Factors influencing communities of foliar fungal endophytes in riparian woody plants

Riparian areas within a given arid region frequently contain broadly similar plant communities despite substantive geographic separation. Whether they also harbor similar communities of fungal symbionts, or feature assemblages unique to each riparian zone, is unknown. We examined fungal endophytes in foliage of woody angiosperms in six riparian areas in Arizona. Abundance and diversity differed among host species according to leaf longevity and phytochemistry, and among sites as a function of rainfall. Community composition varied among sites and host species. Comparison with regional data revealed that riparian areas harbor different subsets of the regional mycota rather than a consistent group of riparian taxa. Overall a high species- and phylogenetic richness of endophytes was recovered, especially among Mycosphaerella and affiliated anamorphs. Variation in endophyte communities across sites despite the relative consistency of plant communities underscores the importance of riparian zones both singly and in combination for harboring fungal biodiversity.     

Family issues: fungal endophyte protects host grass from the closely related pathogen Claviceps purpurea

Certain cool season grasses establish systemic and asymptomatic symbioses with clavicipitaceous fungi of the genus Neotyphodium, which affect multiple biotic interactions within host neighborhood. The presumed symbiont-mediated plant resistance to pathogens is mostly based on studies performed under laboratory and greenhouse conditions. Here we investigated, in two outdoor experiments, the relation between two fungi of the same family with opposite effects on Lolium multiflorum plants: the mutualist endophyte Neotyphodium occultans, and the pathogen Claviceps purpurea. Natural infection and its consequences on symbiotic and non-symbiotic plants were studied under varying conditions of stress by herbicide. In both experiments, N. occultans reduced significantly the infection by C. purpurea at population levels (70 % less). The percentage of spikes infected by C. purpurea was almost three times lower in endophyte-symbiotic plants than in non-symbiotic ones. However, the protective effect was not maintained under stress condition. Our results show that constitutive symbionts such as the systemic fungal endophytes mediate the interaction between host grasses and pathogens, although the effect may depend on the level of stress in the environment.     

A fungal endophyte slows litter decomposition in streams

1. Phyllosphere interactions are known to influence a variety of tree canopy community members, but less frequently have they been shown to affect processes across ecosystem boundaries. Here, we show that a fungal endophyte (Rhytisma punctatum) slows leaf litter decomposition of a dominant riparian tree species (Acer macrophyllum) in an adjacent stream ecosystem. 2. Patches of leaf tissue infected by R. punctatum show significantly slower decomposition compared to both nearby uninfected tissue from the same leaf, and completely uninfected leaves. These reduced rates of decomposition existed despite 50% greater nitrogen in infected tissues and may be driven by slower rates of decomposition for fungal tissues themselves or by endophyte–hyphomycete interactions. 3. Across a temperate forest in the Pacific Northwest, approximately 72% of all A. macrophyllum leaves were infected by R. punctatum. Since R. punctatum infection can influence leaf tissue on entire trees and large quantities of leaf litter at the landscape scale, this infection could potentially result in a mosaic of ‘cold spots’ of litter decomposition and altered nutrient cycling in riparian zones where this infection is prevalent.     

植物内生菌研究及其科学意义

植物内生菌是近三十年来在国内外迅速受到关注的微生物类群,研究的角度不同,概念也比较混乱。本文就植物内生菌研究及其科学意义进行了综述和讨论。植物内生菌在国外广受关注,始于禾本科植物内生真菌以及林木内生真菌的特殊作用。产紫杉醇的红豆杉内生真菌被报道后,植物内生菌研究在生理活性物质领域开始暴发式的增加。通过对一年生草本植物、多年生草本植物、木本植物和藤本植物各部位的内生微生物的比较和分析,总结了植物内生菌的一些共性和特殊性,指出了植物内生菌研究的一些发展趋势。本文探讨植物内生菌对地球上的微生物物种总量的贡献。提出"植物体在自然界的实际生存状态实际上是微生物和植物的状态"的观点,导出植物育种实际上是"植物和微生物的共生体的培育"的观点。还讨论了植物内生菌对生态学、生物学、微生物的进化和物种形成、内生菌/宿主的联合代谢、以及植物保护学、畜牧兽医学、林学等领域的意义和影响。本文认为,植物内生菌研究打开了微生物资源的一个新局面,将在多个领域中产生更广泛的影响。植物内生菌研究的真正意义不仅在于其生态独特性,更在于微生物在宿主体内和宿主植物的协同作用及协同作用所产生的新功能和新物质。     

