青藏高原高寒草地AM真菌分布及其对近自然恢复的生态作用

超载过牧以及全球气候变化等导致大部分青藏高原高寒草地呈现持续退化态势。青藏高原高寒草地退化致使地上植物群落逐渐发生更替,地下土壤微生物群落多样性和丰富度发生改变。本文旨在探析青藏高原高寒草地丛枝菌根（arbuscular mycorrhizal,AM）真菌的分布特征、对近自然恢复的生理生态效应及其作用机制。青藏高原高寒草地中已报道4目14属61种AM真菌,约占已知AM真菌物种的20%。高寒草地禾本科植物根围AM真菌物种丰度最高,而莎草科植物根围AM真菌孢子密度最高。3种高寒草地植被类型中,高寒草原AM真菌丰度最高（33种）,山地灌丛草原次之（32种）,高寒草甸最低（22种）。高寒草原以光壁无梗囊霉Acaulospora laevis和闪亮和平囊霉Pacispora scintillans为优势种,山地灌丛草原以摩西斗管囊霉Funneliformis mosseae为优势种,高寒草甸以光壁无梗囊霉A. laevis、近明球囊霉Claroideoglomus claroideum和闪亮和平囊霉P. scintillans为优势种。高寒草地土著AM真菌与植物构建的菌根网络可以通过调节营养元素吸收、分配,促进植物建植和生长;但是毒杂草入侵可以改变土著AM真菌物种多样性和菌根网络,限制本地植被的实际生态位扩张。退化高寒草地中,AM真菌群落具有高的环境适应性和恢复力,其不仅调控地上植物群落建植和多样性,同时AM真菌建植也增加了代谢产物-球囊霉素相关土壤蛋白产生,进而协同改善地下土壤微生态系统,为退化高寒草地早期植被恢复塑造土壤生境。因此,AM真菌在退化高寒草地近自然恢复中具有较大的应用潜力。     

青藏高原高寒生境中丛枝菌根真菌研究进展

极端生境往往蕴藏着具有特殊生理生态功能的生物类群。海拔高、温度低、生长季节短的青藏高原高寒草原生态系统是典型的极端生境之一,目前有关该生境中分布的丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)研究已引起广泛关注。本文从青藏高原高寒生境中AM真菌的研究概况入手,论述青藏高原高寒生境中AM真菌的群落组成、物种多样性与分布特征、菌根侵染发育状况及高寒生境对AM真菌的影响。指出高寒生境中AM真菌群落结构研究方面存在的问题,探讨解决这些问题的可能途径及其研究发展前景,以期为青藏高原高寒草原生态系统稳定性的维持与受损生态系统的恢复提供理论依据。     

不同外源氮对丛枝菌根真菌Rhizophagus irregularis侵染棉花植株和氮磷转运的影响

探究供应外源氮对接种AM真菌的棉花植株的侵染率和氮磷转运的影响。本文以棉花为研究对象,接种丛枝菌根真菌(Rhizophagus irregularis),向根外菌丝额外供应不同外源氮,测AM真菌的侵染率、棉花植株株高、地上部和地下部鲜重、叶绿素含量、菌根精氨酸含量、地上部的氮磷含量。试验结果显示:不同外源氮条件下,AM真菌对棉花植株的生物量无显著性影响;外源氮的供应均提高了AM真菌的侵染率和棉花植株地上部的氮含量,但硫酸铵和硝酸钾更能促进AM真菌侵染宿主植物,提高宿主植物菌根精氨酸水平和地上部氮含量;除了尿素,其他氮源处理均能明显提高棉花植株地上部磷含量,其中,精氨酸最为显著。说明在AM共生系统中外源氮的供应对宿主植物生长无显著作用,但促进AM真菌侵染宿主植物,并能提高宿主植物氮磷含量。     

