Tree Colonization Research Articles

Factors affecting population density and colonization success of two non-native beetle species with different breeding/life-history strategies

IntroductionBark and longhorn beetles have become of increasing concern as invasive pests as they are transported across the globe. The larch bark beetle Ips cembrae and the larch longhorn beetle Tetropium gabrieli are two species that have recently established in Scandinavia. We asked the following questions for both I. cembrae and T. gabrieli: (i) How does habitat availability affect the relative population density? (ii) How is the colonization probability related to the relative population density? (iii) What is the relationship between relative population densities of the beetles and enemy pressure?MethodsThe relative population density of the two beetle species were assessed with two pheromone-baited traps for each beetle species in 36 pure larch stands distributed in southern Sweden and Denmark. In addition, colonization success was recorded on five cut larch trees in 30 of the 36 larch stands.ResultsIps cembrae was trapped in 19 stands and had colonized cut trees in two stands, whereas Tetropium gabrieli was trapped in 18 stands and had colonized cut trees in 12 stands. Both species showed a positive relationship between the relative population density and the probability of colonization of the cut trees. For I. cembrae a higher population size was required for colonization than for T. gabrieli. The relative population density of both species was positively related to the amount of habitat.DiscussionThe difference in the population size required for colonization between the two studied species might be explained by their different reproductive strategies. The results are discussed in terms of host location and mate finding, and predation pressure.

Influence of Growth Support on the Diversity, Composition, and Functionality of Microbial Communities Associated with Tillandsia recurvata

Tillandsia recurvata is an epiphytic plant commonly found in tropical regions and colonizes tree trunks, fences, and power wires. This plant plays an important role in interacting with trees, sharing microorganisms, and performing specific functions in the process of tree colonization. The objective of this study was to evaluate and compare the microbiomes of T. recurvata collected from two different locations (trees and fences) and two plant tissues (leaves and roots). The hypothesis of this study was that the microbiome of T. recurvata is composed of microorganisms that would provide nutritional support to compensate for the lack of nutrients in a particular growth support. The results showed significant differences in microbial diversity between trees and fences, with trees exhibiting higher richness and more complex microbial networks. Proteobacteria was the most prevalent bacterial phylum, with Actinobacteria and Sphingomonas also playing key roles in nitrogen fixation and plant growth. Fungal communities were similar across locations, with Ascomycota and Basidiomycota being predominant, but Paraconiothyrium and Nigrospora showed significant differences in abundance between trees and fences. Functional analysis indicated similar metabolic profiles across leaf and root samples, with key functions for T. recurvata including carbohydrate and amino acid metabolism, stress control, and biofertilization.

Natural forest colonisation as a management strategy to restore soil functioning of abandoned agricultural lands

Abstract Land abandonment promotes forest expansion into abandoned agricultural lands in Europe. This process leads to changes that affect several ecosystem services, but it is considered a low‐cost strategy to restore soil functions in past agricultural lands. Soil microbial communities play a key role in restoring functions. However, the relationship among forest expansion, microbial communities, and soil functioning is unclear. In this study, we used a Juniperus thurifera expansion gradient on abandoned agricultural lands in Alto Tajo National Park (Spain) to discover the changes elicited by the soil microbial communities and their functions along this gradient considering two microhabitats, under the canopy and open areas. Specifically, our objectives were (i) to analyse how soil properties (organic matter and pH), microbial communities (using PLFAs‐NFLAs) and enzymatic activities (related to C, N and P cycling) varied along the forest expansion gradient and between microhabitats and (ii) to decipher the pathways by which soil properties control the carbon and nutrient cycling in soils. The forest expansion gradient had a direct negative effect on phosphatase activity. The microhabitat showed a positive direct effect on organic matter content, pH, actinomycetes and arbuscular mycorrhizal fungi biomass and on soil C and P cycling. Moreover, the biomass of gram‐positive bacteria determined the biomass of other microbial groups. Synthesis and Applications: Though its effectiveness is variable, passive restoration can be more effective than active restoration. Our research indicates that passive tree colonisation of past agricultural land is enough to achieve soil functionality similar to a mature forest for most variables studied. However, some variables would need more time to reach mature forest levels, such as total microbial biomass and organic matter content. Therefore, to support ecosystem recovery, the management of this applied forest ecology strategy requires continuous monitoring of newly established trees and soil to elucidate the time needed to achieve mature soil properties.

