Spatial Segregation and Aggregation of Ectomycorrhizal and Root-Endophytic Fungi in the Seedlings of Two Quercus Species

Diverse clades of mycorrhizal and endophytic fungi are potentially involved in competitive or facilitative interactions within host-plant roots. We investigated the potential consequences of these ecological interactions on the assembly process of root-associated fungi by examining the co-occurrence of pairs of fungi in host-plant individuals. Based on massively-parallel pyrosequencing, we analyzed the root-associated fungal community composition for each of the 249 Quercus serrata and 188 Quercus glauca seedlings sampled in a warm-temperate secondary forest in Japan. Pairs of fungi that co-occurred more or less often than expected by chance were identified based on randomization tests. The pyrosequencing analysis revealed that not only ectomycorrhizal fungi but also endophytic fungi were common in the root-associated fungal community. Intriguingly, specific pairs of these ectomycorrhizal and endophytic fungi showed spatially aggregated patterns, suggesting the existence of facilitative interactions between fungi in different functional groups. Due to the large number of fungal pairs examined, many of the observed aggregated/segregated patterns with very low P values (e.g., < 0.005) turned non-significant after the application of a multiple comparison method. However, our overall results imply that the community structures of ectomycorrhizal and endophytic fungi could influence each other through interspecific competitive/facilitative interactions in root. To test the potential of host-plants'' control of fungus–fungus ecological interactions in roots, we further examined whether the aggregated/segregated patterns could vary depending on the identity of host plant species. Potentially due to the physiological properties shared between the congeneric host plant species, the sign of hosts'' control was not detected in the present study. The pyrosequencing-based randomization analyses shown in this study provide a platform of the high-throughput investigation of fungus–fungus interactions in plant root systems.     

Sharing of Diverse Mycorrhizal and Root-Endophytic Fungi among Plant Species in an Oak-Dominated Cool–Temperate Forest

Most terrestrial plants interact with diverse clades of mycorrhizal and root-endophytic fungi in their roots. Through belowground plant–fungal interactions, dominant plants can benefit by interacting with host-specific mutualistic fungi and proliferate in a community based on positive plant–mutualistic fungal feedback. On the other hand, subordinate plant species may persist in the community by sharing other sets (functional groups) of fungal symbionts with each other. Therefore, revealing how diverse clades of root-associated fungi are differentially hosted by dominant and subordinate plant species is essential for understanding plant community structure and dynamics. Based on 454-pyrosequencing, we determined the community composition of root-associated fungi on 36 co-occurring plant species in an oak-dominated forest in northern Japan and statistically evaluated the host preference phenotypes of diverse mycorrhizal and root-endophytic fungi. An analysis of 278 fungal taxa indicated that an ectomycorrhizal basidiomycete fungus in the genus Lactarius and a possibly endophytic ascomycete fungus in the order Helotiales significantly favored the dominant oak (Quercus) species. In contrast, arbuscular mycorrhizal fungi were generally shared among subordinate plant species. Although fungi with host preferences contributed to the compartmentalization of belowground plant–fungal associations, diverse clades of ectomycorrhizal fungi and possible root endophytes were associated not only with the dominant Quercus but also with the remaining plant species. Our findings suggest that dominant-ectomycorrhizal and subordinate plant species can host different subsets of root-associated fungi, and diverse clades of generalist fungi can counterbalance the compartmentalization of plant–fungal associations. Such insights into the overall structure of belowground plant–fungal associations will help us understand the mechanisms that facilitate the coexistence of plant species in natural communities.     

