Spatio-Temporal Dynamic of Tuber magnatum Mycelium in Natural Truffle Grounds

Tuber magnatum produces the world''s most expensive truffle. This fungus produces very rare ectomycorrhizas which are difficult or even impossible to detect in the field. A “real-time” PCR assay was recently developed to quantify and to track T. magnatum mycelium in soil. Here, this technique was used to investigate the spatial distribution of T. magnatum extra-radical mycelium in soil productive patches and its dynamic across seasons. This study was carried out in four different natural T. magnatum truffle grounds located in different Italian regions. During the fruiting seasons, the amount of T. magnatum mycelium was significantly higher around the fruiting points and decreased going farther away from them. Moreover, T. magnatum mycelium inside the productive patches underwent seasonal fluctuations. In early spring, the amount of T. magnatum mycelium was significantly higher than in summer. In summer, probably due to the hot and dry season, T. magnatum mycelium significantly decreased, whereas in autumn it increased again and was concentrated at the putative fruiting points. These results give new insights on T. magnatum ecology and are useful to plan the most appropriate sampling strategy for evaluating the management of a truffle ground.     

Assessment of ectomycorrhizal fungal communities in the natural habitats of Tuber magnatum (Ascomycota, Pezizales)

The ectomycorrhizal (ECM) fungal communities of four natural Tuber magnatum truffle grounds, located in different Italian regions (Abruzzo, Emilia-Romagna, Molise, and Tuscany), were studied. The main objective of this study was to characterize and compare the ECM fungal communities in the different regions and in productive (where T. magnatum ascomata were found) and nonproductive points. More than 8,000 (8,100) colonized root tips were counted in 73 soil cores, and 129 operational taxonomic units were identified using morphological and molecular methods. Although the composition of the ECM fungal communities studied varied, we were able to highlight some common characteristics. The most plentiful ECM fungal taxa belong to the Thelephoraceae and Sebacinaceae families followed by Inocybaceae and Russulaceae. Although several ectomycorrhizas belonging to Tuber genus were identified, no T. magnatum ectomycorrhizas were found. The putative ecological significance of some species is discussed.     

Identification of Internal Transcribed Spacer Sequence Motifs in Truffles: a First Step toward Their DNA Bar Coding

This work presents DNA sequence motifs from the internal transcribed spacer (ITS) of the nuclear rRNA repeat unit which are useful for the identification of five European and Asiatic truffles (Tuber magnatum, T. melanosporum, T. indicum, T. aestivum, and T. mesentericum). Truffles are edible mycorrhizal ascomycetes that show similar morphological characteristics but that have distinct organoleptic and economic values. A total of 36 out of 46 ITS1 or ITS2 sequence motifs have allowed an accurate in silico distinction of the five truffles to be made (i.e., by pattern matching and/or BLAST analysis on downloaded GenBank sequences and directly against GenBank databases). The motifs considered the intraspecific genetic variability of each species, including rare haplotypes, and assigned their respective species from either the ascocarps or ectomycorrhizas. The data indicate that short ITS1 or ITS2 motifs (≤50 bp in size) can be considered promising tools for truffle species identification. A dot blot hybridization analysis of T. magnatum and T. melanosporum compared with other close relatives or distant lineages allowed at least one highly specific motif to be identified for each species. These results were confirmed in a blind test which included new field isolates. The current work has provided a reliable new tool for a truffle oligonucleotide bar code and identification in ecological and evolutionary studies.     

Genetic and Phylogeographic Structures of the Symbiotic Fungus Tuber magnatum

The quality and market price of truffles vary with the species and, traditionally, the place of origin. The premium species Tuber magnatum produces white truffles and has a patchy distribution restricted to Italy and some Balkan areas. We used polymorphic microsatellites to evaluate 316 specimens grouped into 26 populations sampled across the species' geographic range to determine if natural populations of T. magnatum are genetically differentiated. We found that the southernmost and the northwesternmost populations were significantly differentiated from the rest of the populations. The simple sequence repeat data also could be used to make inferences about the postglacial T. magnatum expansion pattern. This study is the first to identify a genetic and phylogeographic structure in T. magnatum. The presence of a genetic structure can be of practical interest in tracing truffle populations according to their geographic origin for marketing strategies. Evidence for extensive outcrossing in field populations of T. magnatum also is provided for the first time.     

