Epiphytic and endophytic microbiome of the seagrass Zostera marina: Do they contribute to pathogen reduction in seawater?

Seagrass meadows provide crucial ecosystem services for coastal environments and were shown to reduce the abundance of waterborne pathogens linked to infections in humans and marine organisms in their vicinity. Among potential drivers, seagrass phenolics released into seawater have been linked to pathogen suppression, but the potential involvement of the seagrass microbiome has not been investigated. We hypothesized that the microbiome of the eelgrass Zostera marina, especially the leaf epiphytes that are at direct interface between the seagrass host and the surrounding seawater, inhibit waterborne pathogens thereby contributing to their removal. Using a culture-dependent approach, we isolated 88 bacteria and fungi associated with the surfaces and inner tissues of the eelgrass leaves (healthy and decaying) and the roots. We assessed the antibiotic activity of microbial extracts against a large panel of common aquatic, human (fecal) and plant pathogens, and mined the metabolome of the most active extracts. The healthy leaf epibiotic bacteria, particularly Streptomyces sp. strain 131, displayed broad-spectrum antibiotic activity superior to some control drugs. Gram-negative bacteria abundant on healthy leaf surfaces, and few endosphere-associated bacteria and fungi also displayed remarkable activities. UPLC-MS/MS-based untargeted metabolomics analyses showed rich specialized metabolite repertoires with low annotation rates, indicating the presence of many undescribed antimicrobials in the extracts. This study contributes to our understanding on microbial and chemical ecology of seagrasses, implying potential involvement of the seagrass microbiome in suppression of pathogens in seawater. Such effect is beneficial for the health of ocean and human, especially in the context of climate change that is expected to exacerbate all infectious diseases. It may also assist future seagrass conservation and management strategies.

The role epiphytes play in particle capture of seagrass canopies

Seagrass epiphytic communities act as ecological indicators of the quality status of vegetated coastal environments. This study aims to determine the effect leaf epiphytes has on the sediment capture and distribution from outside sources. Thirteen laboratory experiments were conducted under a wave frequency of 0.5 Hz. Three epiphyte models were attached to a Zostera marina canopy of 100 plants/m2 density. The sediment deposited to the seabed, captured by the epiphytic leaf surface, and remaining in suspension within the canopy were quantified. This study demonstrated that the amount of epiphytes impacts on the sediment stocks. Zostera marina canopies with high epiphytic areas and long effective leaf heights may increase the sediment captured on the epiphyte surfaces. Also, reducing suspended sediment and increasing the deposition to the seabed, therefore enhancing the clarity of the water column. For largest epiphytic areas, a 34.5% increase of captured sediment mass is observed. The sediment trapped on the leaves can be 10 times greater for canopies with the highest epiphytic areas than those without epiphytes. Therefore, both the effective leaf length and the level of epiphytic colonization are found to determine the seagrass canopy ability at distributing sediment.

Epiphytic proliferation of Zymoseptoria tritici isolates on resistant wheat leaves

The wheat pathogen Zymoseptoria tritici is capable of a long period of pre-invasive epiphytic growth. Studies have shown that virulent isolates vary in the extent, duration and growth form of this epiphytic growth, and the fungus has been observed to undergo behaviours such as asexual reproduction by budding and vegetative fusion of hyphae on the leaf surface. This epiphytic colonisation has been investigated very little during interactions in which an isolate of Z. tritici is unable to colonise the apoplast, as occurs during avirulence. However, avirulent isolates have been seen to undergo sexual crosses in the absense of leaf penetration, and it is widely accepted that the main point of distinction between virulent and avirulent isolates occurs at the point of attempted leaf penetration or attempted apoplastic growth, which fails in the avirulent case. In this work, we describe extensive epiphytic growth in three isolates which are unable or have very limited ability to invade the leaf, and show that growth form is as variable as for fully virulent isolates. We demonstrate that during certain interactions, Z. tritici isolates rarely invade the leaf and form pycnidia, but induce necrosis. These isolates are able to achieve higher epiphytic biomass than fully virulent isolates during asymptomatic growth, and may undergo very extensive asexual reproduction on the leaf surface. These findings have implications for open questions such as whether and how Z. tritici obtains nutrients on the leaf surface and the nature of its interaction with wheat defences.

Functional trait diversity of Cyclanthaceae and its convergent evolution with Araceae in Neotropical forests

The Cyclanthaceae comprise a relatively small family of about 230 species and 12 genera in the Pandanales that is widespread in wet Neotropical forests. The great majority of species can be divided into three growth forms (understory herbs, epiphytes, and root-climbing hemiepiphytes) that share functional traits with similar growth forms present in the Araceae, a member of the Alismatales and not closely related. Our objectives were first to characterize the diversity, functional growth forms, and ecological traits of Cyclanthaceae at the La Selva Biological Station. Specific functional leaf and canopy traits of terrestrial herbs and epiphytes are very similar and associated with ecological success in both families. We further examined the functional traits of root-climbing hemiepiphytes, a specialized growth form that links the two families but rare in other families and argue that their specialized functional traits allow them to be considered as a distinct functional growth form. A key trait in distinguishing hemiepiphytes which are rare outside of the Cyclanthaceae and Araceae is the severance of the main stem hydraulic connection to the soil early in plant development. We used field data to examine the possible evolutionary pathways of developmental and ecological transition from terrestrial to hemiepiphyte growth forms. The broader ecological success of hemiepiphytic Araceae compared to Cyclanthaceae is hypothesized to result from the presence of heteroblasty in developing stems and leaves which allows more efficient utilization of complex canopy light environments of wet tropical forests.