Contrasting Diversity and Host Association of Ectomycorrhizal Basidiomycetes versus Root-Associated Ascomycetes in a Dipterocarp Rainforest

Root-associated fungi, including ectomycorrhizal and root-endophytic fungi, are among the most diverse and important belowground plant symbionts in dipterocarp rainforests. Our study aimed to reveal the biodiversity, host association, and community structure of ectomycorrhizal Basidiomycota and root-associated Ascomycota (including root-endophytic Ascomycota) in a lowland dipterocarp rainforest in Southeast Asia. The host plant chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL) region and fungal internal transcribed spacer 2 (ITS2) region were sequenced using tag-encoded, massively parallel 454 pyrosequencing to identify host plant and root-associated fungal taxa in root samples. In total, 1245 ascomycetous and 127 putative ectomycorrhizal basidiomycetous taxa were detected from 442 root samples. The putative ectomycorrhizal Basidiomycota were likely to be associated with closely related dipterocarp taxa to greater or lesser extents, whereas host association patterns of the root-associated Ascomycota were much less distinct. The community structure of the putative ectomycorrhizal Basidiomycota was possibly more influenced by host genetic distances than was that of the root-associated Ascomycota. This study also indicated that in dipterocarp rainforests, root-associated Ascomycota were characterized by high biodiversity and indistinct host association patterns, whereas ectomycorrhizal Basidiomycota showed less biodiversity and a strong host phylogenetic preference for dipterocarp trees. Our findings lead to the working hypothesis that root-associated Ascomycota, which might be mainly represented by root-endophytic fungi, have biodiversity hotspots in the tropics, whereas biodiversity of ectomycorrhizal Basidiomycota increases with host genetic diversity.     

尖峰岭热带山地雨林根部真菌-植物互作网络结构特征

不同功能群的根部真菌可能会与植物差异性地互作, 并进一步影响地下真菌与植物群落构建。本研究采用Illumina Miseq测序方法检测了海南尖峰岭热带山地雨林中常见植物的根部真菌; 采用网络分析法比较了丛枝菌根(AM)真菌、外生菌根(ECM)真菌, 以及所有根部真菌与植物互作的二分网络(bipartite networks)结构特性。从槭树科、番荔枝科、夹竹桃科、冬青科、棕榈科、壳斗科、樟科和木犀科等8科植物的根系中, 检测到297,831条真菌ITS1序列, 这些序列被划为1,279个真菌分类单元(OTUs), 其中子囊菌门748个、担子菌门354个、球囊菌亚门80个, 以及未知真菌97个。核心根部真菌群落(420个OTUs)中, 至少有三类不同生态功能的真菌常见, 即丛枝菌根真菌(40个OTUs, 占总序列数23.4%)、外生菌根真菌(48个OTUs, 13.9%)和腐生型真菌(83个OTUs, 19.8%)。尖峰岭山地雨林根部真菌-植物互作网络结构特性的指标普遍显著高于/低于假定物种随机互作的零模型期待值。在群落水平, 不同功能型的根部真菌-植物互作网络表现出不同或相反的结构特性, 如丛枝菌根互作网络表现为比零模型预测值高的嵌套性和连接性, 以及比零模型低的专一性, 而外生菌根互作网络呈现出比零模型预测值低的嵌套性和连接性, 以及比零模型高的专一性。在功能群水平, 植物的生态位重叠度在AM互作网络高, 而ECM互作网络低; 真菌的生态位宽度在ECM互作网络窄, 而在AM互作网络较宽。共现(co-occurrence)网络分析进一步揭示, ECM群落的物种对资源的高度种间竞争(植物、真菌高C-score), 以及AM群落的物种无明显种间竞争(低C-score), 可能分别是形成反嵌套ECM互作网络及高嵌套AM互作网络结构的原因。上述结果说明, 尖峰岭山地雨林中至少有两种及以上的种间互作机制调节群落构建: 驱动AM互作网络冗余(nestedness)及ECM互作网络的高生态位分化(专一性)。本研究在同一个森林内探讨了不同功能型的真菌-植物互作特性, 对深入理解热带森林的物种共存机制和生态恢复具有重要意义。     

Fungal communities associated with roots of two closely related Juglandaceae species with a disjunct distribution in the tropics

We studied the biogeography and community structure of root-associated and ectomycorrhizal fungal communities in two related species of tropical Juglandaceae that have disjunct distributions in Asia and Mesoamerica. We tested the effects of environmental and dispersal factors in structuring root-associated fungi at a regional scale. We used Illumina sequencing to document fungi on the roots of Oreomunnea mexicana in Panama and Mexico and Alfaropsis roxburghiana in China. Ectomycorrhizal fungi dominated the communities with both hosts but we detected a more diverse root-associated fungal community in Alfaropsis but higher ectomycorrhizal fungi richness in Oreomunnea. Geographic distance was the best predictor of variation in fungal species composition, when including both hosts and when analyzing each host independently. However, our results showed a high correlation between geographic distance and abiotic variables, and therefore we were not able to determine if the observed changes in fungal community composition were explained also by spatially structured environmental or phylogenetic factors.     

