Distinct orchid mycorrhizal fungal communities among co-occurring Vanilla species in Costa Rica: root substrate and population-based segregation.

Despite being the second largest family of flowering plants, orchids represent community structure variation in plant-microbial associations, contributes to niche partitioning in metacommunity assemblages. Yet, mycorrhizal communities and interactions remain unknown for orchids that are highly specialized or even obligated in their associations with their mycorrhizal partners. In this study, we sought to compare orchid mycorrhizal fungal (OMF) communities of three co-occurring hemiepiphytic Vanilla species (V. hartii, V. pompona, and V. trigonocarpa) in tropical forests of Costa Rica by addressing the identity of their OMF communities across species, root types, and populations, using high-throughput sequencing. Sequencing the nuclear ribosomal internal transcribed spacer (nrITS) yielded 299 fungal Operational Taxonomic Units (OTUs) from 193 root samples. We showed distinct segregation in the putative OMF (pOMF) communities of the three coexisting Vanilla hosts. We also found that mycorrhizal communities associated with the rare V. hartii varied among populations. Furthermore, we identified Tulasnellaceae and Ceratobasidiaceae as dominant pOMF families in terrestrial roots of the three Vanilla species. In contrast, the epiphytic roots were mainly dominated by OTUs belonging to the Atractiellales and Serendipitaceae. Furthermore, the pOMF communities differed significantly across populations of the widespread V. trigonocarpa and showed patterns of distance decay in similarity. This is the first report of different pOMF communities detected in roots of wild co-occurring Vanilla species using high-throughput sequencing, which provides evidence that three coexisting Vanilla species and their root types exhibited pOMF niche partitioning, and that the rare and widespread Vanilla hosts displayed diverse mycorrhizal preferences.

Leaf water relations in epiphytic ferns are driven by drought avoidance rather than tolerance mechanisms.

Opportunistic diversification has allowed ferns to radiate into epiphytic niches in angiosperm dominated landscapes. However, our understanding of how ecophysiological function allowed establishment in the canopy and the potential transitionary role of the hemi-epiphytic life form remain unclear. Here, we surveyed 39 fern species in Costa Rican tropical forests to explore epiphytic trait divergence in a phylogenetic context. We examined leaf responses to water deficits in terrestrial, hemi-epiphytic and epiphytic ferns and related these findings to functional traits that regulate leaf water status. Epiphytic ferns had reduced xylem area (-63%), shorter stipe lengths (-56%), thicker laminae (+41%) and reduced stomatal density (-46%) compared to terrestrial ferns. Epiphytic ferns exhibited similar turgor loss points, higher osmotic potential at saturation and lower tissue capacitance after turgor loss than terrestrial ferns. Overall, hemi-epiphytic ferns exhibited traits that share characteristics of both terrestrial and epiphytic species. Our findings clearly demonstrate the prevalence of water conservatism in both epiphytic and hemi-epiphytic ferns, via selection for anatomical and structural traits that avoid leaf water stress. Even with likely evolutionarily constrained physiological function, adaptations for drought avoidance have allowed epiphytic ferns to successfully endure the stresses of the canopy habitat.

Root morphophysiology changes during the habitat transition from soil to canopy of the aroid vine Rhodospatha oblongata.

BACKGROUND AND AIMS: The aroid vine Rhodospatha oblongata is characterized by a habitat change from terrestrial to canopy, relying on aerial roots at maturity to obtain water and nutrients from the forest soil. We hypothesize that morphophysiological acclimation occurs in roots as they grow under atmospheric conditions. These changes would guarantee the whole-plant survival of aroid vines in the new and potentially stressful habitat of the canopy. METHODS: Terrestrial and aerial roots were compared on a morphophysiological basis. Root anatomy, water balance, water absorption capacity via fluorescent tracer, and photochemical activity via chlorophyll fluorescence were measured. KEY RESULTS: While thin fasciculate roots occur on terrestrial crawling individuals, two clearly distinct aerial roots (anchor and feeder) are produced on canopy individuals, which both adhere to the host trunk. The colour of both aerial roots changes during development from red and brownish to striped and green at maturity. Colour changes are induced by the replacement of epidermis, exodermis and outer cortex by an inner layer of lignified cork on the root region exposed to the atmosphere. In the root region that is in contact with the host, covering substitutions do not occur and both exodermis and lignified cork, along with several epidermal hairs, appear. Water retention capacity was higher in green roots than in other root types. Rehydration capacity via water absorption by hairs of aerial roots was confirmed by fluorescence. Chlorophyll fluorescence data indicated low levels of photosynthetic capacity in aerial roots. CONCLUSIONS: Plants should evolve strategies to survive stress situations. The transition from soil to canopy imposes abiotic changes and potentially stressful situations on R. oblongata. We conclude that the morphophysiological changes observed represent an important strategy that permits the maintenance of aroid roots and the survival of R. oblongata in the canopy.

