Mycorrhizal fungi reduce the negative effects of nitrogen enrichment on plant community structure in dune grassland

Nitrogen (N) inputs to ecosystems have increased worldwide, often leading to large changes in plant community structure and reducing plant diversity. Yet, the interaction of increased N availability with other factors that determine plant community composition, are still poorly understood. Here, we test whether the impact of N addition on plant communities depends on the presence of arbuscular mycorrhizal fungi (AMF). AMF are widespread plant symbionts that facilitate growth of many plant species. We hypothesize that AM fungi reduce the negative impact of N addition on plant communities by supporting growth of species that are sensitive to N enrichment.We established experimental grassland microcosms consisting of 18 plant species. These microcosms were subjected to high and low N supply and were inoculated with AMF or remained nonmycorrhizal. Both N addition and AMF had a big impact on plant community composition, but with opposite effects. N addition induced a 2.8‐fold increase in grass biomass and reduced legume biomass. Grasses dominated the microcosms at high N supply, especially when AMF were absent. In contrast, AMF enhanced biomass of all legumes species (on average 6.8‐fold) and reduced the relative abundance of grasses. The proportion of legume biomass out of total shoot biomass at high N supply was 19% with AMF and only 3% without AMF. Our results show that responses of plant communities to N enrichment depend on AMF and that AMF can reduce the negative impact of increased N availability on plant community structure by reducing grass dominance.     

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

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

Can Arbuscular Mycorrhizal Fungi Reduce the Growth of Agricultural Weeds?

Background

Arbuscular mycorrhizal fungi (AMF) are known for their beneficial effects on plants. However, there is increasing evidence that some ruderal plants, including several agricultural weeds, respond negatively to AMF colonization. Here, we investigated the effect of AMF on the growth of individual weed species and on weed-crop interactions.

Methodology/Principal Findings

First, under controlled glasshouse conditions, we screened growth responses of nine weed species and three crops to a widespread AMF, Glomus intraradices. None of the weeds screened showed a significant positive mycorrhizal growth response and four weed species were significantly reduced by the AMF (growth responses between −22 and −35%). In a subsequent experiment, we selected three of the negatively responding weed species – Echinochloa crus-galli, Setaria viridis and Solanum nigrum – and analyzed their responses to a combination of three AMF (Glomus intraradices, Glomus mosseae and Glomus claroideum). Finally, we tested whether the presence of a crop (maize) enhanced the suppressive effect of AMF on weeds. We found that the growth of the three selected weed species was also reduced by a combination of AMF and that the presence of maize amplified the negative effect of AMF on the growth of E. crus-galli.

Conclusions/Significance

Our results show that AMF can negatively influence the growth of some weed species indicating that AMF have the potential to act as determinants of weed community structure. Furthermore, mycorrhizal weed growth reductions can be amplified in the presence of a crop. Previous studies have shown that AMF provide a number of beneficial ecosystem services. Taken together with our current results, the maintenance and promotion of AMF activity may thereby contribute to sustainable management of agroecosystems. However, in order to further the practical and ecological relevance of our findings, additional experiments should be performed under field conditions.     

接种AM真菌对短命植物生长发育及矿质养分吸收的影响

 采用分室培养方法研究接种幼套球囊霉(Glomus etunicatum,BEG168)、摩西球囊霉(G. mosseae, BEG167)、混合菌剂(M)对两种沙漠早春短命植物小车前(Plantago minuta)和尖喙牻牛儿苗（Erodium oxyrrhynchum）生长发育及矿质养分吸收的影响。结果表明,接种AMF处理的小车前和尖喙牻牛儿苗根系形成了典型的菌根结构,侵染率为22 %～60%;接种AMF提高了小车前和尖喙牻牛儿苗两种植物的生物量、株高及N、P养分吸收量。小车前单独接种BEG167、BEG168以及混合接种都显著提高了单株种子数量,其增幅分别 为67%、50%和78%。上述结果说明,在极端贫瘠和干旱的古尔班通古特沙漠中,丛枝菌根真菌对于早春短命植物小车前和尖喙牻牛儿苗的生态适应性的贡献表现为促进营养生长、提高后代（种子）繁殖数量。     