Plant identity strongly structures the root-associated fungal community in a diverse subtropical forest

Revealing the relationship between plants and root-associated fungi is very important in understanding diversity maintenance and community assembly in ecosystems. However, the community assembly of root-associated fungi of focal plant species along a subtropical plant species diversity gradient is less documented. Here, we examined root-associated fungal communities associated with five ectomycorrhizal (EM) plant species (Betula luminifera, Castanea henryi, Castanopsis fargesii, C. sclerophylla, and Quercus serrate) in a Chinese subtropical woody plant species diversity (1, 2, 4, 8, 16 and 24 species) experiment, using paired-end Illumina MiSeq sequencing of the ITS2 region. In total, we detected 1933 root-associated fungal operational taxonomic units (OTUs) at a 97% sequence similarity level. Plant identity had a significant effect on total and saprotrophic fungal OTU richness, but plant species diversity level had a significant effect on saprotrophic and pathogenic fungal OTU richness. The community composition of total, saprotrophic and EM fungi was structured by plant identity and plant species diversity level. However, the community composition of pathogenic fungi was only shaped by plant identity. This study highlights that plant identity has a stronger effect on the root-associated fungal community than plant species diversity level in a diverse subtropical forest ecosystem.     

三种杓兰根相关真菌多样性和生态功能

【背景】除了菌根真菌(Orchid mycorrhizal fungi,OrMF)外,兰科植物根中还有其它内生真菌,称为根相关真菌(Root-associated fungi,RAF)。【目的】采用分离培养的方法获得同一栖息地针叶林和灌木林两种不同生境西藏杓兰、黄花杓兰和无苞杓兰的RAF菌株,研究其真菌谱系、多样性和生态功能结构。【方法】从杓兰根碎屑中分离RAF,通过总DNA提取、PCR扩增及测序得到ITS(Internaltranscribedspacer)序列;进行系统发育和多样性分析,并通过NCBI数据库比对得到相似性最高序列的注释信息来分析RAF生态学特性。【结果】共分离得到278株RAF,25种OTU类型,包括23个子囊菌门OTU,2个毛霉菌门OTU。RAF物种丰富度分析发现西藏杓兰的较黄花杓兰高,不同生境没有显著差异;不同杓兰物种较不同生境的RAF群落分化程度高。生态功能分析显示25个OTU包括共生型、腐生型和致病型3种营养型,以及外生菌根菌群、植物病原菌群、内生真菌群、动物病原菌群、真菌寄生菌群、杜鹃花类菌根群、未定义的腐生菌群和不确定型8种共位群。【结论】阐明不同生境采集的不同杓兰中RAF的分布特点和生态功能,为未来研究RAF与杓兰属植物的共生关系奠定基础。     

Diversity and Spatial Structure of Belowground Plant–Fungal Symbiosis in a Mixed Subtropical Forest of Ectomycorrhizal and Arbuscular Mycorrhizal Plants

