Organic phosphorus in soil water under a European beech (Fagus sylvatica L.) stand in northeastern Bavaria, Germany: seasonal variability and changes with soil depth

Organically bound phosphorus (P) is a mobile form of phosphorus in many soils and thus its dynamics relevant for the leaching and cycling of this element. Despite its importance, little is known about the chemical composition of dissolved organic P. We studied the concentrations, fluxes, and chemical composition of organic P in forest floor leachates and soil solutions in a Rendzic Leptosol under a 90-year-old European beech (Fagus sylvatica L.) forest over a 27-month period (1997–1999). The chemical composition of organic P was analysed using XAD-8 fractionation and ³¹P-nuclear magnetic resonance (NMR) spectroscopy. Organic P was the dominant P form in forest floor leachates as well as in porewaters of the mineral soil. The largest concentrations of organic P were observed during summer and peaked (330–400 g dissolved organic P l^–1) after rain storms following short dry periods, concurrently with the concentrations of organic carbon (OC). Because of high rainfall, fluxes of organic P (and C) were greatest in autumn although concentrations of organic C and P were lower than in summer. In forest floor leachates, the hydrophilic fraction of dissolved organic matter contained 83 ± 13% of the bulk organic P. In soil solutions from 90 cm depth, organic P was almost exclusively in the hydrophilic fraction. Because of the low retention of the hydrophilic fraction of dissolved organic matter in the mineral soils, concentrations of organic P in soil water remained almost constant with depth. Consequently, organic P contributed > 95% of the total P leached into deeper subsoils. The overall retention of organic P in the weakly developed mineral soils was little and so the average annual fluxes of organic P in subsoils at 90 cm depth (38 mg m^–2) comprised 67% of those from the forest floors (57 mg m^–2) during the study period. Hence, organic P proved to be mobile in the studied soil. ³¹P-NMR spectroscopy confirmed the dominance of organic P species in soil water. Signals due to inorganic P occurred only in spectra of samples collected in winter and spring months. Spectra of samples from summer and autumn revealed traces of condensed phosphates. Due to low P contents, identification of organic P species in samples from winter and spring was not always possible. In summer and autumn, monoester and diester phosphates were the dominant organic species and varied little in their relative distributions. The distribution of organic species changed little from forest floor leachates to the subsoil solutions indicating that the composition of P-containing compounds was not influenced by sorptive interactions or biological transformation.     

Modelling the production and transport of dissolved organic carbon in forest soils

DyDOC describes soil carbon dynamics, with a focus on dissolved organic carbon (DOC). The model treats the soil as a three-horizon profile, and simulates metabolic carbon transformations, sorption reactions and water transport. Humic substances are partitioned into three fractions, one of which is immobile, while the other two (hydrophilic and hydrophobic) can pass into solution as DOC. DyDOC requires site-specific soil characteristics, and is driven by inputs of litter and water, and air and soil temperatures. The model operates on hourly and daily time steps, and can simulate carbon cycling over both long (hundreds-to-thousands of years) and short (daily) time scales. An important feature of DyDOC is the tracking of ¹⁴C, from its entry in litter to its loss as DO¹⁴C in drainage water, enabling information about C dynamics to be obtained from both long-term radioactive decay, and the characteristic ¹⁴C pulse caused by thermonuclear weapon testing during the 1960s ("bomb carbon"). Parameterisation is performed by assuming a current steady state. Values of a range of variables, including C pools, annual DOC fluxes, and ¹⁴C signals, are combined into objective functions for least-squares minimisation. DyDOC has been applied successfully to spruce forest sites at Birkenes (Norway) and Waldstein (Germany), and most of the parameters have similar values at the two sites. The results indicate that the supply of DOC from the surface soil horizon to percolating water depends upon the continual metabolic production of easily leached humic material. In contrast, concentrations and fluxes of DOC in the deeper soil horizons are controlled by sorption processes, involving comparatively large pools of leachable organic matter. Times to reach steady state are calculated to be several hundred years in the organic layer, and hundreds-to-thousands of years in the deeper mineral layers. It is estimated that DOC supplies 89% of the mineral soil carbon at Birkenes, and 73% at Waldstein. The model, parameterised with "steady state" data, simulates short-term variations in DOC concentrations and fluxes, and in DO¹⁴C, which are in approximate agreement with observations.     