Predicting the climatic suitability of non-native drought resistant trees in the face of desertification – A case study with Argania spinosa in the Iberian Peninsula

Climate change is driving a poleward shift in the optimal distributions of terrestrial organisms, including trees. Consequently, trees are expected to decrease in climatically unfavourable areas as their optimal climatic conditions shift poleward. This is the case of Mediterranean High Nature Value agroforestry systems in Iberian Peninsula, dominated by holm oaks (Quercus rotundifolia) and cork oaks (Quercus suber), which are expected to shift their future distribution northward. Failure to keep pace with climate warming poses a heightened risk of extinction for these tree species, as well as the loss of crucial ecosystem services they provide. A similar situation is found for argan trees (Argania spinosa) in the southwestern region of Morocco, where it also supports an agroforestry system. The optimum climate for these trees is also shifting northward, toward the Iberian Peninsula. As the argan tree thrives in more arid conditions with irregular precipitation, the future climatic conditions in the Iberian Peninsula may become favourable for the persistence of this tree. In light of this situation, the assisted colonization of the argan tree could potentially contribute to protecting and preserving the tree-associated ecosystem services in Iberian Peninsula. We conducted climate suitability modelling using maximum entropy approach, for both the current and future timeframes, for North of Morocco and Algeria (native range) and the whole Iberian Peninsula (non-native range). Accordingly, there appears to be a significant area with highly suitable climatic conditions (>80 %) for argan tree occurrence, covering approximately 6.7 % of the territory, over 38,000 km2. This area is projected to increase significantly in the future, covering 9–22 % of the territory, or about 55,000 and 127,000 km2. With this study, we aim to contribute to the discussion on the benefits of assisted colonization of argan trees into Iberian Peninsula, as well as potential drawbacks such as the risk of this species becoming invasive.

Hydrological variability of middle European peatland during the Holocene, inferred from subfossil bog pine and bog oak dendrochronology and high-resolution peat multiproxy analysis of the Budwity peatland (northern Poland)

Subfossil pine and oak tree trunks were excavated during exploitation of the Budwity peatland in Northern Poland. Based on dendrochronological analysis, the woodland successions in peatland were reconstructed and correlated with moisture dynamics of the peatland ecosystem inferred from the high-resolution multi-proxy analysis of the peatland deposits. From the results of dendrochronological analysis and the 14C wiggle matching methods, four floating pine chronologies (5882–5595; 5250–5089; 3702–3546; and 2222–1979 mod. cal BP) and two oak chronologies (4932–4599 and 4042–3726 mod. cal BP) were developed. The organic sediments of the peatland (6 m thick) were deposited over approximately nine thousand years. The lower complex (525–315 cm) comprises minerogenic peat, while the upper complex (315.0–0.0 cm) is composed of ombrogenic peat. Subfossil tree trunks are distributed across various peat horizons, which suggests multiple stages of tree colonisation followed by subsequent dying-off phases. Multiproxy sediment analyses (lithological, geochemical and δ13C stable isotope, pollen, plant macrofossils, Cladocera, diatom, and Diptera analyses) indicate that the two earliest phases of pine colonisation (5882–5595 and 5250–5089 mod. cal BP) and the two stages of oak colonisation (4932–4599 and 4042–3726 mod. cal BP) were associated with periodic drying of the peatland. Conversely, tree dying-off phases occurred during periods of increased water levels in the peatland, coinciding with stages of increasing climate humidity during the Holocene. The two most recent phases of pine colonisation occurred during the ombrogenic stage of mire development. Remnants of the dead forest from these phases, marked by subfossil trunks still rooted in the ground, were preserved and exposed presently during peat exploitation, approximately 2.5 m below ground level. The identified phases of tree colonisation and subsequent dying-off phases show correlation with analogical phenomena observed in the other investigated European peatlands.