Functional diversity of arbuscular mycorrhizal fungal isolates in relation to extraradical mycelial networks

We investigated the functional significance of extraradical mycorrhizal networks produced by geographically different isolates of the arbuscular mycorrhizal fungal (AMF) species Glomus mosseae and Glomus intraradices. A two-dimensional experimental system was used to visualize and quantify intact extraradical mycelium (ERM) spreading from Medicago sativa roots. Growth, phosphorus (P) and nitrogen (N) nutrition were assessed in M. sativa plants grown in microcosms. The AMF isolates were characterized by differences in extent and interconnectedness of ERM. Phenotypic fungal variables, such as total hyphal length, hyphal density, hyphal length per mm of total or colonized root length, were positively correlated with M. sativa growth response variables, such as total shoot biomass and plant P content. The utilization of an experimental system in which size, growth rate, viability and interconnectedness of ERM extending from mycorrhizal roots are easily quantified under realistic conditions allows the simultaneous evaluation of different isolates and provides data with a predictive value for selection of efficient AMF.     

The influence of arbuscular mycorrhizae and light on Wisconsin (USA) sand savanna understories 1

To explain the complex community composition found in Wisconsin (USA) oak savannas, we investigated potentially interacting effects of light gradients and arbuscular mycorrhizal fungi (AMF) on community composition in the greenhouse, using a fully randomized block experimental design. We used plant species, soil, and AMF from a remnant sand savanna in setting up the experiment, using two light and five AMF treatments. Eleven plant species were seeded into 80 microcosms, and they were grown together for 20 weeks. Plant numbers and biomass were measured, and Simpsons index was calculated for both. Data were analyzed using ANOVA and nonparametric ANOVA. We found significant light effects on biomass and on numbers of four species. There were no treatment effects on Simpsons index, and only Schizachyrium numbers showed a significant AMF effect. These findings are consistent with results from other studies of the sand savanna, and, collectively, these data suggest that plant community composition in this species-rich savanna is not strongly influenced by arbuscular mycorrhizae. This is a novel finding with important implications for understanding interactions between plant and AMF diversity in wild communities.     

Arbuscular mycorrhizal fungi reduce effects of physiological integration in Trifolium repens

Background and Aims

One of the special properties of clonal plants is the capacity for physiological integration, which can increase plant performance through mechanisms such as resource sharing and co-ordinated phenotypic plasticity when plants grow in microsites with contrasting resource availabilities. However, many clonal plants are colonized by arbuscular mycorrhizal fungi (AMF). Since AMF are likely to reduce contrasts in effective resource levels, they could also reduce these effects of clonal integration on plasticity and performance in heterogeneous environments.

Methods

To test this hypothesis, pairs of connected and disconnected ramets of the stoloniferous herb Trifolium repens were grown. One ramet in a pair was given high light and low nutrients while the other ramet was given high nutrients and low light. The pairs were inoculated with zero, one or five species of AMF.

Key Results

Pairs of ramets grown without AMF developed division of labour and benefited from resource sharing, as indicated by effects of connection on allocation to roots, accumulation of mass, and ramet production. Inoculation with five species of AMF significantly reduced these effects of connection, both by inhibiting them in ramets given high nutrients and inducing them in ramets given high light. Inoculation with one species of AMF also reduced some effects of connection, but generally to a lesser degree.

