A review on the effects of invasive plants on mycorrhizal fungi of native plants and their underlying mechanisms

菌根真菌共生是植物吸收养分的一个重要策略。外来植物可以干扰本地植物与菌根真菌的共生关系从而抑制本地植物生长, 这是近年来被发现的一种重要入侵机制, 在研究中得到日益广泛的关注。该文从以下几个方面着重综述这种入侵机制: 1)外来植物对本地植物菌根真菌的影响, 包括菌根真菌侵染率、菌根内部结构、根外菌丝的量、菌根真菌的群落组成、非菌根真菌的影响及网络结构; 2)外来植物对本地植物菌根真菌上述影响的机制, 包括资源竞争、化感作用和土壤肥力等生态机制以及相关的分子机制; 3)上述两个方面随入侵时间的变化格局。尽管干扰本地植物菌根真菌是一种重要的入侵机制, 但相对其他的入侵机制(例如天敌逃逸、新武器假说等)来说, 这类机制的研究目前仍很匮乏。鉴于此, 该文提出了未来需要重点关注的几个方面: 1)全球变化背景下, 入侵植物对本地植物菌根真菌的影响如何变化; 2)包括这种菌根机制在内的多种入侵机制之间的关系; 3)深入探究入侵的这种菌根机制在大的时空尺度上的变化规律。     

外来入侵植物对本地植物菌根真菌的影响及其机制

菌根真菌共生是植物吸收养分的一个重要策略。外来植物可以干扰本地植物与菌根真菌的共生关系从而抑制本地植物生长, 这是近年来被发现的一种重要入侵机制, 在研究中得到日益广泛的关注。该文从以下几个方面着重综述这种入侵机制: 1)外来植物对本地植物菌根真菌的影响, 包括菌根真菌侵染率、菌根内部结构、根外菌丝的量、菌根真菌的群落组成、非菌根真菌的影响及网络结构; 2)外来植物对本地植物菌根真菌上述影响的机制, 包括资源竞争、化感作用和土壤肥力等生态机制以及相关的分子机制; 3)上述两个方面随入侵时间的变化格局。尽管干扰本地植物菌根真菌是一种重要的入侵机制, 但相对其他的入侵机制(例如天敌逃逸、新武器假说等)来说, 这类机制的研究目前仍很匮乏。鉴于此, 该文提出了未来需要重点关注的几个方面: 1)全球变化背景下, 入侵植物对本地植物菌根真菌的影响如何变化; 2)包括这种菌根机制在内的多种入侵机制之间的关系; 3)深入探究入侵的这种菌根机制在大的时空尺度上的变化规律。     

丛枝菌根真菌（AMF）对外来植物入侵反馈机制的研究进展

丛枝菌根真菌（AMF）在植物群落竞争演替、物种多样性的形成及群落空间分布格局、植物群落对全球变化的响应中均起着重要的调节作用;同样也能影响外来植物与本地植物的互作,影响外来植物入侵过程中植物群落演替进程,甚至决定入侵的成败。因此,AMF与外来植物共生及其对外来植物入侵的反馈已成为国际上外来植物入侵机制研究的一个热点。本文基于外来植物的入侵过程,从AMF对外来植物生长、外来植物与本地植物竞争关系的影响,以及外来植物入侵对AMF的影响及AMF对入侵的反馈3个方面综述了AMF对外来植物入侵的反馈机制。外来植物可以通过多种途径改变土著AMF的群落结构和功能,而土著AMF也能直接或间接地改变甚至逆转外来植物与入侵地植物的互作关系。未来的研究不仅需要考虑AMF与外来植物共生的菌根特性和对竞争关系的影响,还需要通过大尺度条件下的野外试验及室内补充试验深入探究影响AMF在外来植物与本地植物竞争演替中的作用的生物和非生物因子,以全面解释AMF影响外来植物入侵的反馈机制。     

Breeding system and pollination ecology of introduced plants compared to their native relatives

Identifying how plant-enemy interactions contribute to the success of introduced species has been a subject of much research, while the role of plant-pollinator interactions has received less attention. The ability to reproduce in new environments is essential for the successful establishment and spread of introduced species. Introduced plant species that are not capable of autonomous self-fertilization and are unable to attract resident pollinators may suffer from pollen limitation. Our study quantifies the degree of autogamy and pollination ecology of 10 closely related pairs of native and introduced plant species at a single site near St. Louis, Missouri, USA. Most of these species pairs had similar capacities for autogamy; however, of those that differed, the introduced species were more autogamous than their native congeners. Most introduced plants have pollinator visitation rates similar to those of their native congeners. Of the 20 species studied, only three had significant pollen limitation. We suggest that the success of most introduced plant species is because they are highly autogamous or because their pollinator visitation rates are similar to those of their native relatives. Understanding and identifying traits related to pollination success that are key in successful introductions may allow better understanding and prediction of biological invasions.     

