接种AM真菌对玉米和油菜种间竞争及土壤无机磷组分的影响

在温室盆栽条件下,分别模拟单作、间作和尼龙网分隔种植,比较接种丛枝菌根(arbuscular mycorrhizal, AM)真菌Glomus intraradices和Glomus mosseae对菌根植物玉米和非菌根植物油菜生长和磷吸收状况的影响,并分析土壤中各无机磷组分的变化。结果发现,接种AM真菌可以促进土壤中难溶性磷(Ca₁₀-P和O-P)向有效态磷转化,并显著降低总无机磷含量 (P<0.05),显著提高菌根植物玉米的生物量和磷吸收量(P<0.05),特别是在间作体系中使玉米的磷营养竞争比率显著提高了45.0%-104.1% (P<0.05),显著降低了油菜的生物量和磷吸收量(P<0.05),从而增强了了菌根植物的竞争优势,降低了非菌根植物与菌根植物的共存能力。揭示了石灰性土壤中AM真菌对植物物种多样性的影响,有助于更加全面地理解AM真菌在农业生态系统中的作用。     

AM真菌和磷对小马安羊蹄甲幼苗生长的影响

丛枝菌根(arbuscular mycorrhizal,AM)真菌在退化生态系统恢复与重建实践中具有重要作用。采用盆栽模拟方法,重点分析不同土壤磷条件下小马鞍羊蹄甲(Bauhinia faberi)幼苗接种AM真菌后,幼苗的形态、生物量积累、菌根侵染率和菌根效应(mycorrhizal growth response, MGR)在一个生长季内的动态变化。结果表明,Glomus mosseae和 Glomus coronatum能较好地侵染幼苗,两种AM真菌显著地增加幼苗根系、叶片数和生物量;接种AM真菌显著影响幼苗的生物量分配,而土壤磷对幼苗的生物量分配影响不明显,AM真菌和土壤磷对幼苗生长的交互作用显著;G. mosseae是小马鞍羊蹄甲的优势AM菌,其接种的幼苗根长、叶片数、生物量、侵染率和菌根效应都显著高于G. coronatum处理的幼苗;菌根效应显著,接种AM真菌能有缓解土壤磷素缺乏的限制作用,且随着苗龄增大促生作用表现更为明显。不同AM菌种对小马鞍羊蹄甲幼苗生长的促生作用表现出的差异,提示在多元资源限制的干旱贫瘠环境中进行生物修复须为目标恢复物种筛选出高效的优势AM真菌。     

不同磷水平土壤接种丛枝菌根真菌对植物生长和养分吸收的影响

通过盆栽试验研究了不同磷水平土壤接种丛枝菌根真菌Glomus mosseae对三叶草(Clover)和黑麦草(Ryegrass)生长、P浓度及N ∶ P比的影响.试验结果表明,Glomus mosseae显著提高了三叶草中P浓度和生物量,降低了植株N ∶ P比,对黑麦草植株P含量、生物量及N ∶ P比没有显著影响;在不同磷水平土壤中,接种处理对单种时三叶草中P含量的影响程度不同,以中磷和高磷水平下的影响较显著,这表明Glomus mosseae对三叶草的菌根效应在不同磷水平下并不相同;另外,两种植物混合种植情况下,黑麦草的竞争能力高于三叶草,使得其P浓度和生物量都显著高于三叶草,而接种Glomus mosseae增加了混种中三叶草的生物量和P浓度,降低了黑麦草的生物量,表明Glomus mosseae能提高混种中三叶草的竞争能力,从而改变群落中物种的竞争关系.此外,在一定磷水平下,菌根真菌的存在降低了三叶草中N ∶ P比, 这会改变三叶草的受限制方式,由受P元素限制变为受N元素限制.     

