The Canopy Starts at 0.5 m: Predatory Mites (Acari: Mesostigmata) Differ between Rain Forest Floor Soil and Suspended Soil at any Height

Suspended soils in forest canopies are thought to harbor a substantial fraction of canopy biomass and many arboreal specialists, but do forest floor generalist predators with high vagility also use this habitat? We tested the hypothesis of no difference between forest floor and suspended-soil predatory mite faunas (Acari: Mesostigmata) in an Australian rain forest. Our results show that instead of being habitat generalists, many predatory mites partition soil into two main strata: soil suspended aboveground irrespective of height (0.5–20 m) and soil on the ground. Of 53 species of Mesostigmata in suspended soil, 53 percent (28 species) were absent from or rarely found on the ground. This increased to 60 percent (15/25 species) if only common species are considered. Among these 15 ‘suspended-soil specialists’, all but the three least abundant were found throughout the arboreal strata. Moreover, ten species also occurred in litter accumulated on the surface of decaying logs or boulders close to the forest floor. Thus, although the arboreal predatory mite fauna is distinct from that on the forest floor, it is not restricted to the high canopy: even slightly elevated substrate appears acceptable as habitat for these suspended-soil specialists. Our data suggest that a substantial portion of a rain forest's soil and litter fauna is held above the forest floor.     

Comparative ecophysiology of CAM and C3 bromeliads. II. Field measurements of gas exchange of CAM bromeliads in the humid tropics

Abstract The results described represent the first detailed measurements of gas exchange of epiphytic plants with crassulacean acid metabolism (CAM) in the humid tropics. A portable steady-state CO₂ and H₂O porometer was used to measure net exchange rates of CO₂ and H₂O vapour (J_CO2, J_H2O), leaf temperature (T₁), air temperature (T_A), air relative humidity (RH) and photosynthetically active radiation (PAR) for bromeliads in the field during the dry season in February and March 1983 on the tropical island of Trinidad. Different lengths of tubing (up to 25 m) were used so that the gas exchange could be measured of bromeliads in situ in their epiphytic habitats. Derived parameters such as leaf-air water-vapour-concentration difference (Δ_w), water-vapour conductance of leaves (g) and internal CO₂ partial pressure (pⁱ_CO2) could be calculated. The particular problems of making such measurements in the humid tropics due to high relative humidities and high dew-point temperatures are discussed. The long and often broad, strap-like leaves of bromeliads are well suited for measurements with the steady-state porometer. It is shown that CAM activity varies along the length of individual leaves, and variability between different leaves is also demonstrated. The major phases of CAM, i.e. nocturnal stomalal opening, CO₂ uptake and dark fixation as malic acid (Phase I), daytime stomatal closure and light-dependent assimilation of CO₂ derived from decarboxylation of the malic acid (Phase III), and late-afternoon stomatal opening with direct light-dependent assimilation of atmospheric CO₂ (Phase IV) were all clearly shown by CAM bromeliads in situ. Their expression and magnitude depended on the environmental conditions. An early-morning peak of CO₂ uptake as is characteristic of Phase II of CAM was not detected during the night-day transition. A bromeliad intermediate between C₃ and CAM, Guzmania monostachia, showed substantial net CO₂ uptake in the early morning but no net uptake integrated over the whole of the night.     

Protozoan communities in chalk streams

This study assessed the individual effects of three mayflies (Paraleptophlebia sp., Ephemerella subvaria McDunnough and Epeorus sp.) and one caddisfly (Psilotreta sp.) on periphyton communities associated with clay tiles and leaves. Algal densities were estimated for leaf discs and tiles from experimental chambers (with individual grazers) and control chambers (i.e., no grazers). Scanning electron micrographs (SEM) of leaf discs and tiles also were taken for all mayfly grazing experiments. Densities of algae on leaf discs were two to five times lower than on tiles. Mouthpart morphology influenced how different insects grazed the periphyton community. Paraleptophlebia had typical collector-gatherer mouthparts and had no effect on diatom densities associated with leaves whereas diatom densities on grazed tiles were higher than densities on tiles from control chambers. Epeorus had brusher mouthparts and had little impact on diatom densities regardless of substratum type. The other two grazers had the blade-like mandibles of a scraper. Psilotreta did not reduce the numerical abundance of diatoms on either substratum, but did alter community structure by significantly reducing densities of stalked Gomphonema olivaceum and large species of Navicula and Nitzschia; densities of smaller diatoms (Achnanthes spp) increased. However, E. subvaria reduced densities of most algal species regardless of size on both substrata and also significantly altered community structure. SEMs of substrata grazed by mayflies showed reductions in fungal hyphae on all grazed leaf discs, decreases in filamentous algal forms on grazed tiles, and greatly shortened stalks of G. olivaceum (Paraleptophlebia only). Thus, periphyton communities are different on leaves versus tiles and grazers with different mouthpart morphologies have varying effects on both algal and heterotrophic microbial community structure.     

