Arbuscular mycorrhizal fungi reduce decomposition of woody plant litter while increasing soil aggregation

The decomposition of plant organic matter and the stability of soil aggregates are important components of soil carbon cycling, and the relationship between decomposition rate and arbuscular mycorrhizal fungi (AMF) has recently received considerable attention. The interaction of AMF with their associated microorganisms and the consequences for litter decomposition and soil aggregation still remain fairly unclear. In a laboratory pot experiment we simultaneously tested the single and combined effects of one AMF species (Rhizophagus irregularis) and a natural non-AMF microbial community on the decomposition of small wooden sticks and on soil aggregation. To disentangle effects of hyphae and roots we placed mesh bags as root exclusion compartments in the soil. The decomposition of the wooden sticks in this compartment was significantly reduced in the presence of AMF, but not with the non-AMF microbial community only, compared to the control, while aggregation was increased in all treatments compared to the control. We suggest that AMF directly (via localized nutrient removal or altered moisture conditions) or indirectly (by providing an alternative carbon source) inhibited the activity of decomposers, leading to different levels of plant litter degradation under our experimental settings. Reduced decomposition of woody litter in presence of AMF can be important for nutrient cycling in AMF-dominated forests and in the case of woody plants and perennials that develop lignified roots in grasslands.     

Dual plant host effects on two arbuscular mycorrhizal fungi

Mycorrhizal fungi may simultaneously associate with multiple plant hosts, and the implications of this for the fungi involved are not well understood. To address this question, two arbuscular mycorrhizal fungi (AMF), Glomus clairoideum (a treatment referred to as “Glo”) and Scutellospora fulgida (a treatment referred to as “Scut”), were grown separately in pots that each consisted of two plant compartments separated by a root-free-compartment (RFC). Fungi within each two-plant-compartment pot were exposed to either two individuals of indiangrass (Sorghastrum nutans), two individuals of big bluestem (Andropogon gerardii), or one of each. A non-inoculated treatment (“Non”) was included to help gauge the potential influence of greenhouse contaminant fungi, cross-contamination, or any misidentification of non-AMF hyphae. The two host species had additive effects on the growth of AM hyphae in plant compartments of Scut, Glo, and Non pots, and in the RFCs of Scut pots. In Glo RFCs, however, they were antagonistic in their effects. Synergism between hosts in Non RFCs suggested that any potential contaminants or misidentification could not explain this result. Underyielding was not seen in shoot weight, root weight, or root length in dual host pots, and also therefore could not explain the result. Hyphal growth in the Scut treatment was evenly distributed between the RFC and plant compartments (or marginally skewed toward the RFC), while hyphal growth in the Glo treatment was skewed toward plant compartments (nearer roots). However, hyphal lengths were more highly correlated across plant compartments within a common pot in the Glo treatment, suggesting that this AMF bridged the RFC to experience the entire two-host pot as a single environment to a greater extent than Scut did. These AMF differed in how they responded to both the species composition of the two-host environment and its spatial structure; potential implications for mycorrhizal community dynamics are discussed.     

Global diversity and distribution of arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungi form associations with most land plants and can control carbon, nitrogen, and phosphorus cycling between above- and belowground components of ecosystems. Current estimates of AM fungal distributions are mainly inferred from the individual distributions of plant biomes, and climatic factors. However, dispersal limitation, local environmental conditions,and interactions among AM fungal taxa may also determine local diversity and global distributions. We assessed the relative importance of these potential controls by collecting 14,961 DNA sequences from 111 published studies and testing for relationships between AM fungal community composition and geography, environment, and plant biomes. Our results indicated that the global species richness of AM fungi was up to six times higher than previously estimated, largely owing to high beta diversity among sampling sites. Geographic distance, soil temperature and moisture, and plant community type were each significantly related to AM fungal community structure, but explained only a small amount of the observed variance. AM fungal species also tended to be phylogenetically clustered within sites, further suggesting that habitat filtering or dispersal limitation is a driver of AM fungal community assembly. Therefore, predicted shifts in climate and plant species distributions under global change may alter AM fungal communities.     