丛枝菌根真菌对入侵植物南美蟛蜞菊生长及竞争力的影响

【背景】丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)能促进植物的养分吸收及生长发育。入侵中国华南地区的外来入侵植物南美蟛蜞菊(Wedelia trilobata)常分布于养分匮乏的荒地,却能迅速生长并排挤本地植物而快速扩张领地。【目的】探究丛枝菌根真菌是否促进南美蟛蜞菊的生长与竞争能力。【方法】采用南美蟛蜞菊及其同属本地植物蟛蜞菊(Wedelia chinensis)的盆栽对比控制试验,并设置接种及不接种AMF变形球囊霉(Glomus versiforme)、不同磷营养水平以及单种或混种的种植方式3种处理对两种植物的生长及竞争能力进行比较。【结果】AMF均能侵染上述两种植物,并且AMF对南美蟛蜞菊根系的侵染率显著高于其对蟛蜞菊根系的侵染,尤其是在低磷水平下南美蟛蜞菊的菌根侵染率更高,而且AMF的侵染显著促进了低磷水平下南美蟛蜞菊的生长及其对蟛蜞菊的竞争能力。【结论】丛枝菌根真菌能够促进南美蟛蜞菊的生长,增强其对本地植物的竞争优势,该效应很可能对外来植物南美蟛蜞菊的成功入侵产生一定的作用。     

接种AMF与间作对红壤上玉米和大豆种间氮素竞争的影响

盆栽条件下对间作、尼龙网分隔和单作的玉米和大豆接种丛枝菌根真菌(arbuscular mycorrhizal fungus,AMF)Funneliformis mosseae(FM)和Funneliformis etunicatum(FE),以试验AMF和种植方式对玉米和大豆作物种间氮素竞争的影响。结果表明,接种FM和FE的玉米和大豆植株无论何种种植方式均有一定比例的侵染,侵染率为37%–56%。不管AMF接种与否,玉米的生物量大小依次为间作>尼龙网分隔>单作,大豆生物量大小依次为单作>尼龙网分隔>间作,说明间作促进了玉米的生长,却抑制了大豆的生长。无论何种种植方式,AMF处理均不同程度提高了玉米和大豆植株的氮含量和吸收量,降低了玉米和大豆根际土壤碱解氮的含量。在同一AMF处理3种种植方式内,间作种植对玉米植株氮含量和吸收量的促进作用最为明显,而单作对大豆植株氮含量和吸收量的促进作用最为明显。所有处理中,玉米对营养的竞争力和对氮的竞争比率均优于大豆,无论何种AMF处理,间作处理下的玉米相对于大豆的营养竞争能力均优于尼龙网分隔处理,无论何种种植方式,AMF处理下的玉米相对大豆对氮的竞争比率高于NM处理,可见,玉米始终处于竞争优势地位,而大豆则始终处于劣势。接种AMF均显著地促进了玉米和大豆的生长,并显著提高了玉米相对于大豆的竞争能力,在FM接种及间作模式下,玉米和大豆对土壤碱解氮的吸收利用较多,但玉米相对大豆对营养的竞争力和氮竞争比率最高,表明AMF影响了寄主植物的种间竞争力,并且在AMF和间作协同作用下的影响最为明显。     

混合盐碱胁迫下丛枝菌根真菌对紫花苜蓿生长及2种酚酸含量的影响

将4种盐（NaCl、Na₂SO₄、Na₂CO₃、NaHCO₃）按一定比例混合模拟出16种盐碱 （盐浓度 25~150 mmol·L^-1,pH 8.39~10.90）胁迫环境,通过室内盆栽实验,考察了接种丛枝菌根真菌（AMF）摩西球囊霉（Glomus mosseae）对盐碱混合胁迫下紫花苜蓿（ Medicago sativa）幼苗的存活率、株高、总生物量、可溶性蛋白质含量、脯氨酸含量以及阿魏酸、水杨酸两种酚酸含量的影响。结果显示：（1）非盐碱胁迫条件下,与未接菌处理组相比,接种AMF紫花苜蓿幼苗的株高、总生物量、可溶性蛋白质含量和脯氨酸含量分别提高了20%、130%、9.6%和3%,而其阿魏酸和水杨酸含量分别降低59.1%和623.9%;（2）在盐碱胁迫条件下,随着盐碱梯度的增加,接种AMF和未接菌处理组的紫花苜蓿幼苗的存活率、株高、总生物量、可溶性蛋白质含量均降低,而它们的脯氨酸、阿魏酸与水杨酸含量均增加;接种AMF处理组的存活率、株高、总生物量、可溶性蛋白质含量以及脯氨酸含量显著高于未接菌处理组,其阿魏酸含量比未接菌处理组高但差异不显著,而其水杨酸含量比未接菌处理组显著降低。研究表明,在盐碱混合胁迫条件下,接种丛枝菌根真菌（AMF）能够改变紫花苜蓿体内酚酸的含量,积累渗透调节物质,促进自身生长,从而提高其耐盐碱性,该研究对于提高盐碱地区经济作物产量,推动 AMF 在生产中利用具有理论指导意义。     