Archaeorhizomyces borealis sp. nov. and a sequence-based classification of related soil fungal species

The class Archaeorhizomycetes (Taphrinomycotina, Ascomycota) was introduced to accommodate an ancient lineage of soil-inhabiting fungi found in association with plant roots. Based on environmental sequencing data Archaeorhizomycetes may comprise a significant proportion of the total fungal community in soils. Yet the only species described and cultivated in this class is Archaeorhizomyces finlayi. In this paper, we describe a second species from a pure culture, Archaeorhizomyces borealis NS99-600^T (=CBS138755^ExT) based on morphological, physiological, and multi-locus molecular characterization. Archaeorhizomyces borealis was isolated from a root tip of a Pinus sylvestris seedling grown in a forest nursery in Lithuania. Analysis of Archaeorhizomycete species from environmental samples shows that it has a Eurasian distribution and is the most commonly observed species. Archaeorhizomyces borealis shows slow growth in culture and forms yellowish creamy colonies, characteristics that distinguish A. borealis from its closest relative A. finlayi. Here we also propose a sequence-based taxonomic classification of Archaeorhizomycetes and predict that approximately 500 species in this class remain to be isolated and described.     

Diversity and distribution of fungal foliar endophytes in New Zealand Podocarpaceae

The diversity and distribution of fungal endophytes in the leaves of four podocarps (Dacrydium cupressinum, Prumnopitys ferruginea, Dacrycarpus dacrydioides, and Podocarpus totara, all Podocarpaceae) and an angiosperm (Kunzea ericoides, Myrtaceae) occurring in close stands were studied. The effects of host species, locality, and season on endophyte assemblages were investigated. Host species was the major factor shaping endophyte assemblages. The spatial separation of sites and seasonal differences played significant but lesser roles. The mycobiota of each host species included both generalist and largely host-specialised fungi. The host-specialists were often observed at low frequencies on some of the other hosts. There was no clear evidence for family-level specialisation across the Podocarpaceae. Of the 17 species found at similar frequencies on several of the podocarp species, 15 were found also on Kunzea. Many of the endophytes isolated appear to represent species of fungi not previously recognised from New Zealand.     

Structural features of fragmented woodland communities affect leaf litter decomposition rates

Disruption to the physical structure of plant communities by habitat fragmentation can change microclimates, so leaf litter decomposition rates, being dependent on temperature and moisture, may also be affected. Similarly, smaller-scale structural features of plant communities can modify microclimates, and so may produce distinctive spatial patterns in decomposition rates. We investigated the effects of three types of structural feature having the potential to alter litter layer microclimates: fragmentation-induced modification that diminishes with distance from remnant edges (edge-core); concentric zones of locally modified conditions imposed by individual trees (Belsky–Canham); and highly localised abiotic modification collectively imposed by herbaceous plants (ground cover). We conducted a litter bag experiment in woodland remnants, testing whether the observed spatial variability in litter decomposition was attributable to one or more of these three structural features. The data provided the strongest support for the Belsky–Canham hypothesis, and the least support for the ground cover hypothesis. However, the hypotheses were not mutually exclusive, for each explained a component of the observed variability not explained by either of the other two. Proximity to remnant edge, proximity to trees, canopy light penetration, and ground cover density each explained part of the observed variability between plots. Decomposition rates did not differ with remnant area per se, for the effects of fragmentation were weak, and differed with cardinal direction. In contrast, the effects of individual trees were much stronger, and accounted for most of the between-plot variability. We found that litter decomposition rates in small remnants are only weakly affected by fragmentation, and we consider that the contributions of small remnants to landscape-scale functioning warrant closer attention.     

