There are substantial carbon exchange fluxes among soil, vegetation and atmosphere in the terrestrial ecosystems, which are highly relevant to global climate changes. Mycorrhizal fungi can form symbiotic associations with most terrestrial plants, linking the above- and below-ground ecosystems through mineral nutrient-carbon exchange; thus, mycorrhizal fungi play crucial roles in terrestrial carbon cycling. This review summarized the involvements of mycorrhizal fungi in the terrestrial carbon cycling processes, including the carbon input, and formation, stabilization, and decomposition of soil organic matter. Studies have demonstrated that mycorrhizal fungi markedly influence the terrestrial carbon input processes by alleviating plant nutrient deficiencies, improving plant stress resistance, influencing plant photosynthesis, and regulating plant diversity-productivity relationships, subsequently sustaining or improving primary productivity of terrestrial vegetation. A considerable proportion of photosynthetic carbon is channeled directly into the soil matrix via the fungal mycelial network, where it is partly converted into microbial-derived organic carbon, further changes the composition of soil organic carbon, and be stabilized through association with minerals and/or forming soil aggregates. Mycorrhizal fungi can affect the decomposition and transformation of soil organic matter mainly through two mechanisms: the rhizosphere priming effects and/or hyphosphere biogeochemical processes. These mechanisms involve the secretion of specific extracellular enzymes, shaping hyphosphere microbial communities, induction of chemical oxidation, and competition for limited resources (e.g., nutrients and water) with free-living saprotrophs. Considering the sensitivity of mycorrhizal fungi to environmental and climate changes, we also discuss the impact of global change factors on soil carbon cycling mediated by mycorrhizal fungi. Finally, we proposed future research directions, emphasizing a need for in-depth studies on the role of mycorrhizal fungi in terrestrial carbon cycling and their environmental dependence based on network experiments in typical ecosystems. Quantitative studies should be strengthened to integrate mycorrhizal fungi into ecosystem carbon cycling models, and mycorrhizal technologies should be developed and practiced in ecological restoration and agriculture to facilitate terrestrial carbon sequestration for achieving the national carbon neutrality goals and combating climate changes.

Aims Arbuscular mycorrhizal fungi (AMF) are widely distributed in grassland ecosystems. They make great contribution to the productivity and stability of grassland ecosystems. Our purpose was to explore the AMF community distribution characteristics and driving mechanism in grassland ecosystems.

Methods This study was conducted in 18 different grassland types. We demonstrate the AMF community characteristics and driving factors by investigating plant community characteristics, analyzing soil physicochemical properties and AMF communities.

Important findings In different grassland types, the dominant genera of AMF community were Claroideoglomus, Septoglomus, Diversispora, Rhizophagus, Acaulospora, Glomus and Ambispora. In addition, there exist significant differences in speicies composition and diversity of AMF communities, and the AMF diversity and rare operational taxonomic unites (OTUs) in Stipa purpurea grassland was relatively higher than those of other grassland types. Results from the structural equation model showed that AMF community diversity was significantly influenced by plant community diversity and soil pH, and AMF community composition was significantly influenced by temperature, soil moisture content and plant community composition. To sum up, abundant AMF resources were contained within Chinese natural grassland, and the AMF community characteristics in different grassland types are significantly different. Meanwhile, plant communities have remarkable driving effect on AMF communities in grassland ecosystems. So protecting grassland plant diversity is of great importance for maintaining soil microbial community stability.

Aims Invasive Sphagneticola trilobataseriously endangers the stability of local plant communities and ecosystems. Recently, chemical control is still the most important method for controlling it. Arbuscular mycorrhizal fungi (AMF) play an important role in the growth of host plants and their resistance to environmental stresses. Therefore, this study tested whether AMF played an important role in herbicide resistance of S. trilobata.

Methods In this study, a greenhouse experiment was conducted, in which the stems of S. trilobata were subject to the following four treatments: control (CK), only inoculation of AMF, only application of herbicides (HC), and herbicide plus AMF (AMF + HC).

Important findings The results showed that under the stress of glyphosate ammonium salt, the colonization rate, vesicle number and ratio of colonization abundance class increased significantly. Compared with herbicide application, AMF inoculation significantly increased the leaf area, above-ground biomass and root shoot ratio of S. trilobata, and significantly reduced the flavonol relative content and the damaged leaf number. This study found that the herbicide stress on invasive S. trilobata was alleviated because of the symbiosis with AMF. Therefore, AMF may greatly improve the resistance to chemical herbicides in this invasive forb. The results of this study may provide a new insight into the effective control of invasive weeds.

Aims Fine roots are important organs for absorbing and transporting nutrients during plant growth and development. Investigating the variation and trade-offs among functional traits of seedling fine roots of different mycorrhizal types is conducive to a more comprehensive understanding of their early survival strategies.