Reevaluation of the Life Cycle of Tuber magnatum

Tuber spp. are ectomycorrhizal ascomycetes that produce ascocarps known as truffles. Basic aspects of Tuber biology have yet to be fully elucidated. In particular, there are conflicting hypotheses concerning the mating system and the ploidy level of the mycorrhizal and truffle hyphae. We used polymorphic microsatellites to compare the allelic configurations of asci with those from the network of the surrounding hyphae in single Tuber magnatum truffles. We then used these truffles to inoculate host plants and evaluated the microsatellite configurations of the resulting mycorrhizal root tips. These analyses provide direct evidence that T. magnatum outcrosses and that its life cycle is predominantly haploid. In addition to its scientific significance, this basic understanding of the T. magnatum life cycle may have practical importance in developing strategies to obtain and select nursery-produced mycorrhizal plants as well as in the management of artificial plantations of this and other Tuber spp.     

The Role of the Microbiome of Truffles in Aroma Formation: a Meta-Analysis Approach

Truffles (Tuber spp.) are ascomycete subterraneous fungi that form ectomycorrhizas in a symbiotic relationship with plant roots. Their fruiting bodies are appreciated for their distinctive aroma, which might be partially derived from microbes. Indeed, truffle fruiting bodies are colonized by a diverse microbial community made up of bacteria, yeasts, guest filamentous fungi, and viruses. The aim of this minireview is two-fold. First, the current knowledge on the microbial community composition of truffles has been synthesized to highlight similarities and differences among four truffle (Tuber) species (T. magnatum, T. melanosporum, T. aestivum, and T. borchii) at various stages of their life cycle. Second, the potential role of the microbiome in truffle aroma formation has been addressed for the same four species. Our results suggest that on one hand, odorants, which are common to many truffle species, might be of mixed truffle and microbial origin, while on the other hand, less common odorants might be derived from microbes only. They also highlight that bacteria, the dominant group in the microbiome of the truffle, might also be the most important contributors to truffle aroma not only in T. borchii, as already demonstrated, but also in T. magnatum, T. aestivum, and T. melanosporum.     

Microbial and pigment profile of the reddish patch occurring within Tuber magnatum ascomata

Tuber magnatum Pico, the delectable white truffle, is the most prized truffle species. In this study, we examined the reddish pigmentation that frequently occurs in T. magnatum ascomata for the presence of pigment-producing bacteria.The inner part of the reddish-pigmented region of three T. magnatum ascomata collected in North–Central Italy was analysed. This reddish part was used to establish a bacterial culture collection and to extract the total genomic DNA in order to obtain a library of 16S rRNA genes representative of the bacterial community. The molecular approach revealed limited microbial diversity within the reddish-pigmented regions compared to the wider range of bacterial species commonly found at the same maturation stage and season in T. magnatum ascomata. The pigmented regions showed a prevalence of specific bacterial species belonging to α-, β- and γ- Proteobacteria, Actinobacteria and Firmicutes. From the tandem mass spectrometry analysis of the extracted pigment, four compounds were identified: i) bixin, ii) β-carotene, iii) cis-1-glycosyl-apo-8′- lycopene and iv) the fucoxanthin. Carotenoid producing species such as Microbacterium and Chryseobacterium emerged as the most likely cause of the peculiar reddish pigment production. Indeed, our findings suggest that the peculiar reddish pigment might be produced by these bacterial species.     

