菌根真菌影响森林生态系统碳循环研究进展

森林生态系统在全球碳(C)储量中占据极为重要的地位。菌根真菌广泛存在于森林生态系统中,在森林生态系统C循环过程中发挥重要的作用。阐述了不同菌根类型真菌在森林生态系统C循环过程中的功能,对比了温带/北方森林与热带/亚热带森林中菌根真菌介导的C循环研究方面新近取得的研究结果。发现温带和北方森林的外生菌根(EcM)植物对地上生物量C的贡献相对较小,然而是地下C储量的主要贡献者;以丛枝菌根(AM)共生为主的热带/亚热带森林地表生物量占比较高,表明AM植被对热带/亚热带森林地上生物量C的贡献相对较大。我们还就全球变化背景下,菌根真菌及其介导的森林生态系统C汇功能,以及不同菌根类型树种影响C循环的机制等进行了总结。菌根真菌通过影响凋落物分解、土壤有机质形成及地下根系生物量,进而影响整个森林生态系统的C循环功能。菌根介导的森林C循环过程很大程度上取决于(优势)树木的菌根类型和森林土壤中菌根真菌的群落结构。最后指出了当前研究存在的主要问题以及未来研究展望。本文旨在明确菌根真菌在森林生态系统C循环转化过程中的重要生态功能,有助于准确地评估森林生态系统C汇现状,为应对全球变化等提供重要的依据。     

丛枝菌根真菌对大气CO2浓度升高和增温响应研究进展

全球变化深刻影响着陆地生态系统生物多样性及生态功能。丛枝菌根(AM)真菌可与绝大多数陆生植物根系形成互惠共生体,在协助宿主养分吸收、促进植物生长、维持植物多样性等方面发挥着重要作用。本文主要分析了大气CO₂浓度升高(eCO₂)和增温对森林和草地生态系统AM真菌群落组成及其功能的影响。eCO₂主要通过影响宿主植物、土壤碳(C)输入等方式间接影响AM真菌,可增加AM真菌的多度和活性,影响AM真菌的多样性与群落组成。增温可直接或间接地(通过宿主植物和土壤途径)影响AM真菌,显著改变森林土壤AM真菌的群落组成,但对草地土壤AM真菌群落组成的影响尚无定论。我们提出了当前研究中存在的主要问题及未来应重点关注的内容。本文旨在明晰AM真菌对eCO₂和增温的响应和适应,增进对AM真菌介导的土壤生态功能的认识,为利用AM真菌缓解全球变化、增强土壤功能的韧性和全球变化的生态系统适应性提供依据。     

Plant and soil properties determine microbial community structure of shared Pinus-Vaccinium rhizospheres in petroleum hydrocarbon contaminated forest soils

Rhizosphere communities are critical to plant and ecosystem function, yet our understanding of the role of disturbance in structuring these communities is limited. We tested the hypothesis that soil contamination with petroleum hydrocarbons (PHCs) alters spatial patterns of ecto- (ECM) and ericoid (ERM) mycorrhizal fungal and root-associated bacterial community structure in the shared rhizosphere of pine (Pinus contorta var. latifolia) and lingonberry (Vaccinium vitis-idaea) in reconstructed sub-boreal forest soils. Pine seeds and lingonberry cuttings were planted into containers with an organic (mor humus, FH or coarse woody debris, CWD) layer overlying sandy mineral horizons (Ae and Bf) of forest soils collected from field sites in central British Columbia, Canada. After 4 months, 219 mg cm^-2 crude oil was applied to the soil surface of half of the systems; systems were sampled 1 or 16 weeks later. Composition, relative abundance and vertical distribution of pine ECMs were assessed using light microscopy; community profiles were generated using LH-PCR of ribosomal DNA. Multivariate analysis revealed that plant and soil factors were more important determinants of community composition than was crude oil treatment. Fungal communities differed between pine and lingonberry roots; ECM communities were structured by soil layer whereas ERM communities varied between FH and CWD soil systems. Bacterial communities varied between plants and soil layers, indicating properties of ECM and ERM rhizospheres and the soil environment influence bacterial niche differentiation. This integration of mycorrhizal and bacterial community analysis contributes to a greater understanding of forest soil sustainability in forest ecosystems potentially contaminated with PHCs.     