Methods In this study, we analyzed the variation and trade-offs across different mycorrhizal types, root orders and root functional modules. In particular, we measured three morphological traits (specific root length (SRL), root tissue density (RTD), and root diameter (D)), and four chemical traits (total phosphorus (P) content, total carbon (C) content, total nitrogen (N) content, carbon nitrogen ratio (C:N)), in three arbuscular mycorrhiza (AM) and three ectomycorrhiza (EM) tree species seedlings in mixed broadleaf-Korean pine (Pinus koraiensis) forest in the Liangshui National Nature Reserve, Heilongjiang Province.

Important findings The results showed that EM seedling fine roots exhibited higher RTD compared with AM seedlings, potentially due to the colonization patterns of AM fungi which increased root volumes and increased the absorptive capacity of limiting nutrients. Other traits did not differ significantly between the two types of mycorrhiza, with AM seedling roots aligning with a more resource-acquired strategy, in contrast to EM seedlings. As the root order increased, RTD and D of both mycorrhiza-association seedling roots increased significantly, while SRL decreased, indicating a functional shift from absorption to transportation. Concurrently, C content and C:N of roots increased, while the N content of roots decreased with increasing root order. A notable trade-off was observed between morphological and chemical traits of fine roots, suggesting that changes in root functional modules with root order are accompanied by corresponding shifts in root traits. These findings support the root economics spectrum (RES), highlighting the complex interplay between root morphology, chemistry and ecological strategy.

Aims The nutrient foraging strategies of fine roots and arbuscular mycorrhizal (AM) fungi directly affect plant productivity and carbon sequestration, which are a key factor influencing the stability of forest ecosystems. Nutrient foraging accuracy is an important aspect of the nutrient foraging strategy, which refers to the ability of plants to accurately deploy their roots and mycelia to relatively nutrient-rich patches. However, the tradeoff between foraging precision of root length and foraging precision of mycelia of arbuscular mycorrhizal tree species and whether fine root morphology can predict foraging accuracy are still controversial.
Methods In this study, 17 AM tree species in a natural broadleaf evergreen forest in the central subtropics were tested for responses to phosphorus addition to in situ root bags in the field to simulate phosphorus nutrient patches in the soil. After 4 months application of phosphorus fertilizer, morphological scanning and analysis were carried out on the fine roots of the control group and the phosphorus addition group. Mycelia in the soil were extracted by the membrane filtration method and observed by electron microscope. Mycelia with no septa in the middle and easy to stain were screened as AM mycelia, and their length was calculated. On this basis, root length foraging precision and mycelial foraging precision were calculated to investigate their trade-off and also their correlation with fine root morphology in subtropical AM tree species.
Important findings Root length foraging precision and mycelial foraging precision of AM species were independent of each other. There was a significant positive correlation between fine root tissue density and root length foraging precision, a significant negative correlation between fine root diameter and mycelial foraging precision, and a significant positive correlation between specific root length and mycelial foraging precision. These results can help understand root nutrient foraging strategies of AM species in subtropical evergreen broadleaf forests, and suggest that easily observable metrics such as fine-root morphology can be used for assessing the accuracy of fine-root nutrient foraging of AM species.

Aims This study aimed to illustrate community structure, molecular ecological network and driving factors of ectomycorrhizal fungi associated with Pinus sylvestris var. mongolica at different growth periods, and provide a theoretical basis for sustainable management of P. sylvestris var. mongolica plantation.
Methods Pinus sylvestris var. mongolica with different tree ages (23, 33 and 44 a) in Mau Us Sandy Land were targeted. The species compositions, interaction and main drivers of ectomycorrhizal fungi at the early growth period (Apr.), vigorous growth period (July) and the late growth period (Sept.) were identified by field investigation and sampling, illumina high-throughput sequencing and molecular ecological network analysis, respectively.
Important findings 1) The growth period had significant effect on the richness and Chao1 index of ectomycorrhizal fungi, with significantly higher Chao1 and Simpson diversity index in vigorous growth period than in early and late growth periods. The tree age had no significant effect on the ectomycorrhizal fungal diversity index. 2) In Mau Us Sandy Land, the ectomycorrhizal fungi associated with P. sylvestris var. mongolica were identified into 2 phyla, 4 classes, 7 orders, 18 families, and 28 genera. The dominant genera were Tomentella, Inocybe and Geopora at the early, vigorous and late growth periods, respectively. The Tomentella and Inocybe were the common indicator genera in both vigorous and late growth periods. 3) At the end of the growing season, the nodes and edges of the ectomycorrhizal fungal networks were the largest, indicating that the ectomycorrhizal fungal community was more complex and there was strong interaction between fungal species. 4) Soil pH and annual relative humidity were the key environmental factors that significantly affected the community composition of ectomycorrhizal fungi. Our results demonstrated that the diversity and community composition of ectomycorrhizal fungi were affected by the growth stage and tree age, with a stronger effect in growth stage than in tree age. The seasonal dynamic distribution of ectomycorrhizal fungi mainly depended on soil properties and climate conditions.

Aims Fire is an important disturbance factor in the northern forest ecosystem, and black carbon, a product of fire, widely exists in most forest soils. Many studies have shown the positive impact of black carbon on plant yield, but little is known about the synergy between black carbon and microorganisms (such as mycorrhizal fungi) which can promote plant growth. Ectomycorrhiza (ECM) fungi is like a bridge between coniferous trees and soil in the northern forest ecosystem. Exploring the changes of ECM fungal community after fire can provide a theoretical basis for the carbon pool restoration and help with scientific management of the northern forest ecosystem after fire.