Natural colonisation rates in a UK upland landscape under different conservation management approaches following sheep removal

Abstract Natural colonisation could provide a cost‐effective means to increase woodland coverage across the UK uplands. However, there is a shortage of evidence of which factors affect the success of natural colonisation, including grazing management. The species of grazer, grazing intensity and the stage of regeneration may alter the impact of grazing on the ability of trees to colonise an area. In this study, we quantify the effect of removing sheep from an area in the Yorkshire Dales National Park, England, and explore whether cattle or ungrazed management alters tree colonisation rates. We also tested other environmental factors such as distance from woodland, elevation and soil geology to understand the other constraints on natural colonisation. Naturally colonised trees were recorded within 60 plots at Ingleborough National Nature Reserve and surrounding Yorkshire Wildlife Trust reserves. A series of generalised linear models, with a negative binomial distribution, were created to understand the effects that years since removal of sheep, current management, elevation, distance from woodland and soil geology had on the number of naturally colonising trees. The number of naturally colonising trees per hectare was 16% higher each year after sheep removal, with both cattle and ungrazed management being equally effective in promoting natural colonisation. Natural colonisation decreased by 25% for every additional 100 m from the nearest woodland and naturally colonising trees were much more frequent on limestone soil. Practical implication. This study shows that sheep grazing is a key limiting factor of natural colonisation in the UK uplands. Significant natural colonisation was possible on both cattle grazed and ungrazed sites and developed at a similar rate, highlighting a change in grazing animal can be as important as grazing cessation. Tree planting will still be required to restore tree cover to areas away from seed sources and improve diversity of future woodlands.

Microbial profile of biliary tract infection in patients undergoing therapeutic endoscopic retrograde cholangiopancreatography (ERCP), and baseline risk factors predicting microbial growth and post-ERCP cholangitis.

Stasis of bile flow can result in microbial colonization of the biliary tree. Cholangitis is a common adverse event linked to endoscopic retrograde cholangiopancreatography (ERCP). To establish the bacterial profiles isolated from the bile sample and to evaluate the pre-ERCP risk factors predicting the microbial growth and development of post-ERCP cholangitis (PEC). This was a prospective cohort study, which was conducted at the Department of Hepato-gastroenterology, SIUT from 1 January 2021 to 31 December 2021. Patients of either gender undergoing index ERCP procedure were included in the study. All the patients underwent ERCP, and bile culture (BC) aspirated immediately after cannulation was achieved prior to the contrast injection. There were 2 outcome variables. One was the presence or absence of organisms in bile culture, and the second one was the development of PEC. The total number of patients was 280. Bile culture was positive in 195 (69.6%) patients, and post-ERCP cholangitis developed in 187 (66.8%) patients. The most common organism in BC was Escherichia coli (E. coli), in 82 (42%) patients. History of jaundice, abdominal pain, and weight loss on admission along with ERCP performed for common bile duct (CBD) stricture were independent predictors of positive BC and PEC, while advanced age was an additional risk factor for PEC. Microbial profile and risk factors for positive BC and PEC were evaluated. Advanced age, pre-operative jaundice, and prolonged biliary stasis are the independent risk factors for these conditions.

Atributos das árvores hospedeiras, e não a diversidade da comunidade, conduzem a abundância de epífitas em florestas tropicais sazonais

Abstract Epiphytes are considered indicators of forest ecological integrity, but the factors that explain their abundance are still not well understood. We here evaluated tree colonization by epiphytes in old-growth monospecific reforestation stands of Astronium urundeuva (M.Allemão) Engl. (Anacardiaceae) and Eucalyptus saligna Sm. (Myrtaceae), in comparison to a neighbor seasonal tropical forest fragment under similar environmental conditions. In each forest type, we identified and measured all trees (planted and colonizers) from 5-cm stem diameter in five 200 m² plots and quantified all vascular epiphytes per tree. Tree species were categorized by bark roughness, canopy deciduousness and growth rate. The abundance of epiphytes and the frequency of host trees were higher in the A. urundeuva plantation than in the native forest, with the E. saligna stand in an intermediate position. Also, we found that host traits influenced the abundance of epiphytes in their trunks. Host trees had average stem perimeter and height both higher than non-hosts, which indicates that colonization is more likely to occur in older trees. The average abundance of epiphytes per tree was higher in species with rough bark, but no relationship was found with canopy deciduousness or tree growth rate. We evidenced, therefore, that forest plantations, even if monospecific, can provide habitat for epiphytes. However, at community level, colonization success, either in native or restored forest, depends on the relative abundance of species whose bark type favors epiphytes establishment.

