Changes in the phyllosphere community of the resurrection fern, Polypodium polypodioides, associated with rainfall and wetting

A combination of analyses were used to characterize the changes that occur in a bacterial community present in the phyllosphere of the epiphytic resurrection fern, Polypodium polypodioides, as the fern rehydrates from a desiccation-resistant, physiologically inactive state. Enrichment assays showed an increase in the viable count of bacteria using labile organic substrates following rainfall. Isolates obtained from enrichments were predominantly Gram-positive bacteria affiliated with various groups of the Actinobacteria and Firmicutes. In contrast, sequencing of 16S rRNA genes clones obtained from whole community DNA revealed that much of the community was dominated by other taxa, particularly the Alphaproteobacteria. Similar isolates were obtained from both dry and hydrated P. polypodioides fronds, whereas 16S rRNA gene sequencing of community DNA revealed different ribotypes on the dry and wet fern, and an overall reduction in richness following wetting. Wetting also produced changes in phyllosphere extracellular enzyme activity, with an initial burst of activity following rainfall and a subsequent burst approximately 48 h later. These findings suggest that the resurrection fern harbors a complex phyllosphere community, and that rehydration of the fern following rainfall may act as an enrichment culture stimulating certain bacterial populations and changing the overall community structure and activity.     

Comparison Between Two Methods for Measuring Fruit Production in a Tropical Forest1

We compared fruiting data derived simultaneously from fruit traps placed on the ground and from canopy‐surveyed plots in a terra firme rain forest, Colombian Amazonia. Values derived from the canopy‐surveyed plots were higher than fruit‐trap estimates. Fruiting patterns obtained throughout both methods were not correlated. Our results showed that the fruit‐trap method does not accurately reflect fruiting patterns occurring at the highest levels of the forest, while the canopy‐surveyed plots provided both quantitative and qualitative information on canopy fruit production, and each species contribution.     

Tree age‐dependent changes among epiphytic bryophyte communities in Mediterranean environments. A case study from Sicily (Italy)

Abstract

The epiphytic bryophytes inhabiting trees of different size/age in a Quercus ilex wood from Madonie Mountains (northern Sicily, Italy) were studied with the purpose of describing the changes that take place in the bryophyte stratum during the tree lifespan. Results indicate an increase of bryophyte cover combined with a progressive decrease of epiphytic lichens and the existence of an active process of species and community substitution. The way these processes take place corresponds to a succession sequence, which is characterised by a high number of pioneer species on the youngest trees and a sharp decline of species number on middle‐aged and old trees due to the great spread of Leptodon smithii and a few other pleurocarpous mosses. The comparison of these traits to those from central Spain evidences differences in patterns of tree colonisation by epiphyte bryophytes between the two areas and suggests that climatic conditions play a chief role in the epiphytic bryophyte establishment and succession in Mediterranean areas.     

Small increase in substratum [corrected] pH causes the dieback of one of Europe's most common lichens, Lecanora conizaeoides

Backgrounds and Aims

Lecanora conizaeoides was until recently western and central Europe''s most abundant epiphytic lichen species or at least one of the most common epiphytes. The species is adapted to very acidic conditions at pH values around 3 and high concentrations of SO₂ and its derivatives formed in aqueous solution, and thus spread with increasing SO₂ deposition during the 19th and 20th centuries. With the recent decrease of SO₂ emissions to nearly pre-industrial levels within 20 years, L. conizaeoides declined from most of its former range. If still present, the species is no longer the dominant epiphyte, but is occurring in small densities only. The rapid spread of the L. conizaeoides in Europe from an extremely rare species to the probably most frequent epiphytic lichen and the subsequent rapid dieback are unprecedented by any other organism. The present study aimed at identifying the magnitude of deacidification needed to cause the dieback of the lichen.

Methods

The epiphytic lichen diversity and bark chemistry of montane spruce forests in the Harz Mountains, northern Germany, were studied and the results were compared with data recorded with the same methods 13–15 years ago.

Key Results

Lecanora conizaeoides, which was the dominant epiphyte of the study area until 15 years ago, is still found on most trees, but only with small cover values of ≤1 %. The bark pH increased by only 0·4 pH units.