Methods In this study, Larix gmelinii forest in the Da Hinggan Mountains was taken as the research object. Samples were taken at the beginning of the growing season (June) and at the end of the growing season (September) after fire disturbance. ECM fungi were identified by high-throughput sequencing method to explore the changes and key influencing factors of ECM fungal community under the treatment of fire and black carbon addition.

Important findings The results showed that: (1) During the growing season, compared with CK, the α-diversity of ECM fungal community treated by fire decreased significantly by 31.52%, while it increased significantly by 49.02% under black carbon addition treatment. There were significant differences in the β-diversity of of ECM fungal community under fire and black carbon addition treatments during the growing season. (2) During the growing season, the abundance of ECM fungi treated by fire decreased significantly by 46.35%, but the fire treatment significantly increased Basidiomycetes species abundance, while black carbon addition treatment increased Ascomycetes and Basidiomycetes species abundance. (3) During the growing season, the composition of ECM fungal community in Larix gmelini forest was significantly affected by soil pH, water content and total nitrogen content under the fire and black carbon addition treatments, but it was positively correlated with soil pH and total nitrogen content and negatively correlated with soil water content in the black carbon addition treatment. The results of this study showed that fire reduced the diversity of ECM fungi in Larix gmelinii forest during the growing season, and significantly reduced the abundance of ECM fungi. However, the addition of black carbon after fire may change this negative effect. By affecting the changes of soil pH and soil nitrogen content, black carbon promoted the recovery of ECM fungi and increased its diversity. Therefore, the long-term impact of black carbon on ECM fungal community should be continuously monitored in the future.

Aims The aim of this research was to clarify the effects of intercropping and inoculation with arbuscular mycorrhizal fungi (AMF) on carbon transport and phosphorus uptake in black locust (Robinia pseudoacacia) and konjac (Amorphophallus konjac). The results could provide empirical evidence to reveal the mechanisms of black locust intercropping for disease control and plant growth promotion of konjac, and popularize the green and high-yielding cultivation technique of konjac under black locust.

Methods The experiment was carried out in two-compartment rhizoboxes separated by a 25-μm nylon net, each of which comprised compartment A (non-inoculated or AMF-inoculated black locust) and compartment B (monocropped black locust or intercropped konjac). A ¹³C stable isotope labeling technique was used to label the leaves of black locust in compartment A with ¹³CO₂. Carbon transport from black locust to konjac and the effects of AMF colonization on agronomic traits, ¹³C abundance, and phosphorus content in both crops were investigated.

Important findings The result showed that: (1) After inoculation, the AMF infection rate of black locust and konjac plants by hyphal links in compartment B reached 47.1% and 60.4%, respectively. For black locust, this AMF infection rate was 14.1% lower than that of directly inoculated plants under monocropping. In the case of intercropping, the biomass (dry mass) of AMF-inoculated konjac plants was 9.7% (aboveground parts) and 36.2% (belowground roots) higher than that of non-inoculated plants. (2) Compared with the non-inoculated plants under monocropping, the carbon fixed by photosynthesis of black locust plants in other treatments (non-inoculated + intercropping, inoculated + monocropping, and inoculated + intercropping) was mainly allocated to the plant roots and rhizosphere soil in compartment A, and more carbon passed through the nylon net in the form of root exudates to reach the rhizosphere of neighboring crop plants. (3) Compared with the respective non-inoculated controls, AMF inoculation in the monocropping and intercropping systems prominently improved phosphorus contents in the leaves, stems/petioles, roots, and total plants of black locust and konjac in compartment B. The findings suggest that AMF colonization could facilitate carbon transport from black locust to the rhizosphere soil and plant tissues of konjac. Intercropping konjac with black locust is an effective practice to promote AMF colonization and phosphorus uptake by both host plants.

Arbuscular mycorrhiza (AM) is one of the oldest symbionts between plants and soil microorganisms, and about 80% terrestrial plant species can associate with AM fungi on earth. Because of the stable climate and poor soil phosphorus content in tropical and subtropical forests, this mutualistic symbiosis is much more common there. Previous studies have extensively investigated the diversity of AM fungi in tropical and subtropical forests, and have shown that AM fungi can promote plant recruitment and growth. However, this positive effect of AM fungi on plants (i.e., the positive plant-soil feedback) can weaken the contribution of the negative plant-soil feedback (caused by soil-borne pathogens) to maintaining tree species diversity, which appears to contradict with the surprisingly high tree diversity and high proportion of rare tree species in tropical and subtropical forests. Recently, a mounting number of empirical studies have found that the diversity of AM fungi varies significantly in different habitats and AM colonization depends on the identity of host species, thereby affecting the fitness of plants and further shaping the plant community structure. Through synthesizing the current research about the diversity of AM fungi in promoting plant coexistence and maintaining community diversity, we expect to put forward a promising study direction for testing the “rare species advantage” hypothesis, therefore improving the conservation of rare plant species.

