Ectomycorrhizal fungi reduce the light compensation point and promote carbon fixation of Pinus thunbergii seedlings to adapt to shade environments

Beneficial effects of arbuscular mycorrhizae on Cu detoxification in Mimosa pudica L. grown in Cu-polluted soils

Arbuscular mycorrhizal (AM) fungi are known to have beneficial effects on host plants growing on contaminated soils. The present study aimed at investigating the influence of two different AM fungi (Rhizophagus intraradices and Funneliformis mosseae) on the growth of plants and Cu uptake by Mimosa pudica L. grown in polluted soils containing various levels of Cu (Control, 400, 500, or 600 mg kg^-l soil) in pot experiments. Mycorrhizal colonisation rates by the two AM fungi decreased markedly with the increasing Cu levels in soils. This inhibition was more pronounced to F. mosseae than R. intraradices, indicating that R. intraradices was more tolerant to Cu than F. mosseae. Compared with non-mycorrhizal plants, R. intraradices inoculation increased plant growth (including shoot height, numbers of compound leaves and leaflets, and dry biomass) and P concentrations in the shoots and roots of M. pudica at all levels of Cu. Meanwhile, F. mosseae displayed a capability of growth promotion to M. pudica much later and lower than R. intraradices. F. mosseae and R. intraradices markedly decreased Cu concentration in shoots at 400-600 mg kg^-1 Cu levels. However, R. intraradices was more efficient than F. mosseae in decreasing the shoot Cu concentrations. As for the increasing Cu tolerance by R. intraradices, possibly it was reached though the improvement of phosphorus nutrition and the decline of Cu transport from roots to shoots of M. pudica. R. intraradices showed a good potential for improving medicinal plants growth and declining toxic effects in Cu-contaminated soils.

Ectomycorrhizal Inoculation Enhances the Salt Tolerance of Quercus mongolica Seedlings

Salt stress harms the growth and development of plants, and the degree of soil salinization in North China is becoming increasingly severe. Ectomycorrhiza (ECM) is a symbiotic system formed by fungi and plants that can improve the growth and salt tolerance of plants. No studies to date have examined the salt tolerance of Quercus mongolica, a typical ectomycorrhizal tree species of temperate forests in the northern hemisphere. Here, we inoculated Q. mongolica with two ectomycorrhizal fungi (Gomphidius viscidus; Suillus luteus) under NaCl stress to characterize the effects of ECM. The results showed that the symbiotic relationship of Q. mongolica with G. viscidus was more stable than that with S. luteus. The cross-sectional area of roots increased after inoculation with the two types of ectomycorrhizal fungi. Compared with the control group, plant height, soluble sugar content, and soluble protein content of leaves were 1.62, 2.41, and 2.04 times higher in the G. viscidus group, respectively. Chlorophyll (Chl) content, stomatal conductance (Gs), and intracellular CO2 concentration (Ci) were significantly higher in Q. mongolica inoculated with ectomycorrhizal fungi than in the control, but differences in the net photosynthetic rate (Pn), transpiration rate (Tr), and photosystem II maximum photochemical efficiency (Fv/Fm) were lower. The relative conductivity of Q. mongolica inoculated with the two ectomycorrhizal fungi was consistently lower than that of non-mycorrhizal seedlings, with the effect of G. viscidus more pronounced than that of S. luteus. The malondialdehyde (MDA) content showed a similar pattern. Peroxidase (POD) and catylase (CAT) levels in mycorrhizal seedlings were generally higher than those of non-mycorrhizal seedlings under normal conditions, and were significantly higher than those of non-mycorrhizal seedlings on the 36th and 48th day after salt treatment, respectively. Overall, the results indicated that the salt tolerance of Q. mongolica seedlings was improved by ectomycorrhizal inoculation.

Evolutionary Insights Into Two Widespread Ectomycorrhizal Fungi (Pisolithus) From Comparative Analysis of Mitochondrial Genomes

The genus Pisolithus is a group of global ectomycorrhizal fungi. The characterizations of Pisolithus mitochondrial genomes have still been unknown. In the present study, the complete mitogenomes of two Pisolithus species, Pisolithus microcarpus, and Pisolithus tinctorius, were assembled and compared with other Boletales mitogenomes. Both Pisolithus mitogenomes comprised circular DNA molecules with sizes of 43,990 and 44,054 bp, respectively. Comparative mitogenomic analysis showed that the rps3 gene differentiated greatly between Boletales species, and this gene may be subjected to strong pressure of positive selection between some Boletales species. Several plasmid-derived genes and genes with unknown functions were detected in the two Pisolithus mitogenomes, which needs further analysis. The two Pisolithus species show a high degree of collinearity, which may represent the gene arrangement of the ancestors of ectomycorrhizal Boletales species. Frequent intron loss/gain events were detected in Boletales and basidiomycetes, and intron P717 was only detected in P. tinctorius out of the eight Boletales mitogenomes tested. We reconstructed phylogeny of 79 basidiomycetes based on combined mitochondrial gene dataset, and obtained well-supported phylogenetic topologies. This study served as the first report on the mitogenomes of the family Pisolithaceae, which will promote the understanding of the evolution of Pisolithus species.