Restoration of belowground fungal communities in reclaimed landscapes of the Canadian boreal forest

The trajectory of forests establishing on reclaimed oil sands mines in the Canadian boreal forest is uncertain. Soil microbes, namely mycorrhizal fungi, partly underlie successional trajectories of plant communities, yet their role in restoration is often overlooked. Here, we tested the relative importance of common management tools used in restoration—species planted and soil placement—on the recovery of ectomycorrhizal fungal communities over 4 years. Importantly, we further compared the community assembly of fungi on reclaimed landscapes to that in reference ecosystems disturbed to different degrees. This latter test addresses whether disturbance intensity is more important than common management interventions to restore fungal communities in these ecosystems. Three main findings emerged. (1) The effect of tree species planted and soil placement on ectomycorrhizal fungal communities establishing on reclaimed landscapes was dynamic through time. (2) Disturbances that remove or disrupt the organic layer of soils substantially affect the composition of ectomycorrhizal fungal communities. (3) Shifts in the community composition of ectomycorrhizal fungi were driven to a greater extent by disturbance severity than either tree species planted or soil placement.     

Ectomycorrhizal-Dominated Boreal and Tropical Forests Have Distinct Fungal Communities,but Analogous Spatial Patterns across Soil Horizons

Fungi regulate key nutrient cycling processes in many forest ecosystems, but their diversity and distribution within and across ecosystems are poorly understood. Here, we examine the spatial distribution of fungi across a boreal and tropical ecosystem, focusing on ectomycorrhizal fungi. We analyzed fungal community composition across litter (organic horizons) and underlying soil horizons (0–20 cm) using 454 pyrosequencing and clone library sequencing. In both forests, we found significant clustering of fungal communities by site and soil horizons with analogous patterns detected by both sequencing technologies. Free-living saprotrophic fungi dominated the recently-shed leaf litter and ectomycorrhizal fungi dominated the underlying soil horizons. This vertical pattern of fungal segregation has also been found in temperate and European boreal forests, suggesting that these results apply broadly to ectomycorrhizal-dominated systems, including tropical rain forests. Since ectomycorrhizal and free-living saprotrophic fungi have different influences on soil carbon and nitrogen dynamics, information on the spatial distribution of these functional groups will improve our understanding of forest nutrient cycling.     

农业生态系统中的AM真菌多样性

农业生态系统复杂庞大,是由如麦田生态系统、水稻田生态系统、果园生态系统、草地生态系统、保护地生态系统等组成的一个复合生态系统。重点介绍农业生态系统中丛枝菌根(AM)和AM真菌多样性,探讨农业生态系统中调控AM真菌多样性的途径以及今后研究的动向。     

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。     

Spatial separation of litter decomposition and mycorrhizal nitrogen uptake in a boreal forest

Our understanding of how saprotrophic and mycorrhizal fungi interact to re-circulate carbon and nutrients from plant litter and soil organic matter is limited by poor understanding of their spatiotemporal dynamics. In order to investigate how different functional groups of fungi contribute to carbon and nitrogen cycling at different stages of decomposition, we studied changes in fungal community composition along vertical profiles through a Pinus sylvestris forest soil. We combined molecular identification methods with 14C dating of the organic matter, analyses of carbon:nitrogen (C:N) ratios and 15N natural abundance measurements. Saprotrophic fungi were primarily confined to relatively recently (< 4 yr) shed litter components on the surface of the forest floor, where organic carbon was mineralized while nitrogen was retained. Mycorrhizal fungi dominated in the underlying, more decomposed litter and humus, where they apparently mobilized N and made it available to their host plants. Our observations show that the degrading and nutrient-mobilizing components of the fungal community are spatially separated. This has important implications for biogeochemical studies of boreal forest ecosystems.     