Seasonality and phenology of an epiphytic calcareous red alga, Hydrolithon boreale, on the leaves of Posidonia oceanica (L) Delile in the Turkish water

Epiphytes on Posidonia oceanica play a crucial role for determination of the ecological status of marine environment in time and space besides the seagrasses alone. The study was aimed to estimate the spatiotemporal ecological status linked to variation in biometry of an epiphytic micro-calcareous red alga, Hydrolithon boreale, found on leaves of the meadow with the exclusive environmental parameters along the entire Turkish coast of the Mediterranean Sea. Collection of Posidonia oceanica samples was conducted at 64 stations in winter (December 2018-January 2019) and 112 stations in summer (June-July 2019) by SCUBA (0.4 × 0.4 m of a quadrate frame) in the infralittoral zone along the entire Turkish Mediterranean coast surrounded by the siliciclastic Taurus Mountain Range which favor growth of epiphytic micro-calcareous red algae. Percent occurrence of the epiphyte changed seasonally-lower in winter (25%) than in summer (44%). The epiphyte which is an indicator and sensitive to undisturbed marine area grew up well to 5 mm in diameter, 0.35 mm in thickness of the crust size, and was populated up to 1006 ind/m² in summer owing to the increased utilization of the carbonate by the epiphyte with the increased water temperature. The size was contrasted to the density (abundance and biomass) in space. The biometry was significantly dependent on the siliciclastic-carbonate deposition as inferred from SiO₄-Si of the water in relation to the leaf area index (LAI) of P. oceanica. Therefore, this deposition induced specimens to grow in size, followed by the reduced density concerning the N-based nutrient of the water. Further major environmental parameters which negatively affected the biometry were pH and total suspended matter of the water, analogous to turbidity. Of the trace elements, Ni was negatively correlated with the biometry, whereas the LAI was however positively correlated with all the anthropogenic-sourced trace elements (V, Cu, Zn, As, Cd, and Pb) in the leaves. Of the bottom types, the calcite rock had a higher density than the other soft bottoms in contrast to the size of the epiphyte. Future studies could be based on the present study for determination of the ecological status regarding two dominant epiphytes on leaves of two seagrasses (H. boreale on P. oceanica and partly Pneophyllum fragile on Cymodocea nodosa) found in the different environments and substrates in space and time.

Stem transcriptome screen for selection in wild and cultivated pitahaya (Selenicereus undatus): an epiphytic cactus with edible fruit

Dragon fruit, pitahaya or pitaya are common names for the species in the Hylocereus group of Selenicereus that produce edible fruit. These Neotropical epiphytic cacti are considered promising underutilized crops and are currently cultivated around the world. The most important species, S. undatus, has been managed in the Maya domain for centuries and is the focus of this article. Transcriptome profiles from stems of wild and cultivated plants of this species were compared. We hypothesized that differences in transcriptomic signatures could be associated with genes related to drought stress. De novo transcriptome assembly and the analysis of differentially expressed genes (DEGs) allowed us to identify a total of 9,203 DEGs in the Hunucmá cultivar relative of wild Mozomboa plants. Of these, 4,883 represent up-regulated genes and 4,320, down-regulated genes. Additionally, 6,568 DEGs were identified from a comparison between the Umán cultivar and wild plants, revealing 3,286 up-regulated and 3,282 down-regulated genes. Approximately half of the DEGs are shared by the two cultivated plants. Differences between the two cultivars that were collected in the same region could be the result of differences in management. Metabolism was the most representative functional category in both cultivars. The up-regulated genes of both cultivars formed a network related to the hormone-mediated signaling pathway that includes cellular responses to auxin stimulus and to hormone stimulus. These cellular reactions have been documented in several cultivated plants in which drought-tolerant cultivars modify auxin transport and ethylene signaling, resulting in a better redistribution of assimilates.

Lepisorusmedioximus (Polypodiales, Polypodiaceae), a new species from Shan State of Myanmar

A new species of the species-rich fern genus Lepisorus (Polypodiales, Polypodiaceae) has been found to occur in Shan state, Myanmar. Lepisorusmedioximus is described based on morphological characters and phylogenetic evidence. Phylogenetic analyses showed that the specimens of L.medioximus formed a distinct clade nested in the Pseudovittaria clade. The morphological comparison demonstrated that the species is distinct from phylogenetically related species, namely L.elegans, L.contortus, and L.tosaensis, in the morphology of the rhizome scales, size, and shape of the lamina, position of sori, and paraphyses.

