Variation in Nickel Content in the Nickel-Hyperaccumulating Shrub Psychotria douarrei (Rubiaceae) from New Caledonia1

Plants that hyperaccumulate Ni contain > 1000 ppm (dry wt.) in their tissues. Variation of Ni content within hyperaccumulating plant species is poorly explored. Using the Ni-hyperaccumulating shrub Psychotria douarrei, we documented variation of leaf Ni levels within individual shrubs, and variation with respect to plant size and leaf age. Plant size did not correlate significantly with leaf Ni content, and leaf Ni content did not correlate significantly with soil Ni content. Older leaves contained twice as much Ni as younger leaves. Older leaves also contained greater concentrations of Ca, Fe, and Cr but less K, P, and Cu. Five elements (Zn, Pb, Co, Mn, Mg) showed no significant variation due to leaf age. We also examined the effect of leaf age on epiphyll cover, finding increased epiphyll cover on the upper surface of older leaves. The dominant leafy liverwort epiphyll had a relatively high Ni content (400 ppm), suggesting that epiphylls of Ni hyperaccumulators obtain some Ni from host leaves. Individual shrubs differed in mean leaf Ni content almost two-fold (14,900-27,700 ppm). Variation among branches within individuals also ranged widely; however, this intraplant variability was not strongly correlated with the mean leaf Ni content of an individual shrub. We concluded that Ni contents in leaves of P. douarrei vary considerably due to leaf age, among individual shrubs, and among branches within a shrub.     

CHEMICAL MEDIATION OF COLONIZATION OF SEAWEED SURFACES1

The surfaces of macroalgal thalli are colonized by planktonic propagules (larvae, spores, cells, etc.) from a wide diversity of eukaryotes and prokaryotes. Colonization (here defined broadly to include processes such as settlement, attachment, metamorphosis, biofilm formation, and infection) of seaweed surfaces can be both induced and inhibited by metabolites produced at those surfaces. However, detailed examples of chemically mediated interactions at seaweed surfaces for which chemical cues have been characterized, quantified in situ, a biological effect determined, and the consequences to the demography of the seaweeds or colonizers demonstrated are very rare. Here we briefly review the literature on both deterrents (“natural antifoulants”) and inducers of colonization and on interactions at seaweed surfaces between the hosts and associated bacterial biofilms. One theme that emerges is the strong need to integrate ecology, cell biology, and chemistry to understand the distribution of surface‐active molecules in situ and their ecological consequences. This multidisciplinary approach is further emphasized for research on biofilms on seaweeds, where recently developed molecular tools for characterizing bacterial communities are opening up an entire new area of marine chemical ecology. Finally, we emphasize an integrated approach to the topic, as we believe that many aspects of somewhat disparate fields including, for example, induction of larval settlement, algal pathogenesis, and the molecular biology of bacterial signaling can be usefully viewed within the overall framework of chemical mediation of surface colonization.     

Ecophysiology in Relation to Exposure of Pendant Epiphytic Bryophytes in the Canopy of a Tropical Montane Oak Forest1

We investigated ecophysiological and morphological traits affecting light and water use of four commercially important pendant epiphytic bryophyte species in a montane oak‐bamboo forest in Costa Rica. Predictions based mostly on ecophysiological studies of temperate bryophytes and vascular plants were experimentally tested on tropical montane bryophyte species ranked on the basis of their distributions in the canopy from the most protected (1) to the most exposed sites (4): (1) Phyllogonium viscosum; (2) Pilotrichella flexilis; (3) Dendropogonella rufescens; and (4) Frullania convoluta. As predicted, highly exposed species tended to have higher light saturation and compensation points, higher dark respiration rates, more chlorophyll, higher chlorophyll a:b ratios, and higher nitrogen concentrations. Contrary to predicted trends, exposed‐site species had lower water contents at full saturation; there were no detectable differences among species in the rate of water loss. Rates of carbon gain in all species reached asymptotes with increasing water content, but the moisture compensation point for carbon uptake of the moss D. rufescens was substantially higher than in the other species. Observed patterns result from interactions among processes related to water storage and transport operating at different scales and are determined by various morphological traits including the density, size, and disposition of phylloids, as well as by whole‐clump architecture.     