Forest recovery through applied nucleation: Effects of tree islet size and disperser mobility on tree recruitment in a temperate landscape

The plantation of tree islets within deforested areas (applied nucleation) has been proposed as a restoration strategy able to catalyze tree colonization in the matrix with reasonable costs and labor compared to traditional restoration methods such as extensive plantations. However, recent work has questioned its effectiveness in comparison to natural forest regeneration, and observational studies have eventually reported a limited expansion of tree islets after years of planting. To infer the processes affecting the effectiveness of applied nucleation, we used a stochastic model able to predict avian movement and fruit consumption, tree seed dispersal and seedling establishment in a fragmented temperate forest landscape of northern Spain. First, we simulated scenarios of natural regeneration and compared them to applied nucleation in terms of tree colonization in the remaining deforested matrix. Subsequently, in applied nucleation scenarios we assessed the effects of islet size and matrix area recovered on tree recruitment into the matrix. Also, we evaluated if such effects were mediated by the scale of movement of frugivores. Our results showed that applied nucleation triggers matrix colonization by trees at higher rates than natural regeneration because it avoids frugivore entrapment within forest edges. Also, that large tree islets can hamper matrix colonization despite being visited more frequently. If large tree islets offer abundant resources, animals do not need to leave their boundaries, concentrating seed deposition within islets. As expected, such effects depended on the scale of movement of frugivores. Our work highlights that in nucleated landscapes, islets harboring fruit-producing trees should attract animal dispersers, and also foster animal inter-islet movement. Both conditions should be met to ensure seed deposition and seedling establishment in the deforested matrix, promoting forest recovery independent of islet expansion through vegetative growth. To achieve these restoration goals, we propose establishing islets whose size and inter-islet distances matches the scale of movement of main seed dispersers present in the area.

Foliar herbivory modifies arbuscular mycorrhizal fungal colonization likely through altering root flavonoids

Abstract Insect herbivory may influence arbuscular mycorrhizal (AM) fungal colonisation by changing plant chemistry, and these effects can vary from negative to positive. Yet the underlying mechanisms are unclear. We investigated AM fungal colonization of Chinese tallow tree (Triadica sebifera) after exposing its seedlings to four different foliar‐feeding insects at two levels of herbivory. We then examined the potential role of induced carbon allocation and secondary metabolites, particularly flavonoids, in AM fungal colonization. Light herbivory (ca. 10% leaf area removed) promoted early colonization by AM fungi whereas heavy herbivory (ca. 60% leaf area removed) decreased it. Root flavonoids were increased (in the short‐term) under light herbivory but decreased under heavy herbivory. Further, herbivore‐induced changes to root flavonoids were positively correlated with those of AM fungal colonisation. Moreover, quercitrin, one of the root‐secreted flavonoids, could mediate these AM fungal responses. Surprisingly, however, AM fungal colonization was not correlated with herbivore‐induced carbon allocation in roots or root exudates. We show that AM fungal responses to insect herbivory are at least partially flavonoid‐based and depend on herbivory intensity. Our work highlights the importance of secondary metabolites rather than carbon allocation in interactions between above‐ground herbivory and below‐ground mycorrhiza. Read the free Plain Language Summary for this article on the Journal blog.

Carbon accumulation over 70 years of old-field succession driven by live biomass in a Mediterranean continental environment

Forest expansion in abandoned agricultural lands entails the fixation of atmospheric CO2 in the live biomass, the soil as well as in other ecosystem compartments, and in turn, has strong implications for C budgets and the design of actions to mitigate climate change all over the world. However, changes in C stocks in these compartments are still poorly understood. We assessed the main patterns and drivers of C accumulation over spontaneous colonization of abandoned agricultural lands, considering the above- and below-ground biomass (AGB and BGB, respectively), the woody debris (WD), the litter and the surface soil (SS; 0–6 cm depth), in an area of Central-North Spain. To attain this objective, we established a chronosequence of 30 plots (0.0625 ha) located in agricultural lands abandoned in 1956–1977, 1977–2005 and 2005–2017, in four different forest types. We found that the AGB and the SS accounted for the major proportion of the total C stock, but the BGB was also relatively important. Carbon stocks in all these major compartments increased linearly with the age of tree colonization. But C in the SS did not significantly differ among plots abandoned in the three periods considered and showed decreasing rates of change from youngest (i.e. those in plots abandoned in 2005–2017) to oldest (i.e. those in plots abandoned in 1956–1977) stands. Carbon accumulation was mainly driven by adult stem density and age of tree colonization in the AGB and the BGB, and by the total nitrogen content in the SS. Our findings indicate that, in these new forests, C accumulation in the live biomass is still ongoing and proceeds relatively fast and at an increasing rate, which points toward a clear potential for atmospheric CO2 fixation over the next few decades. This process, however, proceeds more slowly and shows signals of an apparent deceleration in the SS. The C stock in the surface soil is, in fact, largely disconnected from that of live biomass and varies depending on pre-abandonment land-use differences among the study sites.