Maple and hickory leaf litter fungal communities reflect pre-senescent leaf communities

Fungal communities are known to contribute to the functioning of living plant microbiomes as well as to the decay of dead plant material and affect vital ecosystem services, such as pathogen resistance and nutrient cycling. Yet, factors that drive structure and function of phyllosphere mycobiomes and their fate in leaf litter are often ignored. We sought to determine the factors contributing to the composition of communities in temperate forest substrates, with culture-independent amplicon sequencing of fungal communities of pre-senescent leaf surfaces, internal tissues, leaf litter, underlying humus soil of co-occurring red maple (Acer rubrum) and shagbark hickory (Carya ovata). Paired samples were taken at five sites within a temperate forest in southern Michigan, USA. Fungal communities were differentiable based on substrate, host species, and site, as well as all two-way and three-way interactions of these variables. PERMANOVA analyses and co-occurrence of taxa indicate that soil communities are unique from both phyllosphere and leaf litter communities. Correspondence of endophyte, epiphyte, and litter communities suggests dispersal plays an important role in structuring fungal communities. Future work will be needed to assess how this dispersal changes microbial community functioning in these niches.

On the selective advantage of coloniality in staghorn ferns (Platycerium bifurcatum, Polypodiaceae)

The staghorn fern (Platycerium bifurcatum, Polypodiaceae) is an epiphyte from Australasia that displays many life history characteristics commonly associated with eusocial animals. Here, I hypothesize about the selective advantage of living in cooperative groups by comparing the morphological characteristics of colonies to their solitary congeners.

Short-term drought triggers defence mechanisms faster than ABA accumulation in the epiphytic bromeliad Acanthostachys strobilacea

Epiphytic bromeliads might experience drought after a few hours without water, which is especially critical during early life stages. Consequently, juvenile epiphytic bromeliads probably rely on short-term activation of drought tolerance strategies, although the biochemical processes involved are still poorly understood. In this study, we aimed to evaluate the short-term drought response of juvenile plants of the epiphytic bromeliad Acanthostachys strobilacea (Schult. & Schult. f.) Klotzsch. We hypothesized that short-term drought would induce the accumulation of abscisic acid (ABA) and secondary messengers such as reactive oxygen and nitrogen species (ROS and RNS, respectively) before the activation of defence mechanisms. Three-month-old plants were transferred from well-watered to dry substrates and stress markers were assessed at 0, 2, 5, 10, 24, 48, and 72 h. Drought caused a 27.3% decrease in relative water content compared to the well-watered control at 72 h. A nearly 5-fold increment in the ABA content occurred at 72 h of stress, which was about two days after the first detection of peaks in RNS levels and defence mechanisms activation. Indeed, ascorbate peroxidase (EC 1.11.1.11) activities and proline content increased after 10 h, whereas after 24 h a higher catalase (EC 1.11.1.6) activity and osmotic adjustment occurred. Oxidative stress markers and photochemical efficiency of photosystem II indicated no significant damage induced by drought. We concluded that defence mechanisms activation during early drought in juvenile A. strobilacea might be regulated initially by ABA-independent pathways and RNS, while ABA-induced responses are triggered at subsequent stages of stress.

Rapid radiation of angraecoids (Orchidaceae, Angraecinae) in tropical Africa characterised by multiple karyotypic shifts under major environmental instability

Angraecoid orchids present a remarkable diversity of chromosome numbers, which makes them a highly suitable system for exploring the impact of karyotypic changes on cladogenesis, diversification and morphological differentiation. We compiled an annotated cytotaxonomic checklist for 126 species of Angraecinae, which was utilised to reconstruct chromosomal evolution using a newly-produced, near-comprehensive phylogenetic tree that includes 245 angraecoid taxa. In tandem with this improved phylogenetic framework, using combined Bayesian, maximum likelihood and parsimony approaches on ITS-1 and five plastid markers, we propose a new cladistic nomenclature for the angraecoids, and we estimate a new timeframe for angraecoid radiation based on a secondary calibration, and calculate diversification rates using a Bayesian approach. Coincident divergence dates between clades with identical geographical distributions in the angraecoids and the pantropical orchid genus Bulbophyllum suggest that the same events may have intervened in the dispersal of these two epiphytic groups between Asia, continental Africa, Madagascar and the Neotropics. The major angraecoid lineages probably began to differentiate in the Middle Miocene, and most genera and species emerged respectively around the Late Miocene-Pliocene boundary and the Pleistocene. Ancestral state reconstruction using maximum likelihood estimation revealed an eventful karyotypic history dominated by descending dysploidy. Karyotypic shifts seem to have paralleled cladogenesis in continental tropical Africa, where approximately 90% of the species have descended from at least one inferred transition from n = 17-18 to n = 25 during the Middle Miocene Climatic Transition, followed by some clade-specific descending and ascending dysploidy from the Late Miocene to the Pleistocene. Conversely, detected polyploidy is restricted to a few species lineages mostly originating during the Pleistocene. No increases in net diversification could be related to chromosome number changes, and the apparent net diversification was found to be highest in Madagascar, where karyotypic stasis predominates. Finally, shifts in chromosome number appear to have paralleled the evolution of rostellum structure, leaflessness, and conspicuous changes in floral colour.

