Short-term movements of chalk-stream invertebrates

SUMMARY 1. Trays of gravel were implanted for 24 h periods in several chalk streams. The trays were variously modified to monitor colonization from different sources, particularly drift (D), other downstream movements (DSM), upstream movements (USM), and all sources combined (ALL).
2. The abundance of invertebrates in the streams was high (maximum of 717 per 0.04 m²) and colonization of the trays was extensive, especially by Gammarus pulex , the predominant species in all but one of the streams (maximum number of individuals of G. pulex per tray: for D, 473; for DSM, 462; tor USM, 286; and tor ALL, 639). In some cases benthic densities were achieved in the trays in the 24 h exposure period, and in most cases any one source of colonization could provide benthic densities in a few days.
3. Patterns of movement differed between species, between size classes of G. pulex , and between sites for particular species. No one source of colonization could be regarded as generally predominant although downstream movements in total (D + DSM) usually far exceeded USM. DSM was usually an important source of colonization.
4. The extent and direction of movement appeared to be determined by local factors and were explained in terms of the high densities of invertebrates and the current and substratum characteristics of each site.
5. Estimates of the relative importance of different sources of colonization varied greatly according to the criteria used in determining proportions.     

The Effect of Hypoxia and Sulphide on Culture-Grown Wetland and Non-Wetland Plants: II. METABOLIC AND PHYSIOLOGICAL CHANGES

Pearson, J. and Havill, D. C. 1988. The effect of hypoxia andsulphide on culture-grown wetland and non-wetland plants. II.Metabolic and physiological changes.—J. exp. Bot. 39:431–439. Two non-wetland (Agropyron pungens, Hordeum vulgare) and fivewetland species (Oryza sativa, Aster tripolium, three Salicorniaspp.) were grown in aerated, unaerated and sulphide-treatedculture solution. Changes in the activity of alcohol dehydrogenase(ADH) and cytochrome oxidase (COase) in the roots were measured.In the non-wetland species, treatment with hypoxia or sulphideincreased ADH activity by 900–1 800%, whereas COase activitydecreased by 80–92% of the aerated control. In the wetlandspecies, except S. europaea which was not affected, hypoxiaincreased ADH activity by 350–550%, while COase activitywas little affected. Generally, when treated with sulphide theactivity of ADH increased to about 750% in most of the wetlandspecies, but increases as low as 175% (S. europaea) and as highas 1400% (S.fragilis) were recorded. The effect of sulphideon the COase activity in the wetland plants was not as markedas in the non-wetland plants. The Salicornia spp. were the leastaffected by the sulphide treatment and they also had intrinsicallyhigher levels of COase activity than the other species sampled.Of the wetland plants the Salicornia species had the lowestvalue for root aerenchyma, 3–6%. Therefore, there wasno correlation between the possession of aerenchyma and thephysiological changes measured. Measurement of malate, lactateand ethanol in roots of the first four species listed abovegave no evidence for alternative anaerobic fermentation pathways.While in the flood-intolerant species, high ADH activities werenot able to maintain the energy charge. It is suggested thatmaintenance of relatively high COase activity in wetland plantsmay help to ‘scavenge’ any available oxygen withinroots and thus help reduce energy loss. Key words: Cytochrome oxidase, alcohol dehydrogenase, metabolic adaptation     

Diversity and seasonality of adult Trichoptera captured in a light-trap at Yuccabine Creek,a tropical Australian rainforest stream

Seventeen light-trap samples were taken over a 20 month period at Yuccabine Creek, an upland rainforest stream in north-eastern Queensland. Seventy-eight species of Trichoptera were recorded from a total catch of 6431 individuals. The fauna was dominated by the Hydroptilidae (25 species and 5131 individuals) and, though composed primarily of Torresian genera, some Bassian elements were recorded. A seasonal pattern of change of abundance was observed with the majority of tax a exhibiting maxima between December and January (summer) and minima between July and September (winter).     

Cytogenetic Effects of Cyclohexylamine and N-OH-Cyclohexylamine on Human Leucocytes and Chinese Hamster Bone Marrow

SOME humans metabolize the commonly used artificial sweetener, cyclamate, to cyclohexylamine (CHA) and N-hydroxycyclo-hexylamine (N-OHCHA). There have been three reports^1–3 that cyclamate and its metabolic byproducts cause a significant amount of cytogenetic damage in cultured human cells and the bone marrow and spermatogonial cells of the rat, but unfortunately they do not give quantitative cytogenetic data, other than the percentages of cells with “breaks”. In our experiments, we attempted to detect significant cytogenetic damage to human leucocytes treated in vitro or in a host-mediated assay system with CHA or N-OHCHA. At the same time, bone marrow from Chinese hamsters was studied for cytogenetic effects after daily injections of CHA.     

Asymmetric responses of adaxial and abaxial stomata to elevated CO2: impacts on the control of gas exchange by leaves

The response of adaxial and abaxial stomatal conductance in Rumex obtusifolius to growth at elevated atmospheric concentrations of CO₂ (250 μmol mol^?1 above ambient) was investigated over two growing seasons. The conductance of both the adaxial and abaxial leaf surfaces was found to be reduced by elevated concentrations of CO₂. Elevated CO₂ caused a much greater reduction in conductance for the adaxial surface than for the abaxial surface. The absence of effects upon stomatal density indicated that the reductions were probably the result of changes in stomatal aperture. Partitioning of gas exchange between the leaf surfaces revealed that increased concentrations of CO₂ caused increased rates of photosynthesis only via the abaxial surface. Additionally, leaf thickness was found to increase during growth at elevated concentrations of CO₂. The tendency for these amphistomatous leaves to develop a distribution of conductance approaching that of hypostomatous leaves clearly reduced their maximum photosynthetic potential. This conclusion was supported by measurements of stomatal limitation, which showed greater values for the adaxial surfaces, and greater values at elevated CO₂. This reduction in photosynthesis may in part be caused by higher diffusive limitations imposed because of increased leaf thickness. In an uncoupled canopy, asymmetrical stomatal responses of the kind identified here may appreciably reduce transpiration. Species which show symmetrical responses are less likely to show reduced transpirational rates, and a redistribution of water loss between species may occur. The implications of asymmetrical stomatal responses for photosynthesis and canopy transpiration are discussed.