Mycorrhizal Seedlings Research Articles

Effects and Molecular Mechanism of Mycorrhiza on the Growth, Nutrient Absorption, Quality of Fresh Leaves, and Antioxidant System of Tea Seedlings Suffering from Salt Stress

We studied changes in plant growth, nutrient absorption, quality of fresh leaves, and the antioxidant enzyme systems of leaves treated with AMF (Glomus etunicatum) in tea (tea cultivar “Xinyang 10”) seedlings exposed to 0 and 100 mmol/L sodium chloride (NaCl). The AMF colonization in the tea roots decreased observably by 50.1% after a 5-week soil NaCl (100 mmol/L) treatment. The growth, leaf nutrient levels, and leaf quality parameter contents significantly declined by 18–39% in the 100 mmol/L NaCl treatments. In contrast, these variables exhibited observably higher responses in the mycorrhizal seedlings than in the nonmycorrhizal seedlings. Furthermore, AMF improved the leaves’ total amino acid concentrations dramatically, accompanied by the upregulation of the genes of the amino acid synthetic enzymes, such as glutamate dehydrogenase (CsGDH), glutamate synthase (CsGOGAT), and glutamine synthetase (CsGS), while 100 mmol/L NaCl seedlings represented a negative performance. In addition, the 100 mmol/L NaCl treatments dramatically downregulated the expression level of the tea caffeine synthase 1 gene (CsTCS1), the ascorbate peroxidase gene (CsAPX), and the 3-hydroxy-3-methylglutaryl coenzyme gene (CsHMGR) in the leaves, while the AMF seedlings represented positive performances. These results suggest that AMF may play an active role in fresh leaf quality via the partial upregulation of the relevant genes’ expression. In contrast, salt stress represented the opposite result in tea. The seedlings inoculated with AMF showed significantly increased antioxidant enzyme activities, by 13.3–19.6%, including peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD), over the non-AMF inoculated tea seedlings. Still, they did not affect glutathione reductase (GR), irrespective of the NaCl condition. Further studies indicated that AMF observably upregulated the genes’ expressions (i.e., CsCAT and CsSOD) in both the 0 and 100 mmol/L NaCl seedlings. Meanwhile, the 100 mmol/L NaCl seedlings represented markedly lower antioxidant enzyme activities (i.e., SOD, CAT, and POD) and gene expressions (i.e., CsSOD and CsCAT) than the non-NaCl seedlings, irrespective of AMF inoculation. These results imply that AMF has a positive role in strengthening salt tolerance and on the quality of fresh tea leaves.

Management of mushroom resources in Spanish forests: a review

Abstract Mycological resources have attracted considerable interest from the public recently. In this context, forest mycological management of wild mushrooms has emerged a research field and is developing rapidly with the objective to sustainably use and conserve mushrooms in multifunctional forests. Although the term ‘mycosilviculture’ was coined relatively recently, forest management of mycological resources and fungal silviculture began already in the 1980s. This study reviews the literature on the forest management of wild mycological resources with emphasis on studies in Spanish Mediterranean forests. The review covers some of the most important aspects of management, such as the diagnosis of mycological resources through inventory and sampling protocols, predictive models of mushroom yield, stand variables and mycosilvicultural practices that affect mushroom yield and fungal diversity. Finally, the potential of mycorrhizal applications for mycosilviculture is briefly discussed. Most of these studies have been based on carpophore inventories, and few have analyzed soil and air fungal biomass. The Mediterranean climate determines mushroom yields; so far, mushroom yields models have been developed mainly for Boletus gr. edulis and Lactarius gr. deliciosus species and for pine forest ecosystems. In the future, it will be necessary to adjust these models to new climatic conditions, and to investigate the complex interactions between different yield and/or fungal diversity factors, adjust the scale of study and fungus-host specificity. So far, few studies have been carried out on mycosilviculture in Mediterranean forests, addressing the effect of thinning and clearcutting on fungal communities; moreover, experiences of mycological management of shrublands, prescribed burning, management of woody debris or selective planting of mycorrhizal seedlings in forests are scarce. The need to study other Mediterranean forest ecosystems is pointed out.