Fungal Community Shifts in Structure and Function across a Boreal Forest Fire Chronosequence

Forest fires are a common natural disturbance in forested ecosystems and have a large impact on the microbial communities in forest soils. The response of soil fungal communities to forest fire is poorly documented. Here, we investigated fungal community structure and function across a 152-year boreal forest fire chronosequence using high-throughput sequencing of the internal transcribed spacer 2 (ITS2) region and a functional gene array (GeoChip). Our results demonstrate that the boreal forest soil fungal community was most diverse soon after a fire disturbance and declined over time. The differences in the fungal communities were explained by changes in the abundance of basidiomycetes and ascomycetes. Ectomycorrhizal (ECM) fungi contributed to the increase in basidiomycete abundance over time, with the operational taxonomic units (OTUs) representing the genera Cortinarius and Piloderma dominating in abundance. Hierarchical cluster analysis by using gene signal intensity revealed that the sites with different fire histories formed separate clusters, suggesting differences in the potential to maintain essential biogeochemical soil processes. The site with the greatest biological diversity had also the most diverse genes. The genes involved in organic matter degradation in the mature forest, in which ECM fungi were the most abundant, were as common in the youngest site, in which saprotrophic fungi had a relatively higher abundance. This study provides insight into the impact of fire disturbance on soil fungal community dynamics.     

<Emphasis Type="Italic">Monotropastrum humile</Emphasis> var. <Emphasis Type="Italic">humile</Emphasis> is associated with diverse ectomycorrhizal Russulaceae fungi in Japanese forests

Monotropastrum humile is nearly lacking in chlorophyll and obtains its nutrients, including carbon sources, from associated mycorrhizal fungi. We analyzed the mycorrhizal fungal affinity and species diversity of M. humile var. humile mycorrhizae to clarify how the plant population survives in Japanese forest ecosystems. We classified 78 samples of adult M. humile var. humile individuals from Hokkaido, Honshu, and Kyusyu Islands into 37 root mycorrhizal morphotypes. Of these, we identified 24 types as Russula or Lactarius fungal taxa in the Russulaceae, Basidiomycetes, but we could not identify the remaining 13 types as to their genus in the Basidiomycetes. The number of fungal species on M. humile var. humile was the highest in the plant subfamily. The diversity of fungal species revealed its increased trends in natural forests at the stand level, fagaceous vegetation, and cool-temperate climate. The most frequently observed fungus colonized mainly samples collected from sub-alpine forests; the second most frequently observed fungus colonized samples collected from sub-alpine to warm-temperate forests. These results suggest that Japanese M. humile populations are associated with specific but diverse fungi that are common ectomycorrhizal symbionts of various forest canopy trees, indicating a tripartite mycorrhizal relationship in the forest ecosystem.     

Significant and persistent impact of timber harvesting on soil microbial communities in Northern coniferous forests

Forest ecosystems have integral roles in climate stability, biodiversity and economic development. Soil stewardship is essential for sustainable forest management. Organic matter (OM) removal and soil compaction are key disturbances associated with forest harvesting, but their impacts on forest ecosystems are not well understood. Because microbiological processes regulate soil ecology and biogeochemistry, microbial community structure might serve as indicator of forest ecosystem status, revealing changes in nutrient and energy flow patterns before they have irreversible effects on long-term soil productivity. We applied massively parallel pyrosequencing of over 4.6 million ribosomal marker sequences to assess the impact of OM removal and soil compaction on bacterial and fungal communities in a field experiment replicated at six forest sites in British Columbia, Canada. More than a decade after harvesting, diversity and structure of soil bacterial and fungal communities remained significantly altered by harvesting disturbances, with individual taxonomic groups responding differentially to varied levels of the disturbances. Plant symbionts, like ectomycorrhizal fungi, and saprobic taxa, such as ascomycetes and actinomycetes, were among the most sensitive to harvesting disturbances. Given their significant ecological roles in forest development, the fate of these taxa might be critical for sustainability of forest ecosystems. Although abundant bacterial populations were ubiquitous, abundant fungal populations often revealed a patchy distribution, consistent with their higher sensitivity to the examined soil disturbances. These results establish a comprehensive inventory of bacterial and fungal community composition in northern coniferous forests and demonstrate the long-term response of their structure to key disturbances associated with forest harvesting.     

