EPIPHYTES ON CLADOPHORA GLOMERATA IN THE GREAT LAKES AND ST. LAWRENCE SEAWAY WITH PARTICULAR REFERENCE TO THE RED ALGA CHROODACTYLON RAMOSUM (= ASTEROCYTIS SMARGDINA)1

The range of Cladophora glomerata² along the east and north shorelines of the Great Lakes and St. Lawrence Seaway extends form just east of Montreal to Thunder Bay on Lake Superior. However, it does not occur at sites sampled in Georgian Bay, the North Channel or eastern Lake Superior. The dominant epiphytes on Cladophora throughout this range are the blue-green algae, particularly Lyngbya diguetii, L. epiphytica and Chamaesiphon incrustans, which account for 53 to 90% of the cell density. The diatoms Cocconeis pediculus and Rhoicosphenia curvata contribute to much of the remaining density. The red alga Chroodactylon ramosum is a minor component of Cladophora epiphyton but is widespread in Lakes Ontario, Erie and Huron. Filament morphology, cell diameters and lengths of Chroodactylon are quite similar to those of marine forms. In addition, this alga has been reported to be quite tolerant of a wide range of salinities. Chroodactylon has been found in 33 freshwater sites throughout North America and 30 of these are from the Great Lakes or its drainage basin. Therefore, it appears possible that Chroodactylon, like Bangia atropurpurea, has originated in the Great Lakes by a migration from the Atlantic Ocean.     

Seasonal changes in the epiphyte community of natural and artificial macrophytes in Lake Memphremagog (Que. & Vt.)

Seasonal changes in the epiphyte biomass, measured both as chlorophyll a and as cell volume, and species composition were compared on Potamogeton richardsonii and on a similar plastic plant grown together in a shallow bay of Lake Memphremagog (46°06'N, 72°16W). Both substrates exhibited two periods of high biomass during the June to September growing season; one in June, when the community was dominated by loosely attached species with a strong planktonic component (up to 37%), and one in September, when the epiphytes were characterized by species tightly attached to the leaves. Although this seasonal trend was similar, the loosely and tightly attached communities were best developed on the natural and artificial plants, respectively. The diversity of the epiphytes was significantly higher on the natural than on the artificial leaves from July on. Both the diversity differences and differences in community structure appear to be the result of the summer accumulation of CaCO₃ observed only on the upper leaf surfaces of the natural plants. Consequently, P. richardsonii appears to affect epiphyte development largely by its precipitation of CaCO₃, with no evidence for either direct inhibition or stimulation of the epiphytes by the natural plants. The reduced epiphyte biomass on growing tips was no different from that on artificial plants of the same age and exposure and is attributable to an insufficient time for colonization rather than to inhibition by the macrophyte.Contribution No. 8, Lake Memphremagog Project, Limnology Research Group     

Effect of canopy position on germination and seedling survival of epiphytic bromeliads in a Mexican humid montane forest

BACKGROUND AND AIMS: Seeds of epiphytes must land on branches with suitable substrates and microclimates to germinate and for the resulting seedlings to survive. It is important to understand the fate of seeds and seedlings in order to model populations, but this is often neglected when only established plants are included in analyses. METHODS: The seeds of five bromeliad species were exposed to different canopy positions in a Mexican montane forest, and germination and early seedling survival were recorded. Additionally, the survival of naturally dispersed seedlings was monitored in a census over 2.5 years. Survival analysis, a procedure rarely used in plant ecology, was used to study the influence of branch characteristics and light on germination and seedling survival in natural and experimental populations. KEY RESULTS: Experimental germination percentages ranged from 7.2 % in Tillandsia deppeana to 33.7 % in T. juncea, but the seeds of T. multicaulis largely failed to germinate. Twenty months after exposure between 3.5 and 9.4 % of the seedlings were still alive. There was no evidence that canopy position affected the probability of germination, but time to germination was shorter in less exposed canopy positions indicating that higher humidity accelerates germination. More experimental seedlings survived when canopy openness was high, whereas survival in census-seedlings was influenced by moss cover. While mortality decreased steadily with age in juveniles of the atmospheric Tillandsia, in the more mesomorphic Catopsis sessiliflora mortality increased dramatically in the dry season. CONCLUSIONS: Seedling mortality, rather than the failure to germinate, accounts for the differential distribution of epiphytes within the canopy studied. With few safe sites to germinate and high seedling mortality, changes of local climate may affect epiphyte populations primarily through their seedling stage.     

Endophytic diversity of hanging velamen roots in the epiphytic orchid Acampe praemorsa

ABSTRACT

Background

The ecological functions of the aerial hanging roots (velamen roots) in orchids are not yet fully understood.     