Intraspecific Competition Results in Reduced Evenness of Tuber melanosporum Mating-Type Abundance from the Nursery Stage.

The highly prized black truffle is a fungus mostly harvested in orchards planted with mycorrhizal seedlings. It is an obligatory outcrossing fungus with a single MAT locus containing two alternative mating-type idiomorphs. In the orchards, at the mycorrhizal level, these mating types are frequently spatially segregated. Some studies found that this segregation was pronounced from the nursery stage, whereas others did not find such a marked segregation. Besides, information on the host tree species and nursery conditions used in Spain, one of the main truffle-producing countries, are very scarce. In this study, we investigated the temporal dynamics of mating types in nursery seedlings of Quercus ilex and Quercus faginea, as well as the influence of cultural conditions in the nursery. Our results indicated that at the plant level, there was a trend for one of the mating types to dominate over the other from the first to the second year in the nursery, in both host species and both nursery conditions tested. However, this segregation process was not so sharp as previously reported. Our results support the hypothesis that intraspecific competition results in reduced evenness of mating-type abundance from the nursery stage, although almost all seedlings maintained both mating types and, at the seedling batch scale, the occurrence of both mating types was roughly balanced.

Presence and production of Tuber aestivum in relation with the soil environment of a semi-natural experimental truffle orchard in Spoleto, Central Italy

Truffles produced by Tuber species (Ascomycota) represent an additional income in economically marginal areas, especially if cultivating mycorrhized seedlings in dedicated truffle orchards. However, despite the great progress made in cultivation, truffle production has not increased substantially. One of the reasons may be the lack of knowledge on soil as a key component of truffle species habitats. This is the case for Tuber aestivum, whose soil environment has been studied less than those of T. magnatum and T. melanosporum due to the lower economic value of its ascocarps. We did the present study in an experimental truffle orchard submitted to a light tillage before our investigation and characterized by the presence of different host tree species and soil variation in space. We assessed whether truffle production and T. aestivum mycelial DNA in soil varied depending on symbiont tree species, soil type or both by comparing sub-areas characterized by the presence/absence of: i) two landforms; ii) four host tree species; and iii) the truffle brûlé, i.e., the area lacking herbaceous cover when root colonization by T. aestivum occurs.Results show that combined variations in chemical and physical properties determined by soil forming processes can make an area suitable or not for T. aestivum. The establishment of brûlé and higher ascocarp production occurred in the more alkaline and less compact soil type, where the resistance to ascocarp volume enlargement is lower and aeration of the soil surface layer is higher. The tillage carried out in the truffle orchard presumably mimicked the effect of the brûlé on the soil structure, allowing the enlargement of the productive area outside the brûlé itself and showing how the management of a truffle plantation, even if sub-optimal for T. aestivum colonization, can influence its productive capacity. Our results further suggest that even in the best environmental conditions not all host trees will enter in production, while in less suitable soil conditions little or no production should be expected.

Arbuscular mycorrhizal fungi improve legume seedling performance as the competition with conspecific neighbouring adult plants decreases

In temperate grasslands, the balance between competitive and facilitative interactions between adult plants and conspecific seedlings can be affected by defoliation intensity, soil nutrient deficiency and arbuscular mycorrhizal fungi (AMF). Here, we investigated the effect of AMF on the interactions between Lotus tenuis Waldst. & Kit. seedlings grown in the presence or absence of conspecific adult plants defoliated at different intensities (0, 50 and 75%) in a P-deficient soil of the Salado River Basin (Argentina). Mycorrhizal seedlings grown near defoliated and non-defoliated adult plants produced less shoot dry weight (DW) than non-mycorrhizal counterparts, whereas mycorrhizal seedlings alone showed 258% and 504% more shoot DW and shoot P content, respectively than non-mycorrhizal counterparts. This was associated with higher growth and P uptake of mycorrhizal adult plants than non-mycorrhizal counterparts. The competition index between seedlings and adult plants showed competition interaction in mycorrhizal systems (from −2.6 to −1.9) and neutral interaction in non-mycorrhizal systems (near to zero) despite the defoliation intensity. We propose that moderate defoliation (50%) allows maintaining high mycorrhizal benefits in adult plants (110.1% and 168.8% mycorrhizal growth and P response, respectively), whereas high defoliation (75%) decreases mycorrhizal benefits (27.18% and 80.21% mycorrhizal growth and P response, respectively). We highlight AMF symbiosis as an important strategy of L. tenuis adult plants to regulate the growth of neighbouring conspecific seedlings in a P-deficient soil.

