Fluxes of carbon dioxide and water vapour over an undisturbed tropical forest in south-west Amazonia

• 1 Carbon dioxide and water vapour fluxes were measured for 55 days by eddy covariance over an undisturbed tropical rain forest in Rondonia, Brazil. Profiles of CO₂ inside the canopy were also measured.
• 2 During the night, CO₂ concentration frequently built up to 500 ppm throughout the canopy as a result of low rates of exchange with the atmosphere. In the early morning hours, ventilation of the canopy occurred.
• 3 Ecosystem gas exchange was calculated from a knowledge of fluxes above the canopy and changes of CO₂ stored inside the canopy. Typically, uptake by the canopy was 15 μmol m^?2 s^?1 in bright sunlight and dark respiration was 6-7 μmol m^?2 s^?1 The quantum requirement at low irradiance was: 40 mol photons per mol of CO₂.
• 4 Bulk stomatal conductance of the ecosystem was maximal in the early morning (0.4-1.0 mol m^?2 s^?1) and declined over the course of the day as leaf-to-air vapour pressure difference increased.

     

A Comparative Electron Microscopic Study of the Morphology of Toxoplasma gondii by Freeze-Etch Replication and Thin Sectioning Technic

SYNOPSIS. Freeze-etch preparations of Toxoplasma gondii reveal details of structure and organelles in 3-dimensional relationships. The subpellicular microtubules and their relationship to the polar ring, the tripartite pellicle, the pellicle constituents, and the spatial relationship of the rhoptries to the conoid and conoid canal are clearly demarcated.     

The histology and affinities of sinacanthid fishes: primitive gnathostomes from the Silurian of China

On the basis of well preserved specimens from the Lower Silurian of the Tarim Basin, Xinjiang Uygur Autonomous Region and Shiqian County, Guizhou Province, People's Republic of China we describe in detail the histological structure of sinacanthid spines, the only known remains of a group of fishes common in Silurian strata from China. The sinacanthids have previously been assigned either to the acanthodians or to the chondrichthyans. The spine structure is composed of an outer layer of atubular dentine and an inner layer of globular calcified cartilage, and the nature and distribution of these tissues indicates that the spines were formed as a result of interaction between the endoskeleton and dermoskeleton. The tissue distribution and style of growth described herein places the sinacanthids crownwards of the placoderms, and possibly within the total group Chondrichthyes. However, before they can be firmly placed within a phylogenetic scheme, further evidence is required both on the general anatomy of sinacanthids and on the nature of chondrichthyan apomorphies.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 144 , 379–386.     

Chronic catchment nitrogen enrichment and stoichiometric constraints on the bioavailability of dissolved organic matter from leaf leachate

1. Chronic nitrogen (N) deposition may alter the bioavailability of dissolved organic matter (DOM) in streams by multiple pathways. Elevated N deposition may alter the nutrient stoichiometry of DOM as well as nutrient availability in stream water. 2. We evaluated the influence of a decadal‐scale experimental N enrichment on the relative importance of DOM nutrient content and inorganic nutrient availability on the bioavailability of DOM. We measured the consumption of dissolved organic carbon (DOC) and changes in nutrient concentration, DOM components and enzyme activity in a bottle incubation assay with different DOM and nutrient treatments. To evaluate the effect of DOM stoichiometry, we used leaf leachates of different carbon/N/phosphorus (C : N :P) ratio, made from leaf litter sourced in the reference and N‐enriched catchments at the Bear Brook Watershed in Maine (BBWM). We also manipulated the concentration of inorganic N and P to compare the effect of nutrient enrichment with DOM stoichiometry. 3. DOC from the N‐enriched catchment was consumed 14% faster than that from the reference catchment. However, mean DOC consumption for both leachates was more than doubled by the simultaneous addition of N and P, compared to controls, while the addition of N or P alone increased consumption by 42 and 23%, respectively. The effect of N and/or P enrichment consistently had a greater effect than DOM source for all response variables considered. 4. We subsequently conducted DOC uptake measurements using leaf leachate addition under ambient and elevated N and P in the streams draining the reference and N‐enriched catchments at BBWM. In both streams, DOC uptake lengths were shorter when N and P were elevated. 5. Although both DOM stoichiometry and inorganic nutrient availability affect DOM bioavailability, N and P co‐limitation appears to be the dominant driver of reach‐scale processing of DOM.     

MAINTENANCE OF IONS,PROTEINS AND WATER IN LENS FIBER CELLS BEFORE AND AFTER TREATMENT WITH NON-IONIC DETERGENTS

If the plasma membrane and its associated transport proteins are solely responsible for maintenance of the asymmetric solute distribution then disruption of the plasma membrane would quickly lead to the symmetric distribution of all unattached inorganic ions between the cell and the extracellular environment. To test this hypothesis fresh pig lenses were incubated in Hanks ’ balanced salt solution in either absence or presence of non-ionic detergents (0.2 % Triton X-100 or 0.2 % Brij 58). Both detergents caused permeabilization of every lens fiber cell as shown by electron microscopy. The flux kinetics of K⁺, Mg^{2 +}, Na⁺, Ca^{2 +}, water and protein out of and into the permeabilized lens fiber cells was measured. Triton X-100 caused a faster flux rate of all solutes than did Brij 58. The Triton X-100 induced flux of solutes and water was associated with a decrease in lens ATP. Incubation of untreated lenses in solutions of different osmotic pressures at 0 °C demonstrated that the major fraction of lens water was osmotically unresponsive. Thus the asymmetric distribution of solutes in lens fiber cells is dependent on an intact plasma membrane and on a co-operative ATP-dependent association between K⁺, Mg^{2 +}, water and cytomatrix proteins.     

Evidence for Hybridization by Multilocus Enzyme Electrophoresis and Random Amplified Polymorphic DNA Between Leishmania braziliensis and Leishmania panamensis/guyanensis in Ecuador

ABSTRACT. The taxonomic attribution of four Leishmania stocks isolated from humans in Ecuador has been explored by both multilocus enzyme electrophoresis and random amplified polymorphic DNA. For three loci, MLEE results showed patterns suggesting a heterozygous state for a diploid organism, while the corresponding homozygous states are characteristic of the Leishmania panamensis/guyanensis complex and Leishmania braziliensis . RAPD profiles exhibited for several primers a combination of the Leishmania panmensis/guyanensis complex and L. braziliensis characters. These data hence suggest that the four stocks are the results of hybridization between L. panamensis/guyanensis and L. braziliensis . MLEE data show that the results cannot be attributed to either mixture of stocks, or an F1 in the framework of a simple Mendelian inheritance.