Aims Root hairs and mycorrhizal fungi, by increasing absorbing area of plant roots, promote ability of plants in acquiring soil resources such as phosphorus (P). The combination of absorptive roots, root hairs, and mycorrhizal fungi differs among distinct plant species, resulting in variations in acquisition of soil resources. At present, in situ quantifications of microstructures on the surface of roots is difficult, and relationships among absorptive roots, root hairs, and mycorrhizal fungi underlying the adaptation of soil P gradient in different woody plants remain largely unknown.
Methods We investigated 21 tree species in a subtropical forest and examined the existence of root hairs. We quantified the variation of root hair characteristics and analyzed the relationships between root hairs, mycorrhizal colonization rate, root traits along with soil P availability.
Important findings 1) Root hairs did not commonly exist in 21 subtropical tree species. We only observed root hairs in seven species, including four arbuscular mycorrhizal (AM) trees and three ectomycorrhizal (ECM) trees. Root hair occurrence rate was highest in Pinus massoniana (86%). 2) Mycorrhizal type is key to understanding the relationships between root hairs and mycorrhizal fungi. Root hair density was significantly positively correlated with mycorrhizal fungi colonization rate in AM trees. In contrast, in ECM trees, root hair diameter was significantly negatively correlated with mycorrhizal fungi colonization rate. 3) Root hair length and diameter were negatively correlated with soil available P content in AM trees, while root hair occurrence rate decreased with the soil available P content in ECM trees. Our results improve the understanding of root hairs and their interaction with other plant traits in natural forest stands, which lay the foundation for better predictions of nutrient acquisition strategies.

Aims Phosphorus is one of the major limiting nutrients for plant growth in subtropical areas, whereas increasing nitrogen deposition may be a limiting factor in determining the availability of soil phosphorus. Here, focusing on soil microorganisms and plant fine roots, we explored the transformation of soil phosphorus to unravel the maintenance of soil phosphorus supply and plant productivity with low availability under nitrogen deposition.

Methods At the Fuzhou Changʼan Mountain in Fujian Province, China, control (0 kg·hm^-2·a^-1), low nitrogen (40 kg·hm^-2·a^-1), and high nitrogen (80 kg·hm^-2·a^-1) treatments were set up to simulate nitrogen addition. Soil and root samples of Cunninghamia lanceolata seedlings were then collected to comprehensively analyze soil phosphorus and nutrient contents as well as microbiological-plant root characteristics.

Important findings The results showed that the contents of soil labile organic phosphorus, moderately labile inorganic phosphorus and occluded phosphorus were significantly increased, whereas those of primary mineral phosphorus and moderately labile organic phosphorus decreased under the low nitrogen treatment as compared to the control treatment. However, there were no significant changes under the high nitrogen treatment. Redundancy analysis indicated that soil acid phosphatase activity, relative abundance of mycorrhizal fungi, soil microbial biomass phosphorus content, and root biomass were important soil microbiological-plant root characteristics factors that could explain the changes in soil phosphorus components. Variance partitioning analysis revealed that the soil microbiological-plant root characteristics synergy explained 57% of the alternations in soil phosphorus components, whereas correlation analysis showed a significant positive correlation between the relative abundance of mycorrhizal fungi and root biomass. Overall, these results suggest that mycorrhizal colonization is promoted under a low level of nitrogen input and the synergistic action of mycorrhizal fungi and C. lanceolata fine roots promotes the conversion of moderately labile organic and primary mineral phosphorus to labile phosphorus, thus maintaining the growth of C. lanceolata seedlings.

Orchid is typical of mycorrhizal plants. Orchid mycorrhiza (OM), the symbiotic association between orchid roots and fungi, is unique to orchids. The nutrient sources of orchid mycorrhizal fungi (OMF) affect the lifestyle and nutrient levels of its host plants. Nitrogen (N) is the main limiting factor of plant growth. Orchids generally have higher tissue N levels compared to neighbor autotrophic plants, meaning N enrichment of plants. This paper reviewed the types and taxa of OMF, N nutrition characteristics of orchids, and N transfer mechanism in OM to provide a reference for the research on protection, regeneration, and sustainable utilization of orchid resources.

Arbuscular mycorrhizal (AM) fungi are a group of soil-dwelling fungi that can form symbiotic associations with most terrestrial plants. The extraradical mycelium can colonize different plant roots in addition to hyphal fusion, thus form extensive arbuscular mycorrhizal networks (AMNs) underground. AMNs can transport and recycle water and nutrients including carbon, nitrogen, phosphorus among plants, recent evidences show that AMNs can also transfer defensive signals to neighboring plants when plants suffer environmental stresses, thus providing early warning to surrounding neighbors. However, the research on AMNs-mediated signal transfer is still in its infancy. Here, we firstly reviewed current research progresses in this research area, then proposed the unanswered questions that worth exploration in the future, including the possible pathways and mechanisms of signal transfer via AMNs among plants, the possible regulation of mycorrhizal symbionts by AMNs-mediated signal transfer, and the common techniques and their development used in the study of AMNs. Finally, we discussed about the possible ecological applications of AMNs such as filed crop protection.