Effects of arbuscular mycorrhizal fungi inoculation on non-structural carbohydrate contents and C:N:P stoichiometry of Heptacodium miconioides under drought stress

A pot experiment was conducted to investigate the effects of drought stress and arbuscular mycorrhizal fungi (AMF) inoculation on C:N:P stoichiometry and non-structural carbohydrate (NSC) contents in two-year-old Heptacodium miconioides seedlings. There were four treatments, including control (CK), drought stress (D), AMF inoculation (AMF), and combined drought stress and AMF inoculation (D+AMF). The results showed that drought stress significantly reduced AMF colonization rate, whereas plant height and leaf number of inoculated treatment were significantly higher than the non-inoculated treatment. Inoculation with AMF significantly increased soluble sugar and NSC content in root and leaf, as well as starch content in stem and leaf. The inoculation significantly decreased the stem and leaf soluble sugar to starch ratio under drought stress. Drought stress caused a significant increase in C content in roots and leaves, and a significant decrease in P content in stems. Compared with no inoculation drought stress, P content in roots, stems, leaves, and C content in leaves of mycorrhizal seedlings were significantly increased by inoculation under drought stress, whereas root C and N content and stem C content were significantly reduced. Under drought stress, AMF inoculation significantly decreased C:N, C:P, and N:P ratios in roots and stems, and N:P ratios in leaves of H. miconioides. P content in roots and leaves were significantly positively correlated with soluble sugar and NSC content. Stem P content was significantly positively correlated with starch and NSC content. N:P ratios in each organ was significantly negatively correlated with NSC content. In all, inoculation with AMF can improve the drought tolerance of H. miconioides seedling by increasing soluble sugar content in roots and leaves and the soluble sugar/starch ratio in roots, improving starch content in above-ground organs, promoting the P absorption, and reducing N:P ratios in each organ. Therefore, AMF colonization could improve the survival rate of H. miconioides seedling in dry environments.

Effect of inoculation with arbuscular mycorrhizal fungi on growth of Catalpa bungei

Background: Catalpa bungei is a well-known, valuable, ornamental, high-quality timber tree traditionally cultivated in China because of its excellent quality, decay resistance, wide applicability, and attractive form. The aim of this study was to evaluate the effects of inoculation with arbuscular mycorrhizal fungus (AMF) on the transplant survival rate and growth of C. bungei seedlings under greenhouse conditions. Methods: Two treatments were applied in a completely randomized experimental design: inoculation with Rhizophagus intraradices, and, as a control, soil without inoculum. Results: Four months after inoculation, AMF had colonized 76.05% of plant roots and significantly improved plant growth. With the establishment of the symbiotic relationship, AMF inoculation significantly improved the seedling transplant survival rate by 20%, promoted major growth traits (plant height, basal diameter, leaf area, and specific leaf area), accelerated biomass accumulation (roots, stems, and leaves), and changed the biomass allocation patterns. In addition, compared with non-inoculated treatments, inoculation with AMF increased photosynthetic parameters and chlorophyll contents, elevated major root morphological parameters, changed the proportion of particle sizes of soil micro-aggregates, and promoted the accumulation of nutrients in roots and leaves. Conclusions: The effects on transplant survival, growth and development were more pronounced in C. bungei seedlings inoculated with R. intraradices. Mycorrhizal seedlings of C. bungei can therefore be widely applied in plant transplantation and production practices.

