Growth of Wolinella succinogenes with polysulphide as terminal acceptor of phosphorylative electron transport

Polysulphide was formed according to reaction (1), when tetrathionate was (1) $${\text{S}}_4 {\text{O}}_6^{2 - } + {\text{HS}}^ - \to 2{\text{S}}_2 {\text{O}}_3^{2 - } + {\text{S(O)}} + {\text{H}}^ + $$ added to an anaerobic buffer (pH 8.5) containing excess sulphide. S(O) denotes the zero oxidation state sulphur in the polysulphide mixture S _infn ^sup2- . The addition of formate to the polysulphide solution in the presence of Wolinella succinogenes caused the reduction of polysulphide according to reaction (2). The bacteria grew in a medium containing formate and sulphide, (2) $${\text{HCO}}_2^ - + {\text{S(O)}} + {\text{H}}2{\text{O}} \to {\text{HCO}}_3^ - + {\text{HS}}^ - + {\text{H}}^ + $$ when tetrathionate was continuously added. The cell density increased proportional to reaction (3) which represents the sum of reactions (1) and (3) $${\text{HCO}}_2^ - + {\text{S}}_{\text{4}} {\text{O}}_6^{2 - } + {\text{H}}2{\text{O}} \to {\text{HCO}}_3^ - + 2{\text{S}}_{\text{2}} {\text{O}}_3^{2 - } + 2{\text{H}}^ + $$ (2). The cell yield per mol formate was nearly the same as during growth on formate and elemental sulphur, while the velocity of growth was greater. The specific activities of polysulphide reduction by formate measured with bacteria grown with tetrathionate or with elemental sulphur were consistent with the growth parameters. The results suggest that W. succinogenes grow at the expense of formate oxidation by polysulphide and that polysulphide is an intermediate during growth on formate and elemental sulphur.     

Do oaks have different strategies for uptake of N, K and P depending on soil depth?

The uptake of nutrients from deep soil layers has been shown to be important for the long-term nutrient sustainability of forest soils. When modelling nutrient uptake in forest ecosystems, the nutrient uptake capacity of trees is usually defined by the root distribution. However, this leads to the assumption that roots at different soil depths have the same capacity to take up nutrients. To investigate if roots located at different soil depths differ in their nutrient uptake capacity, here defined as the nutrient uptake rate under standardized conditions, a bioassay was performed on excised roots (<1 mm) of eight oak trees (Quercus robur L.). The results showed that the root uptake rate of ⁸⁶Rb⁺ (used as an analogue for K⁺) declined with increasing soil depth, and the same trend was found for . The root uptake rate of , on the other hand, did not decrease with soil depth. These different physiological responses in relation to soil depth indicate differences in the oak roots, and suggest that fine roots in shallow soil layers may be specialized in taking up nutrients such as K⁺ and which have a high availability in these layers, while oak roots in deep soil layers are specialized in taking up other resources, such as P, which may have a high availability in deep soil layers. Regardless of the cause of the difference in uptake trends for the various nutrients, these differences have consequences for the modelling of the soil nutrient pool beneath oak trees and raise the question of whether roots can be treated uniformly, as has previously been done in forest ecosystem models. Responsible Editor: Herbert Johannes Kronzucker.     

Quantifying the risk of mis-estimating correlation significance of climate–tree growth relationships

In dendroecology, sampling effort has a strong influence of both regional chronology properties and climate–tree growth relationships assessment. Recent studies evidenced that decreasing sample size leads to a weakening of the bootstrapped correlation coefficients ( ${\text{BCC}}$ BCC ). The present analysis focused on the risk of mis-estimating the significance of population ${\text{BCC}}\,\left( {{\text{BCC}}_{\text{POP}} } \right)$ BCC ( BCC POP ) from a sample of N trees, and then proposed an approach to detect and correct mis-estimations using the properties of the sample. The sample size effect and the limits of the correction were illustrated from 840 individual growth chronologies of Corsican pine (Pinus nigra Arnold ssp. laricio Poiret var. Corsicana) sampled in Western France. The 840 trees were used to assess the population characteristics, and the effect of sampling effort was investigated through a simulation approach based on a resampling procedure of N trees amongst 840 (N ? [5; 50]). Our results evidenced that the risk strongly varied amongst the climatic regressors. The highest risks were evidenced for significant ${\text{BCC}}_{\text{POP}}$ BCC POP , with a percentage of mis-estimation ranging from 25 to 80. On the contrary, small samples allowed providing an reliable estimation of the significance of non-significant ${\text{BCC}}_{\text{POP}}$ BCC POP . To a lesser extent, the risk slightly decreased with increasing N, according to a negative exponential trend. The detection and correction method was found relevant to detect mis-estimation only for significant ${\text{BCC}}_{\text{POP}}$ BCC POP ; otherwise, the ${\text{BCC}}_{\text{POP}}$ BCC POP significance was generally overestimated.     