高山森林林窗对凋落叶分解的影响

林窗对降水和光照等环境条件的再分配以及分解者群落的影响可能深刻作用于森林凋落物分解过程,但有关高山森林林窗大小对凋落物分解的影响尚无研究报道。采用凋落物分解袋法,研究了川西高山森林不同大小林窗对非生长季节和生长季节红桦(Betula albo-sinensis)和岷江冷杉(Abies faxoniana)凋落叶质量损失的影响。结果显示,经过1a的分解,不同生境下红桦和岷江冷杉凋落叶分别分解了27.25%—30.12%和27.04%—27.96%,其中非生长季节占53.83%—60.18%和50.23%—59.09%。林窗对红桦和岷江冷杉凋落叶质量损失的影响因物种不同而呈现季节差异。总体上,林窗加快了岷江冷杉凋落叶的分解而延缓了红桦凋落叶的分解。与郁闭林下相比,林窗显著增加了2种凋落叶非生长季节的质量损失速率,显著降低了生长季节2种凋落叶的质量损失速率;2种凋落叶质量损失速率在非生长季节随林窗面积增大而加快,在生长季节随林窗面积增大而减慢。林窗显著影响了初冻期、深冻期和融化期岷江冷杉凋落叶的质量损失率,但对红桦凋落叶质量损失率影响不显著。可见,高山森林凋落物分解过程受到林窗的显著影响,并且阔叶和针叶凋落叶在非生长季节和生长季节对林窗的响应具有明显差异。     

Home-field advantage in decomposition of leaf litter and insect frass

Home-field advantage (HFA) hypothesis regarding litter decomposition states that litter is decomposed more rapidly in the habitat from which it is derived (i.e., home) than in other habitat (i.e., away) due to local adaptation of soil decomposers. We tested the HFA hypothesis regarding decomposition of leaf litter, insect frass, and their mixtures, using laboratory incubation of leaf litter from an evergreen (Pinus densiflora) and a deciduous (Quercus acutissima) tree species, frass excreted by two insect herbivores (Dendrolimus spectabilis and Lymantria dispar) fed on one of the two trees, and soil collected underneath the two trees. We found evidence that decomposers in each soil were specialized to decompose the litter derived from the tree species above them, indicating that the HFA occurred in litter decomposition. In contrast, the HFA was not detected in the decomposition of insect frass or litter-frass mixtures. Mixing with D. spectabilis frass non-additively decelerated, while mixing with L. dispar frass non-additively accelerated, decomposition of the mixtures, independent of soil and litter types. These indicate that the presence of insect herbivores may make it difficult to form and maintain a decomposer community specialized to a certain leaf litter, and that it may consequently cancel or weaken HFA in litter decomposition.     

Effects of temperature and litter type on fungal growth and decomposition of leaf litter

The dependence of fungal decomposition of leaf litter on incubation temperature and litter types used as substrata was assessed under pure culture conditions. Isolates of Xylaria sp., a major ligninolytic fungus in cool temperate forests in Japan, were used as the fungal material. Xylaria sp. is mesophilic; maximum growth and decomposition occurred at 25°C. In the temperature test, the decomposition pattern of beech leaf litter by three isolates of Xylaria sp. changed at a threshold at 25°C. Cellulolytic activity increased with temperature from 5 to 25°C, whereas above 25°C ligninolytic activity increased at the expense of cellulolytic activity, leading to suppressed overall decomposition as a result of the higher temperature. The mass loss of leaf litter caused at 20°C by an isolate of Xylaria sp. was variable among 15 litter types and was correlated negatively with acid-unhydrolyzable residue (AUR) content and positively with total carbohydrate content for the 15 litter types. The effects of temperature and litter type on the growth and decomposition of leaf litter by Xylaria sp. may have implications for changes in fungal decomposition of leaf litter that would be predicted in response to future environmental changes.     

Communities of fungal endophytes in leaves of Fraxinus ornus are highly diverse

Communities of endophytic fungi in leaves of Manna ash (Fraxinus ornus) were examined to both the north and south of the Alps, i.e. within and beyond the native range of this tree species. Almost all leaves examined had been colonized by endophytic fungi. One hundred and two morphotypes were found, and 62 of them were identified to genus or species level using ITS sequencing and micromorphology. Venturia orni was most frequent and occurred in almost one third (32%) of the 1536 examined leaf segments. It was five times more abundant than Colletotrichum acutatum, the second most frequent endophyte. Other frequently isolated endophytes include Paraconiothyrium sp. 1, Mycosphaerella aurantia, Septoria cretae, Botryosphaeria dothidea and Boeremia exigua. The ash dieback pathogen was not isolated. The endophyte communities differed between the north and south of the Alps and the individual tree types had a distinct influence within sites.     