First record of Vanilla labellopapillata (Orchidaceae: Vanilloideae) in the state of Amazonas, Brazil

The first record of Vanilla labellopapillata is presented for the state of Amazonas, Brazil, in the region of Manaus, now the western limit of the species, which was previously known only from the type locality in the state of Pará. A brief description is provided and taxonomic and ecological aspects of the species are discussed in the light of this new finding. (AU)

First record of Vanilla labellopapillata (Orchidaceae: Vanilloideae) in the state of Amazonas, Brazil / Primero registro de Vanilla labellopapillata (Orchidaceae: Vanilloideae) no Estado do Amazonas, Brasil

The first record of Vanilla labellopapillata is presented for the state of Amazonas, Brazil, in the region of Manaus, now the western limit of the species, which was previously known only from the type locality in the state of Pará. A brief description is provided and taxonomic and ecological aspects of the species are discussed in the light of this new finding.(AU)

É apresentado o primeiro registro de Vanilla labellopapillata para o Estado do Amazonas, Brasil, na região de Manaus, sendo este o limite oeste da espécie, anteriormente só conhecida da localidade tipo no estado do Pará. É apresentada uma breve descrição da espécie e comentários taxonômicos e ecológicos da espécie no contexto da nova localidade.(AU)

Biomonitoring of metals for air pollution assessment using a hemiepiphyte herb (Struthanthus flexicaulis).

This work presents first results on elemental characterization of a parasite plant, Struthanthus flexicaulis, collected in urban, industrial and rural areas of Rio de Janeiro state, Brazil, in order to evaluate this plant as a biomonitor of metals pollution. The results were also compared to those obtained for fine particulate matter (PM2.5) collected from filters in nearby locales. The concentrations of PM2.5 measured in the filters were between 8.0 and 18.0 µg m(-3); in some places, these measurements were higher than the 10 µg m(-3), concentration recommended by the World Health Organization (WHO). Samples of the leaves and filters with PM were submitted to acid extraction, and the extracts were employed to determine major elements (Ba, Ca, Fe, K, Mg, P and S) by ICP OES and minor elements (Cr, Cu, La, Mn, Pb, Sr, Ti and Zn) by ICP-MS. Elements' extraction efficiency was evaluated by applying the method to the certified reference materials (CMR) of tomato leaves (NIST 1573(rd)) and urban dust (NIST 1648a). The concentrations of Ca, K and Mg were higher in leaves, while Ba, Ca, K and Zn showed higher concentrations in the PM. As expected, rural sites presented lower metal content. Enrichment factor (EF) and principal component analysis with multiple linear regression analysis (PCA-MLRA) were applied to the concentrations of elements in PM2.5 and in the leaves. Anthropogenic sources could be identified with both tools, which supports the use of S. flexicaulis as a biomonitor.

Water relations of epiphytic and terrestrially-rooted strangler figs in a Venezuelan palm savanna.

Water use patterns of two species of strangler fig, Ficus pertusa and F. trigonata, growing in a Venezuelan palm savanna were contrasted in terms of growth phase (epiphyte and tree) and season (dry and wet). The study was motivated by the question of how C3 hemiepiphytes accommodate the marked change in rooting environment associated with a life history of epiphytic establishment followed by substantial root development in the soil. During the dry season, stomatal opening in epiphytic plants occurred only during the early morning, maximum stomatal conductances were 5 to 10-fold lower, and midday leaf water potentials were 0.5-0.8 MPa higher (less negative) than in conspecific trees. Watering epiphytes of F. pertusa during the dry season led to stomatal conductances comparable to those exhibited by conspecific trees, but midday leaf water potentials were unchanged. During the rainy season, epiphytes had lower stomatal conductances than conspecific trees, but leaf water potentials were similar between the two growth phases. There were no differences in ∂13C between the two growth phases for leaves produced in either season. Substrate water availability differed between growth phases; tree roots extended down to the permanent water table, while roots of epiphytic plants were restricted to material accumulated behind the persistent leaf bases of their host palm tree, Copernicia tectorum. Epiphytic substrate moisture contents were variable during both seasons, indicating both the availability of some moisture during the dry season and the possibility of intermittent depletion during the rainy season. Epiphytic strangler figs appear to rely on a combination of strong stomatal control, maintenance of high leaf water potentials, and perhaps some degree of stem water storage to cope with the fluctuating water regime of the epiphytic environment.