Effects of Ca(II) ions on Mn(II) dynamics in chick glia and rat astrocytes: Potential regulation of glutamine synthetase

Previous studies have demonstrated that in glia and astrocytes Mn(II) is distributed with ca. 30–40% in the cytoplasm, 60–70% in mitochondria. Ca(II) ions were observed to alter both the flux rates and distribution of Mn(II) ions in primary cultues of chick glia and rat astrocytes. External (influxing) Ca(II) ions had the greatest effect on Mn(II) uptake and efflux, compared to internal (effluxing) or internal-external equilibrated Ca(II) ions. External (influxing) Ca(II) ions inhibited the net rate and extent of Mn(II) uptake but enhanced Mn(II) efflux from mitochondria. These observations differ from Ca(II)–Mn(II) effects previously reported with brain (neuronal) mitochondria. Overall, increased cytoplasmic Ca(II) acts to block Mn(II) uptake and enhance Mn(II) release by mitochondria, which serve to increase the cytoplasmic concentration of free Mn(II). A hypothesis is presented involving external L-glutamate acting through membrane receptors to mobilize cell Ca(II), which in turn causes mitochondrial Mn(II) to be released. Because the concentration of free cytoplasmic Mn(II) is poised near the K_d for Mn(II) with glutamine synthetase, a slight increase in cytoplasmic Mn(II) will directly enhance the activity of glutamine synthetase, which catalyzes removal of neurotoxic glutamate and ammonia.     

Effects of aluminium on growth and cation uptake in seedlings of Eucalyptus mannifera and Pinus radiata

This experiment was designed to examine the effects of aluminium (Al) on the growth of Pinus radiata (D. Don) and Eucalyptus mannifera subsp. mannifera (Mudie) seedlings in culture solutions in a glasshouse to help explain the failure of radiata pine trees on some acid, low fertility soils in Australia on which the native eucalypts flourish. Aluminium (Al) in culture solution increased the growth of roots and shoots of seedlings of both species but while growth of the eucalypt continued to increase with increases in Al to 2.222 μM, growth of the pine was largest at 370 μM Al. In addition to total root length, specific root length (length per unit dry weight), a measure of fineness of the root, increased in the eucalypt seedlings as the substrate Al increased. Growth of the shoots and roots of the pine in the absence of any added Al was extremely poor suggesting that Al, in low concentrations, may be an essential element or ameliorate some other factors in solution culture at low pH. Root and shoot concentrations of K increased with increasing Al, whilst Ca and Mg Concentrations decreased and Mn concentrations were unaffected in both species. Tissue Ca and Mg concentrations were 2 to 3 times higher in the eucalypt seedlings than the pine at all levels of added Al due to greater uptake of these elements by the eucalypt. In contrast, at the highest concentration of Al in the medium, shoot Al concentrations were lower in the cucalypt than in the pine due to a greater proportion of Al being retained in the eucalypt roots. These differences between the seedlings in terms of root growth and tissue cation concentrations may help explain the ability of eucalypt species to maintain vigorous growth on acid soils high in Al and low in Ca and P, where growth of the pines failed.     

Nutrient fluxes in the shifting cultivation system of south-west Côte d'Ivoire

At two sites, one with a 4-year-old (4-Y) secondary vegetation and the other with a 20-year-old (20-Y) vegetation, the influence of burning slashed vegetation on crop performance was studied during three seasons. In the first season after clearing, also the influence on weed growth was studied. At both sites, burning significantly decreased the number of weed seedlings. The lowest number of seedlings was found on the burnt plots of the 20-Y site. Burning increased yield and nutrient uptake significantly in the first and second season after clearing. In the third season after burning, only at the 4-Y site a significantly higher yield and nutrient uptake were found. At the 20-Y site the effect had disappeared. Calculations of efficiency of utilization of absorbed N, P and K indicated that P was the least available nutrient, also after burning. At both sites three consecutive crops absorbed approximately 40% of P applied in ash, while the cumulative recovery of K was at least 36% at the 4-Y site and at least 59% at the 20-Y site. On non-burnt plots, yields were not lower in the third season than in the first season after clearing, thus indicating that the inherent soil fertility did not decrease. Hence, yield decline on the burnt plots could be ascribed to ash depletion. It was concluded that in the local shifting cultivation system, the combination of ash depletion and infestation of weeds are the main reasons for abandoning the fields.     

