Sebastián Fracchia

Mycorrhizal status of plant species in the Chaco Serrano Woodland from central Argentina

We examined the mycorrhizal type of 128 plant species in two patches of native vegetation of the Chaco Serrano Woodland, central Argentina, the largest dry forest area in South America. Of the 128 plant species investigated (belonging to 111 genera in 53 families), 114 were colonized by arbuscular mycorrhizal fungi (AM), orchid mycorrhizal associations were present in the five terrestrial orchid species analyzed, one ectomycorrhiza was only present in Salix humboldtiana Willd., and 96 harbored a dark septate endophyte (DSE) association. Co-occurrence of AM and DSE was observed in 88 plant species. We determine morphological types of arbuscular mycorrhizal fungi (Arum, Paris, and intermediate AM structures) and report the mycorrhizal status in 106 new species, 12 of which are endemic to central Argentina and two, Aa achalensis Schltr. and Buddleja cordobensis Griseb., are declared to be vulnerable species. Root colonization in the Chaco Serrano Woodland is widespread and should be considered in revegetation programs due to the deterioration of this particular ecosystem. Considering the predominance of AM and DSE associations and the various potential benefits that these associations may bring to plant establishment, they should receive special attention in conservation and reforestation of these woodlands.

Mycorrhizal compatibility and symbiotic reproduction of Gavilea australis, an endangered terrestrial orchid from south Patagonia

Gavilea australis is a terrestrial orchid endemic from insular south Argentina and Chile. Meeting aspects of mycorrhizal fungi identity and compatibility in this orchid species is essential for propagation and conservation purposes. These knowledge represent also a first approach to elucidate the mycorrhizal specificity of this species. In order to evaluate both the mycorrhizal compatibility and the symbiotic seed germination of G. australis, we isolated and identified its root endophytic fungal strains as well as those from two sympatric species: Gavilea lutea and Codonorchis lessonii. In addition, we tested two other strains isolated from allopatric terrestrial orchid species from central Argentina. All fungal strains formed coilings and pelotons inside protocorms and promoted, at varying degrees, seed germination, and protocorm development until seedlings had two to three leaves. These results suggest a low mycorrhizal specificity of G. australis and contribute to a better knowledge of the biology of this orchid as well as of other sympatric Patagonian orchid species, all of them currently under serious risk of extinction.

Seed oil content and fatty acid profiles of five Euphorbiaceae species from arid regions in Argentina with potential as biodiesel source

Five Euphorbiaceae species ( Jatropha macrocarpa , J. hieronymi , J. excisa , Cnidoscolus tubulosus and Manihot guaranitica ) were analysed for seed oil content and fatty acid profiles in order to evaluate their potential as sources of biodiesel. The five species are perennial shrubs adapted to arid and semi-arid environments of north-western Argentina. The seed oil content for all species ranged from 27.9 to 38.7% by dry weight. Fatty acid composition consisted mainly of linolenic, myristic, palmitic, stearic, arachidic, oleic and linoleic acids, with linoleic and oleic acid being the most abundant. Among the five species analysed, J. macrocarpa has the best potential to be used as a biodiesel source. The average total seed oil content (35.8%) and a high value of oleic acid (27.3%) together with the lowest values of linoleic acid (55.8%) make this species a promising crop as a source of biodiesel in arid and semi-arid regions.

Pogonomyrmexcunicularius as the keystone disperser of elaiosome-bearing Jatropha excisa seeds in semi-arid Argentina