丛枝菌根菌丝桥介导刺槐-魔芋间碳转运和磷吸收

明确间作和接种丛枝菌根真菌(AMF)对刺槐(Robinia pseudoacacia)与魔芋(Amorphophallus konjac)碳转运和磷吸收的影响,可为揭示间作刺槐对魔芋的防病促生机制和推广刺槐林下魔芋绿色高产栽培技术提供科学依据。该研究使用孔径25μm尼龙网设置两室根箱隔网系统,分为A室(刺槐不接种/接种AMF)和B室(单作刺槐/刺槐间作魔芋);采用¹³C稳定性同位素技术对A室刺槐叶片进行标记,研究其同化的碳与B室魔芋之间的传递,以及AMF定植对两种作物的农艺性状、¹³C丰度和磷含量的影响。结果表明:(1)在接种条件下,菌丝桥对B室刺槐和魔芋的侵染率分别达到47.1%和60.4%;其中,刺槐侵染率与单作直接接种处理相比降低14.1%。在间作体系中,接种AMF提高了魔芋的生物量,其地上干质量和地下根系干质量分别较未接种处理显著增加9.7%和36.2%。(2)与单作未接种处理相比,间作未接种、单作接种和间作接种的刺槐同化的碳被更多地分配到根系和根际土壤(A室),并以根系分泌物的形式穿越尼龙网到达邻近作物根际(B室)。(3)与各自未接...     

接种微生物对大豆生长及其根际土壤的影响

对沙土中的大豆接种丛枝菌根真菌及丛枝菌根真菌与解磷菌和根瘤菌联合接种, 动态监测大豆的生长状况和营养吸收情况。结果表明, 在沙土中, 根瘤菌与丛枝菌根真菌的组合效应对豆科植物营养元素的改善最为有效。接种丛枝菌根真菌以及丛枝菌根真菌与其他微生物联合应用对宿主矿质营养吸收尤其是磷吸收有明显的促进作用, 种植30 d、45 d 和64 d 接菌处理植物叶片的平均全磷含量比对照分别高1.45%、73%和56%。接种微生物使植物从土壤中吸收氮、磷、钾元素的强度比对照高, 接菌植物根际土壤养分浓度低于对照。接菌植物生物量显著高于对照, 单接种丛枝菌根真菌处理、双接种丛枝菌根真菌与解磷菌、双接种丛枝菌根真菌与根瘤菌以及丛枝菌根真菌、解磷菌与根瘤菌三种菌剂混合处理的总生物量分别比对照高出181%、134%、153%和89%。丛枝菌根真菌与解磷菌和根瘤菌三种菌剂混合接种对植物的促生作用并不明显。     

丛枝菌根真菌促进入侵植物紫茎泽兰的生长和对本地植物竞争效应

外来植物与入侵地土壤丛枝菌根真菌(AMF)的互作和反馈已被认为是许多入侵植物的重要入侵机制之一。为进一步探究入侵植物紫茎泽兰(Ageratina adenophora)竞争替代本地植物过程中AMF的作用,本研究首先测定了林下和林地边缘两类生境中紫茎泽兰和本地植物的AMF侵染率和AMF含量,结果表明,2种生境中紫茎泽兰的菌根侵染率和AMF含量均显著高于本地植物,且菌根侵染率与AMF含量呈显著正相关。温室盆栽试验结果进一步表明,接种AMF显著促进了紫茎泽兰的生长,且对硝态氮和有效磷的吸收能力优于本地植物香茶菜(Rabdosia amethystoides),同时降低了竞争中本地植物香茶菜的菌根依赖性,提高了紫茎泽兰对香茶菜的竞争优势度。本研究进一步证实AMF有利于促进紫茎泽兰的竞争性扩张。     

丛枝菌根真菌对豆科作物生长和生物固氮及磷素吸收的影响

本研究以大豆为材料,采用盆栽和田间试验,探讨丛枝菌根真菌(AMF)对豆科作物生长的影响。盆栽试验设置了接种(+AMF)和不接种(-AMF)丛枝菌根真菌处理,田间试验设置了AMF菌丝非限制与限制处理。盆栽试验结果表明: 接种AMF显著提高了大豆地上部生物量(16.5%)和大豆根瘤数(131.4%),地上部磷含量、磷吸收量、氮含量和氮吸收量也显著增加。田间试验中,AMF菌丝非限制处理下大豆的地上部生物量、根系生物量、根瘤数量分别比限制处理下显著提高了123.6%、61.5%和212.5%,地上部和根系磷吸收量、氮含量、氮吸收量均显著高于限制处理,大豆根际土壤速效氮和有效磷含量也均显著高于限制处理。本研究可为进一步认识豆科作物与AMF的共生关系及田间磷肥高效利用提供理论参考。     