NMR imaging of root water distribution in intact Vicia faba L plants in elevated atmospheric CO2

The effect of elevated atmospheric CO₂ on water distribution in the intact roots of Vicia faba L. bean seedlings grown in natural soil was studied noninvasively with proton (¹H) nuclear magnetic resonance (NMR) imaging. Exposure of 24-d-old plants to atmospheric CO₂-enriched air at 650 cm³ m^?3 produced significant increases in water imaged in upper roots, hypogeal cotyledons and lower stems in response to a short-term drying-stress cycle. Above ground, drying produced negligible stem shrinkage and stomatal resistance was unchanged. In contrast, the same drying cycle caused significant depletion of water imaged in the same upper root structures in control plants subject to ambient CO₂ (350 m³ m^?3), and stem shrinkage and increased stomatal resistance. The results suggest that inhibition of transpiration caused by elevated CO₂ does not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO₂ environments may be a mitigating factor in assessing deleterious effects of greenhouse changes on crops during periods of dry climate.     

REACTION NORMS OF MORPHOLOGICAL AND LIFE-HISTORY TRAITS TO LIGHT AVAILABILITY IN IMPATIENS CAPENSIS

For plants, light availability is an important environmental factor that varies both within and between populations. Although the existence of sun and shade “ecotypes” is controversial, it is often assumed that trade-offs may exist between performance in sun and in shade. This study therefore investigated variation in reaction norms to light availability within and between two neighboring natural populations of the annual Impatiens capensis, one in full sun and the other in a forest understory. Seedlings were collected randomly from both populations and grown to maturity in a greenhouse under two light conditions: full light and 18% of full light. Selfed full-sib seed families were collected from plants from both populations grown in both parental light environments. To characterize family reaction norms, seedlings from each family were divided into the same two light treatments and individuals were scored for a variety of morphological and life-history traits. The maternal light environment had little impact on progeny reaction norms. However, the two study populations differed both qualitatively and quantitatively in plastic response to light availability (indicated by significant population x environment interactions in mixed-model ANCOVA). Much of this difference was attributable to population differences in light sensitivity of axillary meristem allocation patterns, which produced concurrent differences in reaction norms for a suite of developmentally linked traits. Within each population, different sets of traits displayed significant variation in plasticity (indicated by significant family x environment interactions). Thus, the genetic potential for evolutionary response to selection in heterogeneous light environments may differ dramatically between neighboring plant populations. Between-environment genetic correlations were largely positive in the woods population and positive or nonsignificant in the sun population; there was no evidence for performance trade-offs across environments or sun or shade “specialist” genotypes within either population. There was little evidence that population differences represented adaptive differentiation for sun or shade; rather, the results suggested the hypothesis of differential selection on patterns of meristem allocation caused by population differences in timing of mortality and intensity of competition.     

Chronic toxicity of methylparathion to the rotifer Brachionus calyciflorus fed on Nannochloris oculata and Chlorella pyrenoidosa

The effect of sublethal levels of methylparathion (0, 1, 3, 5, 7 mg l^–1) on the freshwater rotifer, Brachionus calyciflorus, during their entire life cycle was studied. Rotifers were fed on two species of unicellular algae: Nannochloris oculata and Chlorella pyrenoidosa; both algal concentrations were 5 × 10⁵ cell ml^–1.The parameters used to determine the toxicity of this compound were survival, fecundity, net reproductive rate (R)_o, generation time (T), intrinsic rate of natural increase (r), reproductive value (V _x/V_o) and life expectancy at hatching (eo). All the demographic parameters studied were affected by methyl-parathion exposure on rotifers fed on both species of algae, but the toxic effect was larger when animals were fed on Chlorella pyrenoidosa; in this case, animals showed a decreased in fertility and also a delayed first reproduction. Sublethal methylparathion levels produced a reduction in most of the parameters selected, especially after exposure to 7 mg l^–1, where the animals died before reproducing.     

Carryover effects from environmental change in early life: An overlooked driver of the amphibian extinction crisis?