Diversity of potencial pathogenic Cryptococcus species isolated from environment in country side São Paulo state, Brazil

Cryptococcosis is a systemic disease caused by two species. C. neoformans species complexes are associated with cases of cryptococcosis in immunosuppressed patients, being commonly isolated from the soil and birds feces. C. gattii species complexes affects mainly immunocompetent individuals and is often isolated in native or exotic tree species in state of biodegradation. This study aimed to perform the environmental mapping of pathogenic species of the genus Cryptococcus in tree samples of public places of the city of Birigui, São Paulo. The samples were collected from regions with greater traffic in this city. After processing, morphophysiological, biochemical, carbon and nitrogen assimilation, URA5 PCR and RFLP with double enzymatic digestion tests were performed to characterize the Cryptococcus species/species complexes. The percentage of tree colonization by the C. gattii VGII was 5%, for C. neoformans VNIV was 1%, and was found 6% of C. laurentii and 3% of C. albidus species. These results suggest that there are a micro-foci and diversity of pathogenic Cryptococcus species in arboreal environment locations investigated in this study.

High mountain trees: altitudinal records recently broken for eleven different tree species in Britain

In 2022 a project was initiated utilising citizen science to document observations of trees growing in Britain above 900 m. This focused recording effort contributed to eleven new altitudinal records for tree species in this country, including Sorbus aucuparia at 1150 m and Picea sitchensis at 1125 m (both East Inverness-shire, v.c.96). Some of these observations involved increases of at least 200 m above previous known altitudinal limits. The new records were a mix of small, stunted plants not expected to reach maturity in these extreme environments, as well as arctic-alpine Salix shrubs adapted to low temperatures and exposed conditions. Although these findings are currently too restricted to draw broad conclusions on the impacts of climate warming and land management on tree colonisation in mountain environments, long-term data collection may allow an analysis of drivers of change in the future. Out of a total of 72 tree records above 900 m collated by the author in 2022, 56% were Picea sitchensis, highlighting the ability of this neophyte to spread into high elevation habitats. The project has been useful for generating public interest in biological recording at and above the altitudinal treeline, and the continuation of such work will assist with mountain woodland restoration projects for a variety of ecologically important taxa and plant communities.

The Use of Compost Tea in a Containerized Urban Tree Nursery Shows No Evident Benefits to Tree Growth or Mycorrhizal Colonization

Compost tea is a liquid organic amendment that has been reported to benefit plant growth and performance through positive effects on microbial communities and plant nutrition. However, few studies have demonstrated this for containerized plants produced in tree nurseries. Five common urban tree species (Acer negundo, Corymbia maculata, Ficus platypoda, Hymenosporum flavum, Jacaranda mimosifolia) were grown in a containerized experiment to investigate the effects of compost tea application on tree growth and root mycorrhizal colonization over six months. The microbial composition of compost tea was also determined with 16S (bacteria) and ITS1 (fungi) metabarcoding. No significant positive effect of compost tea on plant growth or root mycorrhizal colonization was observed. Roots of all tree species were colonized by one type of mycorrhizal fungi, ectomycorrhizae (ECM), or vesicular–arbuscular mycorrhizae (VAM). However, no relationship between the mycorrhizal colonization percentage and plant growth was detected. Thus, there was no evidence that a once-off application of compost tea had benefits for mycorrhizal colonization and growth of containerized trees in a nursery setting. Further research is needed to investigate whether any benefit from compost tea is evident once containerized trees are planted into urban landscapes where growth conditions may be more challenging.