Morphoanatomical and phylogenetic characterization of the ectomycorrhiza between Laccaria squarrosa with Pinus pseudostrobus and its relevance for reforestation programs

Background: Pinus (Coniferophyta) and Laccaria (Basidiomycota) establish ectomycorrhizal symbioses in natural forests . However, their detailed morphoanatomical and phylogenetic characterization have received little attention. Accurate identification of native host symbionts is of paramount relevance to the production of mycorrhized seedlings for successful reforestation programs.
 Questions/Objective: We aimed to determine if L. squarrosa is able to establish ectomycorrhizal symbiosis with gymnosperms, thereby widening its host range and highlighting its relevance as a potential inoculant for pine seedlings. Currently, L. squarrosa is only known from its type collection associated with the angiosperm Fagus grandifolia var. mexicana .
 Studied species: The fungus L. squarrosa and Pinus pseudostrobus , a tree endemic to Mexico. 
 Study site and dates: A Pinus - Quercus forest in Piedra Canteada, Nanacamilpa, Tlaxcala; 2018-2020.
 Methods: L. squarrosa basidiomata were identified and ectomycorrhizal roots were collected and morphoanatomically characterized. For molecular identification, DNA was extracted, PCR was performed targeting the nuclear ribosomal internal transcribed spacer region (nucrDNA ITS) for the mycobiont identification and the chloroplastic single-locus trnL region for the phytobiont.
 Results: In the phylogenetic analyses, our sequences from basidiomata and ectomycorrhizae clustered together with L. squarrosa with high values of supporting identity. Meanwhile, P. pseudostrobus was molecularly identified as the phytobiont.
 Conclusions: This is one of the few worldwide characterizations of Laccaria ectomycorrhiza under field conditions and contributes to the understanding of the ecology, distribution, and economic relevance of the symbiotic association. Our data suggest that L. squarrosa has potential for use as a native inoculant for P. pseudostrobus tree production.
 
 
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Defense responses of arbuscular mycorrhizal fungus-colonized poplar seedlings against gypsy moth larvae: a multiomics study

Arbuscular mycorrhizal (AM) fungi may help protect plants against herbivores; however, their use for the pest control of woody plants requires further study. Here, we investigated the effect of Glomus mosseae colonization on the interactions between gypsy moth larvae and Populus alba × P. berolinensis seedlings and deciphered the regulatory mechanisms underlying the mycorrhizal-induced resistance in the leaves of mycorrhizal poplar using RNA-seq and nontargeted metabolomics. The resistance assay showed that AM fungus inoculation protected poplar seedlings against gypsy moth larvae, as evidenced by the decreased larval growth and reduced larval survival. A transcriptome analysis revealed that differentially expressed genes (DEGs) were involved in jasmonic acid biosynthesis (lipoxygenase, hydroperoxide dehydratase, and allene oxide cyclase) and signal transduction (jasmonate-ZIM domain and transcription factor MYC2) and identified the genes that were upregulated in mycorrhizal seedlings. Except for chalcone synthase and anthocyanidin synthase, which were downregulated in mycorrhizal seedlings, all DEGs related to flavonoid biosynthesis were upregulated, including 4-coumarate-CoA ligase, chalcone isomerase, flavanone 3-hydroxylase, flavonol synthase, and leucoanthocyanidin reductase. The metabolome analysis showed that several metabolites with insecticidal properties, including coumarin, stachydrine, artocarpin, norizalpinin, abietic acid, 6-formylumbelliferone, and vanillic acid, were significantly accumulated in the mycorrhizal seedlings. These findings suggest the potential of mycorrhiza-induced resistance for use in pest management of woody plants and demonstrate that the priming of JA-dependent responses in poplar seedlings contributes to mycorrhiza-induced resistance to insect pests.

Effects of arbuscular mycorrhizal inoculation on the growth, photosynthesis and antioxidant enzymatic activity of Euonymus maackii Rupr. under gradient water deficit levels.