Proteome analysis of fungal and bacterial involvement in leaf litter decomposition

Fungi and bacteria are key players in the decomposition of leaf litter, but their individual contributions to the process and their interactions are still poorly known. We combined semi‐quantitative proteome analyses (1‐D PAGE‐LC‐MS/MS) with qualitative and quantitative analyses of extracellular degradative enzyme activities to unravel the respective roles of a fungus and a bacterium during litter decomposition. Two model organisms, a mesophilic Gram‐negative bacterium (Pectobacterium carotovorum) and an ascomycete (Aspergillus nidulans), were grown in both, pure culture and co‐culture on minimal medium containing either glucose or beech leaf litter as sole carbon source. P. carotovorum grew best in co‐culture with the fungus, whereas growth of A. nidulans was significantly reduced when the bacterium was present. This observation suggests that P. carotovorum has only limited capabilities to degrade leaf litter and profits from the degradation products of A. nidulans at the expense of fungal growth. In accordance with this interpretation, our proteome analysis revealed that most of the extracellular biodegradative enzymes (i.e. proteases, pectinases, and cellulases) in the cultures with beech litter were expressed by the fungus, the bacterium producing only low levels of pectinases.     

Impacts of tree species diversity on litter decomposition in northern temperate forests of Wisconsin, USA: a multi-site experiment along a latitudinal gradient

Over the past decade an increasing amount of research has sought to understand how the diversity of species in an ecosystem can influence fluxes of biologically important materials, such as the decomposition of organic matter and recycling of nutrients. Generalities among studies have remained elusive, perhaps because experimental manipulations have been performed at relatively small spatial scales where site-specific variation generates patterns that appear idiosyncratic. One approach for seeking generality is to perform parallel experiments at different sites using an identical species pool. Here we report results from a study where we manipulated the diversity of leaf litter from the same six dominant tree species in the litter layer of three forested ecosystems. These ecosystems spanned a 300 km latitudinal transect in Wisconsin, USA, and were characterized by a large gradient in temperature and moisture, and thus, rates of decomposition. After allowing combinations of one, two, four, and six species of leaf litter to decompose for 1 year, we found that increasing leaf litter richness led to slower rates of decomposition and higher fractions of nitrogen lost from litter. Across all sites, climate and initial litter chemistry explained more of the variation in decomposition rates than did litter richness. Effects of leaf litter diversity were non-additive, meaning they were greater than expected from the impacts of individual species, and appeared to be strongly influenced by the presence/absence of just 1–2 species (Tilia americana and Acer saccharum). The rate of decomposition of these two species was highly site-specific, which led to strong negative effects of litter richness only being observed at the southernmost sites where T. americana and A. saccharum decomposed more quickly. In contrast, litter diversity increased nitrogen loss at the northernmost sites where decomposition of T. americana was notably slowed. Our study shows that species diversity affected at least one of the two litter processes at each site along this 300-km gradient, but the exact nature of these effects were spatially variable because the performance of individual species changed across the heterogeneous landscape.     

Interactions among fungal community structure, litter decomposition and depth of water table in a cutover peatland

Peatlands are important reservoirs of carbon (C) but our understanding of C cycling on cutover peatlands is limited. We investigated the decomposition over 18 months of five types of plant litter (Calluna vulgaris, Eriophorum angustifolium, Eriophorum vaginatum, Picea sitchensis and Sphagnum auriculatum) at a cutover peatland in Scotland, at three water tables. We measured changes in C, nitrogen (N) and phosphorus (P) in the litter and used denaturing gradient gel electrophoresis to investigate changes in fungal community composition. The C content of S. auriculatum litter did not change throughout the incubation period whereas vascular plant litters lost 30-40% of their initial C. There were no differences in C losses between low and medium water tables, but losses were always significantly less at the high water table. Most litters accumulated N and E. angustifolium accumulated significant quantities of P. C, N and P were significant explanatory variables in determining changes in fungal community composition but explained <25% of the variation. Litter type was always a stronger factor than water table in determining either fungal community composition or turnover of C, N and P in litter. The results have implications for the ways restoration programmes and global climate change may impact upon nutrient cycling in cutover peatlands.     