Drivers of tree colonization, species richness, and structural variation during the initial three decades of natural forest colonization in abandoned agricultural soils

Natural colonization of abandoned agricultural soils has been proposed as a cost-effective strategy for simultaneously mitigating the climate crisis, restoring ecological integrity, and promoting the re-establishment of native biodiversity. The success and speed at which forests develop in the presence of land-use legacies are highly variable, and empirical knowledge on the drivers of the initial phase of temperate forest colonization in a range of site conditions is lacking. We analyzed and compared drivers of the initial three decades of natural forest colonization in 33 afforestation sites laid out between 1990 and 2018, in Denmark. We analyzed how the age of colonization, size of the area, soil type, topography, and abundance of neighboring woody vegetation influenced woody vegetation cover, species richness, and variation in vegetation structure of the colonizing woody species. We found that woody vegetation cover, species richness, and structural variation increased significantly with time since abandonment. Woody vegetation cover was significantly higher in sites with abundant neighboring vegetation and on loamy soils compared to sand or clay. Woody vegetation cover tended to be higher in sites with sloping terrain. Species richness increased significantly in sites with loamy or clay soil and sites with sloping terrain. After accounting for the other drivers, none of the elements were influenced by the size of the area. The results suggest that time since abandonment, neighboring mature woody vegetation, soil and topography are key drivers of the different elements of colonization. This knowledge can be used to prioritize areas for natural colonization and to improve active afforestation methods, especially in new forests where the main focus is on nature quality and biodiversity.

Postrestoration colonization suggests slow regeneration, plant translocation barriers, and other host/symbiont lessons during the United Nations' Decade on Ecosystem Restoration

Mycorrhizal restoration benefits are widely acknowledged, yet factors underpinning this success remain unclear. To illuminate when natural regeneration might be sufficient, we investigated the degree mycorrhizal fungi would colonize Populus fremontii (Fremont cottonwood) 2 years after the restoration of a riparian corridor, in the presence of an adjacent source. We compared colonization levels across plant populations and ecotypes, and from trees in the planted area to those in natural source populations. Four findings contribute to the theory and application of host–symbiont interactions. (1) Median ectomycorrhizal colonization of trees in the planted area was less than one‐tenth of that within natural source populations (p < 0.05), suggesting that even with adjacent intact habitat, sluggish regeneration would make proactive mycorrhizal restoration beneficial. (2) Within the planted area, median ectomycorrhizal and arbuscule colonization of trees sourced from greater distances were less than one‐third of that for trees sourced locally (p < 0.05), suggesting translocation poses barriers to symbioses. (3) Changes in colonization did not align with plant ecotypes, suggesting that geographic scales of selection for plants and fungi differ. (4) Slight increases in median mycorrhizal colonization (from 0% to 5%) were strongly correlated with increased survival for the plant provenance with lowest survival (r2 = 46% and rs = 48%, p < 0.05), suggesting mycorrhizae are particularly beneficial when plants are under stress (including translocation‐induced stress). This study is novel in demonstrating that mycorrhizal regeneration is slow even in the presence of adjacent intact habitat, and that when colonization could seem negligible, it may still have biological significance.

Volatiles of fungal cultivars act as cues for host-selection in the fungus-farming ambrosia beetle Xylosandrus germanus.

Many wood-boring insects use aggregation pheromones during mass colonization of host trees. Bark beetles (Curculionidae: Scolytinae) are a model system, but much less is known about the role of semiochemicals during host selection by ambrosia beetles. As an ecological clade within the bark beetles, ambrosia beetles are obligately dependent on fungal mutualists for their sole source of nutrition. Mass colonization of trees growing in horticultural settings by exotic ambrosia beetles can occur, but aggregation cues have remained enigmatic. To elucidate this mechanism, we first characterized the fungal associates of the exotic, mass-aggregating ambrosia beetle Xylosandrus germanus in Southern Germany. Still-air olfactometer bioassays documented the attraction of X. germanus to its primary nutritional mutualist Ambrosiella grosmanniae and to a lesser extent another common fungal isolate (Acremonium sp.). During two-choice bioassays, X. germanus was preferentially attracted to branch sections (i.e., bolts) that were either pre-colonized by conspecifics or pre-inoculated with A. grosmanniae. Subsequent analyses identified microbial volatile organic compounds (MVOCs) that could potentially function as aggregation pheromones for X. germanus. To our knowledge, this is the first evidence for fungal volatiles as attractive cues during host selection by X. germanus. Adaptive benefits of responding to fungal cues associated with an infestation of conspecifics could be a function of locating a suitable substrate for cultivating fungal symbionts and/or increasing the likelihood of mating opportunities with the flightless males. However, this requires solutions for evolutionary conflict arising due to potential mixing of vertically transmitted and horizontally acquired symbiont strains, which are discussed.