The role of arbuscular mycorrhizal (AM) fungus (Rhizophagus intraradices) in the amelioration of the water deficit-mediated negative influence on the growth, photosynthesis, and antioxidant system in Euonymus maackii Rupr. was examined. E. maackii seedlings were subjected to 5 water deficit levels, soil water contents of 20%, 40%, 60%, 80% and 100% field capacity (FC), and 2 inoculation treatments, with and without AM inoculation. The water deficit increasingly limited the seedling height, biomass accumulation in shoots and roots, chlorophyll content, gas exchange and chlorophyll fluorescence parameters with an increasing water deficit level. In addition, water deficit stimulated the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), in both shoots and roots, except under 20% FC conditions. E. maackii seedlings under all water deficit conditions formed symbiosis well with AM fungi, which significantly ameliorated the drought-mediated negative effect, especially under 40% and 60% FC conditions. Under 40% to 80% FC conditions, AM formation improved seedling growth and photosynthesis by significantly enhancing the biomass accumulation, chlorophyll content and assimilation. Mycorrhizal seedlings showed better tolerance and less sensitivity to a water deficit, reflected in the lower SOD activities of shoots and roots and CAT activity of shoots under 40% and 60% FC conditions. Downregulation of the antioxidant system in mycorrhizal seedlings suggested better maintenance of redox homeostasis and protection of metabolism, including biomass accumulation and assimilation. All the results advocated the positive role of R. intraradices inoculation in E. maackii against a water deficit, especially under 40% FC, which suggested the distinct AM performance in drought tolerance and the potential role of the combination of E. maackii-AM fungi in ecological restoration in arid regions.

The mycorrhizal-induced growth promotion and insect resistance reduction in Populus alba × P. berolinensis seedlings: a multi-omics study.

Arbuscular mycorrhizal (AM) fungi are an alternative to chemical insecticides or fertilizers, and there is an urgent need to extend the application of AM fungi to woody plants. This study aims to investigate the growth and resistance against the gypsy moth larvae (Lymantria dispar) in Glomus intraradices-colonized Populus alba × P. berolinensis seedlings, and to unravel the transcriptome and metabolome phenotypes recruited by AM fungus colonization that affect plant growth and insect resistance. Our results showed a positive mycorrhizal growth response, i.e., growth and biomass of mycorrhizal seedlings were enhanced. However, AM fungus inoculation reduced the resistance of poplar to gypsy moth larvae, as evidenced by the decreased carbon/nitrogen ratio in leaves, as well as the increased larval growth and shortened larval developmental duration. Transcriptome analysis revealed that in both auxin and gibberellin signaling transductions, all nodes were responsive to AM symbiosis and most differentially expressed genes belonging to effectors were up-regulated in mycorrhizal seedlings. Furthermore, the two key enzymes (4-coumarate-CoA ligase and trans-cinnamate 4-monooxygenase) involved in the synthesis of p-Coumaroyl-CoA, an initial metabolite in flavonoid biosynthesis and the first rate-limiting enzyme (chalcone synthase) in flavonoid biosynthesis, were down-regulated at the transcriptional level. Consistent with the transcriptome results, metabolome analysis found that the amounts of all differentially accumulated flavonoid compounds (e.g., catechin and quercetin) identified in mycorrhizal seedlings were decreased. Taken together, these findings highlight the diverse outcomes of AM fungi-host plant-insect interaction and reveal the regulatory network of the positive mycorrhizal growth response and mycorrhizal-induced reduction of insect resistance in poplar.

Growth responses of ectomycorrhizal and arbuscular mycorrhizal seedlings to low soil nitrogen availability in a tropical montane forest