Carbon allocation in mycelia of arbuscular mycorrhizal fungi during colonisation of plant seedlings

The direction of carbon (C) allocation in mycorrhizal mycelia is of fundamental importance to coexistence of individual plants. We therefore investigated the transfer of C from established plants to plant seedlings through fungal mycelia. C allocation by the arbuscular mycorrhizal (AM) fungus Glomus intraradices, from ‘donor’ plants to mycelia in soil and two different species of introduced ‘receiver’ seedlings, was investigated in a pot experiment using ¹³C labelling and fatty acid analysis. After ¹³CO₂ application to the shoots of Trifolium subterraneum or Plantago lanceolata, used as donor plants, T. subterraneum and P. lanceolata receiver seedlings were introduced. Samples were collected 4-20 days after ¹³CO₂ application and analysed regarding ¹³C and the fatty acid 16:1ω5, the signature of AM fungi. ¹³C transfer from T. subterraneum donor plants was demonstrated by ¹³C enrichment of the roots of the receiver seedlings, but not from the P. lanceolata donor plants. ¹³C allocation to the neutral lipid fatty acid 16:1ω5 was only 1 ng in each receiver seedling, but 2 μg of the fatty acid in whole soil. The results indicate that C allocation through mycelial networks is influenced by the donor plant species, but is not directed towards receiver seedlings to any higher degree than towards other directions. The importance of the extraradical AM fungal mycelium as a C sink was demonstrated.     

丛枝菌根与植物寄生性线虫相互作用及抗性机制

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)能够与大多数陆地植物互惠共生,促进植物对养分的吸收,提高植物对各种生物和非生物胁迫的抗逆性,对植物健康生长有重要的作用。在土壤中丛枝菌根真菌与植物寄生性线虫共同依靠寄主植物根系完成生命循环,但二者对寄主植物作用完全相反,引起研究者广泛兴趣,成为菌根研究的热点和焦点之一。本文分析了丛植菌根真菌与植物寄生线虫的相互作用,并探讨了菌根提高植物对线虫抗性的可能机制:菌根真菌改善植物的生长和营养状况、改变植物根系形态结构、影响根系分泌物和根际微生物区系、诱导寄主植物产生防御反应等,旨在深入挖掘丛枝菌根真菌的生物学功能,进一步发挥其在农业生产中的应用潜力。     

Suppressive effects of seed-applied fungicides on arbuscular mycorrhizal fungi (AMF) differ with fungicide mode of action and AMF species

Seed-applied fungicides are commonly used to prevent or suppress fungal disease organisms in pulse crop production. However, non-target beneficial fungi, such as arbuscular mycorrhizal fungi (AMF), also may be affected. Seed-applied fungicides Agrox^® FL (active ingredient: captan), Allegiance™ FL (metalaxyl), Apron Maxx^® RTA^® (fludioxonil and metalaxyl), Thiram 75WP (thiram), Vitaflo^® 280 (carbathiin and thiram), Crown^® (carbathiin and thiabendazole), and Trilex^® AL (trifloxystrobin and metalaxyl) were assessed in a greenhouse study for their effects on colonization and development of AMF in pea and chickpea, and the consequent impact on plant growth. In the absence of disease pressure, systemic fungicides Allegiance™ FL, Apron Maxx^® RTA^®, Vitaflo^® 280, Crown^® and Trilex^® AL restricted mycorrhizal colonization, host growth and P uptake to different levels. In contrast, contact fungicides Agrox^® FL and Thiram 75WP had minimal effects on mycorrhizal colonization, host growth and P uptake. Although consequent sporulation and glomalin-related protein production were not significantly affected by fungicides at an early host growth stage, the compositional structure of the AMF community in host roots was significantly altered in response to Agrox^® FL, Allegiance™ FL, Apron Maxx^® RTA^®, and Trilex^® AL as revealed by pyrosequencing-based analysis of fungal 18S rRNA. These results indicate that the suppressive effects of seed-applied fungicides on AMF development depend on specific fungicide-AMF interactions.     