Conclusions

The results show that AMF can significantly modify the effects of clonal integration on the plasticity and performance of clonal plants in heterogeneous environments. In particular, AMF may partly replace the effects and benefits of clonal integration in low-nutrient habitats, possibly more so where species richness of AMF is high. This provides the first test of interaction between colonization by AMF and physiological integration in a clonal plant, and a new example of how biotic and abiotic factors could interact to determine the ecological importance of clonal growth.Key words: Arbuscular mycorrhizal fungi, biomass allocation, clonal plant, division of labour, environmental heterogeneity, light availability, nutrients, white clover     

Restoration of plant communities in The Netherlands through the application of arbuscular mycorrhizal fungi

The aim of plant restoration projects is usually the recovery of the original native plant communities. However, in The Netherlands after restoration management practices have been completed, novel plant communities often develop and there is a return of only 50% to 60% of the desired plant species. A potential cause could be that the biological communities of the soil develop insufficiently to support a high diversity of plant species. This research project focused on the role of the soil biological community in controlling plant diversity. In particular, this project studied whether arbuscular mycorrhizal fungi a major component of the soil biological community, promote native plants. Field research indicated that arbuscular mycorrhizal fungi were present in the soil, even though colonization levels of arbuscules were low, 10% or less. The greatest abundance of arbuscular mycorrhizal fungi was observed at locations where the top soil was removed and where nutrient concentrations were reduced. The results of pot experiments showed that applied arbuscular mycorrhizal fungi significantly promoted the growth of native plant species. A cost benefit analysis revealed that the benefits of applying arbuscular mycorrhizal fungi exceeded the costs. This makes the application of arbuscular mycorrhizal fungi an attractive proposition.     

The influence of arbuscular mycorrhizae and light on Wisconsin (USA) sand savanna understories 2. Plant competition

Wisconsin (USA) oak savannas are endangered plant communities that have remarkably high plant species diversity. To investigate factors underlying this richness, we experimentally investigated the potentially interacting effects of light gradients and arbuscular mycorrhizal fungi (AMF) on plant competition in the greenhouse, using a fully randomized block design. We used four plant species, soil, and AMF from a remnant sand savanna, under two light and five AMF treatments. Plants were grown four per pot under two competition treatments (either one or four species per pot) for 20 weeks. Using ANOVA, we found that all species showed significant treatment effects on total and shoot biomass, primarily due to differences in competition and light, less to AMF. However, effects were the opposite of predictions. Putatively mycorrhizal plants showed neutral to negative responses to AMF, and a nonmycorrhizal species outcompeted AMF species in infected pots. We concluded that our experimental setup of small pots, sandy soil, and long growing period had induced parasitism by the AMF on susceptible hosts. This unexpected result is consistent with field data from the sand savanna, and may help explain how nonmycorrhizal plants can compete successfully with AMF species in established, species-rich communities.     

The arbuscular mycorrhizal fungus Rhizophagus intraradices and other microbial groups affect plant species in a copper-contaminated post-mining soil

Background and aimArbuscular mycorrhizal fungi (AMF) have an important role in plant-microbe interactions. But, there are few studies in which the combined effect of AMF with a stress factor, such as the presence of a metal, on plant species were assessed. This study investigated the effect of arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices and other soil microbial groups in the presence of copper on three plant species in a microcosm experiment.MethodsTwo grass species Poa compressa and Festuca rubra and one herb species Centaurea jacea were selected as model plants in a pot-design test in which soils were artificially contaminated with copper. Treatments were bacteria (control), saprophytic fungi, protists, and a combined treatment of saprophytic fungi and protists, all in the presence or absence of the AM fungal species. After sixty days, plants were harvested and the biomass of grass and herb species and microbial respiration were measured.ResultsThe results showed almost equal above- and belowground plant biomass and microbial respiration in the treatments in the presence or absence of R. intraradices. The herb species C. jecea responded significantly to the soil inoculation with AM fungus, while grass species showed inconsistent patterns. Significant effect of AMF and copper and their interactions was observed on plant biomass when comparing contaminated vs. non-contaminated soils.ConclusionStrong effect of AMF on the biomass of herb species and slight changes in plant growth with the presence of this fungal species in copper-spiked test soils indicates the importance of mycorrhizal fungi compared to other soil microorganisms in our experimental microcosms.     

