Vascular epiphytes in the temperate zones-a review

Vascular epiphytes are typically associated with tropical rainforests, whereas their occurrence in temperate forests is little appreciated. This review summarises the available information on epiphytism in the temperate zones (> 23.5 latitude), which has not been reviewed omprehensively for more than a century, and critically analyses the proposed mechanisms behind the observed biogeographical patterns. Although in the temperate zone epiphytic vascular plants are rarely as impressive as in tropical forests, there are noteworthy exceptions. Temperate rain forests of Chile and New Zealand, or montane forests in the Himalayas are comparable to many tropical forests in terms of epiphyte biomass and diversity, but differ in their taxonomic spectrum temperate epiphyte communities are generally dominated by ferns and fern-allies. Other temperate areas are not, however, necessarily barren of epiphytes, as repeatedly implied. Quite in contrast, local populations of epiphytes in a large number of other non-tropical areas in both the southern and the northern hemisphere can be quite conspicuous. The proposed reasons for the latitudinal gradients in epiphyte abundance and diversity (water scarcity or low tempera-tures). are not fully convincing and, moreover, still await experimental verification. Other factors, both historical (e.g., Pleistocene extinctions) and ecological (e.g., prevalence of conifers in the northern hemisphere), should also be taken into consideration to obtain a comprehensive explanation of the extant global distribution of vascular epiphyte

How prevalent is crassulacean acid metabolism among vascular epiphytes?

The occurrence of crassulacean acid metabolism (CAM) in the epiphyte community of a lowland forest of the Atlantic slope of Panama was investigated. I hypothesized that CAM is mostly found in orchids, of which many species are relatively small and/or rare. Thus, the relative proportion of species with CAM should not be a good indicator for the prevalence of this photosynthetic pathway in a community when expressed on an individual or a biomass basis. In 0.4ha of forest, 103species of vascular epiphytes with 13,099individuals were found. As judged from the C isotope ratios and the absence of Kranz anatomy, CAM was detected in 20 species (19.4% of the total), which were members of the families Orchidaceae, Bromeliaceae, and Cactaceae. As predicted, the contribution of CAM epiphytes to the total number of individuals and to total biomass (69.6kg ha-1) was considerably lower (3.6% or 466 individuals and, respectively, 3.0% or 2.1kg ha-1

Neither Host-specific nor Random: Vascular Epiphytes on Three Tree Species in a Panamanian Lowland Forest

• Background and Aims A possible role of host tree identity in the structuring of vascular epiphyte communities has attracted scientific attention for decades. Specifically, it has been suggested that each host tree species has a specific subset of the local species pool according to its own set of properties, e.g. physicochemical characteristics of the bark, tree architecture, or leaf phenology patterns. • Methods A novel, quantitative approach to this question is presented, taking advantage of a complete census of the vascular epiphyte community in 0·4 ha of undisturbed lowland forest in Panama. For three locally common host-tree species (Socratea exorrhiza, Marila laxiflora, Perebea xanthochyma) null models were created of the expected epiphyte assemblages assuming that epiphyte colonization reflected random distribution of epiphytes in the forest. • Key Results In all three tree species, abundances of the majority of epiphyte species (69-81 %) were indistinguishable from random, while the remaining species were about equally over- or under-represented compared with their occurrence in the entire forest plot. Permutations based on the number of colonized trees (reflecting observed spatial patchiness) yielded similar results. Finally, a third analysis (canonical correspondence analysis) also confirmed host-specific differences in epiphyte assemblages. In spite of pronounced preferences of some epiphytes for particular host trees, no epiphyte species was restricted to a single host. • Conclusions The epiphytes on a given tree species are not simply a random sample of the local species pool, but there are no indications of host specificity eithe

Changes in Carbohydrate and Nutrient Contents Throughout a Reproductive Cycle Indicate that Phosphorus is a Limiting Nutrient in the Epiphytic Bromeliad, Werauhia sanguinolenta