The role of the external mycelium in early colonization for three arbuscular mycorrhizal fungal species with different colonization strategies

Arbuscular mycorrhizal fungi (AMF) differ in their rate and extent of colonization of both plant roots and soil but the mechanism responsible for these differences is unclear. We compared the external mycelium of three AMF isolates (Glomus intraradices, Glomus etunicatum and Gigaspora gigantea) during early colonization of plant roots. We investigated whether an AMF with the most rapid colonization would have higher numbers of infective structures (i.e., infection hyphae and contact points), an AMF with extensive root colonization would have more infection units, and (3) AMF with extensive soil colonization would have large numbers of all external features (including absorptive hyphae, runner hyphae and hyphal bridges). Using specially designed soil and root observation chambers, we followed the development of the external mycelium for 7 weeks. We found that rapid colonization rate was due, in part, to the presence of more infective structures, in particular more infection hyphae and root contact points. Second, the extensive root colonizer had more, larger infection units. Third, data did not support the hypothesis that the extensive soil colonizer had more external structures. These results show that differences in the architecture of the external mycelium are responsible, in part, for variation in the colonization strategy of AMF.     

AM菌对三叶草吸收、累积重金属的影响

采用4室根箱培养系统,探讨了Cu、Zn、Pb、Cd 4种重金属复合污染土壤中,丛枝菌根菌对三叶草生长及吸收、累积重金属的作用,结果表明:重金属Cu 100mg/kg、Zn 600mg/kg、Pb 300mg/kg、Cd 10mg/kg的复合污染对三叶草生物量影响较小,但土壤重金属处理使丛枝菌根菌Glomus intraradices和Glomus caledonium对三叶草的侵染率分别降低53%和56%,菌种G.intraradice的菌丝密度降低73%;接种菌根真菌能明显减少重金属复合污染土壤中三叶草对Cu、Cd和Pb的吸收,并强化根系在限制重金属Pb和Cd向地上部运输中的作用,地上部Pb和Cd含量分别下降24.2%~55.3%和65%~97.9%,使三叶草地上部Cd和Pb含量均低于我国牧草重金属安全含量,提高了三叶草可食部分的质量;不同菌根真菌对三叶草吸收、累积及分配重金属的影响有明显差异,Glomus intraradices对减少三叶草对重金属的吸收及其在地上部可食部分的累积的作用大于Glomus caledonium。丛枝菌根菌对于强化三叶草根系对重金属的固持作用,调节生态系统中重金属的生物循环,减轻重金属对食物链的污染风险方面起着重要作用。     

Species composition of arbuscular mycorrhizal fungi in two mountain meadows with differing management types and levels of plant biodiversity

Species composition of arbuscular mycorrhizal fungi (AMF) was analysed in two differently managed mountain grasslands in Thuringia (Germany). Arbuscular mycorrhizal fungi were studied in the roots of 18 dominant plant species from a total of 56 (32%). Additionally, spores of AMF were isolated from soil samples. Arbuscular mycorrhizal fungi species composition was analysed based on 96 sequences of the internal transcribed spacer of the nuclear ribosomal DNA, 72 originated from mycorrhizal roots, and 24 originated from AMF spores. Phylogenetic analyses revealed a total of 19 AMF species representing all genera of the Glomeromycota except Scutellospora and Pacispora. Despite a different farming intensity, resulting in remarkable differences concerning their plant species diversity (27 against 43 plant species), the diversity of AMF was found to be similar with 11 species on the intensively farmed meadow and ten species on the extensively farmed one. Nevertheless, species composition between both sites was clearly different. It thus seems likely that the AMF species composition, but not necessarily the species number, is related to above ground plant biodiversity in the system under study.     

AM真菌接种对甘薯产量和品质的影响

通过田间试验方法研究了接种AM真菌对甘薯产量和品质的影响。结果表明,种植6周时接种能够提高甘薯的菌根侵染率、生长和吸P量,收获时可提高甘薯的产量和品质。从接种效果看,本地分离的菌株接种效果好于异地分离菌株,混合菌株好于单一菌株。     