Different native arbuscular mycorrhizal fungi influence the coexistence of two plant species in a highly alkaline anthropogenic sediment

Different species of arbuscular mycorrhizal fungi (AMF) can produce different amounts of extraradical mycelium (ERM) with differing architectures. They also have different efficiencies in gathering phosphate from the soil. These differences in phosphate uptake and ERM length or architecture may contribute to differential growth responses of plants and this may be an important contributor to plant species coexistence. The effects of the development of the ERM of AMF on the coexistence of two co-occurring plant species were investigated in root-free hyphal chambers in a rhizobox experimental unit. The dominant shrub (Salix atrocinerea Brot.) and herbaceous (Conyza bilbaoana J. Rémy) plant species found in a highly alkaline anthropogenic sediment were studied in symbiosis with four native AMF species (Glomus intraradices BEG163, Glomus mosseae BEG198, Glomus geosporum BEG199 and Glomus claroideum BEG210) that were the most abundant members of the AMF community found in the sediment. Different AMF species did not influence total plant productivity (sum of the biomass of C. bilbaoana and S. atrocinerea), but had a great impact on the individual biomass of each plant species. The AMF species with greater extracted ERM lengths (G. mosseae BEG198, G. claroideum BEG210 and the four mixed AMF) preferentially benefited the plant species with a high mycorrhizal dependency (C. bilbaoana), while the AMF species with the smallest ERM length (G. geosporum BEG199) benefited the plant species with a low mycorrhizal dependency (S. atrocinerea). Seed production of C. bilbaoana was only observed in plants inoculated with G. mosseae BEG198, G. claroideum BEG210 or the mixture of the four AMF. Our results show that AMF play an important role in the reproduction of C. bilbaoana coexisting with S. atrocinerea in the alkaline sediment and have the potential to stimulate or completely inhibit seed production. The community composition of native AMF and the length of the mycelium they produce spreading from roots into the surrounding soil can be determinant of the coexistence of naturally co-occurring plant species.     

The impact of arbuscular mycorrhizal fungi on tomato plant resistance against Tuta absoluta (Meyrick) in greenhouse conditions

The symbiotic relationship between plants and arbuscular mycorrhizal fungi (AMF) improves plant growth and increases its resistance to pests and diseases. Mycorrhizal fungi are among the specialized fungi associated with the rhizosphere and are completely dependent on plant organic carbon. In this research tomato, Solanum lycopersicum L. was used as the host plant to evaluate the interaction effects between inoculation of tomato plant with AMF and feeding of tomato leaf miner, Tuta absoluta (Meyrick). In addition, plant growth parameters and growth rate of insect were assessed. The mycorrhizal treatment included a mixture of four fungal species (Funneliformis mosseae, Rhizophagus intraradices, R. irregularis and Glomus iranicus). The results of the experiment showed that tomato plant roots were well colonized (66.29%) by AMF and there was a significant mutual relationship between the insects feeding on the plants and the fungi. Feeding by the insects on plants inoculated with the fungus increased percentage of colonization by AMF in plants infested with the insect as compared to the control plants. The results also indicated that growth parameters and phosphorus content of the plants inoculated with fungi significantly increased compared to the control group. Moreover, significantly lower growth rate and consumption index observed in the T. absoluta larvae were fed on the leaves of plants treated with AMF compared to leaves of plants not inoculated with AMF.     