• Background and Aims This study examined the physiological basis of the cost of reproduction in the epiphytic bromeliad Werauhia sanguinolenta, growing in situ in a tropical lowland forest in Panama. • Methods Entire mature plants were sampled repeatedly over the course of 2 years, which represents the common interval between reproductive events. Due to the uncertainty concerning the appropriate currency of resource allocation to reproduction, the temporal changes of the contents of total non-structural carbohydrates (TNC) and of all major nutrient elements in different plant parts were studied (stems, green leaves, non-green leaf bases, roots and reproductive structures when present). • Key Results Although TNC varied with time in all compartments, this variation was more related to seasonal fluctuations than to reproductive status. The contents of the nutrient elements, N, P, K, Mg and S, on the other hand, showed significant differences between reproductive and non-reproductive individuals, while Ca did not change with reproductive status. Differences in nutrient contents were most pronounced in stems. Seeds were particularly enriched in P, much less so in N and the other nutrient elements. Model calculations of nutrient fluxes indicate that a plant needs about 2 years to accumulate the amount of P invested in a fruit crop, while the estimated uptake rates for N were much faster. • Conclusions Since most mature individuals of this species fruit every other year, it is hypothesized that P is the prime limiting factor for reproduction. These findings therefore add to an increasing body of evidence that P rather than N is limiting growth and reproduction in vascular epiphyte

Getting a Grip on the Adhesion Mechanism of Epiphytic Orchids – Evidence From Histology and Cryo-Scanning Electron Microscopy

Plants and animals evolve different attachment structures and strategies for reversible or permanent adhesion to different substrate types. For vascular epiphytes, having the ability to permanently attach to their host plants is essential for establishment and survival. Unlike mistletoe roots, roots of vascular epiphytes do not penetrate the host tissues but instead achieve attachment by growing in close contact to the surface of the substrate. However, the fundamental understanding of the attachment functions of epiphytic roots remains scarce, where majority of studies focused on the general root morphology, their functional properties and the descriptions of associated microbial endophytes. To date, research on attachment strategies in plants is almost entirely limited to climbers. Therefore, this study aims to fill the knowledge gap and elucidate the attachment functions of roots of epiphytic orchids. With the use of histology and high-resolution cryo-scanning electron microscopy (cryo-SEM) technique with freeze fracturing, the intimate root-bark substrate interface of epiphytic orchid Epidendrum nocturnum Jacq was investigated. Results showed a flattened underside of the root upon contact with the substrate surface, and the velamen layer appeared to behave like a soft foam, closely following the contours of the substrate. Root hairs emerged from the outermost velamen layer and entered into the crevices in the substrate, whenever possible

A Simulation Study on the Importance of Size‐related Changes in Leaf Morphology and Physiology for Carbon Gain in an Epiphytic Bromeliad

This study addresses the question of how size‐related changes in leaf morphology and physiology influence light absorption and carbon gain of the epiphytic bromeliad Vriesea sanguinolenta. A geometrically based computer model, Y‐plant, was used for the three‐dimensional reconstruction of entire plants and for calculation of whole plant light interception and carbon gain. Plants of different sizes were reconstructed, and morphological and physiological attributes of young and old leaves, and small and large plants were combined to examine the individual effects of each factor on light absorption and carbon gain of the plant. The influence of phyllotaxis on light absorption was also explored. Departure of measured divergence angles between successive leaves from the ideal 137·5° slightly decreased light absorption. The only morphological parameter that consistently changed with plant size was leaf shape: larger plants produced more slender foliage, which substantially reduced self‐shading. Nevertheless, self‐shading increased with plant size. While the maximum rate of net CO2 uptake of leaves increased linearly with plant size by a factor of two from the smallest to the largest individual, the potential plant carbon gain (based on total foliage area) showed a curvilinear relationship, but with similar numerical variation. We conclude that leaf physiology has a greater impact on plant carbon gain than leaf and plant morphology in this epiphytic bromelia