Aims The increasing deposition of nitrogen (N) has led to an imbalance of N and phosphorus (P) in forest soils, and has become the focus of ecological studies. Fungi, as one of the main microorganisms in soils, plays an important role in maintaining nutrient balance and promoting plant growth. Enhancing the understanding of the growth status of Cunninghamia lanceolata seedlings and the changes of soil fungal community structure and functional groups under the treatments of N addition, are helpful to study the process of soil nutrient cycling, and provide references for scientific management and sustainable development of C. lanceolata plantation.

Methods In this study, we used high-throughput sequencing and FUNGuild functional prediction to determine changes in soil fungal structural composition and functional groups of C. lanceolatain response to the application of control (0 kg N·hm^-2·a^-1), low N (40 kg N·hm^-2·a^-1), and high N (80 kg·N hm^-2·a^-1) treatments.

Important findings The results showed that N addition reduced biomass and leaf P content of C. lanceolata seedlings. Ascomycota, Basidiomycota, and Mortierellomycota were the three dominant phyla in the experimental soils, and accounted for 76.71%-86.72% of the relative abundance among the entire fungal community. The effect of short-term N addition on fungal composition was not significant at the phylum level. However, the relative abundance of Glomeromycota increased significantly with the low N treatment. At the order level, compared with the control, low N treatment significantly increased the relative abundance of Mortierellales. High N treatment significantly increased the relative abundance of Tremellales, but significantly reduced that of Sordariales. In addition, low N treatment significantly increased soil available P content, and there were significant positive correlations with the relative abundances of Glomeromycota and Mortierellales. These results indicate that N addition may maintain P availability of C. lanceolatagrowth by altering the fungi associated with P transformation. In addition, the relative abundance of saprotroph group was significantly reduced under low N treatment, but the relative abundance of arbuscular mycorrhizal fungi was significantly increased. In conclusion, soil fungal functional groups can participate in soil nutrient cycling by changing the relative abundance of different functional groups.

Aims Plants absorb mineral nutrients such as nitrogen (N) mainly through their roots. The nutrient uptake of plants with different root morphologies differs. Many studies have shown that arbuscular mycorrhizal fungi (AMF) can help their symbiotic associates absorb mineral N. However, there is little research on whether the effect of AMF on nutrient uptake of plant roots is affected by root morphology.

Methods In this study, we selected three rice mutants and one wild type (root hairless (rhl1), lateral rootless (iaa11), adventitious rootless (arl1) and wild type (Kas)) to investigate the role of root morphology in plant nutrient uptake. Subsequently, we used the ¹⁵N isotope labeling method to explore the effects of arbuscular mycorrhizal fungi and N addition (low N: 20 mg·kg^-1 NH₄⁺-N; high N: 100 mg·kg^-1 NH₄⁺-N) on N uptake of rice mutants with different root morphologies.

Important findings The results show that the leaf ¹⁵N concentrations of rhl1,Kas, iaa11 and arl1 were increased by 60%, 72%, 128% and 118%, respectively, under the high N compared to the low N treatment. This result indicates that the addition of N significantly promoted rice N uptake with the most evident effect occurring in iaa11 and arl1. The average effect sizes of AMF on rhl1, Kas, iaa11 and arl1 were 17%, 31%, 42% and 51% under the low N level, indicating that root morphology can alter the effect of AMF on plant N uptake. Compared to the low N treatment, high N significantly downregulated the AMF effect on N uptake by rice plants with different root morphologies, indicating that N addition may mediate the complementary effect of AMF and root morphology on plant nutrient uptake. In conclusion, our data provide direct experimental evidence of funcitonal complementarity of mycrrohzal fungi and their associated roots with different root morphogy.

Mycorrhizal fungi symbiosis is an important strategy for plant to uptake soil nutrients. Alien plants could thwart the symbiotic relationship between native plants and mycorrhizal fungus, and thus suppress the growth of native plants, which is an important mechanism for alien plant invasion, and has been increasingly emphasized in recent studies. In the present review, we summarized several key aspects of such mycorrhizal-related mechanism of plant invasion: 1) the impacts of alien plants on mycorrhizal fungi of native plants (i.e. mycorrhizal colonization rate, internal structures of mycorrhizal hyphae, amount of external hyphae, mycorrhizal and non-mycorrhizal composition, and mycorrhizal network); 2) mechanisms of alien-plant impacts on mycorrhizal fungi of native plants, including ecological mechanisms such as resource competition, allelopathy and edaphic fertility, as well as their molecular mechanisms; 3) variations of the above mentioned alien-plant impacts and related mechanisms at different durations of plant invasion. Despite thwarting mycorrhizal fungi of native plants is an important mechanism for alien plant invasion, researches on such mechanism are still scarce comparing to other mechanisms such as natural enemy release and new weapon hypothesis. Therefore, we proposal several research areas that need to be focused on in future studies: 1) how do global changes affect the alien-plant-invasion impacts on mycorrhizal fungi of native plants; 2) what are the relationships among different mechanisms including the mycorrhizal-related mechanism; 3) how does the mycorrhizae-related mechanism change at large spatio-temporal scales.

