

Enhanced concentrations of elements and secondary metabolites in Viola tricolor L. induced by arbuscular mycorrhizal fungi

Viola tricolor L. (heartsease, wild pansy) is a valuable medicinal plant obtained for pharmaceutical purposes by cultivation. Given that the species is usually strongly colonized by arbuscular mycorrhizal fungi (AMF), we tested in a pot experiment whether these microorganisms were able to influence V. tricolor mass, vitality, and the concentrations of selected elements, phenolic acids and flavonoids. The following treatments were prepared: (1) control: sterile soil without AMF inoculation; (2) Rhizophagus irregularis BEG144; (3) Funneliformis mosseae BEG12; and (4) both isolates. Using a combination of physiological, phytochemical and biophysical methods, we evaluated the effects of these AMF on the performance of heartsease. The intensity of mycorrhizal colonization and arbuscule formation was higher when F. mosseae and R. irregularis were introduced separately than when both isolates were present. None of the AMF treatments had an impact either on V. tricolor vitality as expressed by photosynthetic performance index (PI) or on its shoot and root mass. However, in general, a negative correlation was found between the extent of mycorrhizal colonization and shoot mass. We found AMF species specificities in their influence on element, phenolic acid and flavonoid concentrations. Viola tricolor showed no response to F. mosseae. The plants inoculated with R. irregularis had higher concentrations of P, Zn, Mg, and Ca, as well as p-hydroxybenzoic acid and rutin, in comparison to control. Dual AMF species inoculation increased concentrations of Cu, Mg and rutin. The enhanced production of secondary metabolites in V. tricolor shoots may be due to improved mineral nutrition by AMF and/or a result of general plant defense reaction to fungal colonization. The tendency towards biomass decrease in AMF treatments could be explained by the allocation of plant carbon both to the maintenance of symbionts and enhanced production of secondary compounds.

Global patterns of plant root colonization intensity by mycorrhizal fungi explained by climate and soil chemistry

AbstractAimMost vascular plants on Earth form mycorrhizae, a symbiotic relationship between plants and fungi. Despite the broad recognition of the importance of mycorrhizae for global carbon and nutrient cycling, we do not know how soil and climate variables relate to the intensity of colonization of plant roots by mycorrhizal fungi. Here we quantify the global patterns of these relationships.LocationGlobal.MethodsData on plant root colonization intensities by the two dominant types of mycorrhizal fungi world‐wide, arbuscular (4887 plant species in 233 sites) and ectomycorrhizal fungi (125 plant species in 92 sites), were compiled from published studies. Data for climatic and soil factors were extracted from global datasets. For a given mycorrhizal type, we calculated at each site the mean root colonization intensity by mycorrhizal fungi across all potentially mycorrhizal plant species found at the site, and subjected these data to generalized additive model regression analysis with environmental factors as predictor variables.ResultsWe show for the first time that at the global scale the intensity of plant root colonization by arbuscular mycorrhizal fungi strongly relates to warm‐season temperature, frost periods and soil carbon‐to‐nitrogen ratio, and is highest at sites featuring continental climates with mild summers and a high availability of soil nitrogen. In contrast, the intensity of ectomycorrhizal infection in plant roots is related to soil acidity, soil carbon‐to‐nitrogen ratio and seasonality of precipitation, and is highest at sites with acidic soils and relatively constant precipitation levels.Main conclusionsWe provide the first quantitative global maps of intensity of mycorrhizal colonization based on environmental drivers, and suggest that environmental changes will affect distinct types of mycorrhizae differently. Future analyses of the potential effects of environmental change on global carbon and nutrient cycling via mycorrhizal pathways will need to take into account the relationships discovered in this study.

A Rice GRAS Gene Has an Impact on the Success of Arbuscular Mycorrhizal Colonization

Arbuscular mycorrhiza (AM) is one of the most spread symbiosis established between 80% of land plants and soil fungi belonging to the Glomeromycota. Molecular determinants involved in the formation of arbuscular mycorrhizas are still poorly understood. It has been demonstrated that in both Legumes and rice plants, several GRAS transcription factors are directly involved in both mycorrhizal signaling and colonization, namely NSP1, NSP2, RAM1, DELLA, DELLA-interacting protein (DIP1) and RAD1. Here, we focused on a rice GRAS protein, named Arbuscular Mycorrhizal 18 (OsAM18), previously identified as specifically expressed in rice mycorrhizal roots, and considered as an AM-specific gene. Phylogenetic analysis revealed that OsAM18 had a peculiar amino acid sequence, which clustered with putative SCARECROW proteins, even though it formed a separate branch. Allelic osma18 mutant displayed a drastic reduction in mycorrhizal colonization in-tensity and in arbuscule abundance, as mirrored by OsPT11 expression level. Non-mycorrhizal osam18 plants displayed a comparable plant development and root apparatus compared with the WT, while mycorrhizal osam18 mutants showed a reduction of plant biomass compared with mycorrhizal WT plants. The results suggest that OsAM18 is a rice protein, which is likely to have an impact not only on the colonization process and AM functionality, but also on the systemic effects of the AM symbiosis.