Plant–mycorrhizal fungal interactions are ubiquitous in forest ecosystems. While ectomycorrhizal plants and their fungi generally dominate temperate forests, arbuscular mycorrhizal symbiosis is common in the tropics. In subtropical regions, however, ectomycorrhizal and arbuscular mycorrhizal plants co-occur at comparable abundances in single forests, presumably generating complex community structures of root-associated fungi. To reveal root-associated fungal community structure in a mixed forest of ectomycorrhizal and arbuscular mycorrhizal plants, we conducted a massively-parallel pyrosequencing analysis, targeting fungi in the roots of 36 plant species that co-occur in a subtropical forest. In total, 580 fungal operational taxonomic units were detected, of which 132 and 58 were probably ectomycorrhizal and arbuscular mycorrhizal, respectively. As expected, the composition of fungal symbionts differed between fagaceous (ectomycorrhizal) and non-fagaceous (possibly arbuscular mycorrhizal) plants. However, non-fagaceous plants were associated with not only arbuscular mycorrhizal fungi but also several clades of ectomycorrhizal (e.g., Russula) and root-endophytic ascomycete fungi. Many of the ectomycorrhizal and root-endophytic fungi were detected from both fagaceous and non-fagaceous plants in the community. Interestingly, ectomycorrhizal and arbuscular mycorrhizal fungi were concurrently detected from tiny root fragments of non-fagaceous plants. The plant–fungal associations in the forest were spatially structured, and non-fagaceous plant roots hosted ectomycorrhizal fungi more often in the proximity of ectomycorrhizal plant roots. Overall, this study suggests that belowground plant–fungal symbiosis in subtropical forests is complex in that it includes “non-typical” plant–fungal combinations (e.g., ectomycorrhizal fungi on possibly arbuscular mycorrhizal plants) that do not fall within the conventional classification of mycorrhizal symbioses, and in that associations with multiple functional (or phylogenetic) groups of fungi are ubiquitous among plants. Moreover, ectomycorrhizal fungal symbionts of fagaceous plants may “invade” the roots of neighboring non-fagaceous plants, potentially influencing the interactions between non-fagaceous plants and their arbuscular-mycorrhizal fungal symbionts at a fine spatial scale.     

四川都江堰亚热带针阔混交林中主要晚生型外生菌根真菌类群的空间分布

晚生型外生菌根真菌通常出现在森林演替的后期,是成熟林中的优势外生菌根真菌类群.对四川都江堰一片亚热带针阔混交林中的菌根真菌地上群落进行调查,并应用二元逻辑回归分析对晚生型外生菌根真菌的主要类群,即鹅膏菌科、牛肝菌科和红菇科,与周围(5 m×5 m样方)树种组成的关系进行研究.还应用次级变量分析方法对主要外生菌根真菌类群的空间格局进行了分析.结果表明,非外生菌根树种及某些外生菌根树种对特定类群菌根真菌子实体的出现有抑制作用,而不同类群外生菌根真菌在克隆生长上的差异并不是子实体空间分布的决定因素.我们认为,当研究自然林中外生菌根子实体的空间分布时,除了宿主植物的分布,也应考虑非宿主植物的分布以及菌根真菌相互作用的影响.     

Shrub range expansion alters diversity and distribution of soil fungal communities across an alpine elevation gradient

Global climate and land use change are altering plant and soil microbial communities worldwide, particularly in arctic and alpine biomes where warming is accelerated. The widespread expansion of woody shrubs into historically herbaceous alpine plant zones is likely to interact with climate to affect soil microbial community structure and function; however, our understanding of alpine soil ecology remains limited. This study aimed to (i) determine whether the diversity and community composition of soil fungi vary across elevation gradients and to (ii) assess the impact of woody shrub expansion on these patterns. In the White Mountains of California, sagebrush (Artemisia rothrockii) shrubs have been expanding upwards into alpine areas since 1960. In this study, we combined observational field data with a manipulative shrub removal experiment along an elevation transect of alpine shrub expansion. We utilized next‐generation sequencing of the ITS1 region for fungi and joint distribution modelling to tease apart effects of the environment and intracommunity interactions on soil fungi. We found that soil fungal diversity declines and community composition changes with increasing elevation. Both abiotic factors (primarily soil moisture and soil organic C) and woody sagebrush range expansion had significant effects on these patterns. However, fungal diversity and relative abundance had high spatial variation, overwhelming the predictive power of vegetation type, elevation and abiotic soil conditions at the landscape scale. Finally, we observed positive and negative associations among fungal taxa which may be important in structuring community responses to global change.     