Abstract Differences in nutrient acquisition pathways between arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi are associated with greater soil organic matter accumulation and reduced inorganic nitrogen (N) availability in EM‐dominated forests. These plant–soil feedbacks are expected to influence seedling recruitment and the maintenance of diversity. Montane forests of Central America are characterized by a mosaic of AM and EM dominance. We used a seedling transplant and soil manipulation experiment on Volcán Barú, Panama, to evaluate whether patches of oak (EM‐dominated) forest and mixed (AM‐dominated) forest affect seedling growth. We predicted that (a) plant–soil feedbacks would result in lower soil inorganic N availability in oak than in mixed forests, (b) consequently AM seedlings would grow more slowly and have lower foliar N concentrations in oak forest and (c) dependence of EM seedlings on organic N uptake via mycorrhiza would mean that inorganic N addition would increase seedling performance for AM but not EM (i.e. oak) seedlings. As soil organic matter accumulation may affect seedling performance beyond altering nutrient supply, we also tested whether organic matter removal differentially affected AM and EM seedlings. Nitrogen availability was six times lower and the soil organic layer three times deeper in oak‐dominated stands compared to mixed stands. Foliar N was lower for AM seedlings growing in oak than in mixed forest, but did not differ for oak seedlings and was increased only marginally by N addition for both AM and EM seedlings growing in both AM and EM forests. Seedling growth did not respond to N addition or organic matter removal. However, AM seedlings generally grew slower in oak forest compared with AM forest, consistent with lower foliar N concentration and low‐light availability. These results suggest that changes in soil nitrogen availability have a limited effect on seedling growth. In the neotropics, EM tree communities occur at high elevation. Future upslope migration of trees may result in AM‐dominated tree communities encountering unfavourable soil conditions generated by EM‐dominated canopies. While longer term experiments are needed, our results suggest that AM seedlings may not be able to tolerate conditions associated with EM forest. A free Plain Language Summary can be found within the Supporting Information of this article.

Bracken fern does not diminish arbuscular mycorrhizal fungus inoculum potential in tropical deforested areas.

Tropical montane forests are threatened by uncontrolled fire events because of agricultural expansion. Consequently, deforested areas frequently are dominated by the bracken fern, Pteridium spp., for long periods, and forest regeneration is limited. Despite considerable research on bracken-dominated ecosystems, little is known about the relationship between bracken mycorrhizal fungi and tree seedlings. Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with terrestrial plants, providing nutrients and protection against pathogens and promoting seedling growth and establishment. Therefore, AMF inoculum have high potential for forest restoration programs. Here, we compare the species diversity of AMF spores, root colonization, and seedling growth of Clusia trochiformis 1year after the addition of different liquefied root inocula: forest conspecific, forest heterospecific, and from Pteridium rhizomes. Thirteen morphospecies of arbuscular mycorrhizal fungi were identified on the roots of C. trochiformis, and Glomus spp. were the most abundant in all treatments. No differences were observed in spore species richness and diversity among treatments, but spore density was the highest subsequent to the Pteridium inoculum. There was no significant difference in mycorrhizal root colonization and seedling growth of C. trochiformis among inoculated treatments. We found a positive relation between root colonization and total biomass. This study shows that the AMF communities in bracken areas and forests present similar characteristics and that the bracken fern does not limit AMF inoculum potential, favouring seedling growth of Clusia.

Effect of Rhizophagus intraradices on growth and physiological performance of Finger Millet (Eleusine coracana L.) under drought stress

Under abiotic stress conditions, arbuscular mycorrhizal (AM) fungi help plants by improving nutrient and water uptake. Finger millet (Eleusine coracana L.) is an arid crop having soils with poor water holding capacity. Therefore, it is difficult for the plants to obtain water and mineral nutrients from such soil to sustain life. To understand the role of mycorrhizal symbiosis in water and mineral up-take from the soil, we studied the role of Rhizophagus intraradices colonization and its beneficial role for drought stress tolerance in finger millet seedlings. Under severe drought stress condition, AM inoculation led to the significant increase in plant growth (7 %), phosphorus and chlorophyll content (29 %). Also, under drought stress the level of osmolytes such as proline and soluble sugars were found to be increased in AM inoculated seedlings. Under water stress, the lipid peroxidation in leaves of mycorrhized seedlings was reduced by 29 %. The flavonoid content of roots in AM colonized seedlings was found 16 % higher compared to the control, whereas the leaves were accumulated more phenol. Compared to the control, ascorbate level was found to be 25 % higher in leaf tissue of AM inoculated seedlings. Moreover, glutathione (GSH) level was also increased in mycorrhiza inoculated seedlings with a maximum increment of 182 % under severe stress. The results demonstrated that AM provided drought tolerance to the finger millet seedlings through a stronger root system, greater photosynthetic efficiency, a more efficient antioxidant system and improved osmoregulation.

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.