Diversity of epiphytic fungi on the surface of Kyoho grape berries during ripening process in summer and winter at Nanning region, Guangxi, China

The two-harvest-per-year farming system allow table grape to be harvested a year both in summer and winter in southern China. Herein, we used high-throughput sequencing to investigate the diversity of fungi on grape fruits surface during the ripening process in summer and winter at subtropical Nanning region, Guangxi, China. The results showed that 23 fungal species existed in all samples. Among them, the five most dominant species were Cladosporium ramotenellum, Pseudozyma aphidis, Gyrothrix spp., Gibberella intricans and Acremonium alternatum, with abundance from 61.62 % to 91.26 %. Analysis using the student's t-test for Shannon index indicated that components of fungal community varied significantly between the two ripening seasons. The dominant genera of core fungal community were Cladosporium, Gyrothrix, Paramycosphaerella, Acremonium, Penicillium and Tilletiopsis in the summer and Cladosporium, Pseudozyma, Gibberella, Colletotrichum, Sporobolomyces, Rhodosporidium, Alternaria and Aspergillus in the winter. Overall, fungi diversity on grape fruits surface at Nanning showed significantly differences between different ripening seasons. Our results ennrich the understanding of epiphytic communities of grape fruits in subtropics.

Spatio-temporal patterns of orchids flowering in Cameroonian rainforests

We characterized the flowering patterns of 45 epiphytic orchid species occurring in Cameroonian rainforests to explore the environmental and evolutionary forces driving their phenology. We used a dataset of 3470 flowering events recorded over a period of 11 years in the Yaoundé living collection (82% of the flowering events) and from in situ observations (18% of the flowering events) to (i) describe flowering frequency and timing and synchronization among taxa; (ii) test flowering patterns for phylogenetic relatedness at the generic level; and (iii) investigate the spatial patterns of phenology. An annual flowering pattern prevailed among the species selected for this study. The species-rich African genera Angraecum and Polystachya are characterized by subannual and annual frequency patterns, respectively. However, in terms of flowering time, no phylogenetic signal was detected for the four most diverse genera (Ancistrorhynchus, Angraecum, Bulbophyllum, and Polystachya). Results suggest also an important role of photoperiod and precipitation as climatic triggers of flowering patterns. Moreover, 16% of the taxa cultivated ex situ, mostly Polystachya, showed significant differences in flowering time between individuals originating from distinct climatic regions, pointing toward the existence of phenological ecotypes. Phenological plasticity, suggested by the lack of synchronized flowering in spatially disjunct populations of Polystachya, could explain the widespread radiation of this genus throughout tropical Africa. Our study highlights the need to take the spatial pattern of flowering time into account when interpreting phylogeographic patterns in central African rainforests.

Epiphyte type and sampling height impact mesofauna communities in Douglas-fir trees

Branches and boles of trees in wet forests are often carpeted with lichens and bryophytes capable of providing periodically saturated habitat suitable for microfauna, animals that include tardigrades, rotifers, nematodes, mites, and springtails. Although resident microfauna likely exhibit habitat preferences structured by fine-scale environmental factors, previous studies rarely report associations between microfaunal communities and habitat type (e.g., communities that develop in lichens vs. bryophytes). Microfaunal communities were examined across three types of epiphyte and three sampling heights to capture gradients of microenvironment. Tardigrades, rotifers, and nematodes were significantly more abundant in bryophytes than fruticose lichen or foliose lichen. Eight tardigrade species and four tardigrade taxa were found, representing two classes, three orders, six families, and eight genera. Tardigrade community composition was significantly different between bryophytes, foliose lichen, fruticose lichen, and sampling heights. We show that microenvironmental factors including epiphyte type and sampling height shape microfaunal communities and may mirror the environmental preferences of their epiphyte hosts.

Epibionts on Turbinaria ornata, a secondary foundational macroalga on coral reefs, provide diverse trophic support to fishes

Worldwide, many coral reef ecosystems have shifted from coral to algal dominance, yet the ecological function of these emergent communities remains relatively unknown. Turbinaria ornata, a macroalga with a rapidly expanding range in the South Pacific, forms dense stands on hard substrate, likely providing ecological services unique from corals. While generally unpalatable, T. ornata can function as a secondary foundation species and hosts an epibiont community that may provide overlooked trophic resources in phase shifted reef ecosystems. Results from video recorded field experiments designed to quantify consumer pressure on T. ornata epibionts showed that both consumer pressure and epibiont cover increased with thallus size. Additionally, most fish species, including herbivores, omnivores, and detritivores, exhibited higher bite rates on thalli with epibionts compared to thali with epibionts experimentally removed. Juvenile parrotfishes were responsible for 50% of total bites recorded and also had the highest bite rates. Results indicate that epibionts, particularly on large T. ornata, are a food resource for a diversity of fishes, representing a previously undescribed function of this macroalga in coral reef ecosystems. Exploring the functions of macroalgal dominated reef communities will be increasingly important as reefs continue to phase shift toward macroalgal dominance in the Anthropocene.

Variation in the leaf and root microbiome of sugar maple (Acer saccharum) at an elevational range limit

Background

Bacteria, archaea, viruses and fungi live in various plant compartments including leaves and roots. These plant-associated microbial communities have many effects on host fitness and function. Global climate change is impacting plant species distributions, a phenomenon that will affect plant-microbe interactions both directly and indirectly. In order to predict plant responses to global climate change, it will be crucial to improve our understanding of plant-microbe interactions within and at the edge of plant species natural ranges. While microbes affect their hosts, in turn the plant’s attributes and the surrounding environment drive the structure and assembly of the microbial communities themselves. However, the patterns and dynamics of these interactions and their causes are poorly understood.