Aims Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with most terrestrial plants, contributing to the nutrient uptake of host plants. While little is known on how rhizospheric microorganisms affect the relationships between AMF and host plants under nutritional stress. We hypothesize that AMF may compete for nutrients with host plants in extremely nutrient-limited environments, such as nitrogen deficient habitats, and nitrogen-fixing bacteria will alleviate the competition.
Methods In order to test our hypotheses, we grew Solidago canadensis plants under nitrogen deficient treatments. We inoculated plants with AMF and a nitrogen-fixing bacterium to test the relationships among the host plant and microorganisms.
Important findings Under the lowest nitrogen level (0.025 mmol·L^-1 N of ammonium nitrogen), the growth of S. canadensis was more restricted with AMF colonization, suggesting competition between AMF and the host. However, with the inoculation of nitrogen-fixing bacterium, AMF colonization was promoted and plant growth was increased. These results indicate that nitrogen-fixing bacteria could moderate the competition for nutrients between AMF and their host under nitrogen deficiency. This study improves our understanding of the invasion mechanisms of alien plants, where they interact with different microorganisms under extreme nutrient stress.

Aims Orchid plants generally grow better when they are mycorrhizal since mycorrhizal fungi are likely to assist in orchid seeds’ germination. However, there is little quantitative work on it. Thus we hope to better understand this mechanism to benefit the orchid plants protection.
Methods We studied nine small population species of orchids grown in Liaoning Province, China. We analyzed the composition of orchid mycorrhizal fungi (OMF) and fungal communities in the roots, in the rhizosphere soil as well as bulk soil, by taking advantage of the next generation sequencing technology.
Important findings Our study showed that there was a significant difference in fungal communities among in the roots, the rhizosphere soil and the bulk soil, especially in the total operational taxonomic unit (OTU) number. Although the OTU number was far smaller in the roots than in the rhizosphere soil and bulk soil, the species and abundances of OMF were less relative to each other. FunGuild, an indicator to predict the functional fungi, indicated that Arbuscular Mycorrhizal fungi were abundence in the rhizosphere while were rare in the roots of orchids. In general, the fungal communities in the roots were not tightly correlated with that in the root-associated soil.

Aims Null model is an important basis for nesting judgment. Highly asymmetric structures often appear in plant symbolic fungal networks. This study aims to explore the influence of matrix asymmetric changes on network nesting judgment.
Methods The study was conducted based on various null model construction methods.
Important findings Constraints vary with changing null models, with reducing null space when additional qualifications were added during null model establishment. Highly constrained nulls are prone to causing type II errors. Highly asymmetric networks increase matrix temperature (NT) deviation based on random (Equiprobable- equiprobable, r00) null model while reducing overlap and decreasing fill (NODF) deviation. Values of z-score show that highly asymmetric networks contribute to the significant determination level of NT and NODF. The impacts on the judgment of nestedness of asymmetric networks differ between row and column fixed null models. The effects of network asymmetry change on nesting detection based on column constrained (c0) nulls are similar to that of random null model, but with smaller nesting deviation and standard deviations. No significant differences in both NT and NT deviations were observed among different asymmetry networks based on the row fixed (r0) nulls, with a lower NODF deviation in highly asymmetric network based on c0 nulls. To more accurately determine whether the asymmetric networks would have nested structures, we recommend using a combination of random and constrained null models. Our results also demonstrate that the r0 null model performs better than either the r00 null model or the c0 null model when comparing nesting level of different asymmetric networks.

AimsPrevious studies have shown that Dendrobium plants form a specific symbiotic relationship with fungi at differentiation stages during natural seed germination. In order to explore the evolution and adaptation of this symbiotic relationship in interspecific hybrid progenies, this study was to understand whether the strong specificity with symbiotic fungi during seedling formation and differentiation was also an important factor limiting the formation of hybrid progenies in Dendrobium, and the relationship between hybrid progenies of orchids and symbiotic fungi during seed germination stage.
MethodsThe effects of fungi on germination of interspecific hybrid seeds of D. officinale and D. tortile were studied using the highly specific fungi strains Tulasnella SSCDO-5 and Epulorhiza FDd1, which can effectively promote seed germination and seedling formation in D. officinale and D. devonianum, respectively.
Important findings The results showed that both SSCDO-5 and FDd1 strains could effectively promote the protocorm and seedling formation of hybrid seeds after 68 days incubation with no significant difference. The SSCDO-5 strain from D. officinale did not show any advantages, and the seedling formation rate of hybrid was lower than that of FDd1 strain from D. devonianum. The seedling formation rate incubation with SSCDO-5 strain was (22.13 ± 6.62)% while with FDd1 strain was (29.53 ± 5.51)%. The specificity of SSCDO-5 strain with D. officinale at seedling formation and development stage was not inherited or expressed in hybrid progenies, indicating that hybridization broke the symbiotic relationship of this specificity, which enabled hybrid progenies to establish new symbiotic relationship with different fungi. Our results do not support the hypothesis that the specificity of symbiotic fungi is an important limiting factor for the formation of hybrid progenies in Dendrobium. We speculate that the symbiotic relationship between Dendrobium plants and fungi during seedling differentiation and development is formed and established in the process of adapting to specific ecological environment.