Interactive effects of mycorrhizae and a root hemiparasite on plant community productivity and diversity

Plant communities can be affected both by arbuscular mycorrhizal fungi (AMF) and hemiparasitic plants. However, little is known about the interactive effects of these two biotic factors on the productivity and diversity of plant communities. To address this question, we set up a greenhouse study in which different AMF inocula and a hemiparasitic plant (Rhinanthus minor) were added to experimental grassland communities in a fully factorial design. In addition, single plants of each species in the grassland community were grown with the same treatments to distinguish direct AMF effects from indirect effects via plant competition. We found that AMF changed plant community structure by influencing the plant species differently. At the community level, AMF decreased the productivity by 15–24%, depending on the particular AMF treatment, mainly because two dominant species, Holcus lanatus and Plantago lanceolata, showed a negative mycorrhizal dependency. Concomitantly, plant diversity increased due to AMF inoculation and was highest in the treatment with a combination of two commercial AM strains. AMF had a positive effect on growth of the hemiparasite, and thereby induced a negative impact of the hemiparasite on host plant biomass which was not found in non-inoculated communities. However, the hemiparasite did not increase plant diversity. Our results highlight the importance of interactions with soil microbes for plant community structure and that these indirect effects can vary among AMF treatments. We conclude that mutualistic interactions with AMF, but not antagonistic interactions with a root hemiparasite, promote plant diversity in this grassland community. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Topsin-M: the new benomyl for mycorrhizal-suppression experiments

The fungicide benomyl was the most commonly used biocide for both field and greenhouse experiments in which arbuscular mycorrhizal fungal (AMF) suppression is desired. Unfortunately benomyl is no longer manufactured and therefore is not available for experimental use and no fungicide has been proposed as a successful alternative for experimentally suppressing mycorrhizal fungi. In this study we examined the potential for the fungicide Topsin M (topsin) to suppress mycorrhizal symbiosis in both field and greenhouse experiments. Topsin reduced AMF colonization of the obligately mycotrophic, warm-season grass Andropogon gerardii with a large and significant reduction in plant biomass production. Topsin reduced AMF colonization of the facultatively mycotrophic, cool-season grass Pascopyron smithii but did not significantly reduce biomass production. Fertilization with nitrogen and phosphorus was able to compensate for reductions in biomass due to the application of fungicide because biomass production of plants that received topsin fungicide was not significantly different from fertilized controls not receiving topsin. While we are not advocating that topsin fungicide is a universal mechanism for mycorrhizal-suppressed controls, in systems where benomyl was found to be successful topsin appears to be a useful, available and successful alternative.     

Neighbouring weeds influence the formation of arbuscular mycorrhiza in grapevine

Grapevine (Vitis vinifera L.) and two selected weeds from Mediterranean Croatian vineyards (Plantago lanceolata L. and Tanacetum cinerariifolium (Trevir.) Sch.Bip.) were examined in pot culture experiments, individually or when combined, to see whether multiple hosts influenced the formation of the symbiosis with arbuscular mycorrhizal fungi (AMF). The results after six-month period showed that plant identity and density significantly influenced development of mycorrhizal intra- and extraradical mycelium and/or sporulation. Grapevine and T. cinerariifolium individually and in combination resulted in a greater development of arbuscular mycorrhizae in terms of spore production, extraradical mycelium length and root colonization compared with pots containing P. lanceolata. Herbaceous weed species seemed to promote a different set of dominant AMF, potentially providing a wider spectrum of AMF for colonising grapevine roots. This indicates the value of encouraging host plant diversity in vineyards. AMF sequences obtained in this study are the first data reported for soils in Croatia.     