四川都江堰亚热带针阔混交林中主要晚生型外生菌根真菌类群的空间分布

晚生型外生菌根真菌通常出现在森林演替的后期,是成熟林中的优势外生菌根真菌类群。对四川都江堰一片亚热带针阔混交林中的菌根真菌地上群落进行调查,并应用二元逻辑回归分析对晚生型外生菌根真菌的主要类群,即鹅膏菌科、牛肝菌科和红菇科,与周围(5m×5m样方)树种组成的关系进行研究。还应用次级变量分析方法对主要外生菌根真菌类群的空间格局进行了分析。结果表明,非外生菌根树种及某些外生菌根树种对特定类群菌根真菌子实体的出现有抑制作用,而不同类群外生菌根真菌在克隆生长上的差异并不是子实体空间分布的决定因素。我们认为,当研究自然林中外生菌根子实体的空间分布时,除了宿主植物的分布,也应考虑非宿主植物的分布以及菌根真菌相互作用的影响。     

Succession of root-associated fungi in Pisum sativum during a plant growth cycle as examined by 454 pyrosequencing

Purpose

Roots are inhabited by a broad range of fungi, including pathogens and mycorrhizal fungi, with functional traits related to plant health and nutrition. Management of these fungi in agroecosystems requires profound knowledge about their ecology. The main objective of this study was to examine succession patterns of root-associated fungi in pea during a full plant growth cycle.

Methods

Plants were grown in pots with field soil in a growth chamber under controlled conditions. Fungal communities in pea roots were analyzed at different plant growth stages including the vegetative growth, flowering and senescence, using 454 pyrosequencing.

Results

One hundred and twenty one non-singleton operational taxonomic units (OTUs) representing fungal species were detected. Pathogenic and arbuscular mycorrhizal fungi dominated during the vegetative growth stage, whereas saprotrophic fungi dominated during plant senescence.

Conclusions

In conclusion, the results from the present study demonstrated highly diverse fungal communities in pea roots with clear succession patterns related to fungal traits.     

丛枝菌根真菌的生态分布及其影响因子研究进展

丛枝菌根(arbuscular mycorrhiza,AM)共生体系对于植物适应各种逆境胁迫具有重要积极作用。AM真菌还能够通过根外菌丝网络调节植物群落结构和演替,深刻影响生态系统结构和功能的稳定性。AM真菌生态生理功能的发挥主要取决于其生态适应性,明确AM真菌在不同环境中的多样性、生态适应性以及对各种生态因子的响应机制,是AM真菌资源管理、功能发掘与利用的前提。迄今为止,有关各种生态因子对AM真菌多样性的影响已有不少研究,但是AM真菌生态分布及其形成机制仍缺乏系统的研究和理论分析。综述了生物因子和非生物因子对AM真菌生态分布的影响,结合大型生物空间分布理论探讨了AM真菌生态分布规律和建成机制,分析了当前本研究领域所存在的问题和动向,以期推动相关研究进展。     

Impacts of experimental warming and northern light climate on growth and root fungal communities of Scots pine populations

Global warming is driving plant range shifts towards higher latitudes, where plants encounter different light environment (photoperiod and light spectral quality) than that to which they are adapted. Light environment may indirectly influence the belowground part of the plant, where trees associate with ectomycorrhizal (ECM) and other biotrophic fungi. We studied joint impacts of warming and light climate on Scots pine (Pinus sylvestris) and its root-associated fungi in a reciprocal transplantation study, where pine seedlings from southern and northern tree populations were grown under similar experimental temperature in southern (60°N) and northern (69°N) Finland. Based on fungal ITS rDNA, the abundance of Basidiomycota, and ECM fungi in particular, was highest in the roots of southern pines in the south and in northern pines in the north, and seedling biomass was determined by population origin. Our results imply that root-associated fungi may respond differentially in native vs. non-native light environment of the host plant.     