Bacterial and fungal communities associated with Tuber magnatum‐productive niches

Abstract

Truffles are hypogeous ectomycorrhizal fungi of ecological interest for forestry in soils of the northern hemisphere, and of economical relevance for food markets worldwide. The molecular mechanisms that control truffle body formation are largely unknown, as well as the environmental factors that are likely involved. Among the latter, it has been hypothesized that soil‐borne communities may have an impact on truffle production. To address this question, we investigated bacterial and fungal communities resident in productive versus adjacent non‐productive grounds of the white truffle Tuber magnatum by using PCR‐DGGE. Although bacterial communities were generally highly similar across all samples within the grounds, profiles did cluster according to the productivity of circumscribed niches, and a Moraxella osloensis population appeared to be associated with productive sites. Fungal communities revealed several populations, yet showed no obvious patterns in relation to productivity, although Mortierella and Fusarium oxysporum appeared to be more abundant in the productive area. Our results offer a first glimpse into microbial communities thriving in truffle productive niches, and open the question as to whether microbe‐mediated mechanisms may facilitate/inhibit truffle fruiting‐body production or, vice versa, i.e. whether truffle sporocarps have an impact on the microbes living in the rhizosphere.     

Spread of Mycobacterium avium subsp. paratuberculosis Through Soil and Grass on a Mouflon (Ovis aries) Pasture

The aims of this study were to describe spatial contamination of the environment on a mouflon pasture, as well as to assess the contamination of grass and roots after surface contamination and in depth contamination with feces and buried tissues from animals infected with Mycobacterium avium subsp. paratuberculosis (M. a. paratuberculosis). Samples of soil, roots, and aerial parts of plants were collected from different locations inside the mouflon pasture, and one control sample site was chosen outside the area where the animals are living. M. a. paratuberculosis DNA was present in all the examined sites and was more often detected in roots than in soil. DNA was detected at up to 80 cm of depth and was spatially more widespread than the initial hypothesis of M. a. paratuberculosis leaching vertically into deeper layers of soil. This study broadens our knowledge of the spread and persistence of M. a. paratuberculosis in an environment with highly infected animals.     

Soil influence on the performance of 26 native herbaceous plants suitable for sustainable Mediterranean landscaping

Native herbaceous plants have the potential for renaturalizing and recovering derelict soils, such as urban or anthropized soils.Ecological restoration following the establishment of a native wildflower meadow should lead to a reduction in management costs and to the preservation of native plant populations. This study was aimed at determining the ecological characteristics and the cultivation needs of 26 herbaceous species native to Italy and southern Europe in order to identify their landscape potential in low-maintenance conditions. The species were selected on the basis of their adaptation to unproductive soils in semi-natural and rural areas, and on their ornamental value, including their ability to attract insects. Mono-specific plots were set up in three different soils. Seed germination, seedling emergence, flowering dynamics, and plant growth were determined. Dormancy-breaking treatments were effective in improving the germination of most species. The percentage of field establishment and biomass appeared to be affected by the physical and chemical characteristics of the soil. Soil texture slightly affected seedling emergence, whereas soil texture and the C and N levels affected plant growth, the number of flowers and the duration of flowering. Dianthus carthusianorum, Verbascum blattaria, Matricaria chamomilla and Hypochoeris radicata developed a higher biomass per plant in the soils with a low nutrient content, indicating their adaptability to infertile soils. Daucus carota, Papaver rhoeas, Verbascum sinuatum, Coleostephus myconis produced a higher biomass per plant in the most fertile soil, where they appeared to show a higher potential when competing with other species. The ecological characteristics shown by the native plants are extremely important in terms of combining seeds of different species to create and to maintain semi-natural herbaceous communities in low-maintenance landscapes.     