Myrmecochory or seed dispersal by ants is often described as a diffuse mutualism, because many of the ant species that function as partners are considered to be similar in terms of the frequency and consequences of their interactions. In this work, we test this assumption by conducting ant community surveys and seed removal experiments in six study sites located within a semi‐arid region of northwest Argentina. At each site, we characterized the ant assemblage that interacted with the seeds of Jatropha excisa Griseb. (Euphorbiaceae), an ant‐dispersed native shrub. Our results demonstrate that seed removal was dominated by one species, Pogonomyrmex cunicularius Mayr (Hymenoptera: Formicidae: Myrmicinae), which was responsible of 84% of the observed seed removal events. Although several ant species were attracted to the elaiosome‐bearing seeds of J. excisa, seed removal did not depend on ant community composition (species richness and ant activity) but was significantly influenced by the abundance of P. cunicularius. Its physical, behavioral, and ecological attributes are common with other ant species that have been characterized as keystone seed dispersers in other regions of the world. Nest feeding with marked seeds revealed that once P. cunicularius ants consume the elaiosomes, seeds are left inside the nests undamaged and at an appropriate depth for emergence. Our results support the hypothesis that myrmecochory is often an unevenly diffuse mutualism (i.e., one partner species is particularly important) and that at a local scale P. cunicularius is the keystone seed disperser of J. excisa.

Are subordinate ants the best seed dispersers? Linking dominance hierarchies and seed dispersal ability in myrmecochory interactions

True myrmecochory involves the dispersal of elaiosome-bearing seeds by ants. Between the guild of ants that are attracted to these seeds, only a few of them will act as effective dispersers, that is, transporting the seeds to suitable sites (the nests) for germination and plant establishment. Ant communities are known to be highly hierarchical, and subordinate ants quickly deliver resources to their nest rather than consuming it on-site, thereby avoiding encounters with more dominant species. As a result of a series of studies that were carried out during summer in semi-arid Northwest Argentina, we have found that the most important seed disperser of the myrmecochorous plant Jatropha excisa Griseb. (Euphorbiaceae), the ant Pogonomyrmex cunicularius pencosensis Forel, was the most subordinate species during interspecific interactions. The daily timing of release of the J. excisa seeds through ballistic dispersal increased their probability of being removed by the highly thermophilic P. cunicularius pencosensis. Foraging during the warmest hours of the day allowed P. cuniculariuspencosensis ants to avoid the risk of interference competition with dominant species, which also behaved as elaiosome predators. As a conclusion, subordinance behaviour appears to be integral to successful myrmecochory, and also the timing of seed release plays a key role in shaping the dynamics of myrmecochorous interactions. Therefore, ant-dispersed plants should not only favour their discovery by subordinate ants, but also should present their seeds at those times of the day when the behaviourally dominant ants are less active.

Insights into a novel three-partner interaction between ants, coreids (Hemiptera: Coreidae) and extrafloral nectaries: implications for the study of protective mutualisms

Extrafloral nectar of plants and honeydew of hemipterans are the common mediators of facultative interactions that involve ants as a mobile strategy of defence. The outcome of these interactions can vary from mutualistic to commensalistic or even antagonistic, depending on the ecological context and the interacting species. Here, we explore a novel, three-partner interaction involving ants, the coreid Dersagrena subfoveolata (Hemiptera) and the extrafloral nectaries (EFNs) bearing plant Senna aphylla (Fabaceae) in semi-arid Northwest Argentina. We surveyed natural areas and conducted ant exclusion experiments, to understand how each pairwise interaction influences the overall outcome among the three interacting parts. The outcome of the interactions was assessed for experimental plants as the reproductive output and herbivore abundances and for coreids as predator abundances. We found that the coreids occurred exclusively on S. aphylla plants and that at least nine ant species interacted with the EFNs as well as with the coreids. Coreid occurrence and abundance depended on ant densities, which in turn, was determined by the presence of actively secreting EFNs. Coreid and ant presence did not influence plant reproductive success, and ants provided to coreids some biotic defence, mainly against vespid wasp predators, but had no effect on non-coreid herbivores. We conclude that the interaction outcome is commensalistic between ants and plants (assuming that EF nectar is not costly for the plant), antagonistic between coreids and plants, and mutualistic between coreids and ants. The sum of all outcomes is net positive effect for ants and coreids, and net slightly negative to neutral for plants.

