Hydrologic sources of carbon cycling uncertainty throughout the terrestrial–aquatic continuum

Linking hydrologic interactions with global carbon cycling will reduce the uncertainty associated with scaling-up empirical studies and facilitate the incorporation of terrestrial–aquatic linkages within global and regional change models. Much of the uncertainty in estimates of carbon fluxes associated with precipitation and hydrologic transport results from the extensive spatial and temporal heterogeneity in both intrinsic functioning and anthropogenic modification of hydrological cycles. To better understand this variation we developed a landscape ecological approach to coupled hydrologic–carbon cycling that merges local mechanisms with multiple-scale spatial heterogeneity. This spatially explicit framework is applied to examine variability in hydrologic influences on carbon cycling along a continental scale water availability gradient with an explicit consideration of human sources of variability. Hydrologic variation is an important component of the uncertainty in carbon cycling; accounting for this variation will improve understanding of current conditions and projections of future ecosystem responses to global change.     

Variation in allometry along the weapon-signal continuum

Evolutionary Ecology - Structures used in intrasexual competition span a continuum, with pure weapons that are used exclusively in physical fights at one extreme and pure aggressive signals that...     

Platelets and the immune continuum

Platelets are anucleate cells that are crucial mediators of haemostasis. Most immunologists probably don't think about platelets every day, and may even consider these cells to be 'nuisances' in certain in vitro studies. However, it is becoming increasingly clear that platelets have inflammatory functions and can influence both innate and adaptive immune responses. Here, we discuss the mechanisms by which platelets contribute to immunity: these small cells are more immunologically savvy than we once thought.     

Instability of the sexual continuum

Maynard Smith and Szathmary have posed the problem of demonstrating the conjectured instability of a continuum of sexual types with finite interbreeding. Here, I propose a model in which one can analyse exactly when and how the existence of the instability can depend on an Allee effect, and how the growth rate and typical scale of the unstable perturbations depend on the strength and range of competition, mating preference, fecundity and offspring variance due to Mendelian segregation and mutation. Instabilities of various kinds are shown to occur in the majority of parameter regimes. In short, the continuum often breaks up into incipient species.     

Aluminium in human sweat

It is of burgeoning importance that the human body burden of aluminium is understood and is measured. There are surprisingly few data to describe human excretion of systemic aluminium and almost no reliable data which relate to aluminium in sweat. We have measured the aluminium content of sweat in 20 healthy volunteers following mild exercise. The concentration of aluminium ranged from 329 to 5329 μg/L. These data equate to a daily excretion of between 234 and 7192 μg aluminium and they strongly suggest that perspiration is the major route of excretion of systemic aluminium in humans.     

Limitations of the continuum assumption in cancellous bone

Most existing stress analyses of the skeleton which consider cancellous bone assume that it can be modelled as a continuum. In this paper we develop a criterion for the validity of this assumption. The limitations of the continuum assumption appear in two areas: near biologic interfaces, and in areas of large stress gradients. These limitations are explored using a probabilistic line scanning model for density measurement, resulting in an estimate of density accuracy as a function of line length which is experimentally verified. Within three to five trabeculae of an interface, a continuum model is suspect. When results as predicted using continuum analyses vary by more than 20-30% over a distance spanning three to five trabeculae, the results are suspect.     

Sulfur cycling in forests

Sulfur is essential for the production of certain amino acids in plants. As amino acid sulfur is the major form of sulfur in trees, there is a strong relationship between organic S and organic N in tree tissue. Sulfur deficiencies occur in parts of southeastern Australia and northwestern North America, remote from pollutant inputs. Since bilogical S requirements of forests are modest (< 5 kg · ha^–1 yr^–1 for net vegetative increment), however, atmospheric S inputs in polluted regions (10–80 kg · ha^–1 yr^–1 ) often exceed not only the forest ecosystem S requirement but also its ability to biologically accumulate S. There is some increase in the SO^2– ₄–S content of forest vegetation in response to elevated atmospheric S inputs, but this capacity is apparently easily saturated. Soil SO^2–2 ₄adsorption is often the dominant feature of S cycling in polluted ecosystems and often accounts for net ecosytem S accumulations.Contribution from a symposium on the role of sulfur in ecosystem processes held August 10, 1983, at the annual meeting of the A.I.B.S., Grand Forks, ND; Myron Mitchell, convenor.     