海南濒危树种保育圃白木香与降香黄檀幼苗根部真菌谱系与生态型多样性比较

【背景】根部真菌是影响植物幼苗存活、定植和生长的重要因子之一,但是苗圃培育的幼苗根部真菌物种组成与生态学特性尚不清楚。【目的】研究苗圃培育的白木香(Aquilaria sinensis)与降香黄檀(Dalbergia odorifera)幼苗根部真菌群落谱系与生态型多样性,以及宿主植物对根部真菌群落结构的影响。【方法】采集幼苗根尖样品提取基因组DNA,用真菌通用引物与丛枝菌根真菌(AMF)特异性引物扩增真菌r DNA-ITS区,经克隆、测序、序列分析鉴定真菌。通过基于核酸与Metadata数据关联分析的FUNGuild软件,划分根部真菌的营养型和共位群。采用非公制多维尺度分析法(NMDS)研究幼苗根部真菌群落物种组成差异与宿主植物物种及形态指标的关系。【结果】白木香与降香黄檀幼苗根部真菌物种丰富,达51个OTU;谱系多样性较高,涉及毛霉菌门(Mucoromycota,51%)、子囊菌门(Ascomycota,43%)以及担子菌门(Basidiomycota,6%)。这些根部真菌涉及不同的营养型与共位群,包括共生型真菌29种,频度较高的如Glomeromycetes sp.2、Rhizophagus irregularis等,二者均属于AMF共位群;腐生营养型真菌5种,如Talaromyces pinophilus、Rhizopycnis vagum等;病原型真菌2种,是Mycoleptodiscus sp.和Fusarium phaseoli;还有15种其生态类型不确定。NMDS分析结果表明,宿主植物物种、株高、地径、叶面积对根部真菌群落物种组成的影响不显著。然而,株高对AMF群落的物种组成有较弱的影响。【结论】本苗圃条件下,土壤中本土性根部真菌繁殖体较为充足,白木香与降香黄檀幼苗根部真菌群落谱系多样性较高,多种营养型与共位群的根部真菌共存;此外,采用真菌通用引物对ITS1F/ITS4研究根部真菌群落物种多样性时,AMF多样性可能会被极度低估。     

Novel root fungal consortium associated with a dominant desert grass

The broad distribution and high colonization rates of plant roots by a variety of endophytic fungi suggest that these symbionts have an important role in the function of ecosystems. Semiarid and arid lands cover more than one-third of the terrestrial ecosystems on Earth. However, a limited number of studies have been conducted to characterize root-associated fungal communities in semiarid grasslands. We conducted a study of the fungal community associated with the roots of a dominant grass, Bouteloua gracilis, at the Sevilleta National Wildlife Refuge in New Mexico. Internal transcribed spacer ribosomal DNA sequences from roots collected in May 2005, October 2005, and January 2006 were amplified using fungal-specific primers, and a total of 630 sequences were obtained, 69% of which were novel (less than 97% similarity with respect to sequences in the NCBI database). B. gracilis roots were colonized by at least 10 different orders, including endophytic, coprophilous, mycorrhizal, saprophytic, and plant pathogenic fungi. A total of 51 operational taxonomic units (OTUs) were found, and diversity estimators did not show saturation. Despite the high diversity found within B. gracilis roots, the root-associated fungal community is dominated by a novel group of dark septate fungi (DSF) within the order Pleosporales. Microscopic analysis confirmed that B. gracilis roots are highly colonized by DSF. Other common orders colonizing the roots included Sordariales, Xylariales, and Agaricales. By contributing to drought tolerance and nutrient acquisition, DSF may be integral to the function of arid ecosystems.     

Fungal soil communities in a young transgenic poplar plantation form a rich reservoir for fungal root communities

Fungal communities play a key role in ecosystem functioning. However, only little is known about their composition in plant roots and the soil of biomass plantations. The goal of this study was to analyze fungal biodiversity in their belowground habitats and to gain information on the strategies by which ectomycorrhizal (ECM) fungi form colonies. In a 2-year-old plantation, fungal communities in the soil and roots of three different poplar genotypes (Populus × canescens, wildtype and two transgenic lines with suppressed cinnamyl alcohol dehydrogenase activity) were analyzed by 454 pyrosequencing targeting the rDNA internal transcribed spacer 1 (ITS) region. The results were compared with the dynamics of the root-associated ECM community studied by morphotyping/Sanger sequencing in two subsequent years. Fungal species and family richness in the soil were surprisingly high in this simple plantation ecosystem, with 5944 operational taxonomic units (OTUs) and 186 described fungal families. These findings indicate the importance that fungal species are already available for colonization of plant roots (2399 OTUs and 115 families). The transgenic modification of poplar plants had no influence on fungal root or soil communities. Fungal families and OTUs were more evenly distributed in the soil than in roots, probably as a result of soil plowing before the establishment of the plantation. Saprophytic, pathogenic, and endophytic fungi were the dominating groups in soil, whereas ECMs were dominant in roots (87%). Arbuscular mycorrhizal diversity was higher in soil than in roots. Species richness of the root-associated ECM community, which was low compared with ECM fungi detected by 454 analyses, increased after 1 year. This increase was mainly caused by ECM fungal species already traced in the preceding year in roots. This result supports the priority concept that ECMs present on roots have a competitive advantage over soil-localized ECM fungi.     