高寒草甸植物叶片碳含量及其可塑性与系统发育的关系

植物的系统发育极大地影响着植物的功能性状,高寒草甸草本植物叶片碳含量、性状及其可塑性是否受植物遗传背景的影响目前仍不明确。为此,本研究测定了土壤氮、磷异质条件下高寒草甸生态系统12种优势植物叶片碳含量、比叶面积及其可塑性,并分析其在种、科水平上的差异以及系统发育保守性。结果显示,在不同土壤氮条件下,植物叶片碳含量和比叶面积在种、科水平差异显著(P0.05)。不同土壤磷条件下,植物叶片碳含量在种、科水平无显著差异,但比叶面积差异显著(P0.05)。叶片碳含量和比叶面积没有相关性,但两者的可塑性呈显著正相关,说明不同植物的这两个性状对土壤氮、磷的变化有相似的响应方式。叶片碳含量、比叶面积及其两者的可塑性均没有检测出显著的系统发育信号,说明相对于遗传背景,叶片碳含量、比叶面积主要受环境变化的影响。本研究有助于理解全球变化背景下高寒草甸碳循环过程,也可以为退化高寒草甸的恢复和管理提供科学依据。     

盐渍化土壤根际微生物群落及土壤因子对AM真菌的影响

为探明盐渍化土壤影响下AM真菌与根际土壤间的关系,试验选取宁夏碱化龟裂土、草甸盐土、盐化灌淤土3种类型4个样地上典型植被群落,测定了植物根际土壤养分含量、微生物群落结构、AM真菌侵染率以及孢子密度。结果显示:盐渍化土壤根际微生物碳源利用类型显著不同,对芳香类化合物的代谢能力整体较弱;红寺堡草甸盐土上微生物优势群落为氨基酸代谢类群,惠农盐化灌淤土为多聚化合物代谢群,西大滩碱化龟裂土为碳水化合物代谢群。AM真菌孢子密度与微生物碳源代谢群间的关系比较复杂。其中,惠农样点根际土壤孢子密度与多聚化合物微生物代谢群呈显著正相关,西大滩地区孢子密度与碳水化合物微生物代谢群呈显著正相关。土壤有机质、全盐、全氮、碱解氮等土壤肥力因子及土壤中的HCO-3、Na+、Cl-等盐基离子含量能解释AM真菌孢子密度与土壤环境因子之间相互关系的大部分信息。较高的HCO-3浓度促进了AM真菌侵染率的提高,但高盐浓度下Na+和Cl-降低了菌根侵染率。土壤对AM真菌孢子密度、侵染率的影响因土壤盐分组成类型的不同而异。研究结果为深入了解AM真菌多样性,促进宁夏盐碱地的合理开发与利用提供了理论依据。     

AM真菌与非菌根植物的相互作用关系

丛枝菌根(AM)真菌作为一类在全球分布广泛的土壤微生物,能够与陆地上大多数的维管植物形成专性共生关系,对于植物营养吸收和生态系统功能具有重要作用.而较少量的维管植物如苋科、黎科、石竹科、十字花科等植物被认为是非菌根植物.目前,对于这些非菌根植物与AM真菌之间的相互作用关系研究少且分散,缺乏系统总结.本文综述了非菌根植物的类型以及低侵染的原因,邻体植物形成的菌丝网络对AM真菌侵染非菌根植物的影响,并探讨AM真菌和非菌根植物之间可能存在的相互作用,以及植物-AM真菌之间的物质交换及可能存在的生态功能,旨在为进一步发挥非菌根植物在脆弱生态系统的功能潜力提供新思路.     

丛枝菌根真菌群落与植物系统发育的相关性分析

为弄清丛枝菌根(arbuscular mycorrhiza, AM)真菌群落随宿主植物演化的变异规律,通过对MaarjAM数据库进行数据挖掘, 根据每个分子虚拟种(virtual taxa, VT)包含的DNA序列不少于5条的标准, 筛选出188种菌根植物。通过分析植物与其根内AM真菌的关系发现: AM真菌的物种丰富度随着寄主植物的分化而增加; 在不同的植物系统类群中, AM真菌的物种丰富度显著不同; 在起源时间较晚的被子植物和裸子植物中, AM真菌的物种丰富度显著高于起源较早的苔类、角苔类和蕨类植物类群, 而与寄生植物共生的AM真菌物种丰富度与早期植物无显著差异; 不同寄主植物进化类群间AM真菌组成差异显著。以上结果表明: AM真菌群落随着寄主植物进化而发生变化。在进化过程中, 寄主植物倾向于选择保留共生效率较高的AM真菌。     