Hypericin and pseudohypericin concentrations of a valuable medicinal plant <Emphasis Type="Italic">Hypericum perforatum</Emphasis> L. are enhanced by arbuscular mycorrhizal fungi

Hypericum perforatum L. (St. John’s-wort, Hypericaceae) is a valuable medicinal plant species cultivated for pharmaceutical purposes. Although the chemical composition and pharmacological activities of H. perforatum have been well studied, no data are available concerning the influence of arbuscular mycorrhizal fungi (AMF) on this important herb. A laboratory experiment was therefore conducted in order to test three AMF inocula on H. perforatum with a view to show whether AMF could influence plant vitality (biomass and photosynthetic activity) and the production of the most valuable secondary metabolites, namely anthraquinone derivatives (hypericin and pseudohypericin) as well as the prenylated phloroglucinol—hyperforin. The following treatments were prepared: (1) control—sterile soil without AMF inoculation, (2) Rhizophagus intraradices (syn. Glomus intraradices), (3) Funneliformis mosseae (syn. Glomus mosseae), and (4) an AMF Mix which contained: Funneliformis constrictum (syn. Glomus constrictum), Funneliformis geosporum (syn. Glomus geosporum), F. mosseae, and R. intraradices. The application of R. intraradices inoculum resulted in the highest mycorrhizal colonization, whereas the lowest values of mycorrhizal parameters were detected in the AMF Mix. There were no statistically significant differences in H. perforatum shoot mass in any of the treatments. However, we found AMF species specificity in the stimulation of H. perforatum photosynthetic activity and the production of secondary metabolites. Inoculation with the AMF Mix resulted in higher photosynthetic performance index (PI_total) values in comparison to all the other treatments. The plants inoculated with R. intraradices and the AMF Mix were characterized by a higher concentration of hypericin and pseudohypericin in the shoots. However, no differences in the content of these metabolites were detected after the application of F. mosseae. In the case of hyperforin, no significant differences were found between the control plants and those inoculated with any of the AMF applied. The enhanced content of anthraquinone derivatives and, at the same time, better plant vitality suggest that the improved production of these metabolites was a result of the positive effect of the applied AMF strains on H. perforatum. This could be due to improved mineral nutrition or to AMF-induced changes in the phytohormonal balance. Our results are promising from the biotechnological point of view, i.e. the future inoculation of H. perforatum with AMF in order to improve the quality of medicinal plant raw material obtained from cultivation.     

Studies on the diversity of arbuscular mycorrhizal fungi and the efficacy of two native isolates in a highly alkaline anthropogenic sediment

A field survey of the arbuscular mycorrhizal status of herbaceous plant species was conducted in a highly alkaline anthropogenic sediment resulting from the disposal of waste from an acetylene and polyvinyl chloride factory. Most plant species found at the site were mycorrhizal and the dominant mycotrophic plant species was Conyza bilbaoana. Fungal species richness was assessed by identification of spores extracted from the sediment and from continuously propagated trap pot cultures. All of the six species of arbuscular mycorrhizal fungi (AMF) found were from the genus Glomus. Glomus intraradices and G. mosseae were found in field-collected sediment samples and also occurred most frequently in trap cultures. To test the symbiotic effectiveness of these two fungi, seedlings of C. bilbaoana were inoculated with either native G. intraradices BEG163 or G. mosseae BEG198 and non-native G. intraradices BEG75 or G. mosseae BEG25 isolates in sterile and non-sterile sediment collected from the study site. All four isolates were able to colonise C. bilbaoana. However, AMF native to the target sediments were generally more effective than the non-native fungi in promoting plant establishment and growth under highly alkaline conditions. The non-native G. intraradices was, however, more effective than the non-native G. mosseae. The results of this study suggest the use of adapted AMF as inoculants for phytorestoration of alkaline anthropogenic-stressed sediments.     

Mycorrhizal colonization impacts on phenolic content and antioxidant properties of artichoke leaves and flower heads two years after field transplant

Greenhouse and field experiments were carried out in order to investigate the influence of mycorrhizal inoculation on total phenolic content (TPC) and antioxidant activity, expressed as antiradical power (ARP), of artichoke (Cynara cardunculus L. var. scolymus F.) leaves and flower heads extracts. The establishment of mycorrhizal symbiosis was monitored in pot and field grown plants, and the persistence of the inoculated AMF in roots after 2 years’ growth in the field was assessed by fungal ITS sequencing. Both in the greenhouse and in the field, marked increases in TPC and ARP were detected in leaves and flower heads of artichoke plants inoculated with the AM fungal species Glomus intraradices, either alone or in mixture with Glomus mosseae. In the field, plants inoculated with Glomus mix showed flower heads ARP content increases of 52.7 and 30.0% in the first and second year, respectively, compared with uninoculated plants. After 2 years’ growth in the field ITS rDNA sequences clustering with those of G. mosseae and G. intraradices were retrieved only from inoculated plant roots. Our data show that mycorrhizal inoculation may represent an efficient and sustainable strategy to improve productivity and enhance plant biosynthesis of secondary metabolites with health promoting activities.     