Conclusions

The data suggest that only slight deacidification of the substratum causes the breakdown of the L. conizaeoides populations. Neither competitors nor parasites of L. conizaeoides that may have profited from reduced SO₂ concentrations are likely causes of the rapid dieback of the species.     

Uptake of ant-derived nitrogen in the myrmecophytic orchid Caularthron bilamellatum

Background and Aims Mutualistic ant-plant associations are common in a variety of plant families. Some myrmecophytic plants, such as the epiphytic orchid Caularthron bilamellatum, actively form hollow structures that provide nesting space for ants (myrmecodomatia), despite a substantial loss of water-storage tissue. This study aimed at assessing the ability of the orchid to take up nitrogen from ant-inhabited domatia as possible trade-off for the sacrifice of potential water storage capacity. Methods Nitrogen uptake capabilities and uptake kinetics of (15)N-labelled compounds (NH(4)(+), urea and l -glutamine) were studied in field-grown Caularthron bilamellatum plants in a tropical moist forest in Panama. Plants were either labelled directly, by injecting substrates into the hollow pseudobulbs or indirectly, by labelling of the associated ants in situ. Key Results Caularthron bilamellatum plants were able to take up all tested inorganic and organic nitrogen forms through the inner surface of the pseudobulbs. Uptake of NH(4)(+) and glutamine followed Michaelis-Menten kinetics, but urea uptake was not saturable up to 2 mm. (15)N-labelled compounds were rapidly translocated and incorporated into vegetative and reproductive structures. By labelling ants with (15)N in situ, we were able to prove that ants transfer N to the plants under field conditions. Conclusions Based on (15)N labelling experiments we were able to demonstrate, for the first time, that a myrmecophytic orchid is capable of actively acquiring different forms of nitrogen from its domatia and that nutrient flux from ants to plants does indeed occur under natural conditions. This suggests that beyond anti-herbivore protection host plants benefit from ants by taking up nitrogen derived from ant debris.     

Orchid conservation: making the links

Orchidaceae, one of the largest families of flowering plants, present particular challenges for conservation, due in great part to their often complex interactions with mycorrhizal fungi, pollinators and host trees. In this Highlight, we present seven papers focusing on orchids and their interactions and other factors relating to their conservation.     

Community structure of vascular epiphytes: a neutral perspective

Vascular epiphytes form a diverse group of almost 30 000 species, yet theory concerning their community structure is still largely lacking. We therefore employed the simplest models of biodiversity, (near-)neutral models, to generate hypotheses concerning their community structure. With recently developed tools for (near-)neutral models we analyzed species abundance data from many samples in Central and South America which we divided into four metacommunities (Mesoamerica, Central America, Amazonia and Paraná), where for each metacommunity we considered two subsets differing in dispersal syndrome: an animal-dispersed guild and a wind-dispersed guild. We considered three models differing in the underlying speciation mode. Across all metacommunities, we found observed patterns to be indistinguishable from patterns generated by neutral or near-neutral processes. Furthermore, we found that subdivision in different dispersal guilds was often supported, with recruitment limitation being stronger for animal-dispersed species than for wind-dispersed species. This is the first time that (near-)neutral theory has been applied to epiphyte communities. Future efforts with additional data sets and more refined models are expected to further improve our understanding of community structure in epiphytes and will have to test the generality of our findings.     

Germination and Establishment of Tillandsia eizii (Bromeliaceae) in the Canopy of an Oak Forest in Chiapas, Mexico

We assessed the effectiveness of repopulating the inner canopy and middle canopy of oak trees with seeds and seedlings of the epiphytic bromeliad Tillandsia eizii. Canopy germination was 4.7 percent, considerably lower than in vitro (92%). Of the tree-germinated seedlings, only 1.5 percent survived 6 mo. In contrast, 9.3 percent of transplanted laboratory seedlings survived 15 mo. To repopulate trees, we recommend transplanting laboratory-grown seedlings, as large as practically possible, to branches in the middle canopy.