The epiphyte vegetation of Annona glabra on Barro Colorado Island, Panama

Aim Information on the community composition, structure, and dynamics of epiphyte vegetation is scarce. A survey of the epiphytes occurring on all individuals of one particular host tree species in a well-studied neotropical research site allowed us a comparison of the epiphyte flora of this tree with the local epiphyte flora, the analysis of spatial distribution patterns and the use of these patterns as indications for changes in time. In the future, our results can be used as a baseline data-set for the direct observation of the long-term dynamics in epiphyte communities. Location The study was conducted on Barro Colorado Island (BCI), Panama. Methods We recorded all individuals of the vascular epiphytes growing on Annona glabra L., a flood-tolerant, multiple-stemmed tree, which is restricted to the shoreline of BCI. Data on tree biometrics, epiphyte species, and epiphyte abundances were collected for more than 1200 trees. Results In total, we encountered almost 15,000 epiphytic individuals in sixty-eight species, corresponding to more than one third of the entire epiphyte flora of Barro Colorado Island. The component species differed strongly in abundance: the four most important species accounted for >75% of all individuals. In most cases, the same four species were also the first to colonize a tree (=phorophyte). Colonization patterns indicated no replacement of early colonizers by late arrivals. Species richness and epiphyte abundances showed a positive correlation with the size and the density of the host trees. All species showed a highly clumped distribution and the physiognomy of epiphyte communities of individual trees was dominated either by one or several of the four most common species or by a set of frequently co-occurring tank bromeliads. Other species were dominant only in exceptional cases. Most species were always rare. A distance effect on community composition was mostly confined to a local scale with an increased similarity in the species assemblage of stems of a tree v. neighbouring trees. Main conclusions The epiphytes on a single small phorophyte species may encompass a surprisingly large proportion of the local epiphyte flora. The observations that most tree crowns are inhabited by a single or only very few species, and that all epiphyte species show highly clumped distributions suggest a predominance of very local dispersal within a tree crown, which is only infrequently interrupted by successful long-distance dispersal between crowns.     

西双版纳热带森林附生维管植物的物种多样性与区系特征

附生植物是山地森林生态系统中重要的结构性成分。因受林冠调查技术限制, 人们对林冠附生植物知之甚少。本文在前人有关西双版纳植物区系研究的基础上, 结合野外调查和标本资料, 对该地区附生植物的物种组成与分布进行了整理。结果表明, 西双版纳热带森林附生维管植物共有29科134属486种, 约占全部维管植物的11%。附生兰科是最丰富的类群(69属293种), 其中以石斛属(Dendrobium) (49种)和石豆兰属(Bulbophyllum) (48种)物种数最多。蕨类是仅次于兰科的附生类群(13科38属97种), 其中水龙骨科(51种)占附生蕨类总数的50%以上。基于生活史和养分来源的划分标准, 该地区48%的附生物种属于兼性附生, 其次是以兰科为主的专性附生(46%), 半附生仅占6%。从区系上看, 西双版纳附生植物属的分布具有明显的热带亚洲性质。附生植物主要分布于资源受限的林冠生境, 对环境变化极为敏感, 在人为干扰日益加剧的背景下, 这类植物正面临严重威胁。因此, 需要加强对西双版纳林冠亚系统的保护。     

Species richness in macroalgae and macrofauna assemblages on Fucus serratus L. (Phaeophyceae) and Zostera marina L. (Angiospermae) in Skagerrak, Norway

The macrophytes Fucus serratus and Zostera marina form similar substrates for associated flora and fauna in shallow waters in Norway. While F. serratus forms a more or less continuous belt on rocky substrate along the coast, Z. marina forms disjunct populations on sandy or muddy bottoms. This study focused on the organisms associated with these two macrophytes in two localities in the Skagerrak region. In total, 130 taxa of epiphytic organisms were identified: 22 green algae, 41 red algae, 32 brown algae, eight diatoms and 27 sessile animals. One hundred and twenty-seven taxa of mobile macrofauna were registered. The dominant group was crustaceans, with amphipods as the order containing most species. Many species of both plants and animals preferred one or the other habitat. It is concluded that coastal macrophyte systems have high species diversity.     