高寒草甸生态系统食物链结构分析--来自稳定性碳同位素的证据

稳定性同位素技术应用于生态系统物质流动和食物链营养关系的研究方法 ,是基于生物体内天然存在的同位素比值与它们食物密切相关这一原理建立起来的。即将生物体内的稳定性同位素比值 (如δ1 3C)作为一自然标记 ,根据物种间该值的相对差异 ,追踪生态系统中的主要物质 (如碳源 )的来源和物质流动。于 2 0 0 2年 4～8月测定了高寒草甸生态系统主要生物群落中物种的稳定性碳同位素比值 (δ1 3C) ,依据得到的系统的富集因子( 1 0 5± 0 4 5 )‰ ,分析并确定了所测物种间的取食与被取食关系。结果发现 :高寒草甸生态系统由 5条主要的食物链构成 ,其中 1条为“植物→小型哺乳类→食肉兽 /猛禽”的三节点食物链 ,2条为“植物→牲畜和植物→植食性鸟类”的二节点食物链 ,2条分别为“植物→昆虫→雀形目鸟类→猛禽 /食肉兽”和“植物→昆虫→两栖类→猛禽 /食肉兽”的四节点食物链 ;系统食物链的最大长度为 3 5 3 ,与系统的最大节点数相近。表明稳定性碳同位素可以作为分析高寒草甸生态系统食物网和食物链结构以及食物链长度的有效代理 (proxy)。     

Correlation analysis between arbuscular mycorrhizal fungal community and host plant phylogeny

 为弄清丛枝菌根(arbuscular mycorrhiza, AM)真菌群落随宿主植物演化的变异规律,通过对MaarjAM数据库进行数据挖掘, 根据每个分子虚拟种(virtual taxa, VT)包含的DNA序列不少于5条的标准, 筛选出188种菌根植物。通过分析植物与其根内AM真菌的关系发现: AM真菌的物种丰富度随着寄主植物的分化而增加; 在不同的植物系统类群中, AM真菌的物种丰富度显著不同; 在起源时间较晚的被子植物和裸子植物中, AM真菌的物种丰富度显著高于起源较早的苔类、角苔类和蕨类植物类群, 而与寄生植物共生的AM真菌物种丰富度与早期植物无显著差异; 不同寄主植物进化类群间AM真菌组成差异显著。以上结果表明: AM真菌群落随着寄主植物进化而发生变化。在进化过程中, 寄主植物倾向于选择保留共生效率较高的AM真菌。     

关于进化真菌学教学内容的讨论

核酸序列的比较研究使进化真菌学的面貌发生了革命性的变化,分子系统发育揭示的关系反映出真菌进化的复杂性和多样性,真菌系统学反映真菌进化关系的自然系统还有很大的距离,有赖于新物种的不断发现和分子系统发育证据的不断丰富。     

Predicting plant responses to mycorrhizae: integrating evolutionary history and plant traits

We assessed whether (1) arbuscular mycorrhizal colonization of roots (RC) and/or plant responses to arbuscular mycorrhizae (MR) vary with plant phylogeny and (2) MR and RC can be more accurately predicted with a phylogenetic predictor relative to a null model and models with plant trait and taxonomic predictors. In a previous study, MR and RC of 95 grassland species were measured. We constructed a phylogeny for these species and found it explained variation in MR and RC. Next, we used multiple regressions to identify the models that most accurately predicted plant MR. Models including either phylogenetic or phenotypic and taxonomic information similarly improved our ability to predict MR relative to a null model. Our study illustrates the complex evolutionary associations among species and constraints of using phylogenetic information, relative to plant traits, to predict how a plant species will interact with AMF.     