The role of plant–mycorrhizal mutualisms in deterring plant invasions: Insights from an individual‐based model

Understanding the factors that determine invasion success for non‐native plants is crucial for maintaining global biodiversity and ecosystem functioning. One hypothesized mechanism by which many exotic plants can become invasive is through the disruption of key plant–mycorrhizal mutualisms, yet few studies have investigated how these disruptions can lead to invader success. We present an individual‐based model to examine how mutualism strengths between a native plant (Impatiens capensis) and mycorrhizal fungus can influence invasion success for a widespread plant invader, Alliaria petiolata (garlic mustard). Two questions were investigated as follows: (a) How does the strength of the mutualism between the native I. capensis and a mycorrhizal fungus affect resistance (i.e., native plant maintaining >60% of final equilibrium plant density) to garlic mustard invasion? (b) Is there a non‐linear relationship between initial garlic mustard density and invasiveness (i.e., garlic mustard representing >60% of final equilibrium plant density)? Our findings indicate that either low (i.e., facultative) or high (i.e., obligate) mutualism strengths between the native plant and mycorrhizal fungus were more likely to lead to garlic mustard invasiveness than intermediate levels, which resulted in higher resistance to garlic mustard invasion. Intermediate mutualism strengths allowed I. capensis to take advantage of increased fitness when the fungus was present but remained competitive enough to sustain high numbers without the fungus. Though strong mutualisms had the highest fitness without the invader, they proved most susceptible to invasion because the loss of the mycorrhizal fungus resulted in a reproductive output too low to compete with garlic mustard. Weak mutualisms were more competitive than strong mutualisms but still led to garlic mustard invasion. Furthermore, we found that under intermediate mutualism strengths, the initial density of garlic mustard (as a proxy for different levels of plant invasion) did not influence its invasion success, as high initial densities of garlic mustard did not lead to it becoming dominant. Our results indicate that plants that form weak or strong mutualisms with mycorrhizal fungi are most vulnerable to invasion, whereas intermediate mutualisms provide the highest resistance to an allelopathic invader.     

AM真菌在植物病虫害生物防治中的作用机制

丛枝菌根(Arbuscular Mycorrhizae,AM)真菌是一类广泛分布于土壤生态系统中的有益微生物,能与大约80%的陆生高等植物形成共生体。由土传病原物侵染引起的土传病害被植物病理学界认定为最难防治的病害之一。研究表明,AM真菌能够拮抗由真菌、线虫、细菌等病原体引起的土传性植物病害,诱导宿主植物增强对病虫害的耐/抗病性。当前,利用AM真菌开展病虫害的生物防治已经引起生态学家和植物病理学家的广泛关注。基于此,围绕AM真菌在植物病虫害生物防治中的最新研究进展,从AM真菌改变植物根系形态结构、调节次生代谢产物的合成、改善植物根际微环境、与病原微生物直接竞争入侵位点和营养分配、诱导植株体内抗病防御体系的形成等角度,探究AM真菌在植物病虫害防治中的作用机理,以期为利用AM真菌开展植物病虫害的生物防治提供理论依据,并对本领域未来的发展方向和应用前景进行展望。     

The impact of wildfire on vesicular-arbuscular mycorrhizal fungi and their potential to influence the re-establishment of post-fire plant communities

Wildfires are a typical event in many Australian plant communities. Vesicular-arbuscular mycorrhizal (VAM) fungi are important for plant growth in many communities, especially on infertile soils, yet few studies have examined the impact of wildfire on the infectivity of VAM fungi. This study took the opportunity offered by a wildfire to compare the infectivity and abundance of spores of VAM fungi from: (i) pre-fire and post-fire sites, and (ii) post-fire burned and unburned sites. Pre-fire samples had been taken in May 1990 and mid-December 1990 as part of another study. A wildfire of moderate intensity burned the site in late December 1990. Post-fire samples were taken from burned and unburned areas immediately after the fire and 6 months after the fire. A bioassay was used to examine the infectivity of VAM fungi. The post-fire soil produced significantly less VAM infection than the pre-fire soil. However, no difference was observed between colonization of plant roots by VAM fungi in soil taken from post-fire burned and adjacent unburned plots. Soil samples taken 6 months after the fire produced significantly more VAM than corresponding soil samples taken one year earlier. Spore numbers were quantified be wet-sieving and decanting of 100-g, air-dried soil subsamples and microscopic examination. For the most abundant spore type, spore numbers were significantly lower immediately post-fire. However, no significant difference in spore numbers was observed between post-fire burned and unburned plots. Six months after the fire, spore numbers were the same as the corresponding samples taken 1 year earlier. All plants appearing in the burned site resprouted from underground organs. All post-fire plant species recorded to have mycorrhizal associations before the fire had the same associations after the fire, except for species of Conospermum (Proteaceae), which lacked internal vesicles in cortical cells in the post-fire samples.     