Interaction between root growth allocation and mycorrhizal fungi in soil with patchy P distribution

Aims and Background

Many plants preferentially grow roots into P-enriched soil patches, but little is known about how the presence of arbuscular mycorrhizal fungi (AMF) affects this response.

Methods

Lotus japonicus (L.) was grown in a low-P soil with (a) no additional P, (b) homogeneous P (28 mg pot^?1), (c) low heterogeneous P (9.3 mg pot^?1), and (d) high heterogeneous P (28 mg pot^?1). Each P treatment was combined with one of three mycorrhiza treatments: no mycorrhizae, Glomus intraradices, indigenous AMF. Real-time PCR was used to assess the abundance of G. intraradices and the indigeneous AMF G. mosseae and G. claroideum.

Results

Mycorrhization and P fertilization strongly increased plant growth. Homogeneous P supply enhanced growth in both mycorrhizal treatments, while heterogeneous P fertilization increased biomass production only in treatments with indigenous AMF inoculation. Preferential root allocation into P-enriched soil was significant only in absence of AMF. The abundance of AMF species was similar in P-enriched and unfertilized soil patches.

Conclusion

Mycorrhization may completely override preferential root growth responses of plants to P- patchiness in soil. The advantage of this effect for the plants is to give roots more freedom to forage for other resources in demand for growth and to adapt to variable soil conditions.     

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.     

Impact of arbuscular mycorrhizal fungal inoculants on subsequent arbuscular mycorrhizal fungi colonization in pot-cultured field pea (Pisum sativum L.)

The use of commercial inoculants containing non-resident arbuscular mycorrhizal fungi (AMF) is an emerging technology in field crop production in Canada. The objective of this study was to assess the impact of AMF inoculants containing either a single species (Glomus irregulare) or mixed species (G. irregulare, Glomus mosseae, and Glomus clarum) on AMF root colonization and consequent plant growth parameters of field pea grown using pot cultures. Field pea was grown in both sterilized and non-sterile (i.e., natural) field-collected soil containing resident AMF and received three inoculation treatments: uninoculated control, G. irregulare only, and a mixture of AMF species of G. irregulare, G. mosseae, and G. clarum. After 42 days, the AMF community assembled in field pea roots was assessed by cloning and sequencing analysis on the LSU-ITS-SSU rDNA gene, together with a microscopic assessment of colonization, biomass production, nutrient uptake, and N₂ fixation. The identity of AMF inoculants had a significant effect on field pea performance. The mixed species AMF inoculant performed better than the single species G. irregulare alone by promoting mycorrhizal colonization, field pea biomass, N and P uptake, and N₂ fixation and did not result in a significant compositional change of the AMF community that subsequently assembled in field pea roots. In contrast, the single species G. irregulare inoculant did not significantly enhance field pea biomass, N and P uptake, and N₂ fixation, although a significant compositional change of the subsequent AMF community was observed. No significant interactions affecting these measurements were detected between the resident AMF and the introduced AMF inoculants. The observation that the mixed species AMF inoculant promoted plant growth parameters without necessarily affecting the subsequent AMF community may have important implications regarding the use of non-resident AMF inoculants in agricultural production.     

Response of mycorrhizal grapevine to Armillaria mellea inoculation: disease development and polyamines

A study was conducted with the vine rootstock Richter 110 (Vitis berlandieri Planch. x Vitis rupestris L.) in order to assess whether the colonisation by the arbuscular mycorrhizal fungus (AMF) Glomus intraradices (BEG 72) can delay the disease development in plants inoculated with the root-rot fungus Armillaria mellea (Vahl:Fr) Kummer, and to elucidate if the levels of polyamines (PAs) are modified in response to G. intraradices, A. mellea or by the dual infection. Four treatments were considered: control and G. intraradices-inoculated plants infected or not with A. mellea. Plant growth, mycorrhizal colonisation and disease development were monitored throughout the experiment. High performance liquid chromatography (HPLC) in combination with fluorescence spectrophotometry was used to separate and quantify free root and leaf polyamines. The slower development of pathogenic symptoms and the higher plant biomass of mycorrhizal plants inoculated with A. mellea indicate an increase of tolerance due to the AMF inoculation. The variations in free PA levels detected at the beginning of the pathogenic infection suggest that PAs may have a potential role in the signalling mechanisms of the tolerance of mycorrhizal plants against A. mellea.