Identifying the structure of cycling in ecosystems

Given a steady-state network of flows within an ecosystem, it becomes possible to systematically and automatically enumerate all distinct simple cycles of flows. Cycles may be grouped according to shared smallest arcs. The original network may then be decomposed into a web of purely cycled flow and a residual acyclic graph consisting of once-through pathways. The aggregation of elementary cycles according to shared vulnerable arcs seems particularly effective in locating those transfers which stress is most likely to disturb.     

Aluminium Rhizotoxicity in Cicer arietinum

Russian Journal of Plant Physiology - The effects of aluminium (Al)-induced alterations on elongating radicles of Cicer arietinum L. were studied in relation to growth and biochemical markers of...     

Aluminium in human breast tissue

Aluminium is omnipresent in everyday life and increased exposure is resulting in a burgeoning body burden of this non-essential metal. Personal care products are potential contributors to the body burden of aluminium and recent evidence has linked breast cancer with aluminium-based antiperspirants. We have used graphite furnace atomic absorption spectrometry (GFAAS) to measure the aluminium content in breast biopsies obtained following mastectomies. The aluminium content of breast tissue and breast tissue fat were in the range 4-437 nmol/g dry wt. and 3-192 nmol/g oil, respectively. The aluminium content of breast tissue in the outer regions (axilla and lateral) was significantly higher (P=0.033) than the inner regions (middle and medial) of the breast. Whether differences in the regional distribution of aluminium in the breast are related to the known higher incidence of tumours in the outer upper quadrant of the breast remains to be ascertained.     

Complex nitrogen cycling in the sponge Geodia barretti

Marine sponges constitute major parts of coral reefs and deep‐water communities. They often harbour high amounts of phylogenetically and physiologically diverse microbes, which are so far poorly characterized. Many of these sponges regulate their internal oxygen concentration by modulating their ventilation behaviour providing a suitable habitat for both aerobic and anaerobic microbes. In the present study, both aerobic (nitrification) and anaerobic (denitrification, anammox) microbial processes of the nitrogen cycle were quantified in the sponge Geodia barretti and possible involved microbes were identified by molecular techniques. Nitrification rates of 566 nmol N cm^?3 sponge day^?1 were obtained when monitoring the production of nitrite and nitrate. In support of this finding, ammonia‐oxidizing Archaea (crenarchaeotes) were found by amplification of the amoA gene, and nitrite‐oxidizing bacteria of the genus Nitrospira were detected based on rRNA gene analyses. Incubation experiments with stable isotopes (¹⁵NO₃^‐ and ¹⁵NH₄⁺) revealed denitrification and anaerobic ammonium oxidation (anammox) rates of 92 nmol N cm^?3 sponge day^?1 and 3 nmol N cm^?3 sponge day^?1 respectively. Accordingly, sequences closely related to ‘Candidatus Scalindua sorokinii’ and ‘Candidatus Scalindua brodae’ were detected in 16S rRNA gene libraries. The amplification of the nirS gene revealed the presence of denitrifiers, likely belonging to the Betaproteobacteria. This is the first proof of anammox and denitrification in the same animal host, and the first proof of anammox and denitrification in sponges. The close and complex interactions of aerobic, anaerobic, autotrophic and heterotrophic microbial processes are fuelled by metabolic waste products of the sponge host, and enable efficient utilization and recirculation of nutrients within the sponge–microbe system. Since denitrification and anammox remove inorganic nitrogen from the environment, sponges may function as so far unrecognized nitrogen sinks in the ocean. In certain marine environments with high sponge cover, sponge‐mediated nitrogen mineralization processes might even be more important than sediment processes.