两种丛枝菌根真菌对黄瓜苗期枯萎病的防效及根系抗病相关酶活性的影响

由尖孢镰刀菌引起的黄瓜枯萎病是设施黄瓜生产的主要障碍之一,丛枝菌根真菌(AM真菌)可以和包括黄瓜在内约80%的维管植物的根系形成菌根共生体,适宜的共生体组合对于寄主的生长与抗病性的提高十分有益。为明确Glomus versiforme与Glomus intraradices两种AM真菌对"津绿3号"黄瓜苗期枯萎病的防治效果。试验采用盆钵培养的方法,研究了两种AM真菌对幼苗生长及其根系3种抗病相关酶活性的影响。结果表明:两种AM真菌均可促进黄瓜幼苗的生长,并能减轻病害,但以G.versiforme的促生及生防作用更显著,接种G.versiforme处理的黄瓜幼苗株高、茎粗、叶面积及干重均显著大于对照,该处理的幼苗病情指数较对照降低26.6%。菌根化黄瓜幼苗抗病性的提高一方面与接种病原菌Fusarium oxysporum f.sp.cucumerinum前幼苗生长健壮有关;另一方面与根系抗病相关酶活性的提前诱导有关。接种F.oxysporum f.sp.cucumerinum前,G.versiforme处理的黄瓜幼苗壮苗指数显著高于G.intraradices处理与对照,分别为G.intraradices处理与对照的1.19倍与1.22倍;G.versiforme处理的黄瓜幼苗根系几丁质酶、β-1,3-葡聚糖酶与PAL酶分别比对照提前2 d、7 d、7 d被诱导,且酶活性分别为对照的1.44倍、2.16倍和92.00倍。     

丛枝菌根真菌对棉花耐盐性的影响研究

盆栽灭菌试验研究丛枝(AM)真菌对棉花耐盐性的影响结果表明,自然盐渍化土壤和人工模拟盐渍条件下接种AM真菌处理的生物产量显著高于不接种处理,相同土壤下菌根真菌对棉花植株生长的促进作用随盐水平的提高而增大,表明AM真菌与植株建立的共生关系有利于棉花在盐渍土壤中生长。盐胁迫下棉花植株对P的需要量增加,接种AM真菌可提高植株含P量,促进植株生长,提高棉花的耐盐性。     

Temporal variation outweighs effects of biosolids applications in shaping arbuscular mycorrhizal fungi communities on plants grown in pasture and arable soils

Landspreading of biosolids (treated sewage sludge) in agroecosystems is a common waste management practice worldwide. Evidence suggests biosolids may be detrimental to arbuscular mycorrhizal fungi (AMF); however, previous studies focused on arable systems and often unrealistically high biosolids application levels. We investigated the effects of biosolids on AMF communities in grassland and arable agroecosystems, in the context of the natural seasonal dynamics of AMF community composition and diversity. A pasture and arable system under commercial farming management were amended annually with two different types of biosolids, applied at levels meeting current European Union regulations, in a factorial, replicated field-scale plot experiment. AMF root colonisation and community composition were measured in Lolium perenne roots from the pasture and Trifolium repens roots growing in arable soil across the seasons of two years. AMF community compositions were assessed by terminal-restriction fragment length polymorphism analyses. Biosolids had no significant effect on AMF root colonisation or community composition in either agroecosystem. Soil chemical analyses indicated several changes in the top 0–5 cm layer of the pasture soil, including small increases in heavy metal concentrations in biosolids relative to control plots. Temporal AMF dynamics were detected in soils from both agroecosystem indicating that the effect of seasonality outweighed that of biosolids application.     

Soil tillage and herbicide applications in pea: arbuscular mycorrhizal fungi,plant growth and nutrient concentration respond differently

ABSTRACT

We conducted a field- and pot experiment with peas to investigate the impact of soil tillage and herbicide applications on arbuscular mycorrhizal fungi (AMF), plant growth, phosphorus concentrations, C:N ratio in plants and yield. The field study was carried out in a long-term soil tillage experiment where four tillage treatments have been compared. Field soil from the experimental plots were used for the pot experiment. AMF were not affected by herbicide (MCPB) application, neither in the field nor in the pot experiments. However, AMF root colonization was enhanced by reduced tillage, minimum tillage and no-tillage practices, compared to conventional tillage. In the pot experiment, plant growth and nodulation of pea roots was negatively affected by the high herbicide dosage. In the field experiment neither tillage nor herbicide treatment exert specific effects on root growth parameters, phosphorus concentrations, C:N ratio and plant dry matter. This work demonstrates that an appropriate herbicide usage coupled with conservation soil tillage techniques can favour AMF root colonization and benefit plant growth.