A dynamic mass balance model for phosphorus fluxes and concentrations in coastal areas

This paper presents a general, process-based mass balance model (CoastMab) for total phosphorus (TP) in defined coastal areas (at the ecosystem scale). The model is based on ordinary differential equations and calculates inflow, outflow and internal fluxes on a monthly basis. It consists of four compartments: surface water, deep water, erosion/transportation areas for fine sediments and accumulation areas for fine sediments. The separation between surface water and deep water is not done based on water temperature, but on sedimentological criteria instead (from the theoretical wave base). There are algorithms for all major internal TP fluxes (sedimentation, resuspension, diffusion, mixing and burial). Validations were performed using data from 21 different Baltic coastal areas. The results show that the model predicts monthly TP in water and chlorophyll a very well (generally within the uncertainty bands of the empirical data). The model has also been put through sensitivity tests, which show that the most important factor regulating the predictions of the model is generally the TP concentration in the sea beyond the coast. The model is simple to apply, since all driving variables may be accessed from maps or monitoring programs. The driving variables include coastal area, section area (between the defined coastal area and the adjacent sea), mean and maximum depths, latitude (used to predict water temperatures, stratification and mixing), salinity and TP concentration in the sea. Many of the model structures are general and could be used for areas other than those included in this study, e.g., for open coasts, estuaries or tidal coasts, as well as for other substances than phosphorus.     

Dissolved organic sulphur in soil water under <Emphasis Type="Italic">Pinus sylvestris</Emphasis> L. and <Emphasis Type="Italic">Fagus sylvatica</Emphasis> L. stands in northeastern Bavaria,Germany variations with seasons and soil depth

Organically bound species have been identified as prominent and mobile forms of nitrogen and phosphorus in soils. Since a large portion of sulphur (S) in soil is bonded to carbon (C) also dissolved organic S likely is a significant constituent in soil water. To investigate the role of dissolved organic forms in leaching and cycling of S in forest soils, we examined concentrations, fluxes, and chemical composition of organic S in forest floor leachates and in soil solutions of Rendzic Leptosols under 90-year-old European beech (Fagus sylvatica L.) and Haplic Arenosols under 160-year-old Scots pine (Pinus sylvestris L.) for 27 months. These soils are low in adsorbed SO₄^2- and receive little atmospheric S depositions at present. The chemical composition of organic S was estimated by fractionation with XAD-8 and wet-chemical characterisation (HI reduction) of binding forms. Although not as prominent as the organic forms of other nutrient elements, organic S proved to be an important contributor to S dissolved in forest floor leachates and in mineral soil solutions. Dissolved organic matter contained on average 29% of total S in forest floor leachates at the pine site and 34% at the beech site. The largest portion of organic S occurred in the subsoil solutions under beech in summer and autumn (up to 53%). Mean concentrations of organic S peaked (up to 1.1 mg l^-1) in summer after rainstorms that followed dry periods. Fluxes with forest floor leachates and at 90 cm soil depth were largest in autumn because of huge amounts of rainfall. Organic S contributed significantly to the fluxes of S in the subsoils under beech comprising on average 39% of total dissolved S at 90 cm depth. Organic S produced in the forest floor layers was mainly in the hydrophilic fraction of dissolved organic matter (62 ± 6% at the pine site, 85 ± 4% at the beech site). The major binding form of organic S in the hydrophobic fraction was C-bonded S while in the hydrophilic fraction ester sulphate S, possibly associated with carbohydrates, was more prominent. Since the hydrophobic fraction increased in summer and autumn, C-bonded S was of greater importance during that time of the year than in winter and spring. With depth, concentrations and composition of organic S (and also of C) hardly changed at the pine site because of little retention of dissolved organic matter, presumably because of the small sorption capability of that soil. At the beech where organic C showed a marked decrease with depth, only a slight decrease in organic S, exclusively from the hydrophobic fraction, was found indicating that organic S was mobile compared with organic C. This was probably due to the concentration of S in the hydrophilic fraction of dissolved organic matter. Because of being concentrated in the mobile hydrophilic fraction, ester sulphate S was more mobile in the soil under beech than C-bonded S.     

NaCl absorption across split gill lamellae of hyperregulating crabs: Transport mechanisms and their regulation

The method of mounting split lamellae of crab gills in modified Ussing chambers offers the advantage that active ion transport can be measured as short-circuit current and/or flux of radioactive tracers in relation to the epithelial surface. Moreover, further modern techniques like microelectrode impalements and current-noise analysis can be applied. The epithelium of posterior gills of Chinese crabs (Eriocheir sinensis) acclimated to fresh water actively absorbs Na⁺ and Cl⁻ independent of each other. The epithelium of the gills of shore crabs (Carcinus maenas) acclimated to brackish water actively absorbs NaCl in a coupled mode. The different osmotic gradients maintained by the two crab species are reflected in the characteristics of their gill epithelia. Chinese crabs, migrating to fresh water, have a tight gill epithelium. The gill epithelium of shore crabs, living in brackish water of at least 6–8‰ salinity, is an intermediate between tight and leaky. Regulation of NaCl absorption across the gill epithelium of Chinese crabs is achieved in a hormone-independent way by the haemolymph side osmolarity (autoregulation). Moreover, NaCl absorption is regulated by a hormonal factor of so far unknown chemical nature in the eyestalk extract which stimulates the transport rates via a cAMP-dependent signal transduction pathway, activating apical V-ATPase activity and increasing the number of open apical Na⁺ channels.     