Aims Accumulating evidence suggests that arbuscular mycorrhizal fungi (AMF) can promote the growth of plant roots. However, the effects of AMF on the root growth of dioecious plants, particularly those grown under different sexual combination patterns, remain largely unknown, this study therefore aimed at improving our understanding of the roles of AMF in these systems.
Methods In the present study, homogenized soil (river sand:surface soil:vermiculite = 1:1:1, volume ratio) was used as growth substrate. The Populus cathayana saplings uninoculated and inoculated with AMF under three sex combination patterns (male vs. male, MM; female vs. female, FF; male vs. female, MF) were defined as control (CK) and AMF treatment group, respectively. Subsequently, we compared the differences in colonization rate, root dry mass, root morphology, carbon (C) content and nitrogen (N) content between CK and AMF treatments under different sexual combination patterns.
Important findings Our results indicated that colonization rate, root dry mass, root morphology (except root branching intensity, specific root surface area) and C, N content were remarkably altered upon inoculation with AMF in comparison to uninoculated controls. Furthermore, the sexual combination patterns were shown to significantly affect root dry mass, root morphology and C, N content of male and female P. cathayana. After inoculation with AMF, root dry mass, root morphology and N content of female individuals were increased whereas these parameters of males were decreased or slightly increased in inter-sexual groups compared with the respective intra-sexual groups. Collectively, our data demonstrate the growth-promoting effects of AMF on the roots of P. cathayana individuals grown under different sexual combination patterns, and such beneficial effects are most pronounced in females grown under inter-sexual combination patterns.

Aims Soil respiration component partitioning is pivotal to understand the belowground carbon (C) cycle. Mycorrhizal fungi have been proven to play an important role in the soil C turnover, but only a few studies have been conducted to quantify the contribution of mycorrhizal respiration to total soil respiration in grassland ecosystems.
Methods The mini-trenching mesh method was applied to partition soil respiration components of a semi-arid grassland in Inner Mongolia. A shallow collar (measuring soil total respiration), a deep collar (excluding roots and mycorrhizal hypahe) and a deep collar with 40 μm pore mesh window (excluding roots but not mycorrhizal hyphae) were installed in each plot. Soil respiration rate of each collar was measured every two weeks during the growing season from 2014 to 2016. The differences in the rate of soil respiration among different type of collars were used to partition the components of soil respiration.
Important findings The results showed that the contribution of heterotrophic, root and mycorrhizal respiration to total soil respiration was 49%, 28%, and 23%, respectively. Across the three years, the proportion of mycorrhizal respiration varied from 21%-26%, which is comparable with the results reported by other studies recently. Our results demonstrated that the mini-trenching mesh method is a suitable method for separating mycorrhizal respiration component in grassland ecosystems. Evaluating the contribution of mycorrhizal respiration to total soil respiration is very important for predicting the responses of soil carbon release to future climate change.

Aims Arbuscular mycorrhizal fungi (AMF) can form symbiotic associations with most terrestrial plants to improve plant growth and stress resistance. It has been well demonstrated that AMF can promote plant acquisition of water and enhance plant tolerance to drought. In this study, AMF extraradical hyphae were obtained from in vitro culture of AMF Rhirophagus irregularis with hairy carrot (Daucus carota var. sativa) root to investigate the morphological and physiological changes of hyphae in response to drought stress induced by polyethylene glycol (PEG).

Methods The influence of drought stress on the hyphal morphology was observed by using the field emission-scanning electron microscope-energy dispersive X-ray spectroscopy (FE-SEM-EDS), while H ⁺ and Ca ²⁺ion fluxes through living hyphae were monitored by non-invasive micro-test technique (NMT).

Important findings The results showed that significant H⁺ efflux and Ca²⁺ influx through the tip and side of the extraradical hyphae were detected in response to drought stress induced by PEG for 1 h. Fluorescence probing confirmed that the intracellular pH value and Ca²⁺ concentration of hyphae significantly increased under PEG treatment. The morphology of hyphae changed and the pH value of the growth medium decreased after treatment with PEG for 24 h. The P, Ca, and Fe elements accumulated at the hyphosphere to enhance the nutrient absorption by hyphae. The study confirmed that AMF regulated the transmembrane H⁺ and Ca²⁺ flux to promote the material exchange between hyphae and environment under drought stress. The acidification of the hyphosphere environment potentially promoted the absorption of nutrients and also the signal exchange between AMF and the host plant to enhance plant drought tolerance.

Aims To understand the ecological significance of arbuscular mycorrhizal (AM) fungi associated with Hedysarum scoparium in semi-arid and arid lands, species diversity and ecological distribution of AM fungi associated with Hedysarum scoparium were elucidated in a desert ecosystem of northwestern China.