Herbivory and competition slow down invasion of a tall grass along a productivity gradient

Competition models including competition for light predict that small plant species preferred by herbivores will be outshaded by taller unpreferred plant species with increasing productivity. When the tall plant species is little grazed by the herbivores, it can easily invade and dominate short vegetation. The tall-growing grass Elymus athericus dominates the highly productive stages of a salt-marsh succession in Schiermonnikoog and is not preferred by the herbivores which occur there, hares and geese. We studied how interspecific competition and herbivory affected performance during early establishment of this species with increasing productivity. Seedlings were planted in the field in a full factorial design, manipulating both interspecific competition and herbivory. The experiment was replicated along a natural productivity gradient. Competition reduced aboveground biomass production and decreased the number of ramets that were produced but did not affect survival of seedlings. The negative effects of competition on seedling performance increased with increasing productivity. In contrast to our expectations, herbivory strongly reduced seedling survival, especially at the unproductive sites and had only small effects on seedling growth. The present study shows that unpreferred tall-growing species cannot easily invade vegetation composed of short preferred species. Grazing by (intermediate-sized) herbivores can prevent establishment at unproductive sites, and increased competition can prevent a rapid invasion of highly productive sites. Herbivores can have a long-lasting impact on vegetation succession by preventing the establishment of tall-growing species, such as E. athericus, in a window of opportunity at young unproductive successional stages.Plant nomenclature follows Van der Meijden et al. (1990)     

Estimating switchgrass productivity in the Great Plains using satellite vegetation index and site environmental variables

Switchgrass is being evaluated as a potential feedstock source for cellulosic biofuels and is being cultivated in several regions of the United States. The recent availability of switchgrass land cover maps derived from the National Agricultural Statistics Service cropland data layer for the conterminous United States provides an opportunity to assess the environmental conditions of switchgrass over large areas and across different geographic locations. The main goal of this study is to develop a data-driven multiple regression switchgrass productivity model and identify the optimal climate and environment conditions for the highly productive switchgrass in the Great Plains (GP). Environmental and climate variables used in the study include elevation, soil organic carbon, available water capacity, climate, and seasonal weather. Satellite-derived growing season averaged Normalized Difference Vegetation Index (GSN) was used as a proxy for switchgrass productivity. Multiple regression analyses indicate that there are strong correlations between site environmental variables and switchgrass productivity (r = 0.95). Sufficient precipitation and suitable temperature during the growing season (i.e., not too hot or too cold) are favorable for switchgrass growth. Elevation and soil characteristics (e.g., soil available water capacity) are also an important factor impacting switchgrass productivity. An anticipated switchgrass biomass productivity map for the entire GP based on site environmental and climate conditions and switchgrass productivity model was generated. Highly productive switchgrass areas are mainly located in the eastern part of the GP. Results from this study can help land managers and biofuel plant investors better understand the general environmental and climate conditions influencing switchgrass growth and make optimal land use decisions regarding switchgrass development in the GP.     

湖南双季稻种植区不同生产力水稻土的物理性质

在湖南省东部、中部和西北部8个水稻主产县采集了24个不同生产力水稻土样品,测定了土壤物理性质和黏土矿物组成参数,包括土壤容重、土粒密度、孔隙度、田间持水量、水稳性团聚体、平均质量直径、标准化质量直径、团聚体破坏率、田间持水量、有机碳、有机胶结物质、无机胶结物质和黏土矿物等指标,以研究湖南省双季稻种植区不同生产力水稻土物理性质的差异.结果表明：高产水稻土（>14000 kg·hm^-2）的容重小于1.2 g·cm^-3,总孔隙度大于50%,通气孔隙度多数大于4%,0.5～5mm水稳性团聚体含量多数在20%以上.高产水稻土与中产水稻土(10000～13500 kg·hm^-2)之间的多数物理性质无显著差异,但与低产水稻土(<10000 kg·hm^-2)的差异显著,说明中产水稻土只要在良好的管理条件下可以转变为高产水稻土;而低产水稻土的物理性质较差,应重视这类水稻土的改良.     