Release and uptake of volatile inorganic and organic gases through the snowpack at Niwot Ridge,Colorado

Whole air drawn from four heights within the high elevation (3,340 m asl), deep, winter snowpack at Niwot Ridge, Colorado, were sampled into stainless steel canisters, and subsequently analyzed by gas chromatography for 51 volatile inorganic and organic gases. Two adjacent plots with similar snow cover were sampled, one over bare soil and a second one from within a snow-filled chamber where Tedlar/Teflon-film covered the ground and isolated it from the soil. This comparison allowed for studying effects from processes in the snowpack itself versus soil influences on the gas concentrations and fluxes within and through the snowpack. Samples were also collected from ambient air above the snow surface for comparison with the snowpack air. Analyzed gas species were found to exhibit three different kinds of behavior: (1) One group of gases, i.e., carbon dioxide (CO₂), chloroform (CHCl₃), dimethylsulfide (CH₃)₂S, carbondisulfide (CS₂), and dichlorobromomethane (CHBrCl₂), displayed higher concentrations inside the snow, indicating a formation of these species and release into the atmosphere. (2) A second group of compounds, including carbon monoxide (CO), carbonyl sulfide (COS), the hydrocarbons methane, ethane, ethyne, benzene, and the halogenated compounds methylchloride (CH₃Cl), methylbromide (CH₃Br), dibromomethane (CH₂Br₂), bromoform (CHBr₃), tetrachloromethane (CCl₄), CFC-11, CFC-12, HCFC-22, CFC-113, 1,2-dichloroethane, methylchloroform, HCFC-141b, and HCFC-142b, were found at lower concentrations in the snow, indicating that the snow and/or soil constitute a sink for these gases. (3) For 21 other gases absolute concentrations, respectively concentration gradients, were too low to unequivocally identify their uptake or release behavior. For gases listed in the first two groups, concentration gradients were incorporated into a snowpack gas diffusion model to derive preliminary estimates of fluxes at the snow-atmosphere interface. The snowpack gradient flux technique was found to offer a highly sensitive method for the study of these surface gas exchanges. Microbial activities below this deep, winter snowpack appear to be the driving mechanism behind these gas sources and sinks. Flux results were applied to a simple box model to assess the potential contribution of the snowpack uptake rates to atmospheric lifetimes of these species.     

Chemical composition of interstitial water and diffusive fluxes within the diatomaceous sediment in Lake Myvatn, Iceland

The sub-arctic Lake Myvatn is one of the most productive lakes in the Northern Hemisphere, despite an ice-cover of 190 days per year. This is due to relatively high solar radiation, nutrient rich inflow waters, N₂ fixation and internal nutrient loading. In order to define direction and magnitude of diffusive fluxes, soil water samplers were used to collect interstitial water from 25–150 cm depth, from within the diatomaceous sediment at the bottom of Lake Myvatn. Water depth at the sampling site was 225 cm. The pH of the interstitial water ranged from 7.16 to 7.30, while the pH of the lake water was 9.80–10.00. The concentrations of most solutes were similar 16 cm above the bottom of the lake at the sampling site and at the lake outlet. The concentrations of NO₃, S, F, O₂, Al, Cr, Mo, V, U, Sn and Sb were higher in the lake water than in the interstitial water. They will therefore diffuse from the lake water into the interstitial water. The concentrations of orthophosphates, PO₄, and total dissolved P were highest at 25 cm depth, but Co and NH₄ concentrations were highest at 50 to 100 cm depth. Thus they diffuse both up towards the lake bottom and down deeper into the sediments. The concentrations of Na, K, Ca, Mg, Sr, Mn, Li and alkalinity were greater within the sediments than in the lake water and increased continuously with depth. The Si concentration of the interstitial water was higher than in the lake water, it was highest at 25 cm depth and decreased slightly down into the sediments. The concentration gradient was greatest for bicarbonate, HCO₃ ^–, 1.5×10^–7 mol cm^–3 cm^–1, and then in declining order for the solutes with the highest gradient; NH₄, Si, Na, Ca, Mg, -S (diffusion into the sediments), K, PO₄, Cl, Fe and Mn. The estimated annual diffusive flux of PO₄ for Lake Myvatn was 0.1 g P m^–2 yr^–1, about 10% of the total PO₄ input to Lake Myvatn. The H₄SiO₄° flux was 1.3 g Si m^–2 yr^–1, <1% of both the input and the annual net Si fixation by diatoms within the lake and the diffusive flux of dissolved inorganic carbon was 1% of the annual net C fixation by diatoms. Annual diffusive flux of NH₄ ⁺ was 1.9 g N m^–2 yr^–1 similar to the input of fixed N to the lake and 24% of the net N fixation within Lake Myvatn. Thus it is important for the nitrogen budget of Lake Myvatn and the primary production in the lake since fixed nitrogen is the rate determining nutrient for primary production.     