Long-term analysis of Hubbard Brook stable oxygen isotope ratios of streamwater and precipitation sulfate

In response to decreasing atmospheric emissions of sulfur (S) since the 1970s there has been a concomitant decrease in S deposition to watersheds in the Northeastern U.S. Previous study at the Hubbard Brook Experimental Forest, NH (USA) using chemical and isotopic analyzes ( $ \delta^{34} {\text{S}}_{{{\text{SO}}_{4} }} $ ) combined with modeling has suggested that there is an internal source of S within these watersheds that results in a net loss of S via sulfate in drainage waters. The current study expands these previous investigations by the utilization of δ¹⁸O analyzes of precipitation sulfate and streamwater sulfate. Archived stream and bulk precipitation samples at the Hubbard Brook Experimental Forest from 1968–2004 were analyzed for stable oxygen isotope ratios of sulfate ( $ \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} $ ). Overall decreasing temporal trends and seasonally low winter values of $ \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} $ in bulk precipitation are most likely attributed to similar trends in precipitation $ \delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}} $ values. Regional climate trends and changes in temperature control precipitation $ \delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}} $ values that are reflected in the $ \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} $ values of precipitation. The significant relationship between ambient temperature and the $ \delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}} $ values of precipitation is shown from a nearby site in Ottawa, Ontario (Canada). Although streamwater $ \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} $ values did not reveal temporal trends, a large difference between precipitation and streamwater $ \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} $ values suggest the importance of internal cycling of S especially through the large organic S pool and the concomitant effect on the $ \delta^{18} {\text{O}}_{{{\text{SO}}_{4} }} $ values in drainage waters.     

Release of non-exchangeable {}^{{{\text{15}}}}{\text{NH}}^{{\text{ + }}}_{{\text{4}}} from subgrade, decomposed granite substrates and uptake by non-mycorrhizal and mycorrhizal California native annual grass, Vulpia microstachys

Release rates of recently fixed $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ from non-exchangeable interlayer sites in 2:1 silicate minerals were determined for decomposed granite (DG) saprolites from three locations in California, USA. Recently-fixed $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ release from the DG substrate was quantified by extracting diffused $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ with H-resin, as well as a native, annual grass Vulpia microstachys. The $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ release data varied with via the method of extraction, which included H-resin pre-treatments (Na⁺ or H⁺) and V. microstachys uptake (mycorrhizal inoculated or uninoculated). After 6 weeks (1008 h), more $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ was recovered from fixed interlayer positions by the H-resins as compared to uptake by V. microstachys. The H⁺ treated H-resins recovered more released $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ (≈94 mg ${\text{NH}}^{{\text{ + }}}_{{\text{4}}} - {\text{N}}\;{\text{kg}}^{1} $ or (12%) of total fixed $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ ) in two of the three DG samples as compared to the Na⁺ treated resins, (which recovered ≈70–78 mg ${\text{NH}}^{{\text{ + }}}_{{\text{4}}} - {\text{N}}\;{\text{kg}}^{{{\text{ - 1}}}} $ (or 9–10%) of the total fixed $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ ). The V. microstachys assimilated 8–9% of the total fixed $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ with mycorrhizal inoculum as compared to only 2% without a mycorrhizal inoculum, over the same time period. The fixed $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ release kinetics from the H-resin experiments were most accurately described by first order and power function models, and can be characterized as biphasic using a heterogeneous diffusion model. Uptake of both the ¹⁵N and ambient, unlabelled N from the soils was closely related to plant biomass. There was no significant difference in percent of N per unit of biomass between the control and mycorrhizal treatments. The findings presented here indicate that observed, long-term $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ release rates from DG in studies utilizing resins, may overestimate the levels of fixed $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ made available to plants and microorganisms. Additionally, the study suggested that mycorrhizae facilitate the acquisition and plant uptake of fixed $ {\text{NH}}^{{\text{ + }}}_{{\text{4}}} $ , resulting in markedly increased plant biomass production.     

Estimation of viscosity from passage time of liquids flowing through a microchannel array

Recently, a microchannel flow analyzer (MC-FAN) has been used to study the flow properties of blood. However, the correlation between blood passage time measured by use of the MC-FAN and hemorheology has not been clarified. In this study, a simple model is proposed for estimation of liquid viscosity from the passage time t _p of liquids. The t _p data for physiological saline were well represented by the model. According to the model, the viscosity of Newtonian fluids was estimated reasonably well from the t _p data. For blood samples, although the viscosity $ \eta_{\text{mc}} $ estimated from t _p was shown to be smaller than the viscosity $ \eta_{{450{\text{s}}^{ - 1} }} $ measured by use of a rotatory viscometer at a shear rate of 450 s^?1, $ \eta_{\text{mc}} $ was correlated with $ \eta_{{450{\text{s}}^{ - 1} }} $ . An empirical equation for estimation of $ \eta_{{450{\text{s}}^{ - 1} }} $ from $ \eta_{\text{mc}} $ of blood samples is proposed.     