Abbreviations: AMF: arbuscular mycorrhizal fungi; CT: conventional tillage; RT: reduced tillage; MT: minimum tillage; NT: no tillage; P: Phosphorus; C:N ratio: carbon:nitrogen ratio     

“Afterlife” effects of mycorrhization on the decomposition of plant residues

The symbiosis with arbuscular mycorrhizal fungi is known to affect growth and tissue quality of plants. Therefore, mycorrhization may also have “afterlife” effects on decomposition dynamics. We tested this hypothesis with plant material of mycorrhized and non-mycorrhized plants of seven grassland species. We found that mycorrhization increased the decomposition rate and interpret this result as a consequence of the enhanced nutritive status of the plant tissue with positive effects on decomposer activity. The turn-over of organic matter and nutrients in ecosystems may therefore be indirectly influenced by the symbiosis with mycorrhizal fungi.     

丛枝菌根真菌在植物修复砷污染土壤中的作用

丛枝菌根真菌能增强植物对矿质元素的吸收、提高植物的抗逆性、增强抗病性、改善植物根际微环境,减轻重金属对植物的毒害,影响植物对重金属的吸收和转运,在重金属污染土壤的植物修复中显示出极大的应用潜力。近年来,As污染已成为全球非常突出且急需解决的环境问题之一,对As污染土壤的生物修复也因而成为研究热点。本文主要从丛枝菌根真菌改变土壤pH和酶活性、增强植物对As的耐性和影响植物对As的吸收方面综述了丛枝菌根在As污染土壤修复中应用的研究进展,揭示出菌根应用在As污染土壤中的作用潜力和研究方向。     

N,P Contribution and soil adaptability of four arbuscular mycorrhizal fungi

Abstract

A glasshouse study was conducted to investigate the symbiotic efficiency and soil adaptability of four AMF using glass-bead cultivation systems. The results showed that efficiency and adaptability of four fungi varied among three soils. Particularly, efficiency of BEG167 shifted from positive in Beijing soil to negative in Guangdong soil. Furthermore, BEG167 had high adaptability in all three soils. Intraspecific differences of BRG168 and BEG221 were found in efficiency and adaptability in three soils. Taking efficiency and adaptabilty into consideration, it was concluded that BEG167, BEG168 and BEG221 in Beijing soil, BEG151 in Hubei soil, and BEG151 and BEG168 in Guangdong soil were effective AMF for maize.     

AM 菌根真菌诱导对提高玉米纹枯病抗性的初步研究

试验研究玉米接种摩西球囊霉后对纹枯病抗性反应的结果表明,接种摩西球囊霉能明显减轻玉米纹枯病的发病率和病情指数,减轻病害。接种摩西球囊霉还能促进玉米营养生长,但立枯丝核菌侵袭会降低菌根的侵染率,表明摩西球囊霉与立枯丝核菌间存在相互作用。     

Estimation of the root colonization of soybean by an arbuscular mycorrhizal fungus,Gigaspora rosea,based on specific fatty acid profiles

Root colonization by arbuscular mycorrhizal (AM) fungi has traditionally been analyzed by microscopy. However, this method is time consuming and it is often difficult to distinguish between AM and non-AM fungi. In this study, we analyzed the fatty acid profiles in soybean roots colonized by AM fungi to determine if specific fatty acids derived from AM fungi can be used as markers for the intensity of the AM fungal colonization. The wild-type Enrei and hypernodulating Kanto100 soybean cultivars were inoculated with an AM fungus (Gigaspora rosea) alone or with Bradyrhizobium diazoefficiens, which nodulates soybean roots. Fatty acids 20:1ω9, 20:4ω6, and 20:5ω3 were specifically detected in the lateral roots of AM fungus-inoculated and dual-inoculated soybean plants. In the second lateral roots, the percentage of AM-specific fatty acids (i.e., 20:1ω9, 20:4ω6, and 20:5ω3) derived from AM fungi was closely correlated with the intensity of the AM fungal colonization. We propose that the AM-specific fatty acids represent useful markers for estimating the degree of AM fungal colonization. The percentage of AM-specific fatty acids was more than twofold higher in the second lateral roots than in the first lateral roots. Thus, the degree of AM fungal colonization is probably twofold higher in the second lateral roots than in the first lateral roots.