Sources of inocula influence mycorrhizal colonization of plants in restoration projects: a meta‐analysis

Inoculation may influence mycorrhizal colonization and provide benefits to plants in restoration projects. However, it is unclear whether inoculation has consistent effects across ecosystem types, if it has long‐term effects on colonization, and whether sources of inocula differ in their effectiveness. To address these issues, we performed a meta‐analysis of published restoration studies across a variety of ecosystems to examine the effects of mycorrhizal inoculation on mycorrhizal establishment and plant growth under field conditions. Although we included trials from a variety of geographic locations, disturbance types, and ecosystem types, the majority were based in temperate ecosystems in the Northern Hemisphere, and fewer trials were from tropical ecosystems. Across ecosystem types, we found that inoculation consistently increased the abundance of mycorrhizal fungi in degraded ecosystems, and thus improved the establishment of plants. These benefits did not significantly attenuate over time. Moreover, inocula from different sources varied in their effects on mycorrhizal colonization. Inocula sourced from reference ecosystems and inocula with specific fungal species yielded higher increases in mycorrhizal colonization than did inocula from commercial sources. These results suggest that inocula source matters, and that an initial investment into mycorrhizal inoculation could provide lasting benefits for facilitating the establishment of the below‐ and aboveground components of restored ecosystems.     

Contrasting patterns of soil N-cycling in model ecosystems of Fennoscandian boreal forests

The low plant productivity of boreal forests in general has been attributed to low soil N supply and low temperatures. Exceptionally high productivity occurs in toe-slope positions, and has been ascribed to influx of N from surrounding areas and higher rates of soil N turnover in situ. Despite large apparent natural variations in forest productivity, rates of gross soil N mineralization and gross nitrification have never been compared in Fennoscandian boreal forests of contrasting productivity. We report contrasting patterns of soil N turnover in three model ecosystems, representing the range in soil C-to-N ratios (19–41) in Fennoscandian boreal forests and differences in forest productivity by a factor close to 3. Gross N mineralization was seven times higher when soil, microbial, and plant C-to-N ratios were the lowest compared to the highest. This process, nitrification and potential denitrification correlated with inorganic, total and microbial biomass N, but not microbial C. There was a constant ratio between soil and microbial C-to-N ratio of 3.7±0.2, across wide ratios of soil C-to-N and fungi-to-bacteria. Soil N-cycling should be controlled by the supplies of C and N to the microbes. In accordance with plant allocation theory, we discuss the possibility that the high fungal biomass at high soil C-to-N ratio reflects a particularly high supply of plant photosynthates, substrates of high-quality C, to mycorrhizal fungi. Methods to study soil N turnover and N retention should be developed to take into account the impact of mycorrhizal fungi on soil N-cycling.     

Defining nutritional constraints on carbon cycling in boreal forests – towards a less `phytocentric' perspective

Growing interest in possible global climate change has underlined the need for better information concerning the way in which carbon partitioning between ecosystem components is influenced by constraints on nutrient availability. Micro-organisms play a fundamental role in the cycling of carbon and nutrients in all ecosystems but the role of fungi in particular is pivotal in boreal forest ecosystems. Traditional models of nutrient cycling are based on methods and concepts developed in agricultural systems where microorganisms are considered primarily as nutrient processors providing plants with inorganic nutrients. The filamentous nature of fungi, their ability to translocate carbon and nutrients between different substrates and the capacity of ectomycorrhizal fungi to utilise organic nutrients have all been largely ignored. In this article, a new model is suggested which emphasises competition for organic nutrients between decomposer organisms and plants, with the plants depending on their associated mycorrhizal fungi for nutrient acquisition. Antagonistic interactions involving nutrient transfer between decomposer and mycorrhizal fungi are proposed as important pathways in nutrient cycling. Due to the nutrient conservative features of decomposer fungi, inorganic nutrients are considered less important for plant nutrition. The implications of the new nutrient cycling model on the carbon balance of boreal forests are discussed.     