Methods

In this study, we quantified the microbial communities of the leaves and roots of seedlings of the deciduous tree species sugar maple (Acer saccharum Marshall) within its natural range and at the species’ elevational range limit at Mont-Mégantic, Quebec. Using high-throughput DNA sequencing, we quantified the bacterial and fungal community structure in four plant compartments: the epiphytes and endophytes of leaves and roots. We also quantified endophytic fungal communities in roots.

Results

The bacterial and fungal communities of A. saccharum seedlings differ across elevational range limits for all four plant compartments. Distinct microbial communities colonize each compartment, although the microbial communities inside a plant’s structure (endophytes) were found to be a subset of the communities found outside the plant’s structure (epiphytes). Plant-associated bacterial communities were dominated by the phyla Proteobacteria, Acidobacteria, Actinobacteria and Bacteroidetes while the main fungal taxa present were Ascomycota.

Discussion

We demonstrate that microbial communities associated with sugar maple seedlings at the edge of the species’ elevational range differ from those within the natural range. Variation in microbial communities differed among plant components, suggesting the importance of each compartment’s exposure to changes in biotic and abiotic conditions in determining variability in community structure. These findings provide a greater understanding of the ecological processes driving the structure and diversity of plant-associated microbial communities within and at the edge of a plant species range, and suggest the potential for biotic interactions between plants and their associated microbiota to influence the dynamics of plant range edge boundaries and responses to global change.

Cryopreservation without vitrification suitable for large scale cryopreservation of orchid seeds

BACKGROUND

Orchids are under threat from human activities and climate change, with populations limited to small geographic hotspots. This makes them ideal candidates for ex situ conservation. Orchid seeds are desiccation tolerant, but often have poor longevity in seed banks and cryopreservation of orchid protocorms is complex and expensive. Therefore, simple methods for large-scale storage programs are essential to store orchid seeds of different life forms. Seeds of five species representing epiphytic, lithophytic and terrestrial orchids from the Central Highlands of Madagascar were studied to find a simple and effective system of cryopreservation. The use of a vitrification solution prior to cryopreservation to improve survival was investigated, as well as the use of symbiotic and asymbiotic germination media to maximise germination after cryopreservation. Using the filter paper packet method, dried seeds were stored in vapour phase above liquid nitrogen and recovered after thawing with both symbiotic and asymbiotic media.

RESULTS

The study revealed that cryoprotection is not essential for the species in this study, which represented a range of lifeforms. Vitrification generally led to a decrease in germination post cryopreservation. The use of a symbiotic germination medium post cryopreservation was found to be successful in the species in which it was tested. However, the use of an asymbiotic medium was successful for all the species in this study.

CONCLUSIONS

Vitrification was not essential for the species in this study as the orchid seeds were already ultralow temperature and desiccation tolerant. However, further studies using more species are required to validate this approach. This may be an ecophysiological or genetic trait of these species. Therefore, this form of dry seed cryopreservation could form part of ex situ orchid seed conservation using a standard method. The methods developed here will store greater genetic diversity compared to what can be achieved with protocorms and are suitable for both asymbiotic and symbiotic recovery after cryopreservation. This will help reduce the time and cost of ex situ conservation, and help develop universal protocols for large genera, compared to custom protocols required for protocorm cryopreservation.

Comparative physiological and proteomic analyses reveal different adaptive strategies by Cymbidium sinense and C. tracyanum to drought

A terrestrial orchid, Cymbidium sinense appears to utilizes "remedy strategy", while an epiphytic orchid, C. tracyanum , employs a "precaution strategy" to drought stress based on morphological, physiological and proteomic analysis. Drought condition influences plant growth and productivity. Although the mechanism by which plants adapt to this abiotic stress has been studied extensively, the water-adaptive strategies of epiphytes grown in water-limited habitats remain undefined. Here, root and leaf anatomies, dynamic changes in physiological and proteomic responses during periods of drought stress and recovery studied in an epiphytic orchid (Cymbidium tracyanum) and a terrestrial orchid (C. sinense) to investigate their strategies for coping with drought. Compared with C. sinense, C. tracyanum showed stronger drought-resistant adaptive characteristics to drought because its leaves had more negative water potential at turgor loss point and roots had higher proportion of velamen radicum thickness. Although both species demonstrated quick recovery of photosynthesis after stress treatment, they differed in physiological and proteomic responses. We detected and functionally characterized 103 differentially expressed proteins in C. sinense and 104 proteins in C. tracyanum. These proteins were mainly involved in carbon and energy metabolism, photosynthesis, and defense responses. The up-regulated expression of plastid fibrillin may have contributed to the marked accumulation of jasmonates only in stressed C. sinense, while ferredoxin-NADP reductase up-regulation was only found in C. tracyanum which possibly related to the stimulation of cyclic electron flow that is linked with photoprotection. These physiological and proteomic performances suggest distinct adaptive strategies to drought stress between C. sinense (remedy strategy) and C. tracyanum (precaution strategy). Our findings may help improve our understanding about the ecological adaptation of epiphytic orchids.