Phylogenetic trait conservatism and the evolution of functional trade-offs in arbuscular mycorrhizal fungi

The diversity of functional and life-history traits of organisms depends on adaptation as well as the legacy of shared ancestry. Although the evolution of traits in macro-organisms is well studied, relatively little is known about character evolution in micro-organisms. Here, we surveyed an ancient and ecologically important group of microbial plant symbionts, the arbuscular mycorrhizal (AM) fungi, and tested hypotheses about the evolution of functional and life-history traits. Variation in the extent of root and soil colonization by AM fungi is constrained to a few nodes basal to the most diverse groups within the phylum, with relatively little variation associated with recent divergences. We found no evidence for a trade-off in biomass allocated to root versus soil colonization in three published glasshouse experiments; rather these traits were positively correlated. Partial support was observed for correlated evolution between fungal colonization strategies and functional benefits of the symbiosis to host plants. The evolution of increased soil colonization was positively correlated with total plant biomass and shoot phosphorus content. Although the effect of AM fungi on infection by root pathogens was phylogenetically conserved, there was no evidence for correlated evolution between the extent of AM fungal root colonization and pathogen infection. Variability in colonization strategies evolved early in the diversification of AM fungi, and we propose that these strategies were influenced by functional interactions with host plants, resulting in an evolutionary stasis resembling trait conservatism.     

Plant traits determine the phylogenetic structure of arbuscular mycorrhizal fungal communities

Functional diversity in ecosystems has traditionally been studied using aboveground plant traits. Despite the known effect of plant traits on the microbial community composition, their effects on the microbial functional diversity are only starting to be assessed. In this study, the phylogenetic structure of arbuscular mycorrhizal (AM) fungal communities associated with plant species differing in life cycle and growth form, that is, plant life forms, was determined to unravel the effect of plant traits on the functional diversity of this fungal group. The results of the 454 pyrosequencing showed that the AM fungal community composition differed across plant life forms and this effect was dependent on the soil collection date. Plants with ruderal characteristics tended to associate with phylogenetically clustered AM fungal communities. By contrast, plants with resource‐conservative traits associated with phylogenetically overdispersed AM fungal communities. Additionally, the soil collected in different seasons yielded AM fungal communities with different phylogenetic dispersion. In summary, we found that the phylogenetic structure, and hence the functional diversity, of AM fungal communities is dependent on plant traits. This finding adds value to the use of plant traits for the evaluation of belowground ecosystem diversity, functions and processes.     

Patterns in root traits of woody species hosting arbuscular and ectomycorrhizas: implications for the evolution of belowground strategies

Root traits vary enormously among plant species but we have little understanding of how this variation affects their functioning. Of central interest is how root traits are related to plant resource acquisition strategies from soil. We examined root traits of 33 woody species from northeastern US forests that form two of the most common types of mutualisms with fungi, arbuscular mycorrhizas (AM) and ectomycorrhizas (EM). We examined root trait distribution with respect to plant phylogeny, quantifying the phylogenetic signal (K statistic) in fine root morphology and architecture, and used phylogenetically independent contrasts (PICs) to test whether taxa forming different mycorrhizal associations had different root traits. We found a pattern of species forming roots with thinner diameters as species diversified across time. Given moderate phylogenetic signals (K = 0.44–0.68), we used PICs to examine traits variation among taxa forming AM or EM, revealing that hosts of AM were associated with lower branching intensity (r_PIC = −0.77) and thicker root diameter (r_PIC = −0.41). Because EM evolved relatively more recently and intermittently across plant phylogenies, significant differences in root traits and colonization between plants forming AM and EM imply linkages between the evolution of these biotic interactions and root traits and suggest a history of selection pressures, with trade-offs for supporting different types of associations. Finally, across plant hosts of both EM and AM, species with thinner root diameters and longer specific root length (SRL) had less colonization (r_PIC = 0.85, −0.87), suggesting constraints on colonization linked to the evolution of root morphology.     

Plastome-based phylogeny improves community phylogenetics of subtropical forests in China