Invasion success of non-indigenous aquatic and semi-aquatic plants in their native and introduced ranges. A comparison between their invasiveness in North America and in France

Aquatic and semi-aquatic plants comprise few species worldwide, yet the introduction of non-indigenous plants represents one of the most severe examples of biological invasions. My goal is to compare the distribution and the biology of aquatic and semi-aquatic plants in their introduced ranges and in their native ranges. The primary objective of this study is to test the hypothesis that invasive species have evolved traits likely to increase their success in the new range. I made two reciprocal comparisons, i.e. I compared European species in France and in North America, and North American species in France and in North America. Twenty-seven species were classified according to their invasiveness in their introduced area. I␣found six invasive macrophyte species in France native to North America and 17 invasive species in North America native to Europe. Four species are invasive in both areas. There is no general tendency for macrophytes to be more vigorous in their introduced ranges. Most non-indigenous aquatic and semi-aquatic species are potentially invasive or widespread and well-established in their introduced country, while few species seem to be restricted in their distribution.     

丛枝菌根真菌在内的土壤真菌对入侵植物紫茎泽兰的正反馈：证据来自野外实验

包括紫茎泽兰在内的许多外来植物都能够与新入侵生境的丛枝菌根真菌（ AMF）形成互利共生,因此菌根真菌如何调节外来植物种的入侵是当前亟待研究的问题。测定了紫茎泽兰入侵不同阶段（紫茎泽兰呈零星丛状分布于本地植物群落中[部分入侵生境]及紫茎泽兰单优群落形成期[入侵生境]）的土壤化学性状,而后通过野外试验,采用杀真菌剂处理,研究了包括AMF在内的土壤真菌对紫茎泽兰入侵的反馈作用。紫茎泽兰入侵改变了土壤化学性状。施用杀真菌剂降低了紫茎泽兰叶面积、叶片碳、氮、磷、和δ13 C含量。综合分析发现,在紫茎泽兰与本地植物混生群落中,土壤真菌能够增加紫茎泽兰叶片碳和δ13 C含量,但是不能提高紫茎泽兰的光合作用,表明碳和δ13 C含量的提高,不是光合作用的结果,而是通过其他机制实现的。因此可以得出,在部分入侵生境中,碳从土壤或临近植物经由菌丝网向紫茎泽兰转移。紫茎泽兰入侵不同阶段土壤养分的变化利于紫茎泽兰种群建立,同时利于紫茎泽兰借助真菌（尤其是AMF）从土壤或临近植物转移碳,促进种群扩散,这可能是紫茎泽兰入侵的机制之一。     

Species of plants and associated arbuscular mycorrhizal fungi mediate mycorrhizal responses to CO2 enrichment

It has been suggested that enrichment of atmospheric CO₂ should alter mycorrhizal function by simultaneously increasing nutrient‐uptake benefits and decreasing net C costs for host plants. However, this hypothesis has not been sufficiently tested. We conducted three experiments to examine the impacts of CO₂ enrichment on the function of different combinations of plants and arbuscular mycorrhizal (AM) fungi grown under high and low soil nutrient availability. Across the three experiments, AM function was measured in 14 plant species, including forbs, C₃ and C₄ grasses, and plant species that are typically nonmycorrhizal. Five different AM fungal communities were used for inoculum, including mixtures of Glomus spp. and mixtures of Gigasporaceae (i.e. Gigaspora and Scutellospora spp.). Our results do not support the hypothesis that CO₂ enrichment should consistently increase plant growth benefits from AM fungi, but rather, we found CO₂ enrichment frequently reduced AM benefits. Furthermore, we did not find consistent evidence that enrichment of soil nutrients increases plant growth responses to CO₂ enrichment and decreases plant growth responses to AM fungi. Our results show that the strength of AM mutualisms vary significantly among fungal and plant taxa, and that CO₂ levels further mediate AM function. In general, when CO₂ enrichment interacted with AM fungal taxa to affect host plant dry weight, it increased the beneficial effects of Gigasporaceae and reduced the benefits of Glomus spp. Future studies are necessary to assess the importance of temperature, irradiance, and ambient soil fertility in this response. We conclude that the affects of CO₂ enrichment on AM function varies with plant and fungal taxa, and when making predictions about mycorrhizal function, it is unwise to generalize findings based on a narrow range of plant hosts, AM fungi, and environmental conditions.     