Phytoremediation competence of short-term crops on magnesite mine tailing

The soil pollution emerging from mining action is a major environmental concern, the finding of biological resolution for these disputes is substantial to reduce and recover metal harmfulness and spreading. Hence, this research was designed to appraise the phytoremediation capability of short-term cereal crops on magnesite mine tailing. Many sources reported that it took several months or a year for phytoremediation process. We provided for the first time the removal of metals from mine tailing in a shorter period at 56 days and obtained a huge percentage of removal results states that out of 14 crops, 7 crops such as J. curcas (47.2-72.3%), R. communis (41.7-67.1%), M. uniflorum (42.1-58.4%), O. sativa (35.6-61.5%), V. ungiculata (39.3-67.5%), P. glaucum (37.3-58.9%), and G. hirsutum (45.5-68.2%) removed in the range of 35.6-72.3% from the tailing of magnesite mine. Besides that, this results also alarming us the possibilities of entering these metals into the human and animals through consumption of foods derived from these types of crops cultivated from metal polluted soil.

Promotion of Zinc Tolerance, Acquisition and Translocation of Phosphorus in Mimosa pudica L. Mediated by Arbuscular Mycorrhizal Fungi

Heavy metal contamination of soil is of increasing concern because of its potential risk to human health. In this study, two AMFs (Rhizophagus intraradices and Funneliformis mosseae) substantially increased the biomass of bashfulgrass in Zn-contaminated soil, even at Zn levels of up to 600 mg kg^-1. Zn uptake in R. intraradices- and F. mosseae-mycorrhizal bashfulgrass was increased by 40-fold and 7-fold, respectively, when plants grown in Zn-contaminated (400 mg kg^-1) soil. Elemental analysis showed that neither AMF had an effect on Zn concentration in plant tissues, including the roots and shoots. However, a significant increase of phosphorus (P) concentration was observed, suggesting the increased is from the improved use efficiency of soil nutrients by AMFs. Comparing the two AMFs, better growth performance with more biomass occurred with R. intraradices-inoculated bashfulgrass in Zn-contaminated soil. This is consistent with R. intraradices being more tolerant to Zn than F. mosseae, indicated by a higher colonization percentage in bashfulgrass roots. Taken together, our data indicate that AMFs possibly improve acquisition and translocation of P to promote increased biomass. Moreover, mycorrhiza did not enhance Zn accumulation in shoots and roots of bashfulgrass at the same Zn level. In the future, developing AMF (especially R. intraradices) inoculation of plants might be a desirable means of safe production of ornamental plants in metal-polluted soil.

Metabolome adjustments in ectomycorrhizal Populus × canescens associated with strong promotion of plant growth by Paxillus involutus despite a very low root colonization rate

It is believed that resource exchange, which is responsible for intensified growth of ectomycorrhizal plants, occurs in the fungus-plant interface. However, increasing evidence indicates that such intensified plant growth, especially root growth promotion, may be independent of root colonization. Nevertheless, the molecular adjustments in low-colonized plants remain poorly understood. Here, we analysed the metabolome of Populus × canescens microcuttings characterized by significantly increased growth triggered by inoculation with Paxillus involutus, which successfully colonized only 2.1 ± 0.3% of root tips. High-throughput metabolomic analyses of leaves, stems and roots of Populus × canescens microcuttings supplemented with leaf proteome data were performed to determine ectomycorrhiza-triggered changes in N-, P- and C-compounds. The molecular adjustments were relatively low in low-colonized (M) plants. Nevertheless, the levels of foliar phenolic compounds were significantly increased in M plants. Increases of total soluble carbohydrates, starch as well as P concentrations were also observed in M leaves along with the increased abundance of the majority of glycerophosphocholines detected in M roots. However, compared with the leaves of the non-inoculated controls, M leaves presented lower concentrations of both N and most photosynthesis-related proteins and all individual mono- and disaccharides. In M stems, only a few compounds with different abundances were detected, including a decrease in carbohydrates, which was also detected in M roots. Thus, these results suggest that the growth improvement of low-colonized poplar trees is independent of an increased photosynthesis rate, massively increased resource (C:N) exchange and delivery of most nutrients to leaves. The mechanism responsible for poplar growth promotion remains unknown but may be related to increased P uptake, subtle leaf pigment changes, the abundance of certain photosynthetic proteins, slight increases in stem and root amino acid levels and the increase in flavonoids (increasing the antioxidant capacity in poplar), all of which improve the fitness of low-colonized poplars.