Epiphytic bryophytes as bio-indicators of atmospheric nitrogen deposition in a subtropical montane cloud forest: Response patterns, mechanism, and critical load

Increasing trends of atmospheric nitrogen (N) deposition due to pollution and land-use changes are dramatically altering global biogeochemical cycles. Bryophytes, which are extremely vulnerable to N deposition, often play essential roles in these cycles by contributing to large nutrient pools in boreal and montane forest ecosystems. To interpret the sensitivity of epiphytic bryophytes for N deposition and to determine their critical load (CL) in a subtropical montane cloud forest, community-level, physiological and chemical responses of epiphytic bryophytes were tested in a 2-year field experiment of N additions. The results showed a significant decrease in the cover of the bryophyte communities at an N addition level of 7.4 kg ha^-1 yr^-1, which is consistent with declines in the biomass production, vitality, and net photosynthetic rate responses of two dominant bryophyte species. Given the background N deposition rate of 10.5 kg ha^-1yr^-1 for the study site, a CL of N deposition is therefore estimated as ca. 18 kg N ha^-1 yr^-1. A disordered cellular carbon (C) metabolism, including photosynthesis inhibition and ensuing chlorophyll degradation, due to the leakage of magnesium and potassium and corresponding downstream effects, along with direct toxic effects of excessive N additions is suggested as the main mechanism driving the decline of epiphytic bryophytes. Our results confirmed the process of C metabolism and the chemical stability of epiphytic bryophytes are strongly influenced by N addition levels; when coupled to the strong correlations found with the loss of bryophytes, this study provides important and timely evidence on the response mechanisms of bryophytes in an increasingly N-polluted world. In addition, this study underlines a general decline in community heterogeneity and biomass production of epiphytic bryophytes induced by increasing N deposition.

Canopy soil bacterial communities altered by severing host tree limbs

Trees of temperate rainforests host a large biomass of epiphytic plants, which are associated with soils formed in the forest canopy. Falling of epiphytic material results in the transfer of carbon and nutrients from the canopy to the forest floor. This study provides the first characterization of bacterial communities in canopy soils enabled by high-depth environmental sequencing of 16S rRNA genes. Canopy soil included many of the same major taxonomic groups of Bacteria that are also found in ground soil, but canopy bacterial communities were lower in diversity and contained different operational taxonomic units. A field experiment was conducted with epiphytic material from six Acer macrophyllum trees in Olympic National Park, Washington, USA to document changes in the bacterial communities of soils associated with epiphytic material that falls to the forest floor. Bacterial diversity and composition of canopy soil was highly similar, but not identical, to adjacent ground soil two years after transfer to the forest floor, indicating that canopy bacteria are almost, but not completely, replaced by ground soil bacteria. Furthermore, soil associated with epiphytic material on branches that were severed from the host tree and suspended in the canopy contained altered bacterial communities that were distinct from those in canopy material moved to the forest floor. Therefore, the unique nature of canopy soil bacteria is determined in part by the host tree and not only by the physical environmental conditions associated with the canopy. Connection to the living tree appears to be a key feature of the canopy habitat. These results represent an initial survey of bacterial diversity of the canopy and provide a foundation upon which future studies can more fully investigate the ecological and evolutionary dynamics of these communities.

Adjustments in CAM and enzymatic scavenging of H2O2 in juvenile plants of the epiphytic bromeliad Guzmania monostachia as affected by drought and rewatering

Juvenile plants of epiphytes such as bromeliads are highly prone to dehydration under drought conditions. It is likely that young epiphytes evolved mostly metabolic strategies to resist drought, which may include the plastic modulation of the enzymatic antioxidant system and crassulacean acid metabolism (CAM). Few studies have investigated such strategies in juvenile epiphytes, although such research is important to understand how these plants might face drought intensification derived from potential climatic alterations. The epiphytic CAM bromeliad Guzmania monostachia (L.) Rusby ex Mez var. monostachia is known to have plastic responses to drought, but no reports have focused on the metabolism of juvenile plants to drought and recovery. Hence, we aimed to verify how juvenile G. monostachia plants adjust malate (indicative of CAM), H₂O₂ content and enzymatic scavenging in response to drought (eight days without irrigation) and rewatering (six days of irrigation post-drought). Interestingly, drought decreased H₂O₂ content and activities of superoxide dismutase, catalase (CAT) and ascorbate peroxidase (APX) in the pre-dusk period, although glutathione reductase (GR) and CAM activity increased. Rewatering restored H₂O₂, but activities of APX, CAT and GR exceeded pre-stress levels in the pre-dusk and/or pre-dawn periods. Results suggest that recovery from a first drought redefines the homeostatic balance of H₂O₂ scavenging, in which rewatered plants stimulate the enzymatic antioxidant system while drought-exposed plants intensify CAM activity to regulate H₂O₂ content, a photosynthetic pathway known to prevent oxidative stress. Such data show that young G. monostachia plants adjust CAM and H₂O₂ scavenging to adapt to water availability.

Development of an epiphyte indicator of nutrient enrichment: threshold values for seagrass epiphyte load

Metrics of epiphyte load on macrophytes were evaluated for use as quantitative biological indicators for nutrient impacts in estuarine waters, based on review and analysis of the literature on epiphytes and macrophytes, primarily seagrasses, but including some brackish and freshwater rooted macrophyte species. An approach is presented that empirically derives threshold epiphyte loads which are likely to cause specified levels of decrease in macrophyte response metrics such as biomass, shoot density, percent cover, production and growth. Data from 36 studies of 10 macrophyte species were pooled to derive relationships between epiphyte load and -25 and -50% seagrass response levels, which are proposed as the primary basis for establishment of critical threshold values. Given multiple sources of variability in the response data, threshold ranges based on the range of values falling between the median and the 75^th quantiles of observations at a given seagrass response level are proposed rather than single, critical point values. Four epiphyte load threshold categories - low, moderate, high, very high, are proposed. Comparison of values of epiphyte loads associated with 25 and 50% reductions in light to macrophytes suggest that the threshold ranges are realistic both in terms of the principle mechanism of impact to macrophytes and in terms of the magnitude of resultant impacts expressed by the macrophytes. Some variability in response levels was observed among climate regions, and additional data collected with a standardized approach could help in the development of regionalized threshold ranges for the epiphyte load indicator.