Relationship between vegetation,hydrology and fluvial landforms on an unregulated sand‐bed stream in the Hunter Valley,Australia

A survey of fluvial landforms was conducted at Widden Brook, an unregulated sand‐bed stream in the Hunter Valley, New South Wales (NSW), Australia, to investigate the physical factors associated with vegetation pattern in Riverine Oak Forest. Groundwater depth and chemistry (pH, dissolved oxygen and electrical conductivity) were measured using piezometers and submersible data loggers on three fluvial landforms (i.e. toe of bank, top of bank and floodplain) along five transects. Floristic composition, canopy cover, bare ground and leaf litter were assessed within 45 quadrats on the three landforms along the five transects. Elevation above the bed and flood return period were determined by cross‐sectional survey and flood frequency analysis, while flow duration was determined from the gauge record. Canonical correspondence analysis demonstrated that vegetation composition was associated with average watertable depth and flood variables to a similar extent. The relative importance of these factors would be expected to vary with flood‐ and drought‐dominated climatic periods on a scale of several decades. Floristic composition was moderately associated with the canopy cover of the dominant woody species, Casuarina cunninghamiana (Miq.), but weakly correlated with bare ground and groundwater chemistry. Suites of species were associated with particular fluvial landforms and their corresponding flood and watertable conditions. The reach examined has characteristics similar to both the semi‐arid and mesic riparian ecosystems of the USA. The coarse sediments, high flood variability, short flood duration and dominance by a pioneer tree that relies on groundwater are similar to riparian ecosystems in the western USA, while the relatively broad floodplain and the development of a forest canopy that is associated with the distribution of understorey plants are similar to the mesic riparian systems in the eastern USA.     

南方红豆杉生长发育及其紫杉醇含量与环境因子的关系

研究了人工种植的3年生南方红豆杉的生长发育特征及其枝叶中紫杉醇的含量,并观测了其生长环境因子的动态特征。通过对南方红豆杉的生长发育特征以及其枝叶中紫杉醇含量与生长环境因子进行相关分析发现,南方红豆杉生长发育与空气和土壤湿度呈极显著的正相关,与空气和土壤温度、土壤N和K含量、土壤有机质和土壤紧实度呈正相关,与净辐射和土壤P含量呈负相关,但相关关系不显著,说明高温、高湿以及遮荫有利于南方红豆杉的生长,且对土壤P含量有较高需求;南方红豆杉枝叶中紫杉醇含量与空气和土壤湿度、土壤N、P和K含量呈负相关,与净辐射、空气和土壤温度、土壤有机质和土壤紧实度呈正相关,但相关关系均不显著,说明高温、高光强和干旱促进南方红豆杉枝叶中紫杉醇含量的增加,且紫杉醇含量的增加对土壤中N、P和K含量有一定的需求,尤其是N和K,对P需求不大;南方红豆杉生长发育与其枝叶中紫杉醇含量呈负相关,相关关系也不显著,推测紫杉醇可能是南方红豆杉的防御物质,以促使南方红豆杉抵御高温、干旱和高光强等不良环境。     

Quantification of extraradical mycelium of Tuber melanosporum in soils from truffle orchards in northern Spain

Quantification of extraradical mycelium of black truffle (Tuber melanosporum) has been carried out in a natural truffle ground and in seven truffle orchards (around 20 years old) established in Tierra Estella and Valdorba sites, within the natural distribution area of the black truffles in Navarre (northern Spain). Specific primers and a Taqman® probe were designed to perform real-time PCR with DNA extracted from soil samples. Amplification of T. melanosporum DNA was obtained from 131 out of the 160 soil samples. The detection limit of the technique was 1.48 μg mycelium/g of soil. The extraradical mycelium biomass detected in the soil from the natural truffle ground was significantly greater (up to ten times higher) than the mycelium biomass detected in any of the orchards. Soil from productive, nonirrigated orchards in the Tierra Estella site contained significantly more extraradical mycelium than the rest of orchards irrigated, productive of T. brumale, or nonproductive. The comparison of soil mycelium biomass in nonirrigated evergreen oak orchards in both sites showed significantly more mycelium biomass in the Tierra Estella site. This study is the first attempt to quantify extraradical mycelium of T. melanosporum in the soil using Taqman® probes. The obtained quantitative results are of special interest to evaluate the fungal response to cultural treatments and to monitor the dynamics of the extraradical mycelium of T. melanosporum in the soil.     

Genetic by environment interactions of two North American Salix species assessed for coppice yield and components of growth on three sites of varying quality

Key message

Field testing of different willow species, and promising genotypes within a species, can maximize biomass yield and quality traits due to strong genotype by environment interactions.