An exotic invader drives the evolution of plant traits that determine mycorrhizal fungal diversity in a native competitor

The symbiosis between land plants and arbuscular mycorrhizal fungi (AMF) is one of the most widespread and ancient mutualisms on the planet. However, relatively little is known about the evolution of these symbiotic plant–fungal interactions in natural communities. In this study, we investigated the symbiotic AMF communities of populations of the native plant species Pilea pumila (Urticaceae) with varying histories of coexistence with a nonmycorrhizal invasive species, Alliaria petiolata (Brassicaceae), known to affect mycorrhizal communities. We found that native populations of P. pumila with a long history of coexistence with the invasive species developed more diverse symbiotic AMF communities. This effect was strongest when A. petiolata plants were actively growing with the natives, and in soils with the longest history of A. petiolata growth. These results suggest that despite the ancient and widespread nature of the plant–AMF symbiosis, the plant traits responsible for symbiotic preferences can, nevertheless, evolve rapidly in response to environmental changes.     

Development of a model system to assess the impact of genetically modified corn and aubergine plants on arbuscular mycorrhizal fungi

We developed an experimental model system to monitor the impact of generically modified (GM) plants on arbuscular mycorrhizal (AM) fungi, a group of non-target soil microorganisms, fundamental for soil fertility and plant nutrition. The system allowed us to study the effects of root exudates of both commercial Bt corn and aubergine plants expressing Dm-AMP1 defensin on different stages of the life cycle of the AM fungal species G. mosseae. Root exudates of Bt 176 corn significantly reduced pre-symbiotic hyphal growth, compared to Bt 11 and non-transgenic plants. No differences were found in mycelial growth in the presence of Dm-AMP1 and control plant root exudates. Differential hyphal morphogenesis occurred irrespective of the plant line, suggesting that both exuded Bt toxin and defensin do not interfere with fungal host recognition mechanisms. Bt 176 affected the regular development of appressoria, 36% of which failed to produce viable infection pegs. Our experimental model system represents an easy assay for testing the impact of GM plants on non-target soil-borne AM fungi.     

Response of endangered plant species to inoculation with arbuscular mycorrhizal fungi and soil bacteria

Three endangered plant species, Plantago atrata and Pulsatilla slavica, which are on the IUCN red list of plants, and Senecio umbrosus, which is extinct in the wild in Poland, were inoculated with soil microorganisms to evaluate their responsiveness to inoculation and to select the most effective microbial consortium for application in conservation projects. Individuals of these taxa were cultivated with (1) native arbuscular mycorrhizal fungi (AMF) isolated from natural habitats of the investigated species, (2) a mixture of AMF strains available in the laboratory, and (3) a combination of AMF lab strains with rhizobacteria. The plants were found to be dependent on AMF for their growth; the mycorrhizal dependency for P. atrata was 91%, S. umbrosus-95%, and P. slavica-65%. The applied inocula did not significantly differ in the stimulation of the growth of P. atrata and S. umbrosus, while in P. slavica, native AMF proved to be the less efficient. We therefore conclude that AMF application can improve the ex situ propagation of these three threatened taxa and may contribute to the success of S. umbrosus reintroduction. A multilevel analysis of chlorophyll a fluorescence transients by the JIP test permitted an in vivo evaluation of plant vitality in terms of biophysical parameters quantifying photosynthetic energy conservation, which was found to be in good agreement with the results concerning physiological parameters. Therefore, the JIP test can be used to evaluate the influence of AMF on endangered plants, with the additional advantage of being applicable in monitoring in a noninvasive way the acclimatization of reintroduced species in nature.     