Fungal Symbionts Alter Plant Drought Response

Grassland productivity is often primarily limited by water availability, and therefore, grasslands may be especially sensitive to climate change. Fungal symbionts can mediate plant drought response by enhancing drought tolerance and avoidance, but these effects have not been quantified across grass species. We performed a factorial meta-analysis of previously published studies to determine how arbuscular mycorrhizal (AM) fungi and endophytic fungal symbionts affect growth of grasses under drought. We then examined how the effect of fungal symbionts on plant growth was influenced by biotic (plant photosynthetic pathway) and abiotic (level of drought) factors. We also measured the phylogenetic signal of fungal symbionts on grass growth under control and drought conditions. Under drought conditions, grasses colonized by AM fungi grew larger than those without mycorrhizal symbionts. The increased growth of grasses conferred from fungal symbionts was greatest at the lowest soil moisture levels. Furthermore, under both drought and control conditions, C3 grasses colonized by AM fungi grew larger than C3 grasses without symbionts, but the biomass of C4 grasses was not affected by AM fungi. Endophytes did not increase plant biomass overall under any treatment. However, there was a phylogenetically conserved increase in plant biomass in grasses colonized by endophytes. Grasses and their fungal symbionts seem to interact within a context-dependent symbiosis, varying with biotic and abiotic conditions. Because plant–fungal symbioses significantly alter plant drought response, including these responses could improve our ability to predict grassland functioning under global change.     

Assessment of root-associated fungal communities colonizing two species of tropical grasses reveals incongruence to fungal communities of North American native grasses

This study characterized the root-associated fungal (RAF) communities inhabiting Eustachys petraea and Panicum maximum, two tropical and weedy grass species on an island off the coast of Honduras, Central America. Media-based analyses revealed that fungi colonizing these grasses exhibited similar morphotypes (albeit in different proportions). Conversely, molecular-based analyses suggested that the community of fungal OTUs were dissimilar, with several OTUs commonly present on only one plant and no AMF sequences present in either plant species. When compared to various datasets of RAF obtained from the North American mainland (with similar methods), the Honduran grasses harbored a different set of fungal OTUs. Interestingly, some cosmopolitan taxonomic clades commonly encountered on the mainland were also isolated in Honduras, though based on ITS rDNA the fungi were only related distantly to those on the mainland. Additional work is necessary to determine how the RAF communities change over geographic distance and whether invasive grasses are constitutionally set up to accept relationships with a different suite of RAF species.     

A variety of melanised root-associated fungi from the Sydney basin form endophytic associations with Trifolium subterraneum

Knowledge of the abundance, diversity, and plant interactions of melanised root-associated fungi remains limited. The objective of this study was to isolate a wide variety of melanised root-associated fungi within the Sydney basin (NSW, Australia) and assess growth response of Trifolium subterraneum to inoculation with individual isolates. Of 902 root-associated fungi isolated from plant roots, 118 were melanised. All but two of these fungi were re-isolated from inoculated T. subterraneum seedlings after 7 weeks in a controlled environment. Approximately 60 % of the melanised root-associated fungi did not reduce plant growth. Twenty-four isolates tended to increase plant growth and were tentatively identified as predominantly ascomycetes, and one zygomycete. Melanised root-associated fungi appeared to form complex interactions with T. subterraneum, the natures of which remain to be further explored. Melanised root-associated fungi could potentially play key ecological roles including positively influencing edaphic conditions.