Ecological carryover effects, or delayed effects of the environment on an organism's phenotype, are central predictors of individual fitness and a key issue in conservation biology. Climate change imposes increasingly variable environmental conditions that may be challenging to early life-history stages in animals with complex life histories, leading to detrimental physiological and fitness effects in later life. Yet, the latent nature of carryover effects, combined with the long temporal scales over which they can manifest, means that this phenomenon remains understudied and is often overlooked in short-term studies limited to single life-history stages. Herein, we review evidence for the physiological carryover effects induced by elevated ultraviolet radiation (UVR; 280–400 nm) as a potential contributor to recent amphibian population declines. UVR exposure causes a suite of molecular, cellular and physiological consequences known to underpin carryover effects in other taxa, but there is a lack of research linking embryonic and larval UVR exposures to fitness consequences post-metamorphosis in amphibians. We propose that the key impacts of UVR on disease-related amphibian declines are facilitated through carryover effects that bridge embryonic and larval UVR exposure with potential increased disease susceptibility post-metamorphosis. We conclude by identifying a practical direction for the study of ecological carryover effects in amphibians that could guide future ecological research in the broader field of conservation physiology. Only by addressing carryover effects can many of the mechanistic links between environmental change and population declines be elucidated.     

Ecosystem-level effects of re-oligotrophication and N:P imbalances in rivers and estuaries on a global scale

Trends and ecological consequences of phosphorus (P) decline and increasing nitrogen (N) to phosphorus (N:P) ratios in rivers and estuaries are reviewed and discussed. Results suggest that re-oligotrophication is a dominant trend in rivers and estuaries of high-income countries in the last two–three decades, while in low-income countries widespread eutrophication occurs. The decline in P is well documented in hundreds of rivers of United States and the European Union, but the biotic response of rivers and estuaries besides phytoplankton decline such as trends in phytoplankton composition, changes in primary production, ecosystem shifts, cascading effects, changes in ecosystem metabolism, etc., have not been sufficiently monitored and investigated, neither the effects of N:P imbalance. N:P imbalance has significant ecological effects that need to be further investigated. There is a growing number of cases in which phytoplankton biomass have been shown to decrease due to re-oligotrophication, but the potential regime shift from phytoplankton to macrophyte dominance described in shallow lakes has been documented only in a few rivers and estuaries yet. The main reasons why regime shifts are rarely described in rivers and estuaries are, from one hand the scarcity of data on macrophyte cover trends, and from the other hand physical factors such as peak flows or high turbidity that could prevent a general spread of submerged macrophytes as observed in shallow lakes. Moreover, re-oligotrophication effects on rivers may be different compared to lakes (e.g., lower dominance of macrophytes) or estuaries (e.g., limitation of primary production by N instead of P) or may be dependent on river/estuary type. We conclude that river and estuary re-oligotrophication effects are complex, diverse and still little known, and in some cases are equivalent to those described in shallow lakes, but the regime shift is more likely to occur in mid to high-order rivers and shallow estuaries.     

Edge effects influence the composition and density of reef residents on subtidal restored oyster reefs

Within estuarine and coastal ecosystems globally, extensive habitat degradation and loss threaten critical ecosystem functions and necessitate widescale restoration efforts. There is abundant evidence that ecological processes and species interactions can vary with habitat characteristics, which has important implications for the design and implementation of restoration efforts aimed at enhancing specific ecosystem functions and services. We conducted an experiment examining how habitat characteristics (presence; edge vs. interior) influence the communities of resident fish and mobile invertebrates on restored oyster (Crassostrea virginica) reefs. Similar to previous studies, we found that restored reefs altered community composition and augmented total abundance and biomass relative to unstructured sand habitat. Community composition and biomass also differed between the edge and interior of individual reefs as a result of species-specific patterns over small spatial scales. These patterns were only weakly linked to oyster density, suggesting that other factors that vary between edge and interior (e.g. predator access or species interactions) are likely more important for community structure on oyster reefs. Fine-scale information on resident species' use of oyster reefs will help facilitate restoration by allowing decision makers to optimize the amount of edge versus interior habitat. To improve the prediction of faunal use and benefits from habitat restoration, we recommend investigations into the mechanisms shaping edge and interior preferences on oyster reefs.