The great potential for phytoremediation of abandoned tailings pond using ectomycorrhizal Pinus sylvestris

To explore the potential of ectomycorrhizal (ECM) Pinus sylvestris (P. sylvestris) utilizing in the phytoremediation of a combined heavy metal contaminated tailings pond, Pisolithus sp.1(P1)-. Pisolithus sp.2 (P2)-. Cenococcum geophilum (Cg)-. Laccaria sp. (L1)- ECM, and non-ectomycorrhizal (NM) P. sylvestris were planted separately in lead (Pb)-zinc-(Zn)-cadmium-(Cd)-combined polluted soil, collected from a tailings pond. After four months, growth, photosynthetic parameters, nutrient and heavy metal levels of the plants were evaluated. The physical and chemical properties and enzyme activities of soil before and after ECM plants planting were also investigated. The results showed that inoculation with ECM fungi improved the survival rates of host plants by increasing the biomass, photosynthesis (photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular CO₂ concentration (Ci)), and mineral nutrients (phosphorus (Pi), magnesium (Mg), iron (Fe), calcium (Ca)), while it decreased the transfer factors of Cd, Pb, and Zn. In addition, ECM P. sylvestris significantly accumulated much more Cd, Pb, and Zn than NM seedlings, while it reduced pH and the availability of heavy metals (DTPA-Cd, DTPA-Pb, DTPA-Zn) in soil and increased activity of soil enzymes (acid phosphatase, alkaline phosphatase, urease). Therefore, the ECM symbionts have the great potential for phytoremediation of abandoned tailings pond, and this study provides a theoretical basis and application premise for the phytoremediation of abandoned tailings pond.

The complete mitochondrial genomes of two model ectomycorrhizal fungi (Laccaria): features, intron dynamics and phylogenetic implications

Laccaria amethystine and L. bicolor have served as model species for studying the life history and genetics of ectomycorrhizal fungi. However, the characterizations and variations of their mitogenomes are still unknown. In the present study, the mitogenomes of the two Laccaria species were assembled, annotated, and compared. The two mitogenomes of L. amethystine and L. bicolor comprised circular DNA molecules, with the sizes of 65,156 bp and 95,304 bp, respectively. Genome collinearity analysis revealed large-scale gene rearrangements between the two Laccaria species. Comparative mitogenome analysis indicated the introns of cox1 genes in Agaricales experienced frequent lost/gain eveants, which promoted the organization and size variations in Agaricales mitogenomes. Evolutionary analysis indicated the core protein-coding genes in the two mitogenomes were subject to strong pressure of purifying selection. Phylogenetic analysis using the Bayesian inference (BI) and Maximum likelihood (ML) methods based on a combined mitochondrial gene set resulted in identical and well-supported tree topologies, wherein the two Laccaria species were most closely related to Coprinopsis cinerea. This study severed as the first study on the mitogenomes of Laccaria species, which promoted a comprehensive understanding of the genetics and evolution of the model ectomycorrhizal fungi.

A Cr(VI)-tolerant strain, Pisolithus sp1, with a high accumulation capacity of Cr in mycelium and highly efficient assisting Pinus thunbergii for phytoremediation

Ectomycorrhizal (ECM) fungi can improve the growth of pine trees and enhance their tolerance to heavy metal stress, and may also be useful during the afforestation and phytoremediation of polluted regions with pine trees. Hebeloma vinosophyllum (Cr(VI)-sensitive strain) and Pisolithus sp1 ((Cr(VI)-tolerant strain) were selected through liquid culture experiment, and were used in symbiosis with Japanese black pine (Pinus thunbergii) in pot experiments, to determine their potential for improving phytoremediation of Cr(VI)-contaminated soils. Our results indicated that Pisolithus sp1 also had a significantly higher accumulation of Cr than H. vinosophyllum in mycelium under the same Cr(VI) treatments in liquid culture experiment. The tolerance index of Pisolithus sp1 ECM seedlings' shoots and roots to Cr(VI) were significantly higher than that of H. vinosophyllum ECM and non-ectomycorrhizal (NM) seedlings while the total accumulated Cr per seedling in Pisolithus sp1 ECM seedlings were 1.50-1.96 and 2.83-27.75 fold higher that of H. vinosophyllum ECM and NM seedlings, respectively, within 0-800 mg kg^-1 Cr(VI) treatments in pot experiments. In addition, the significant differences ratios of photosynthetic rate, stomatal conductance, transpiration rate and intercellular CO₂ concentration between Pisolithus sp1 ECM and NM seedlings were significantly higher than those between H. vinosophyllum ECM and NM seedlings under 400 and 800 mg kg^-1 Cr(VI) treatments. Compared with the control (no plant), and planting NM or H. vinosophyllum ECM seedlings, the planting of Pisolithus sp1 ECM seedlings significantly reduced the percentage content of exchangeable Cr in the soil.