Lichenological evidence for the recognition of inland rain forests in western North America

Aim The coastal temperate rain forests of north‐western North America are internationally renowned as the archetypal expression of the temperate rain forest biome. Less well documented is the existence of somewhat similar forests 500–700 km inland on the windward slopes of the Columbia and Rocky Mountains. Here we attempt to show that these inland ‘wetbelt’ forests warrant rain forest status. Location North‐western North America. Methods We use tree‐dwelling macrolichens to assess the degree of environmental congruence between the coastal temperate rain forests and their inland counterparts. Results We report three key findings: (1) 40% of oceanic, epiphytic macrolichens found in Pacific coastal rain forests occur also in inland regions; (2) epiphytic species richness decreases with decreasing latitude, such that roughly 70% of disjunct oceanic species are restricted to regions north of 51° N; and (3) the southward decline in lichen diversity is correlated with a parallel decrease in summer precipitation, but not with mean annual precipitation. Main conclusions These observations are consistent with the recognition of an inland rain forest formation between 50 and 54° N. Inland rain forests represent a small, biologically significant ecosystem whose continued fragmentation and conversion to tree plantations warrant close scrutiny.     

NUTRIENT EFFECTS ON SEAGRASS EPIPHYTE COMMUNITY STRUCTURE IN FLORIDA BAY1

A field experiment was employed in Florida Bay investigating the response of seagrass epiphyte communities to nitrogen (N) and phosphorus (P) additions. While most of the variability in epiphyte community structure was related to uncontrolled temporal and spatial environmental heterogeneity, P additions increased the relative abundance of the red algae–cyanobacterial complex and green algae, with a concomitant decrease in diatoms. When N was added along with P, the observed changes to the diatoms and the red algae–cyanobacterial complex were in the same direction as P‐only treatments, but the responses were decreased in magnitude. Within the diatom community, species relative abundances, species richness, and diversity responded weakly to nutrient addition. P additions produced changes in diatom community structure that were limited to summer and were stronger in eastern Florida Bay than in the western bay. These changes were consistent with well‐established temporal and spatial patterns of P limitation. Despite the significant change in community structure resulting from P addition, diatom communities from the same site and time, regardless of nutrient treatment, remained more similar to one another than to the diatom communities subject to identical nutrient treatments from different sites and times. Overall, epiphyte communities exhibited responses to P addition that were most evident at the division level.     

Local and landscape drivers of arthropod diversity and decomposition processes in oil palm leaf axils

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Fine partitioning of epiphyte habitat within Johansson zones in tropical Australian rain forest trees

For over three decades, the Johansson zones have been widely used in epiphyte studies as a way of stratifying the host tree into habitat zones. The usefulness of this system, however, has been questioned. We test the effectiveness of the Johansson zones by grouping epiphyte species by the substrate and microclimatic attributes of their individual occurrences and assessing the fidelity of these groups to the Johansson zones. Habitat characteristics were recorded for every individual epiphyte on 30 trees in the lower montane rain forests of northeastern Australia. Twenty‐four epiphyte species were agglomerated into four groups using Ward's method. Group 4 was highly distinct and included shade‐loving species and nomadic vines from the lower zones of the host trees. Group 3 contained species from the most exposed habitats. Group 1 had higher light levels and lower substrate thickness than Group 2, yet both groups had close to identical distributions over the Johansson zones. This suggests that groups of epiphyte species may utilize different micro‐sites within the same zone. While the Johansson zones are a useful tool in epiphyte studies, finer partitioning of habitat within the host tree may be missed.