Arbuscular mycorrhizal fungi can transfer substantial amounts of nitrogen to their host plant from organic material

Nitrogen (N) capture by arbuscular mycorrhizal (AM) fungi from organic material is a recently discovered phenomenon. This study investigated the ability of two Glomus species to transfer N from organic material to host plants and examined whether the ability to capture N is related to fungal hyphal growth. Experimental microcosms had two compartments; these contained either a single plant of Plantago lanceolata inoculated with Glomus hoi or Glomus intraradices, or a patch of dried shoot material labelled with (15)N and (13)carbon (C). In one treatment, hyphae, but not roots, were allowed access to the patch; in the other treatment, access by both hyphae and roots was prevented. When allowed, fungi proliferated in the patch and captured N but not C, although G. intraradices transferred more N than G. hoi to the plant. Plants colonized with G. intraradices had a higher concentration of N than controls. Up to one-third of the patch N was captured by the AM fungi and transferred to the plant, while c. 20% of plant N may have been patch derived. These findings indicate that uptake from organic N could be important in AM symbiosis for both plant and fungal partners and that some AM fungi may acquire inorganic N from organic sources.     

Edaphic and host plant factors are linked to the composition of arbuscular mycorrhizal fungal communities in the root zone of endangered Ulmus chenmoui Cheng in China

Despite the importance of arbuscular mycorrhizal fungi (AMF) within deciduous forest ecosystems, we know little about how natural AMF communities are structured in the root zone of the endangered elm species Ulmus chenmoui. In this study, three U. chenmoui sampling sites, differing with respect to plant health, age, and growth status, were selected in Anhui Province, China. AMF biodiversity in the root zones of individual U. chenmoui trees was investigated using high‐throughput sequencing. In total, 61 AMF operational taxonomic units were detected. Five genera, namely Glomus (62.82%), Paraglomus (17.82%), Rhizophagus (4.29%), Septoglomus (4.06%) and Funneliformis (2.35%), and 29 species of AMF were identified. Correlation analysis indicated that available soil phosphorus and potassium concentrations were the main edaphic factors influencing AMF community structure. There was a difference in AMF species richness among the three U. chenmoui stands. Our study showed that soil nutrient concentrations and plant health, age, and growth status can exert a selective effect on the composition of the AMF population in the soil in the root zones of U. chenmoui trees.     

Factors relating to regional and local success of exotic plant species in their new range

Aim To estimate invasiveness of exotic plant species, many studies have used the frequency of occurrence within a defined region. This measure is informative on how widespread exotics are, however, it does not inform on their local dominance, which is crucial for conservation of biodiversity and ecosystem functioning. The aim of the present study is to determine if regional frequency of occurrence of exotic plant species indeed is indicative of their local dominance. We also determined which plant traits and other factors predict regional and local frequencies best. Location The Netherlands. Methods We used information on exotic plant species established in The Netherlands and compared traits relating to their frequency of occurrence regionally (the entire country) and their frequency of dominance locally (in 1–100 m² quadrats). We created minimal adequate models with factors explaining regional frequency and frequency of local dominance of 111 exotic plant species in The Netherlands. Results The model that used plant traits to explain regional frequency of exotic plant species differed from the models that best explained their frequency of local dominance. Regionally, the factors that correlated with frequency were: life form, height, polyploidy, length of flowering season, residence time, human use and origin. The factors that correlated to frequency of local dominance were lateral vegetative spread and residence time. Main conclusions We conclude that plant traits relating to the regional frequency of exotic plant species differ from those that relate to their frequency of local dominance. The implication of our results is that predictive studies on plant invasiveness based on regional frequencies may not be indicative of the local impacts. Since the prediction of local impacts is crucial for conservation and risk assessment, our study emphasized the need for better information on the local abundance of exotic invaders.     

Parasitoids select plants more heavily infested with their caterpillar hosts: a new approach to aid interpretation of plant headspace volatiles

Plants produce volatile organic compounds (VOCs) in response to herbivore attack, and these VOCs can be used by parasitoids of the herbivore as host location cues. We investigated the behavioural responses of the parasitoid Cotesia vestalis to VOCs from a plant-herbivore complex consisting of cabbage plants (Brassica oleracea) and the parasitoids host caterpillar, Plutella xylostella. A Y-tube olfactometer was used to compare the parasitoids' responses to VOCs produced as a result of different levels of attack by the caterpillar and equivalent levels of mechanical damage. Headspace VOC production by these plant treatments was examined using gas chromatography-mass spectrometry. Cotesia vestalis were able to exploit quantitative and qualitative differences in volatile emissions, from the plant-herbivore complex, produced as a result of different numbers of herbivores feeding. Cotesia vestalis showed a preference for plants with more herbivores and herbivore damage, but did not distinguish between different levels of mechanical damage. Volatile profiles of plants with different levels of herbivores/herbivore damage could also be separated by canonical discriminant analyses. Analyses revealed a number of compounds whose emission increased significantly with herbivore load, and these VOCs may be particularly good indicators of herbivore number, as the parasitoid processes cues from its external environment.