THE RED ALGAL EPIPHYTES MICROCLADIA COULTERI AND M. CALIFORNICA (RHODOPHYCEAE,CERAMIACEAE). II. BASIPHYTE SPECIFICITY1

The phenomenon of basiphyte specificity in the settlement and growth of the red algal epiphytes Microcladia californica Farl. and M. coulteri Harv. was examined by studying the interface with their respective basiphytes and by cross-inoculation experiments. Microcladia californica attaches only to the surface of its single basiphyte Egregia menziesii (Aresch.) Turn. whereas M. coulteri penetrates the tissue of a wide range of basiphytes. The pattern of primary rhizoid development in both epiphytes determines the mode of attachment and may influence the range of basiphytes possible for each epiphyte. Cross-inoculation experiments show that Microcladia californica is not able to colonize the basiphytes of M. coulteri, Iridaea and Prionitis, or Ulva. The mechanisms by which these algae restrict the growth of epiphytes include short life-span, “cuticle peeling” and chemical defense. Microcladia coulteri, which naturally colonizes Iridaea and Prionitis, has evolved mechanisms to counteract the antifouling effects of those basiphytes. The question of why Egregia is the exclusive substratum for M. californica remains undetermined. However, Egregia may provide the appropriate ecological conditions and a surface topography conductive to M. californica spore settlement and growth.     

Differential expression of genes of Pseudomonas syringae on leaves and in culture evaluated with random genomic lux fusions

Differential expression of genes of Pseudomonas syringae strain B728a on plants and in culture was assessed by measuring light production by a large collection of mutant strains containing random genomic insertions of a promoterless lux operon. Reporter gene fusions were made using Tn4431 containing lux CDABE from Vibrio fisheri. Light production reproducibly increased seven-fold when n-decanal was added to cells harvested from plant surfaces, to over 800-fold when added to cells cultured on a solidified culture medium, thus increasing the sensitivity of this reporter gene system. One of the 173 mutants tested exhibited significantly higher light production on plants than on solidified culture media compared to other mutants, while one lux fusion-containing strain produced significantly more light on culture media than on plants relative to the other mutants. The plant-inducible genes identified were not required for pathogenicity of this strain. Approximately 2% of the genes of P. syringae are apparently transcribed more actively in cells growing epiphytically on plants than in common culture media indicating that bacterial cells on plants may have substantially different behaviours than that of cultured cells.     

A decline of melanism in the peppered moth Biston betularia in The Netherlands

Melanic forms of the peppered moth Biston betularia were well established in The Netherlands by the end of the 19th century, indeed the first records of the black carbonaria form in 1867 are only about 20 years later than in England. Analysis of extensive sampling data collected by B. J. Lempke for a period of several years beginning in 1969 shows that carbonaria was at a frequency of about 60 to 70% in most of the country where epiphyte communities on trees were reduced due to the effects of air pollution. The pale typica and the three intermediate insularia forms were each at similar, low frequencies. Only in the extreme north and south-east of The Netherlands where epiphyte floras were richer was carbonaria at a lower frequency of less than 40%. Samples collected from seven localities in 1988 show that carbonaria has dramatically declined to a frequency of less than 10%. In contrast to England, the fully black form is being replaced not only by typica but also by the darkest of the insularia phenotypes. The decline in melanism coincides with a period of decreasing levels of sulphur dioxide and of increasing species diversity of lichens on trees.     

Advances in ecological studies of epiphytes using canopy cranes

Forest canopies are one of the most species-rich habitats, but among the least explored in the biosphere. They play a crucial role in the process of material and energy exchange between the forest and atmosphere. Individual ecosystem members (e.g., epiphytes) and the ecological function of canopies have been given insufficient attention because of inaccessibility. Canopy cranes have been successfully used to guarantee non-destructive and reiterated sampling of epiphytes, thus offering a top-down perspective of the entire canopy. These cranes have become the symbol of canopy research and enable epiphyte research. Globally, western developed countries have conducted many studies of diversity and spatial distributions of epiphytes using canopy cranes, thus accumulating an abundance of valuable results. This review summarizes the structure, development history, and distribution of canopy cranes as well as general information about international canopy research organizations. Ecological studies of epiphytes performed around the world using these canopy cranes are also reviewed. Additionally, the development of canopy ecology and the construction of canopy cranes in China are introduced briefly. In analyzing current research trends in ecological studies of epiphytes in China and globally, the following aspects were considered: biodiversity, spatial patterns and maintenance mechanisms, ecological adaptations of epiphytes, their relationship with canopy animals, and their responses to climate change.     

Photosynthetic Capacity Increases with Plant Size

The photosynthetic capacity of mature leaves of the epiphytic orchid, Dimerandra emarginata, was studied in plants of different size. There was a linear increase of both area-based and dry weight-based rates of O₂-evolution with size by more than 100% from the smallest (1 cm tall) to the largest (50 cm tall) individual. Similar size-related changes were observed in the leaf nitrogen content but not in the chlorophyll content. The results are discussed in the context of the optimal partitioning theory.