Bordetella Adenylate Cyclase Toxin Promotes Calcium Entry into Both CD11b+ and CD11b? Cells through cAMP-dependent L-type-like Calcium Channels

Adenylate cyclase toxin (ACT), a 200 kDa protein, is an essential virulence factor for Bordetella pertussis, the bacterium that causes whooping cough. ACT is a member of the pore-forming RTX (repeats-in-toxin) family of proteins that share a characteristic calcium-binding motif of Gly- and Asp-rich nonapeptide repeats and a marked cytolytic or cytotoxic activity. In addition, ACT exhibits a distinctive feature: it has an N-terminal calmodulin-dependent adenylate cyclase domain. Translocation of this domain into the host cytoplasm results in uncontrolled production of cAMP, and it has classically been assumed that this surge in cAMP is the basis for the toxin-mediated killing. Several members of the RTX family of toxins, including ACT, have been shown to induce intracellular calcium increases, through different mechanisms. We show here that ACT stimulates a raft-mediated calcium influx, through its cAMP production activity, that activates PKA, which in turn activates calcium channels with L-type properties. This process is shown to occur both in CD11b⁺ and CD11b⁻ cells, suggesting a common mechanism, independent of the toxin receptor. We also show that this ACT-induced calcium influx does not correlate with the toxin-induced cytotoxicity.     

Export of DOM from Boreal Catchments: Impacts of Land Use Cover and Climate

Dissolved organic matter (DOM) is an important fraction in carbon (C) and nutrient budgets for aquatic ecosystems and can have broad effects on food webs and nutrient cycling. To look at the role land use cover and climate might play in DOM transport from the boreal region, the export of total organic carbon (TOC), total organic nitrogen (TON) and dissolved organic phosphorus (DOP) was estimated for Finnish main rivers and their sub-catchments, altogether 86 catchments, situated between latitudes 60° N and 69° N and covering 297,322 km², 88% of the total area of Finland. On an average, 94% of the TOC, 90% of the total nitrogen (TN) and 40% of the total phosphorus (TP) in Finnish rivers was in a dissolved form. The majority of the DOM export from Finnish catchments consists of organic C. The TOC export increased with increasing peatland proportion (r = 0.39, p = 0.003), while TON export increased with the increasing percentage of agricultural land (r = 0.60, p <0.001). Although upstream lakes covered only on average 9% of the catchment area, they were the most important predictor for TOC, TON and DOP export (r = −0.83, r = −0.82 and r = −0.61, respectively). The higher the upstream lake percentage, the lower the export indicating organic matter retention in lakes.     

Variability in abundance and fluxes of dimethyl sulphide in the Indian Ocean

Dimethyl sulphide (DMS) is a biogenic gas of climatic significance on which limited information is available from the Indian Ocean. To fill this gap, we collected data on DMS and total dimethylsulphoniopropionate (DMSP_t) by participating in a dozen cruises. Here, we discuss the variability in DMS and DMSP_t in the north and central Indian Ocean in terms of their spatial and temporal variation. DMS and DMSP_t exhibited significant spatial and temporal variability. Apart from the concentration gradients in DMS within the Arabian Sea, Bay of Bengal and Central Indian Ocean basins, differences in average abundances were conspicuous between these basins. The Arabian Sea contained more DMS (mixed layer average was 7.8 nM) followed by the Bay of Bengal (2.8 nM) and the Central Indian Ocean (2.7 nM). The highest concentrations of DMS and DMSP_t (525 nM and 916 nM, respectively) were found in upwelling regimes along the west coast of India during the Southwest monsoon and fall intermonsoon seasons. Average surface DMS was the highest in the Arabian Sea. On the other hand observed sea-to-air fluxes of DMS were higher in the Bay of Bengal due to the prevalence of turbulent conditions. In the Arabian Sea wind speeds were low and hence the sea-to-air fluxes. The total diffusive flux of DMS from the study area to atmosphere is estimated to be about 1.02 × 10¹² g S y⁻¹, which contributes to 4.1–6.3% of the global DMS emission