Effects of Alliaria petiolata (garlic mustard; Brassicaceae) on mycorrhizal colonization and community structure in three herbaceous plants in a mixed deciduous forest

Herbaceous plant species are important components of forest ecosystems, and their persistence in forests may be affected by invasive plant species that reduce mycorrhizal colonization of plant roots. I examined the effect of the invasive plant Alliaria petiolata on arbuscular mycorrhizal fungi (AMF) colonizing the roots of three forest plant species. AMF root colonization and community structure was examined from plants that were growing either in the absence or presence of Alliaria under natural forest conditions. AMF root colonization varied among the plant species but was not significantly affected by Alliaria. With molecular methods, ～12 different taxa of AMF could be distinguished among the root samples, and these taxa belonged to the genera Acaulospora and Glomus, with Glomus dominating AMF communities. There were significant differences between the community of AMF colonizing roots of Maianthemum racemosum and Trillium grandiflorum, but only AMF communities of Maianthemum roots were significantly affected by Alliaria. Indicator species analysis found that an Acaulospora species type was a significant indicator of Maianthemum plants grown in the absence of Alliaria. These results suggest invasive plants like Alliaria may selectively suppress AMF fungi, and this suppression can affect AMF communities colonizing the roots of some native plant species.     

中国大陆地区丛枝菌根真菌菌种资源的分离鉴定与形态学特征

【目的】分离收集保藏中国大陆各个地区不同生态环境的丛枝菌根真菌菌种资源,为丛枝菌根的研究提供资源、奠定基础。【方法】以高粱为宿主植物,采用诱导培养、单孢培养和扩繁培养分离土壤样品中的丛枝菌根真菌菌种并鉴定。【结果】从我国大陆的45个地区50余种宿主植物根区土壤中分离到丛枝菌根真菌135株,隶属于23个种;对各个菌株的形态特征进行了描述。【结论】我国蕴藏着丰富的丛枝菌根真菌菌种资源,文中描述的菌种资源是目前从我国大陆地区获得的种类和数量最多、覆盖范围最广的AM真菌菌种资源。     

Arbuscular mycorrhizal fungi as (agro)ecosystem engineers

Symbiotic interactions have been shown to facilitate shifts in the structure and function of host plant communities. For example, parasitic plants can induce changes in plant diversity through the suppression of competitive community dominants. Arbuscular mycorrhizal (AM) fungi have also be shown to induce shifts in host communities by increasing host plant nutrient uptake and growth while suppressing non-mycorrhizal species. AM fungi can therefore function as ecosystem engineers facilitating shifts in host plant communities though the presumed physiological suppression of non-contributing or non-mycorrhizal plant species. This dichotomy in plant response to AM fungi has been suggested as a tool to suppress weed species (many of which are non-mycorrhizal) in agro-ecosystems where mycorrhizal crop species are cultivated. Rinaudo et al. (2010), this issue, have demonstrated that AM fungi can suppress pernicious non-mycorrhizal weed species including Chenopodium album (fat hen) while benefiting the crop plant Helianthus annuus (sunflower). These findings now suggest a future for harnessing AM fungi as agro-ecosystem engineers representing potential alternatives to costly and environmentally damaging herbicides.     

Enhanced growth of non-photosynthesizing tobacco mutants in the presence of a mycorrhizal inoculum

The symbiosis between higher plants and arbuscular mycorrhizal fungi (AMF) is generally thought to improve the mineral nutrition of many plants. Moreover, AMF seem to play a role in transferring assimilated carbon between plants. To answer the question whether this carbon transfer could be sufficient to enhance the growth of non-assimilating plants, tobacco wild-type plants and non-photosynthesizing mutants were co-cultivated in the presence and absence of a mycorrhizal inoculum. Newly formed leaves were counted and biomass was determined at the final harvest. The mycorrhizal infection was determined in the roots. When the mutants were co-cultivated with a wild-type plant in the presence of a mycorrhizal inoculum, leaf number and the shoot biomass were significantly higher than in etiolated plants co-cultivated with wild-type plants without AMF or with etiolated plants alone.     