Cultivation of Desert Truffles—A Crop Suitable for Arid and Semi-Arid Zones

Desert truffles are edible hypogeous (forming fruit bodies below ground) fungi that grow in semi-arid and arid areas. They are highly valued for both their culinary and medicinal properties in the Mediterranean basin, the Middle East and the Gulf areas. Desert truffles form mycorrhizae mostly with plants belonging to the Cistaceae family, mainly with Helianthemum species. These truffles are still, usually, collected from the wild, but loss of habitats due to urbanization, desertification, intensive agriculture and global warming, along with an urgent need to develop new crops adapted to arid conditions, are currently hastening efforts towards their domestication. Here, we sum up the successful research leading to cultivation of this crop, based on plots that were established in sandy to silt soils with high pH values and low mineral contents. We report suitable methods for production of mycorrhized seedlings and preferred planting methods. We found that under natural conditions yields are affected by water availability, so irrigation regimes to ensure good yields were sought. Although good yields were indeed obtained in some years, fluctuations in yields over the years were significant; the reasons for this are not entirely clear and are currently under study. This crop is particularly well suited to relatively marginal conditions but prospects for establishment of desert truffles as a niche crop for arid and semi-arid areas depend on further improvements in yields.

Mycorrhization of pecans with European truffles (Tuber spp., Tuberaceae) under southern subtropical conditions

Pecan trees are known to form ectomycorrhizae with a wide range of fungi, including commercial truffles that can be cultivated in agroforestry systems. Here, we investigated whether pecans can be successfully mycorrhized by Tuber spp. and whether the mycorrhization affects growth parameters and nutrient content of two productive pecan cultivars under southern subtropical conditions. We also sought to define procedures of mycorrhization adapted to the subtropics. The seedlings of two pecan cultivars (Barton and Importada) were inoculated with both Tuber aestivum and T. brumale and grown in a nursery for 12 months. The levels of ectomycorrhizal colonization and the morphological and chemical parameters of the seedlings were analyzed. The proposed mycorrhization protocol was successful, as all truffle-inoculated seedlings exhibited a high percentage of mycorrhized fine roots, on average 70% with T. aestivum and 88% with T. brumale. In both pecan cultivars, mycorrhization by the Tuber species reached levels at which all seedlings would qualify as suitable for commercialization. Notably, the cultivar Barton inoculated with T. brumale exhibited higher total biomass accumulation and growth of roots and shoots. Shoot and root parameters did not show nutrient deprivation. The nutrient status after one year of cultivation in a nursery also supported that the applied protocol was adequate to maintain healthy mycorrhized seedlings with suitable nutritional status for out-planting of seedlings in a commercial plantation. To our knowledge, this is the first study on the mycorrhization of pecan seedlings with European truffles under southern subtropical conditions. Our results suggested that the tested cultivars have a high potential for truffle production considering the necessary substrate, site, and management adaptations for selected commercial truffle species and the requirements for pecan orchards.

Screening and identification of potassium-dissolving bacteria from different rhizosphere soil of Paris polyphylla var. yunnanensis

The study aiming at exploring the potassium-dissolving capacity of rhizosphere potassium-dissolving bacteria from diffe-rent sources and screen the strains with high potassium-dissolving ability, so as to lay a theoretical foundation for cultivation and quality improvement of Paris polyphylla var. yunnanensis sources. The rhizosphere soil of 10 wild and transplanted species from Yunnan, Sichuan and Guizhou provinces was used as the research object. Potassium-dissolving bacteria were isolated and purified, and their potassium-dissolving capacity was determined by flame spectrophotometry, and identified by physiological, biochemical and molecular biological methods. Twenty-six potassium-dissolving bacteria were purified and 13 were obtained from wild and transplanted strains respectively. It was found through the determination of potassium-dissolving capacity that the potassium-dissolving capacity of 26 strains was significantly different, and the mass concentration of K~+ in the fermentation broth were 1.04-2.75 mg·L~(-1), the mcentration of potassium were 0.01-1.82 mg·L~(-1). The strains were identified as Bacillus, Agrobacterium rhizome and Staphylococcus by physiological, biochemical and 16 S rDNA molecular methods, among them Bacillus amylolyticus(4 strains) was the dominant bacterium of Bacillus. The physiology and biochemistry of rhizosphere potassium-dissolving bacteria in P. polyphylla var. yunnanensis rhizosphere were diffe-rent, and the living environment were different, so the potassium-dissolving capacity also changed. Strain Y4-1 with the highest potassium decomposability was Bacillus amylolytic with a potassium increase of 1.82 mg·L~(-1). The potassium-dissolving ability and the distribution of potassium-dissolving bacteria were different in various habitats. The screening of potassium-dissolving bacteria provided a new strain for the preparation of microbial fertilizer. It is expected that B. amyloidococcus Y4-1 can be used as an ideal strain to cultivate mycorrhizal seedlings of P. polyphylla var. yunnanensis.