Soil Structure and Ectomycorrhizal Root Colonization of Pecan Orchards in Northern Mexico.

Pecan trees form a symbiotic relationship with ectomycorrhizal fungi (ECM), which actively provide nutrition to the roots and protect them from phytopathogens. Although these trees originated in the southern United States and northern Mexico, information on their root colonization by ECM is insufficient in terms of a representative number of samples, both in these regions and worldwide. Therefore, the objectives of this study were to determine the percentage of ectomycorrhizal colonization (ECM) of pecan trees of different ages in conventional and organic agronomic orchards and to identify ectomycorrhizal sporocarps, both morphologically and molecularly. The rhizospheric soil properties and the ECM percentages were analyzed for 14 Western variety pecan tree orchards between 3 and 48 years of age and grouped according to the agronomic management method. DNA extraction, internal transcribed spacer amplification, and sequencing were conducted on the fungal macroforms. The ECM colonization percentage fluctuated between 31.44 and 59.89%. Soils with low phosphorus content showed higher ECM colonization. The ECM concentrations were relatively homogeneous in relation to the ages of the trees, and organic matter content did not affect the percentage of ECM colonization. The highest ECM percentages occurred with the sandy clay crumb texture soil, with an average of 55% ECM, followed by sandy clay loam soils with 49.5%. The Pisolithus arenarius and Pisolithus tinctorius fungi were molecularly identified from sporocarps associated with pecan trees. This is the first study that reports Pisolithus arenarius as being associated with this tree.

Core endophytic mycobiome in Ulmus minor and its relation to Dutch elm disease resistance.

The core microbiota of plants exerts key effects on plant performance and resilience to stress. The aim of this study was to identify the core endophytic mycobiome in U. minor stems and disentangle associations between its composition and the resistance to Dutch elm disease (DED). We also defined its spatial variation within the tree and among distant tree populations. Stem samples were taken i) from different heights of the crown of a 168-year-old elm tree, ii) from adult elm trees growing in a common garden and representing a gradient of resistance to DED, and iii) from trees growing in two distant natural populations, one of them with varying degrees of vitality. Endophyte composition was profiled by high throughput sequencing of the first internal transcribed spacer region (ITS1) of the ribosomal DNA. Three families of yeasts (Buckleyzymaceae, Trichomeriaceae and Bulleraceae) were associated to DED-resistant hosts. A small proportion (10%) of endophytic OTUs was almost ubiquitous throughout the crown while tree colonization by most fungal taxa followed stochastic patterns. A clear distinction in endophyte composition was found between geographical locations. By combining all surveys, we found evidence of a U. minor core mycobiome, pervasive within the tree and ubiquitous across locations, genotypes and health status.

Ecological Impacts of Exotic Species on Native Seed Dispersal Systems: A Systematic Review.

Exotic species are one of the main threats to biodiversity, leading to alterations in the structure and functioning of natural ecosystems. However, they can sometimes also provide ecological services, such as seed dispersal. Therefore, we assessed the ecological impacts of exotic species on native dispersal systems and the mechanisms underlying the disruption of mutualistic plant-disperser interactions. Exotic species negatively affect dispersal mutualisms by (i) altering dispersal behavior and visitation rates of native dispersers, (ii) predating native dispersers, (iii) transmitting forest pathogens, and (iv) predating seeds. Conversely, positive impacts include the dispersal of native plants, forest regeneration, and native habitat restoration via (i) increasing the visitation rates of frugivorous birds, (ii) facilitating the colonization and establishment of native forest trees, (iii) enhancing forest species seedling survival, and (iv) facilitating seed rain and seedling recruitment of early and late successional native plants. The reviewed studies provide similar results in some cases and opposite results in others, even within the same taxa. In almost all cases, exotic species cause negative impacts, although sometimes they are necessary to ensure native species' persistence. Therefore, exotic species management requires a comprehensive understanding of their ecological roles, since the resulting effects rely on the complexity of native-exotic species interactions.