氮磷添加对红壤区城郊湿地松林凋落叶分解的影响

城市化易导致城市森林氮(N)沉降和磷(P)富集,进而对凋落物分解过程产生影响。以位于南昌市郊的湿地松(Pinuse lliottii Engelm.)林为研究对象,采用尼龙网袋分解法,模拟N沉降(10g N·m-2·a-1,[N])、P积累(2.5g P·m-2·a-1,[P])和N沉降+P积累(10N·m-2·a-1+2.5g P·m-2·a-1,[N+P])对凋落叶分解速率与C、N、P含量及其化学计量比动态变化的影响。结果表明:与对照(CK)相比,[N]、[P]和[N+P]均促进凋落叶的前期(0～180d)分解速率,抑制中期(180～360d)、后期(360～540d)的分解速率;至540d时分解速率表现为[N]、[P]和CK无差异,但均高于[N+P](P0.05)。[N]提高分解过程中凋落叶N浓度,N含量表现为分解前期积累、后期释放;[P]提高分解过程中凋落叶P浓度,P含量持续积累;[N+P]提高N和P浓度,分解前期N、P含量积累,后期释放;而不同处理的C含量均表现为释放。凋落物基质C/N/P比与分解速率的相关性随分解阶段而表现各异。综合来看,城市化导致的N沉降和P富集叠加效应具有抑制城市森林凋落物分解过程的潜在性。     

Diversity and phylogenetic affinities of foliar fungal endophytes in loblolly pine inferred by culturing and environmental PCR

We examined endophytic fungi in asymptomatic foliage of loblolly pine (Pinus taeda) in North Carolina, U.S.A., with four goals: (i) to evaluate morphotaxa, BLAST matches and groups based on sequence similarity as functional taxonomic units; (ii) to explore methods to maximize phylogenetic signal for environmental datasets, which typically contain many taxa but few characters; (iii) to compare culturing vs. culture-free methods (environmental PCR of surface sterilized foliage) for estimating endophyte diversity and species composition; and (iv) to investigate the relationships between traditional ecological indices (e.g. Shannon index) and phylogenetic diversity (PD) in estimating endophyte diversity and spatial heterogeneity. Endophytes were recovered in culture from 87 of 90 P. taeda leaves sampled, yielding 439 isolates that represented 24 morphotaxa. Sequence data from the nuclear ribosomal internal transcribed spacer (ITS) for 150 isolates revealed 59 distinct ITS genotypes that represented 24 and 37 unique groups based on 90% and 95% sequence similarity, respectively. By recoding ambiguously aligned regions to extract phylogenetic signal and implementing a conservative phylogenetic backbone constraint, we recovered well supported phylogenies based on ca. 600 bp of the nuclear ribosomal large subunit (LSUrDNA) for 72 Ascomycota and Basidiomycota, 145 cultured endophytes and 33 environmental PCR samples. Comparisons with LSUrDNA-delimited species showed that morphotaxa adequately estimated total species richness but rarely corresponded to biologically meaningful groups. ITS BLAST results were variable in their utility, but ITS genotype groups based on 90% sequence similarity were concordant with LSUrDNA-delimited species. Environmental PCR yielded more genotypes per sampling effort and recovered several distinct clades relative to culturing, but some commonly cultured clades were never found (Sordariomycetes) or were rare relative to their high frequency among cultures (Leotiomycetes). In contrast to traditional indices, PD demonstrated spatial heterogeneity in endophyte assemblages among P. taeda trees and study plots. Our results highlight the need for caution in designating taxonomic units based on gross cultural morphology or ITS BLAST matches, the utility of phylogenetic tools for extracting robust phylogenies from environmental samples, the complementarity of culturing and environmental PCR, the utility of PD relative to traditional ecological indices, and the remarkably high diversity of foliar fungal endophytes in this simplified temperate ecosystem.     