丛枝菌根真菌对玉米和棉花内源激素的影响*

在温室盆栽条件下研究了丛枝菌根（Ａｒｂｕｓｃｕｌａｒ　ｍｙｃｏｒｒｈｉｚａｓ,ＡＭ）真菌：ＧｉｇａｓｐｏｒａｒｏｓｅａＮｉｃｏｌ．＆Ｓｃｈｅｎｃｋ、Ｇｌｏｍｕｓ　ｍｏｓｓｅａｅ（Ｎｉｃｏｌ．＆　Ｇｅｒｄ．）Ｇｅｒｄｅｍａｎｎ　＆Ｔｒａｐｐｅ和Ｇｌｏｍｕｓ　ｖｅｒｓｉｆｏｒｍｅ　（Ｋａｒｓｔｅｎ）Ｂｅｒｅｈ对玉米和棉花植株内源激素的影响。结果表明,ＡＭ真菌在正常供水和干旱条件下均能显著提高玉米和棉花植株叶片和根内玉米素、生长素和赤霉素的含量,并降低脱落酸的含量。在植物体内含磷量、生长量及其生长发育阶段等一致、仅存在接种与不接种唯一差异条件下,供试ＡＭ真菌同样能改变玉米和棉花植株内源激素的平衡状况。接种处理植株的脱落酸含量与气孔阻力呈正相关关系。表明玉米和棉花植株抗旱性和生长状况的改善与ＡＭ真菌改变内源激素的平衡状况有关。接种ＡＭ真菌的植株表现较强的抗旱性;其生长量也显著大于不接种的对照。ＧＩ．ｖｅｒｓｉｆｏｒｍｅ的效应最大。     

Genetic variability in a population of arbuscular mycorrhizal fungi causes variation in plant growth

Different species of arbuscular mycorrhizal fungi (AMF) alter plant growth and affect plant coexistence and diversity. Effects of within-AMF species or within-population variation on plant growth have received less attention. High genetic variation exists within AMF populations. However, it is unknown whether genetic variation contributes to differences in plant growth. In our study, a population of AMF was cultivated under identical conditions for several generations prior to the experiments thus avoiding environmental maternal effects. We show that genetically different Glomus intraradices isolates from one AMF population significantly alter plant growth in an axenic system and in greenhouse experiments. Isolates increased or reduced plant growth meaning that plants potentially receive benefits or are subject to costs by forming associations with different individuals in the AMF population. This shows that genetic variability in AMF populations could affect host-plant fitness and should be considered in future research to understand these important soil organisms.     

Early responses of wild plant seedlings to arbuscular mycorrhizal fungi and pathogens

Many plants form associations with arbuscular mycorrhizal fungi (AMF) because they profit from improved phosphorus nutrition and from protection against pathogens. Whereas mycorrhiza-induced pathogen protection is well understood in agricultural plant species, it is rarely studied in wild plants. As many pathogens infest plants in the first days after germination, mycorrhiza-induced pathogen protection may be especially important in the first few weeks of plant establishment.Here, we investigated interacting effects of AMF and the seedling pathogen Pythium ultimum on the performance of six- to seven-week-old seedlings of six wild plant species of the family Asteraceae in a full factorial experiment.Plant species differed in their response to AMF, the pathogen and their interactions. AMF increased and the pathogen decreased plant biomass in one and three species, respectively. Two plant species were negatively affected by AMF in the absence, but positively or not affected in the presence of the pathogen, indicating protection by AMF. This mycorrhiza-induced pathogen protection is especially surprising as we could not detect mycorrhizal structure in the roots of any of the plants.Our results show that even seedlings without established intraradical hyphal network can profit from AMF, both in terms of growth promotion in the absence of a pathogen and pathogen protection. The function of AMF is highly species-specific, but tends to be similar for more closely related plant species, suggesting a phylogenetic component of mycorrhizal function. Further studies should test a wider range of plant species, as our study was restricted to one plant family, and investigate whether plants profit from early mycorrhizal benefits in the long term.