Endophytic Microbial Community DNA Extraction from the Plant Phyllosphere

The plant phyllosphere, which represents all plant parts that are above the ground, is considered one of the most extensive ecosystems to be colonized by microorganisms, both at the surface as epiphytes or as endophytes within the plant. These plant-associated microbial communities are reservoirs of microbial diversity and they can be important for plant health. The characterization of microbial communities in diverse plants, such as Espeletia plants that are endemic to the Paramo ecosystem in the Andes Mountains, can shed light regarding possible interactions among microorganisms and microbial functional properties. Obtaining DNA from plant endophytic microbial communities involves various steps to ensure that samples are free of contamination from microorganisms present on the plant surface (epiphytes). Plant leaves are first surface sterilized, cut into pieces, homogenized using glass beads, and then used for DNA extraction using a commercially available kit. DNA samples are then quantified and analyzed using Qubit^® 2.0 for use in PCR amplification of 16S rRNA genes.

Are seagrass beds indicators of anthropogenic nutrient stress in the rocky intertidal?

It is well established that anthropogenic nutrient inputs harm estuarine seagrasses, but the influence of nutrients in rocky intertidal ecosystems is less clear. In this study, we investigated the effect of anthropogenic nutrient loading on Phyllospadix spp., a rocky intertidal seagrass, at local and regional scales. At sites along California, Washington, and Oregon, we demonstrated a significant, negative correlation of urban development and Phyllospadix bed thickness. These results were echoed locally along an urban gradient on the central California coast, where Phyllospadix shoot δ¹⁵N was negatively associated with Phyllospadix bed thickness, and experimentally, where nutrient additions in mesocosms reduced Phyllospadix shoot formation and increased epiphytic cover on Phyllospadix shoots. These findings provide evidence that coastal development can threaten rocky intertidal seagrasses through increased epiphytism. Considering that seagrasses provide vital ecosystem services, mitigating eutrophication and other factors associated with development in the rocky intertidal coastal zone should be a management priority.

Decontamination treatments to eliminate problem biota from macroalgal tank cultures of Osmundea pinnatifida, Palmaria palmata and Ulva lactuca

The effect of a range of chemical disinfectants at different concentration and exposure times was investigated on five macroalgal species and the marine gastropod Littorina spp. Palmaria palmata, Osmundea pinnatifida and Ulva lactuca are commercially valuable and are often cultivated in tanks for food or feed. Ectocarpus siliculosus and Ulva intestinalis are common epiphytes of P. palmata and O. pinnatifida cultures, whilst Littorina spp. are common herbivorous epibionts within U. lactuca culture tanks. These contaminants reduce the productivity and quality of the culture as a food. Differential tolerance to the treatments was seen between the algal species using pulse-amplitude modulation (PAM) chlorophyll a fluorescence, a few hours and a week following treatment. We identified treatments that selectively damaged the epiphyte but not the basiphyte species. Ectocarpus siliculosus had a significantly lower tolerance to 1 % sodium hypochlorite than P. palmata, and to 25 % methanol than O. pinnatifida, with a 1-5 min exposure appearing most suitable. Ulva intestinalis had a significantly lower tolerance than P. palmata and O. pinnatifida to many disinfectants: 0.1-1 % sodium hypochlorite for 10 min, 0.5 % potassium iodide for up to 10 min, and 0.25 % Kick-start (a commercial aquaculture disinfectant solution) for 1-5 min. No treatment was able to kill the gastropod snails without also damaging U. lactuca, although agitation in freshwater for an hr may cause them to detach from the basiphyte, with little to no photophysiological impact seen to U. lactuca. This experiment forms the basis for more extended commercial trials.

Differences in the Effect of Coal Pile Runoff (Low pH, High Metal Concentrations) Versus Natural Carolina Bay Water (Low pH, Low Metal Concentrations) on Plant Condition and Associated Bacterial Epiphytes of Salvinia minima

Numerous wetlands and streams have been impacted by acid mine drainage (AMD) resulting in lowered pH and increased levels of toxic heavy metals. Remediation of these contaminated sites requires knowledge on the response of microbial communities (especially epiphytic) and aquatic plants to these altered environmental conditions. We examined the effect of coal pile runoff waters as an example of AMD in contrast to natural water from Carolina Bays with low pH and levels of metals on Salvinia minima, a non-native, metal accumulating plant and associated epiphytic bacteria. Treatments included water from two Carolina Bays, one AMD basin and Hoagland's Solution at two pH levels (natural and adjusted to 5.0-5.5). Using controlled replicated microcosms (N = 64) we determined that the combination of low pH and high metal concentrations has a significant negative impact (p < 0.05) on plant condition and epiphytes. Solution metal concentrations dropped indicating removal from solution by S. minima in all microcosms.