Phylogenetic trees have been extensively used in community ecology. However, how the phylogeny construction affects ecological inferences is poorly understood. In this study, we constructed three different types of phylogenetic trees (a synthetic-tree generated using V.PhyloMaker, a barcode-tree generated using rbcL+matK+trnH-psbA, and a plastome-tree generated from plastid genomes) that represented an increasing level of phylogenetic resolution among 580 woody plant species from six forest dynamic plots in subtropical evergreen broadleaved forests of China. We then evaluated the performance of each phylogeny in estimations of community phylogenetic structure, turnover and phylogenetic signal in functional traits. As expected, the plastome-tree was most resolved and most supported for relationships among species. For local phylogenetic structure, the three trees showed consistent results with Faith's PD and MPD; however, only the synthetic-tree produced significant clustering patterns using MNTD for some plots. For phylogenetic turnover, contrasting results between the molecular trees and the synthetic-tree occurred only with nearest neighbor distance. The barcode-tree agreed more with the plastome-tree than the synthetic-tree for both phylogenetic structure and turnover. For functional traits, both the barcode-tree and plastome-tree detected phylogenetic signal in maximum height, but only the plastome-tree detected signal in leaf width. This is the first study that uses plastid genomes in large-scale community phylogenetics. Our results highlight the improvement of plastome-trees over barcode-trees and synthetic-trees for the analyses studied here. Our results also point to the possibility of type I and II errors in estimation of phylogenetic structure and turnover and detection of phylogenetic signal when using synthetic-trees.     

基于系统发育及功能性状的不同坡向荒漠植物群落构建研究——以博湖县沙化封禁保护区为例

荒漠植物群落构建机制的研究有助于荒漠生态系统植物资源的保护及系统平衡稳定的维持。基于系统发育与功能性状相结合的方法,以博湖县沙化封禁保护区植物群落为研究对象,在研究区内纵向沙垄的不同坡向上(丘间、阴坡、阳坡)设置样方,进行植物群落物种功能性状和土壤因子的调查与测定,通过检验植物群落物种功能性状的系统发育信号,分析不同坡向植物群落物种系统发育结构和功能结构的表现模式,利用主成分分析(PCA)和线性回归模型(Linear regression model)筛选出影响物种共存的环境因子,进而揭示研究区干旱荒漠生态系统植物群落物种共存的驱动因素。结果表明：(1)研究区植被主要以耐旱的灌木和藜科草本植物为优势种;不同坡向土壤因子具有异质性,丘间、阴坡土壤养分、水分更为丰富。(2)研究区样地植物群落物种10个功能性状指标的系统发育信号K值均小于1,说明物种功能性状受系统进化影响较小,物种功能性状未表现出系统发育保守性。(3)不同坡向系统发育结构均趋于发散,限制相似性在植物分布中占主导作用;丘间和阴坡上较丰富的土壤肥力是物种功能结构发散的主要原因,阳坡物种功能结构表现为聚集效应,生境过滤为其驱动因素...     

The ecology of differences: assessing community assembly with trait and evolutionary distances

Species enter and persist in local communities because of their ecological fit to local conditions, and recently, ecologists have moved from measuring diversity as species richness and evenness, to using measures that reflect species ecological differences. There are two principal approaches for quantifying species ecological differences: functional (trait‐based) and phylogenetic pairwise distances between species. Both approaches have produced new ecological insights, yet at the same time methodological issues and assumptions limit them. Traits and phylogeny may provide different, and perhaps complementary, information about species' differences. To adequately test assembly hypotheses, a framework integrating the information provided by traits and phylogenies is required. We propose an intuitive measure for combining functional and phylogenetic pairwise distances, which provides a useful way to assess how functional and phylogenetic distances contribute to understanding patterns of community assembly. Here, we show that both traits and phylogeny inform community assembly patterns in alpine plant communities across an elevation gradient, because they represent complementary information. Differences in historical selection pressures have produced variation in the strength of the trait‐phylogeny correlation, and as such, integrating traits and phylogeny can enhance the ability to detect assembly patterns across habitats or environmental gradients.     

Phylogenetic structure and formation mechanism of shrub communities in arid and semiarid areas of the Mongolian Plateau