Survival and Growth of Juvenile Bromeliads in Coffee Plantations and Forests in Central Veracruz,Mexico

Shade coffee plantations can be important refuges for epiphytes, but are not suitable for all species. To test if the performance of early life stages, often the most sensitive phase, is responsible for the species’ ability to colonize coffee plantations, we compared growth and mortality rates of three epiphytic bromeliad species that differ in their ability to colonize secondary arboreal vegetation by transplanting juveniles to trees in forests, and shade trees in old and young coffee plantations in Central Veracruz, Mexico. Growth rates of Tillandsia viridiflora, generally restricted to forests, and Tillandsia juncea, an early colonizer, were related to the pattern of the species occurrence among habitats with growth rates of T. viridiflora being generally higher in forests and growth of T. juncea higher in coffee plantations. Performance of the third species, Tillandsia heterophylla, which is intermediate in habitat preference, was not clearly related to habitat. No difference in growth rates was found between plants transplanted in wet or dry season. In general, mortality in transplanted bromeliads was relatively low (mostly < 5% per month). In coffee plantations herbivory had a severe effect during part of the wet season, when mortality in young coffee plantations reached between 15 and 24 percent per month. Given the substantial contribution of herbivory to the mortality of juvenile plants and the significant differences between habitats, herbivory may be co‐limiting the colonization of young coffee plantations by some epiphytic bromeliads.     

Root surface acid phosphatase activities of vascular epiphytes of a Costa Rican rain forest

The objective of this work was to compare root surface phosphatase activities of vascular epiphytes typical of a lowland tropical forest. Acid phophatase, measured at pH 5.0 with the substrate p-nitrophenyl phosphate, was detected in 22 species distributed within 10 plant families. Epiphytes were classified as trunk, canopy-mat or bare-limb species based upon their usual occurrence. Phosphatase activity was not significantly correlated with plant occurrence. However, phosphatase activity was generally highest in trunk occurring and canopy-mat epiphytes rooted in mosses and humus-like accumulations, and lowest in species restricted to bare limbs. Epiphyte shoot phosphorus and chlorophyll content were correlated with species occurrence, with phosphatase being positively correlated with plant P content. The observed changes in acid phosphatase production among habitats were consistent with predicted changes in the availability of organic P sources. However, observed changes also reflect accompanying shifts in root structure including: the occurrence of velamen or waxy layers, changes in root diameter, branching and root hair density.     

石斛属植物叶片生物量与叶片养分含量间的关联进化

叶片生物量和元素含量是显著影响叶片生理功能的两类重要的叶片经济性状, 且二者紧密相关。然而过去的研究多数关注C、N和P三种元素含量, 而对其他元素含量关注较少。维管附生植物不能直接从土壤中吸收养分而经常遭受养分胁迫, 养分含量与生物量之间的协同关系在这类植物中表现得尤为突出。选择维管附生石斛属植物为研究对象, 应用系统发育独立对比分析, 检测了叶片生物量和元素含量的系统发育保守性以及这些性状间的关联进化。结果表明, 叶片干物质含量、比叶重、C含量、N含量、P含量以及C/N具有较强的系统发育信号, 并且叶片干物质含量和比叶重与这四个元素含量性状间存在较强的关联进化。另外, 经系统发育校准后, Ca含量和Mg含量间存在显著正相关; P含量与Si含量间存在显著正相关; Zn含量与N含量、N/P以及Mn含量间存在显著正相关, 而与C/N间存在显著负相关。结果为探讨维管附生植物叶片生物量和元素含量的主要影响因素, 以及从进化角度探讨二者在植物进化适应过程中的生态协同功能提供案例, 对进一步了解维管附生植物的功能适应性具有重要意义。