Mycorrhiza-induced plant defence responses in trifoliate orange infected by Phytophthora parasitica

Arbuscular mycorrhizal fungi (AMF) reduce disease incidence of host plants through the competition of carbon sources and direct inhibition of pathogens, as well as through induction of biochemical and molecular responses. However, it is not known whether AMF enhance the resistance to Phytophthora parasitica-induced root rot in citrus and what the underlying mechanisms are. This study was carried out to analyze roles of Funneliformis mosseae (a mycorrhizal fungus) in plant defence responses of Poncirus trifoliata infected by P. parasitica. A week after the pathogen infection, mycorrhizal seedlings possessed higher expression of root mitogen-activated protein kinase 3 (PtMAPK3) regardless of P. parasitica infection. F. mosseae induced higher root salicylic acid (SA) concentrations, accompanied with up-regulation of SA synthesis genes (PtPAL1 and PtEPS1), regardless of being infected with P. parasitica or not. Jasmonic acid (JA) synthesis genes were down-regulated by mycorrhization in the absence of P. parasitica and up-regulated (except for PtAOC) by mycorrhization under P. parasitica infection. Moreover, F. mosseae stimulated higher expression of pathogenesis-related protein gene 1 (PtPR1), PtPR4, and PtPR5, especially under P. parasitica infection. F. mosseae inoculation increased levels of root lignin, calmodulin, and total soluble phenol and activities of root chitinase, phenylalanine ammonialyase, and β-1,3-glucanase, and decreased concentrations of root nitric oxide with or without P. parasitica infection. These results implied that F. mosseae elicited MAPKs cascades as well as SA- and calmodulin-mediated signal pathways to activate disease-defence genes, proteins, and compounds to early-warn P. parasitica infection for enhancing tolerance of root rot in trifoliate orange.

Arbuscular mycorrhizal symbiosis facilitates apricot seedling (Prunus sibirica L.) growth and photosynthesis in northwest China

Arbuscular mycorrhizal (AM) fungi can successfully enhance photosynthesis (Pn) and plants growth in agricultural or grassland ecosystems. However, how the symbionts affect species restoration in sunlight-intensive areas remains largely unexplored. Therefore, this study’s objective was to assess the effect of AM fungi on apricot seedling physiology, within a specific time period, in northwest China. In 2010, an experimental field was established in Shaanxi Province, northwest China. The experimental treatments included two AM fungi inoculation levels (0 or 100 g of AM fungal inoculum per seedling), three shade levels (1900, 1100, and 550 µmol m−2 s−1), and three ages (1, 3, and 5 years) of transplantation. We examined growth, Pn, and morphological indicators of apricot (Prunus sibirica L.) seedling performances in 2011, 2013, and 2015. The colonization rate in mycorrhizal seedlings with similar amounts of shade is higher than the corresponding controls. The mycorrhizal seedling biomass is significantly higher than the corresponding non-mycorrhizal seedling biomass. Generally, Pn, stomatal conductance (Gs), transpiration rate (Tr), and water use efficiency are also significantly higher in the mycorrhizal seedlings. Moreover, mycorrhizal seedlings with light shade (LS) have the highest Pn. WUE is increased in non-mycorrhizal seedlings because of the reduction in Tr, while Tr is increased in mycorrhizal seedlings with shade. There is a significant increase in the N, P, and K fractions detected in roots compared with shoots. This means that LS had apparent benefits for mycorrhizal seedlings. Our results also indicate that AM fungi, combined with LS, exert a positive effect on apricot behavior.