Heavy metal accumulation in Pyrrosia flocculosa (D. Don) Ching growing in sites located along a vehicular disturbance gradient

Monitoring of environment is a key contemporary issue that has necessitated search for bio-indicators. The very fact that epiphytes do not have a direct contact with soil and absorb nutrients from the environment puts them among the best indicators of environmental conditions. We, therefore, selected Pyrrosia flocculosa (D. Don) Ching-an epiphytic fern that commonly occurs in the Himalaya for this study. The study focused on analyzing heavy metal concentrations in the fronds of P. flocculosa growing along a disturbance gradient. For this, three sites representing different levels of disturbance viz., least disturbed, moderately disturbed, and highly disturbed, were identified in Kangra district of Himachal Pradesh. From each site, fronds of P. flocculosa were collected, categorized into three growth stages (juvenile, young, and mature), and brought to the laboratory for analyses. After drying and powdering, the samples were analyzed for Pb, Cd, Fe, Ni, Cu, Mn, and Zn using atomic absorption spectrophotometer. The results obtained were statistically compared using the software package Statistica. As expected, concentration of the metals varied among the sites and also among the identified growth stages of the species. In general, concentration of the metals was in the order Fe (639.28 ± 81.63) > Ni (56.03 ± 4.97) > Mn (7.54 ± 0.69) > Zn (6.51 ± 0.36) > Cd (4.01 ± 0.86) > Cu (1.93 ± 0.74). Barring Mn, concentration of all the metals increased with disturbance and was positively correlated to it. However, except for Cd and Fe, none of the metals reported higher than threshold values. Effective monitoring of the environment can thus be done using P. flocculosa.

Biomechanical consequences of epiphytism in intertidal macroalgae

Epiphytic algae grow on other algae rather than hard substrata, perhaps circumventing competition for space in marine ecosystems. Aquatic epiphytes are widely thought to negatively affect host fitness; it is also possible that epiphytes benefit from associating with hosts. This study explored the biomechanical costs and benefits of the epiphytic association between the intertidal brown algal epiphyte Soranthera ulvoidea and its red algal host Odonthalia floccosa. Drag on epiphytized and unepiphytized hosts was measured in a recirculating water flume. A typical epiphyte load increased drag on hosts by ~50%, increasing dislodgment risk of epiphytized hosts compared with hosts that did not have epiphytes. However, epiphytes were more likely to dislodge from hosts than hosts were to dislodge from the substratum, suggesting that drag added by epiphytes may not be mechanically harmful to hosts if epiphytes break first. Concomitantly, epiphytes experienced reduced flow when attached to hosts, perhaps allowing them to grow larger or live in more wave-exposed areas. Biomechanical interactions between algal epiphytes and hosts are complex and not necessarily negative, which may partially explain the evolution and persistence of epiphytic relationships.

Guzmania panamensis (Bromeliaceae) - a new species from Talamanca Mountain in Veraguas province, Western Panama

Guzmania panamensis (Bromeliaceae), a new species so far endemic to Veraguas province, Western Panama, is described and illustrated. The new species is recognized due to its peduncle much longer than the leaves and its red floral bracts, shorter than the yellow flowers. The new species is compared to morphologically similar species, namely Guzmania monostachia, Guzmania berteroniana, Guzmania elvallensis, and Guzmania skotakii.

High gene flow in epiphytic ferns despite habitat loss and fragmentation

Tropical montane forests suffer from increasing fragmentation and replacement by other types of land-use such as coffee plantations. These processes are known to affect gene flow and genetic structure of plant populations. Epiphytes are particularly vulnerable because they depend on their supporting trees for their entire life-cycle. We compared population genetic structure and genetic diversity derived from AFLP markers of two epiphytic fern species differing in their ability to colonize secondary habitats. One species, Pleopeltis crassinervata, is a successful colonizer of shade trees and isolated trees whereas the other species, Polypodium rhodopleuron, is restricted to forests with anthropogenic separation leading to significant isolation between populations. By far most genetic variation was distributed within rather than among populations in both species, and a genetic admixture analysis did not reveal any clustering. Gene flow exceeded by far the benchmark of one migrant per generation to prevent genetic divergence between populations in both species. Though populations are threatened by habitat loss, long-distance dispersal is likely to support gene flow even between distant populations, which efficiently delays genetic isolation. Consequently, populations may rather be threatened by ecological consequences of habitat loss and fragmentation.

The effects of a rust infection on fitness components in a natural population of Tolumnia variegata (Orchidaceae)

The effects of a rust infection (Sphenosphora saphena, Basidiomycetes) on several fitness components of the orchid Tolumnia (Oncidium) variegata were quantified in a subtropical moist forest of Puerto Rico. Infected and uninfected plants of two size categories were observed and manipulated by increasing natural levels of fruit production to determine the effects of infection on short and long-term sexual reproduction, subsequent vegetative and reproductive growth, and mortality. Under artificially high levels of fruit production, infection had no effect on short or long-term reproduction through male or female function except for a modest decline in seed viability in small plants. Under natural levels of fruit production, infection was only related to a reduction in the number of leaves per shoot. At artificially high levels of fruit production, infection reduced leaf length, leaf width, and the number of live shoots. Survival was not associated with rust occurrence. The rust appears to have minor ecological impact on this orchid population.