The mechanisms of species coexistence within a community have always been the focus in ecological research. Community phylogenetic structure reflects the relationship of historical processes, regional environments, and interactions between species, and studying it is imperative to understand the formation and maintenance mechanisms of community composition and biodiversity. We studied the phylogenetic structure of the shrub communities in arid and semiarid areas of the Mongolian Plateau. First, the phylogenetic signals of four plant traits (height, canopy, leaf length, and leaf width) of shrubs and subshrubs were measured to determine the phylogenetic conservation of these traits. Then, the net relatedness index (NRI) of shrub communities was calculated to characterize their phylogenetic structure. Finally, the relationship between the NRI and current climate and paleoclimate (since the Last Glacial Maximum, LGM) factors was analyzed to understand the formation and maintenance mechanisms of these plant communities. We found that desert shrub communities showed a trend toward phylogenetic overdispersion; that is, limiting similarity was predominant in arid and semiarid areas of the Mongolian Plateau despite the phylogenetic structure and formation mechanisms differing across habitats. The typical desert and sandy shrub communities showed a significant phylogenetic overdispersion, while the steppified desert shrub communities showed a weak phylogenetic clustering. It was found that mean winter temperature (i.e., in the driest quarter) was the major factor limiting steppified desert shrub phylogeny distribution. Both cold and drought (despite having opposite consequences) differentiated the typical desert to steppified desert shrub communities. The increase in temperature since the LGM is conducive to the invasion of shrub plants into steppe grassland, and this process may be intensified by global warming.     

Root colonization and spore abundance of arbuscular mycorrhizal fungi in distinct successional stages from an Atlantic rainforest biome in southern Brazil

The influence of plant functional groups and moderate seasonality on arbuscular mycorrhizal (AM) fungal status (root colonization and spore density) was investigated during 13 consecutive months in a chronosequence of succession in southern Brazil, consisting of grassland field, scrub vegetation, secondary forest and mature forest, in a region of transition from tropical to subtropical zones. AM root colonization and spore density decreased with advancing succession and were highest in early successional sites with grassland and scrub vegetation, intermediary in the secondary forest and lowest in the mature forest. They were little influenced by soil properties, but were sufficiently influenced by the fine root nutrient status and fine root traits among different functional plant groups. AM root colonization and spore density were higher during the favourable plant growth season (spring and summer) than during the less favourable plant growth season (autumn and winter). Spore density displayed significant seasonal variation at all sites, whilst root colonization displayed significant seasonal variation in grassland, scrub and secondary forest, but not in mature forest. The data suggest that (1) different plant functional groups display different relationships with AM fungi, influencing their abundance differentially; (2) plant species from early successional phases are more susceptible to AM root colonization and maintain higher AM sporulation than late successional species; (3) fine root traits and nutrient status influence these AM fungal attributes; and (4) higher AM spore production and root colonization is associated with the season of higher light incidence and temperature, abundant water in soil and higher plant metabolic activity.     

Plant phylogeny drives arboreal caterpillar assemblages across the Holarctic

1. Assemblages of insect herbivores are structured by plant traits such as nutrient content, secondary metabolites, physical traits, and phenology. Many of these traits are phylogenetically conserved, implying a decrease in trait similarity with increasing phylogenetic distance of the host plant taxa. Thus, a metric of phylogenetic distances and relationships can be considered a proxy for phylogenetically conserved plant traits and used to predict variation in herbivorous insect assemblages among co‐occurring plant species.
2. Using a Holarctic dataset of exposed‐feeding and shelter‐building caterpillars, we aimed at showing how phylogenetic relationships among host plants explain compositional changes and characteristics of herbivore assemblages.
3. Our plant–caterpillar network data derived from plot‐based samplings at three different continents included >28,000 individual caterpillar–plant interactions. We tested whether increasing phylogenetic distance of the host plants leads to a decrease in caterpillar assemblage overlap. We further investigated to what degree phylogenetic isolation of a host tree species within the local community explains abundance, density, richness, and mean specialization of its associated caterpillar assemblage.
4. The overlap of caterpillar assemblages decreased with increasing phylogenetic distance among the host tree species. Phylogenetic isolation of a host plant within the local plant community was correlated with lower richness and mean specialization of the associated caterpillar assemblages. Phylogenetic isolation had no effect on caterpillar abundance or density. The effects of plant phylogeny were consistent across exposed‐feeding and shelter‐building caterpillars.
5. Our study reveals that distance metrics obtained from host plant phylogeny are useful predictors to explain compositional turnover among hosts and host‐specific variations in richness and mean specialization of associated insect herbivore assemblages in temperate broadleaf forests. As phylogenetic information of plant communities is becoming increasingly available, further large‐scale studies are needed to investigate to what degree plant phylogeny structures herbivore assemblages in other biomes and ecosystems.