外生菌根菌与森林树木的相互关系

生态系统的每个过程都伴随着各种微生物的活动,其中最重要的功能群之一是菌根真菌(菌根菌)。一般认为,菌根菌是自然界多数植物生存最基本的组成部分,陆地上约90％以上的高等植物都具有菌根菌。这些菌类的菌丝体与植物根系结合形成菌根,使植物生长成为可能,使不同种类植物的根系联在一起。根据菌根菌入侵植物根系的方式及菌根的形态特征,菌根可分为外生菌根、内生菌根和内外生菌根3组共7种类型。外生菌根主要出现在松科、桦木科、壳斗科等树种的森林生态系统中,在根系表面形成菌丝鞘,部分菌丝进入根系皮层细胞间隙形成哈氏网表面。菌根菌剂在森林经营中得到广泛地应用。外生菌根菌对森林树木的作用可归纳为：1)促进造林或育苗成活与生长;2)提高森林生态系统中植物的多样性、稳定性和生产力;3)对森林生态系统的综合效应,主要表现在增加植物一土壤联结,改善土壤结构,促进土壤微生物,增强植物器官的功能;4)抗拮植物根部病害病原菌等。树木与菌根菌相互关系研究主要包括：1)菌根共生的机理;2)菌根菌在退化森林生态系统恢复与改造中的作用;3)菌根菌的分布格局与森林生态系统服务功能的关系;4)菌根菌对森林生态系统的综合效应,如菌根菌与森林植物群落结构、物种多样性以及森林系统稳定性和生产力的研究。     

Spatial Distribution of Fungal Communities in an Arable Soil

Fungi are prominent drivers of ecological processes in soils, so that fungal communities across different soil ecosystems have been well investigated. However, for arable soils taxonomically resolved fine-scale studies including vertical itemization of fungal communities are still missing. Here, we combined a cloning/Sanger sequencing approach of the ITS/LSU region as marker for general fungi and of the partial SSU region for arbuscular mycorrhizal fungi (AMF) to characterize the microbiome in different maize soil habitats. Four compartments were analyzed over two annual cycles 2009 and 2010: a) ploughed soil in 0–10 cm, b) rooted soil in 40–50 cm, c) root-free soil in 60–70 cm soil depth and d) maize roots. Ascomycota was the most dominant phylum across all compartments. Fungal communities including yeasts and AMF differed strongly between compartments. Inter alia, Tetracladium, the overall largest MOTU (molecular operational taxonomic unit), occurred in all compartments, whereas Trichosporon dominated all soil compartments. Sequences belonging to unclassified Helotiales were forming the most abundant MOTUs exclusively present in roots. This study gives new insights on spatial distribution of fungi and helps to link fungal communities to specific ecological properties such as varying resources, which characterize particular niches of the heterogeneous soil environment.     

Australia offers unique insight into the ecology of arbuscular mycorrhizal fungi: An opportunity not to be lost

Typified by ancient soils and unique assemblages of flora, Australia provides opportunities to expand our understanding of arbuscular mycorrhizal (AM) fungi. Despite their ubiquity, key aspects of Australian AM fungal ecology remain buried due to our limited knowledge of their biogeography and their potential adaptation to Australia's environmental conditions. This knowledge gap is particularly extraordinary given that the characteristics of the Australian environment are likely to provide unique insights into AM fungal ecology and evolution. Extensive exploration of the diversity and distribution of AM fungi across the continent is overdue. In pursuit of this goal, ecologists should employ the most effective and pragmatic molecular approaches, while making use of well-curated databases. We urge researchers to examine the biogeography of Australian AM fungi meaningfully, leveraging the distinctive attributes of Australian landscapes, such as the demographics of plant mycorrhizal types and the characteristic interplay with fire. Documenting AM fungal communities across Australia will not only provide unique insights into their ecology but is also pivotal to being able to incorporate these organisms into land management for conservation, restoration and sustainable agriculture.     

Ectomycorrhizal fungi: exploring the mycelial frontier

Ectomycorrhizal (ECM) fungi form mutualistic symbioses with many tree species and are regarded as key organisms in nutrient and carbon cycles in forest ecosystems. Our appreciation of their roles in these processes is hampered by a lack of understanding of their soil-borne mycelial systems. These mycelia represent the vegetative thalli of ECM fungi that link carbon-yielding tree roots with soil nutrients, yet we remain largely ignorant of their distribution, dynamics and activities in forest soils. In this review we consider information derived from investigations of fruiting bodies, ECM root tips and laboratory-based microcosm studies, and conclude that these provide only limited insights into soil-borne ECM mycelial communities. Recent advances in understanding soil-borne mycelia of ECM fungi have arisen from the combined use of molecular technologies and novel field experimentation. These approaches have the potential to provide unprecedented insights into the functioning of ECM mycelia at the ecosystem level, particularly in the context of land-use changes and global climate change.