Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

Recent studies raise the hypothesis that Na shortage restricts decomposition and affects the carbon cycle in tropical forests. When Na concentrations in soils are low and the stands are far off-coast, they do not receive substantial Na inputs from the atmosphere. Since terrestrial plants have low concentrations of Na, which is not considered as an essential element, the demand of soil fauna may not be covered. Yet, in contrast to animals, little is known of Na demands of fungi and phyllosphere microorganisms. We present results from a study on Na limitation in a montane forest ecosystem in South Ecuador, which is located on the eastern cordillera of the Andes. We tested the hypotheses that (1) the study area is characterized by low Na concentrations because of low deposition rates with incident precipitation (wind directions mainly from the Amazonian Basin), (2) decomposition processes are limited by fauna and fungal Na restrictions and (3) Na is retained in the canopy because of Na limitation of microorganisms in phyllosphere. Since 1998, we measure Na fluxes in rainfall, throughfall, stemflow, litter leachate, litterfall and organic layer in a microcatchment under an undisturbed lower montane rainforest. Results reveal comparatively low Na concentrations in the ecosystem and similar Na concentrations in throughfall and stemflow. Since Na fluxes are lower with throughfall than with incident rainfall, we conclude that Na is retained in the canopy. To explore the role of the phyllosphere in Na retention we sampled leaves covered by phyllosphere microorganisms and leaves without phyllosphere cover from several tree species, which were sprayed with a NaCl solution containing 0.5 mg L-1 Na, corresponding to the Na concentration in incident rainfall in our study area. Additionally, responses of litter decomposition to Na additions and the involved interaction of soil fungi and fauna were tested in a litterbag experiment at two sites (1000 and 2000 m a.s.l.). Results revealed enhanced decomposition rates following Na additions, though only in the presence of soil fauna. These results might have future ecosystem implications, since our time series showed that total Na deposition decreased within the past 15 years from ca. 40 kg ha-1 a-1 to 10 kg ha-1 a-1, suggesting a potential role of Na in regulating ecosystem processes.

Abstract:

Orchid mycorrhizal detection, based only on fungal isolation from roots, is biased due to difficulties in isolating the respec- tive fungi. Previous investigations have shown that mostly ascomycetes, housed in the sheltered compartment of the vela- men covering the roots of epiphytic orchids, are isolated on agar plates. Roots of 83 individual epiphytic orchid of Stelis hallii, S. superbiens, S. concinna, Stelis sp. and Pleurothallis lilijae were sampled in the Reserva Biológica San Francisco, Southern Ecuador. The velamen was partly removed and root tissue macerated and transferred to Petri dishes containing corn meal agar, malt extract agar and Melin Norkrans modified medium. DNA was extracted from the cultures and the 5.8S-ITS region and partial nrLSU sequenced. Phylogenetic analysis revealed members of 12 orders of ascomycetes associ- ated with the roots of these orchids, a much higher diversity than previously known. Twelve isolates were related to the Helotiales. Our results have uncovered some of the fungal diversity within the velamen of epiphytic orchids; fungi invading, most likely, from tree bark or humus accumulation close to the roots.

Abstract:

Abstract: For the first time in tropical mountain rain forest, arbuscular mycorrhizal fungal richness and community composition was investigated from planted seedlings of Cedrela montana, Heliocarpus americanus, Juglans neotropica and Tabebuia chrysantha in reforestation plots on degraded pastures. A segment of fungal 18S rDNA was sequenced from the mycorrhizas. Sequences were compared with those obtained from mycorrhizas of adult trees of 30 species in the neighboring, pristine tropical mountain rain forest. In total, 193 glomeromycotan sequences were analyzed, 130 of them previously unpublished. Members of Glomeraceae, Acaulosporaceae, Gigasporaceae and Archaeosporales were found in both habitats, with Glomus Group A sequences being by far the most diverse and abundant. Glomus Group A sequence type richness did not appear to differ between the habitats; a large number was observed in both. Glomus Group A sequence type composition, however, was found distinctly different. Seedlings were rarely colonized by fungi of the pristine forest but trapped a number of fungi known from other areas, which were rarely found in the pristine forest.

Abstract:

Distinctive groups of fungi are involved in the diverse mycorrhizal associations of land plants. All previously known mycorrhiza forming Basidiomycota associated with trees, ericads, liverworts or orchids are hosted in Agaricomycetes, Agaricomycotina. Here we demonstrate for the first time that Atractiellomycetes, members of the ?rust? lineage (Pucciniomycotina), are mycobionts of orchids. The mycobionts of 103 terrestrial and epiphytic orchid individuals, sampled in the tropical mountain rain forest of Southern Ecuador, were identified by sequencing the whole ITS1-5.8S-ITS2 region and part of 28S rDNA. Mycorrhizae of 13 orchid individuals were investigated by transmission electron microscopy. Simple septal pores and symplechosomes in the hyphal coils of mycorrhizae from four orchid individuals indicated members of Atractiellomycetes. Molecular phylogeny of sequences from mycobionts of 32 orchid individuals out of 103 samples confirmed Atractiellomycetes and the placement in Pucciniomycotina, previously known to comprise only parasitic and saprophytic fungi. Thus, our finding reveals these fungi, frequently associated to neotropical orchids, as the most basal living basidiomycetes involved in mycorrhizal associations of land plants.

Abstract:

Aneura pinguis (Aneuraceae) is a cosmopolitan thalloid liverwort that shows a specific mycorrhiza-like interaction with basidiomycetes. To date, tropical specimens have not been studied in great depth. Samples of A. pinguis were collected from 48 individuals in one plot in South Ecuador and 54 individuals in five European countries. Light and transmission electron microscopy and molecular analyses based on nuclear rDNA coding for the ribosomal large subunit (nucLSU) and from the 5.8s-ITS2 regions were carried out to identify the associated mycobionts and to study their phylogenetic relationships. Microscopic and ultrastructural investigations of the fungal colonisation showed a high congruence between the European and the Ecuadorian sites and confirmed previous results. Tulasnellales are the only mycobionts that could be detected from ultrastructural characters with certainty. Molecular phylogenetic analysis indicated the presence of tulasnelloid fungi from at least 13 distinct clades. The composition of the communities of tulasnelloid fungi in A. pinguis differs between Ecuador and Europe. The diversity of tulasnelloid fungal partners was much higher at the Ecuadorian site.