中国森林生态系统凋落叶分解速率的分布特征及其控制因子

凋落物分解是森林生态系统碳循环的重要组成部分。建立中国森林凋落叶分解速率数据库, 分析凋落叶分解速率与其主要影响因素之间的关系, 对精确地预测中国森林生态系统碳收支具有重要意义。该研究通过收集已报道的中国森林凋落叶分解常数(k)及其相关变量, 分析探讨地理因素(纬度、经度和海拔)、气候因素(年平均气温和年降水量)、凋落叶质量(氮、磷、钾、木质素、木质素:氮和碳氮比)和叶特性(常绿与落叶、阔叶与针叶)对中国森林凋落叶分解速率的影响。结果表明, 在国家尺度上, k随年平均气温、年降水量、氮、磷和钾的增加而增加, 随纬度、经度、海拔、碳氮比、木质素和木质素:氮的增大而减小, 叶特性对k的影响不显著。气候与地理因素(年平均气温、年降水量和纬度)能解释k值变异的34.1%, 凋落叶质量(氮、钾、木质素和木质素:氮)能解释k值变异的21.7%, 它们能共同解释k值变异的74.4%。了解森林凋落叶分解速率在国家尺度上的格局和主控因素可为中国森林生态系统碳循环相关模型提供基础参数。     

Spatial characteristics in decomposition rate of foliar litter and controlling factors in Chinese forest ecosystems

凋落物分解是森林生态系统碳循环的重要组成部分。建立中国森林凋落叶分解速率数据库, 分析凋落叶分解速率与其主要影响因素之间的关系, 对精确地预测中国森林生态系统碳收支具有重要意义。该研究通过收集已报道的中国森林凋落叶分解常数(k)及其相关变量, 分析探讨地理因素(纬度、经度和海拔)、气候因素(年平均气温和年降水量)、凋落叶质量(氮、磷、钾、木质素、木质素:氮和碳氮比)和叶特性(常绿与落叶、阔叶与针叶)对中国森林凋落叶分解速率的影响。结果表明, 在国家尺度上, k随年平均气温、年降水量、氮、磷和钾的增加而增加, 随纬度、经度、海拔、碳氮比、木质素和木质素:氮的增大而减小, 叶特性对k的影响不显著。气候与地理因素(年平均气温、年降水量和纬度)能解释k值变异的34.1%, 凋落叶质量(氮、钾、木质素和木质素:氮)能解释k值变异的21.7%, 它们能共同解释k值变异的74.4%。了解森林凋落叶分解速率在国家尺度上的格局和主控因素可为中国森林生态系统碳循环相关模型提供基础参数。     

Interacting effects of leaf litter species and macrofauna on decomposition in different litter environments

The leaf litter environment (single species versus mixed species), and interactions between litter diversity and macrofauna are thought to be important in influencing decomposition rates. However, the role of soil macrofauna in the breakdown of different species of leaf litter is poorly understood. In this study we examine the multiple biotic controls of decomposition – litter quality, soil macrofauna and litter environment and their interactions. The influence of soil macrofauna and litter environment on the decomposition of six deciduous tree species (Fraxinus excelsior L., Acer pseudoplatanus L., Acer campestre L., Corylus avellana L., Quercus robur L., Fagus sylvatica L.) was investigated in a temperate forest, Wytham Woods, Southern England. We used litterbags that selectively excluded macrofauna to assess the relative importance of macrofauna versus microbial, micro and mesofauna decomposition, and placed single species bags in either conspecific single species or mixed species litter environments. The study was designed to separate plant species composition effects on litter decomposition rates, allowing us to evaluate whether mixed species litter environments affect decomposition rates compared to single species litter environments, and if so whether the effects vary among litter species, over time, and with regard to the presence of soil macrofauna. All species had faster rates of decomposition when macrofauna were present, with 22–41% of the total mass loss attributed to macrofauna. Macrofauna were most important for easily decomposable species as soon as the leaves were placed on the ground, but were most important for recalcitrant species after nine months in the field. The mass loss rates did not differ between mixed and single species litter environments, indicating that observed differences between single species and mixed species litterbags in previous field studies are due to the direct contact of neighbouring species inside the litterbag rather than the litter environment in which they are placed.