Seedling stability in waterlogged sediments: an experiment with saltmarsh plants

Saltmarsh seedlings are exposed to extreme soil conditions in combination with mechanical disturbance by waves and tides, especially at the seaward fringe. We tested whether soil waterlogging affects resistance of seedlings to physical disturbance, thereby potentially influencing the distribution of saltmarsh species. A mesocosm experiment was conducted to investigate effects of waterlogging on plant traits, in particular root growth, and tolerance of seedlings to sediment erosion. Three species, each dominating different elevations in NW European salt marshes (Salicornia europaea, Atriplex portulacoides and Elytrigia atherica), were selected for the experiments. Individual seedlings were grown under different waterlogging treatments and finally subjected to an erosion treatment. The depth of erosion at which the seedlings toppled (Ecrit) was determined and related to above- and below-ground morphological traits of the seedlings. Resistance to erosion decreased in all 3 species from drained to completely waterlogged soil conditions, with the strongest negative impact of waterlogging on the upper marsh species E. atherica. Root length and biomass, shoot biomass and the root:shoot biomass ratio were the most important traits positively affecting Ecrit. The experiment demonstrates that rapid root growth is essential for the stability of seedlings, and is presumably of great importance for their successful establishment on tidal flats where sediment erosion may be a limiting factor. Root growth is in turn affected by a species-specific response to waterlogging. Our study suggests that this species-specific effect of waterlogging on seedling stability contributes to species sorting along the inundation gradient of coastal ecosystems

Holding on or falling off: The attachment mechanism of epiphytic Anthurium obtusum changes with substrate roughness

Premise For vascular epiphytes, secure attachment to their hosts is vital for survival. Yet studies detailing the adhesion mechanism of epiphytes to their substrate are scarce. Examination of the root hair-substrate interface is essential to understand the attachment mechanism of epiphytes to their substrate. This study also investigated how substrate microroughness relates to the root-substrate attachment strength and the underlying mechanism(s). Methods Seeds of Anthurium obtusum were germinated, and seedlings were transferred onto substrates made of epoxy resin with different defined roughness. After 2 months of growth, roots that adhered to the resin tiles were subjected to anchorage tests, and root hair morphology at different roughness levels was analyzed using light and cryo scanning electron microscopy. Results The highest maximum peeling force was recorded on the smooth surface (glass replica, 0 µm). Maximum peeling force was significantly higher on fine roughness (0, 0.3, 12 µm) than on coarse (162 µm). Root hair morphology varied according to the roughness of the substrate. On smoother surfaces, root hairs were flattened to achieve large surface contact with the substrate. Attachment was mainly by adhesion with the presence of a glue-like substance. On coarser surfaces, root hairs were tubular and conformed to spaces between the asperities on the surface. Attachment was mainly via mechanical interlocking of root hairs and substrate. Conclusions This study demonstrates for the first time that the attachment mechanism of epiphytes varies depending on substrate microtopography, which is important for understanding epiphyte attachment on natural substrates varying in roughness

Modeling community assembly on growing habitat “islands”: a case study on trees and their vascular epiphyte communities

The number of available sites for establishment is a key determinant of species richness on habitat islands. While most theoretical studies assume habitat size or capacity to be constant, many natural habitats are characterized by dynamic growth in capacity over ecological timescales. A case in point is provided by trees that serve as habitat for vascular and non-vascular epiphytes. Here, we develop a modeling framework, based on neutral theory, to address the effects of habitat growth on community development, i.e., species richness and abundance. The model is parameterized to the situation of vascular epiphyte communities in tropical lowland forests and includes stochastic reproduction, death, and immigration events from a larger metacommunity. Using numerical simulations, we explore the proportion of growing sites occupied by individuals, the number of empty unoccupied sites, as well as changes in species abundances, species richness, colonization and extinction rates, and the dependence on the abundance in the metacommunity throughout the growth of the habitat. Our analysis suggests two characteristic phases of community development in a growing habitat: (i) an initial phase, characterized by a rapid buildup of empty sites, a slow increase in species abundance, and a fast increase in species richness, and (ii) a second phase, in which the number of empty sites reaches an equilibrium, species richness is accumulating very slowly, while the number of individuals increases unabatedly with habitat capacity