Abstract

Coppice yield and components of growth were quantified in eight clones of two widely distributed North American willows, Salix discolor (DIS) and S. eriocephala (ERI), in common-garden field tests on three sites of varying quality. Both species and clones within species varied significantly across different sites and interacted with site for plant yield and components of growth traits. At the species level, ERI was significantly more productive than DIS on the two most productive sites (85 and 57 % greater, respectively), but on the poorest site, a shale coal mine overburden, species ranking was reversed, with DIS showing a 60 % greater biomass yield than ERI. These sites had similar mean temperature, growing degree days, and seasonal precipitation. Site quality differences were thus most probably driven by soil nutrients, physical traits, and water-holding capacity quantified by 13 soil properties, 12 of which were significantly different and showed fairly consistent ranking among sites. At the clonal level, growth trends and differences were mostly consistent among clones across the three test sites, with the exception of one clone of DIS and to a lesser extent a clone of ERI, which showed abnormally strong clone by site interaction for specific growth traits. Productivity reached as high as 6.0 kg green mass in 2-year-old coppices for a clone from each of DIS and ERI on the most productive site. The strong expression of genetic by environment interactions at both the species and clonal levels suggests that biomass production can be optimized by taking advantage of such interactions and highlights the need for testing not only different species, but also a number of clones within a species before selecting clones for biomass production on different site types. Our results highlight variation in coppice form and the potential for genetic selection both among and within species.     

Comparative responses of Achillea millefolium ecotypes to competition and soil type

Summary Achillea millefolium populations from adjacent sites with zonal and serpentime soil were used to test predictions about the relation between growth and the competitive ability of plants in productive and unproductive environments. Under greenhouse conditions, individually-grown plants from both sources grew larger in serpentine soil than in zonal soil; serpentine plants accumulated 72% more biomass than zonal plants. In zonal soil, zonal plants were 71% larger than serpentine plants, although these differences were not statistically significant, and plants from both sources accumulated much less biomass and were shorter than plants growing in serpentine soil. In a high density, fertilized replacement series, zonal plants were taller and heavier but exhibited no more competitive ability than serpentine plants. The predictions that rapid height growth and biomass accumulation contribute significantly to competitive ability are not supported by our results. Although ecotypic differentiation has occurred between these A. millefolium populations, apparently in response to different soil types, the expression of these heritable differences can be masked by other environmental effects. There has been no apparent trade-off in these ecotypes between their response to the physical environment and their competitive ability.     

Influence of community structure on the spatial distribution of critically endangered Dicerandra immaculata var. immaculata (Lamiaceae) at wild, introduced, and extirpated locations in Florida scrub

Community structure at local scales is a major factor controlling population and community dynamics of plant species. Dicerandra immaculata Lakela var. immaculata (Lamiaceae) is a critically endangered plant known only from a few locations in scrub habitat in Florida. Using seven sites where populations of D. immaculata were wild, introduced, and/or extirpated, we sought to answer the following questions: (1) how do habitat characteristics at locations supporting wild D. immaculata plants vary from random locations within the same habitat; (2) how do habitat characteristics differ between wild and extirpated populations; and (3) how do habitat characteristics differ between wild and introduced populations? At locations of wild D. immaculata, community structure had fewer woody stems, shorter understory vegetation, lower percent canopy coverage, and lower percent ground cover of detritus than random locations and locations with extirpated D. immaculata. In addition, bare ground decreased at extirpated locations because other plant species expanded their coverage, water saturation of the soil increased, diversity of shrubs decreased, and composition of the overstory changed compared to that of wild locations. Habitat characteristics associated with introduced plants were more similar to characteristics at randomly chosen locations than those with wild plants. However, introduced plants tended to occupy locations that had drier soil, a higher abundance of conspecifics, and a higher proportion of woody understory plants than that of random locations. Overall, gaps in the canopy and at ground level are likely essential for survival and recruitment of D. immaculata.