Growth dynamics of geographically different arbuscular mycorrhizal fungal isolates belonging to the 'Rhizophagus clade' under monoxenic conditions

The growth dynamics of extraradical mycelium and spore formation of 14 “Rhizophagus” isolates from different sites in Argentina were evaluated under monoxenic conditions. A modified Gompertz model was used to characterize the development of mycelium and spores for each isolate under the same conditions. The lag time, maximal growth rate and total quantity of both extraradical hyphae and spores were determined. Wide variability among isolates was detected, and all growth parameters were significantly altered by fungal isolate. Discriminant analysis differentiated isolates primarily based on the extent of extraradical hyphae produced, yet such differences did not conclusively correspond to phylogenetic relationships among closely related isolates based on partial SSU sequences. Given that the “Rhizophagus” isolates were grown under controlled conditions for many generations, the expression of phenotypic variability could be attributed to genetic differences that are not completely resolved by phylogenetic analysis employing the small ribosomal gene.

Xylariales): Physiological characterization and structural features of its association with wheat.

: Plant roots can be colonized by asymptomatic fungal strains belonging to several taxa, among them, the group defined as Dark Septate Endophytes (DSE). Microdochium bolleyi commonly colonizes wheat roots and other crops. It is considered a weak pathogen or even a non-pathogenic fungal species, which has also been considered as a potential biocontrol agent against aggressive soil-borne pathogens in cereal crops. We isolated a strain of M. bolleyi from wheat roots sampled in a crop field in Argentina, and characterized its abilities to grow in different carbon and nitrogen sources, to produce indole and to solubilize phosphorus; also several enzymatic activities were evaluated. In addition, resynthesis was performed under controlled conditions in order to characterize root fungal colonization under both, optical and transmission microscopy. The strain 22-1 colonized wheat root parenchymal tissue, forming chlamysdospores inside parenchymal cells and root hairs, and poorly grew in carbon and nitrogen sources. This fungus also synthesized indoles in in vitro culture, but it cannot solubilize phosphorus. Only amylase activity was detected out of seven enzymatic activity measured. Microdochium bolleyi (strain 22-1) colonized the roots, it formed typical DSE fungal structures and behaved like a “true endophyte”; however further studies are necessary to elucidate its role in the association with wheat.Fil: Rothen, Carolina Paola. Centro Regional de Investigaciones Cientificas y Transferencia Tecnologica La Rioja (CRILAR) - Provincia de La Rioja - UNLaR - SEGEMAR - UNCa - CONICET; Argentina

Arbuscular mycorrhizal fungal diversity in high-altitude hypersaline Andean wetlands studied by 454-sequencing and morphological approaches

The Laguna Brava Nature Reserve is a stressful habitat in the Andean Mountains (Argentina) dominated by extreme abiotic factors: high altitude and UV radiance, hypersalinity, alkalinity, and high concentrations of toxic elements in the soil. The sparse native vegetation that inhabits Laguna Brava and Mulas Muertas wetlands is frequently colonized by arbuscular mycorrhizal (AM) fungi. It is, however, unknown which AM species can survive in such a harsh environment and how those environmental conditions influence the AM communities. To answer these questions, 454-amplicon pyrosequencing and morphological (based on spore traits) approaches were used to assess fungal diversity. A total of 23 molecular operational taxonomic units and 14 distinct morphospecies of AM fungi were identified. The morphological characterization of AM fungal communities in Laguna Brava and Mulas Muertas, supported by the molecular data, revealed that Glomeraceae and Claroideoglomeraceae were the dominant families, confirming the predominance of generalist and ruderal AM fungal taxa but with stress-tolerant life history traits. Our results showed that the presence of AM fungi is strongly associated with local environmental variations in Laguna Brava (hypersalinity and high Na+, Sr, As and U contents in soils). The AM fungal communities in Laguna Brava and Mulas Muertas wetlands were similar according to the Simpson diversity index and the ecological distance estimated by Bray Curtis index. These results were also supported by the environmental parameters measured, as they did not vary between the studied sites. This study represents the first characterization of AM fungal community in a high-altitude Andean wetland in Argentina, improving our knowledge about these fungi from extreme environments.