Methods Soil samples (0–30 cm depth) under Hedysarum scopariumis were collected at seven different sites (Ordos, Wuhai, Dengkou, Alxa, Shapotou, Minqin, Anxi) in northwest China in July 2015. Based on the morphological characteristics of spores, AM fungi were identified, and redundancy analysis (RDA) was used to distinguish among different groups. Furthermore, the relationship between species diversity of AM fungi and soil factors were evaluated by Pearson’s correlation analysis.

Important findings A total of 42 AM fungal species belonging to six genera were isolated. Among these, 16 species belong to Glomus,17 to Acaulospora four to Claroideoglomus,two to Septoglomus,two to Funneliformis and one to Scutellospora.The abundance, spore density and Shannon-Wiener index of AM fungi decreased gradually along the aridity gradient from east to west. Spore density of AM fungi of different species in the same site were different, and those of the same species in different sites were also different. Soil organic matter, pH,ammonia, and available phosphorus had significant effects on AM fungi. The results showed that the species diversity and distribution of AM fungi have obvious spatial patterns, and were influenced by soil factors, among which soil moisture was the most significant factor.

Aims Arbuscular mycorrhizal (AM) symbiosis plays an important role in plant adaptation to phosphorus (P) deficiency. The mycorrhizal fungi can directly regulate P stress response of the host plants, and can also indirectly influence neighbor plants via AM exudates. This study aimed to reveal the regulation mechanisms of plant response to P deficiency by AM associations. Methods In a compartmentation cultivation experiment with Zea mays ‘B73’ and AM fungus Rhizophagus irregularis ‘DAOM197198’, we investigated mycorrhizal effects on plant P nutrition and the expression of plant and fungal genes related to P and carbon (C) metabolisms under both low P (10 mg?kg^-1) and high P (100 mg?kg^-1) conditions. The cultivation system consisted of three compartments, namely donor compartment, buffer compartment and receiver compartment divided by two pieces of microporous filters with pore size of 0.45 μm. Maize plant in donor compartment inoculated with AM fungus served as a source of AM exudates. The microporous filters could restrict the development of extraradical mycelium of AM fungi, but allow diffusion of AM exudates. Real-time PCR was performed to quantify the gene expression levels both in maize plants and AM fungi. Important findings The experimental results indicated that under low P conditions mycorrhizal colonization increased plant dry weight and P concentration in donor plants, and up-regulated plant genes encoding P transporters Pht1;2, Pht1;6, phosphoenolpiruvate carboxylase (PEPC), inorganic pyrophosphatase (TC289), glycerol-3-phosphate transporter (G3PT) and malate synthase (MAS1). The expression of AM fungal genes encoding P transporter (GiPT), GlcNAc transporter (NGT1), GlcNAc kinase (HXK1b), GlcNAc phosphomutase (AGM1), UDP GlcNAc pyrophosphorylase (UAP1), chitin synthase (CHS1), GlcNAc-6-phosphate deacetylase (DAC1) and glucosamine-6-phosphate isomerase (NAG1) was significantly higher under low P conditions compared with high P conditions. However, for the receiver plants, plant dry mass and P concentration were only significantly increased by higher P addition, while inoculation treatment significantly up-regulated the expression of P transporter genes Pht1;2 and Pht1;6, C metabolism related genes G3PT, PEPC, TC289 and MAS1. The study proved that AM exudates could potentially stimulate plant response to P deficiency by regulating functional genes relevant to P and C metabolisms in the mycorrhizal associations.

Mycorrhiza is defined as a mutualistic symbiosis between plants and fungi localized in roots or root_like structures in which energy moves primarily from plants to fungi and inorganic resources move from fungi to plants. Since most land plants in the world belong to families that are commonly mycorrhizal, mycorrhizal fungi may play important roles in nature. Findings of many researches, especially those of recent studies, are helpful in understanding the role of mycorrhizal fungi in the structure and functioning of ecosystems. In this paper, the following aspects of mycorrhizal fungi research were introduced: 1) As an important part of ecosystems, mycorrhizal fungi consume a great deal of photosynthate and are parts of food chains between autotrophic plants and fungivores; 2) Mycorrhizal fungi have a great effect on the biogeochemical cycling through taking part in the enzymatic decomposition of litter, promoting the absorption of inorganic ions or compounds, accelerating the weathering of miners, and contributing to the process of biological nitrogen fixation; 3) Mycorrhizal fungi affect the structure and functioning of the ecosystems in different ways. They have an interaction with microbes in the soil and thus may have an influence on the composition of soil microbes. They influence the inter-or intra-specific interactions of plants through having beneficial effects on host plants or connecting different plants with mycorrhizal networks. Mycorrhizal fungi play an important role in the maintenance of biodiversity and stability of plant communities, and they can also act as an indicator, participator and promoter of succession of plant communities; 4) The magnitude and species composition of mycorrhizal fungi may indicate the changes of an ecosystem, and mycorrhizal fungi can also be used in the conservation of natural ecosystems or restoration of damaged or desert ecosystems. The focuses of recent mycorrhizal fungi researches and a brief perspective was also discussed in this paper.