The effects of temperature and exercise training on swimming performance in juvenile qingbo (Spinibarbus sinensis)

To investigate the effects of temperature and exercise training on swimming performance in juvenile qingbo (Spinibarbus sinensis), we measured the following: (1) the resting oxygen consumption rate $ \left( {{\dot{\text{M}}\text{O}}_{{ 2 {\text{rest}}}} } \right) $ , critical swimming speed (U _crit) and active oxygen consumption rate $ \left( {{\dot{\text{M}}\text{O}}_{{ 2 {\text{active}}}} } \right) $ of fish at acclimation temperatures of 10, 15, 20, 25 and 30 °C and (2) the $ \dot{M}{\text{O}}_{{ 2 {\text{rest}}}} $ , U _crit and $ \dot{M}{\text{O}}_{{ 2 {\text{active}}}} $ of both exercise-trained (exhaustive chasing training for 14 days) and control fish at both low and high acclimation temperatures (15 and 25 °C). The relationship between U _crit and temperature (T) approximately followed a bell-shaped curve as temperature increased: U _crit = 8.21/{1 + [(T ? 27.2)/17.0]²} (R ² = 0.915, P < 0.001, N = 40). The optimal temperature for maximal U _crit (8.21 BL s^?1) in juvenile qingbo was 27.2 °C. Both the $ \dot{M}{\text{O}}_{{ 2 {\text{active}}}} $ and the metabolic scope (MS, $ \dot{M}{\text{O}}_{{ 2 {\text{active}}}} - \dot{M}{\text{O}}_{{ 2 {\text{rest}}}} $ ) of qingbo increased with temperature from 10 to 25 °C (P < 0.05), but there were no significant differences between fish acclimated to 25 and 30 °C. The relationships between $ \dot{M}{\text{O}}_{{ 2 {\text{active}}}} $ or MS and temperature were described as $ {\dot{\text{M}}\text{O}}_{{ 2 {\text{active}}}} = 1,214.29/\left\{ {1 + \left[ {\left( {T - 28.8} \right)/10.6} \right]^{2} } \right\}\;\left( {R^{2} = 0.911,\;P < 0.001,\;N = 40} \right) $ and MS = 972.67/{1 + [(T ? 28.0)/9.34]²} (R ² = 0.878, P < 0.001, N = 40). The optimal temperatures for $ \dot{M}{\text{O}}_{{ 2 {\text{active}}}} $ and MS in juvenile qingbo were 28.8 and 28.0 °C, respectively. Exercise training resulted in significant increases in both U _crit and $ \dot{M}{\text{O}}_{{ 2 {\text{active}}}} $ at a low temperature (P < 0.05), but training exhibited no significant effect on either U _crit or $ \dot{M}{\text{O}}_{{ 2 {\text{active}}}} $ at a high temperature. These results suggest that exercise training had different effects on swimming performance at different temperatures. These differences may be related to changes in aerobic metabolic capability, arterial oxygen delivery, available dissolved oxygen, imbalances in ion fluxes and stimuli to remodel tissues with changes in temperature.     

Litterfall and litter nutrient dynamics under cocoa ecosystems in lowland humid Ghana

There have been few studies quantifying litterfall, standing litterstock and gross litter decomposition following forest conversion to plantation crops such as cocoa. Additionally, an assessment of changing processes occurring in forest floor litter systems with plantation age is lacking. We investigated litterfall production, standing litter changes and litter decomposition along a chronosequence of shaded cocoa farm fields (secondary forest, 3, 15 and 30-year-old) in the moist semi-deciduous forest belt in the Ashanti Region of Ghana in West Africa over 24 months. Mean annual litterfall production differed significantly among study sites and ranged from 5.0 to 10.4 Mg DM ha^?1. Similarly, standing litter differed significantly between land-use /plot ages. The results showed significant differences in quality between litter from forest and litter from cocoa plantations. Litterfall from forests had higher concentrations of nitrogen and lower concentration of soluble polyphenols and lignin compared to litter from cocoa systems. Monthly decomposition coefficients (k) estimated as $ k = {{\left( {{\text{A}} - \left( {{\text{L}}_1 - {\text{L}}_0 } \right)} \right)} \mathord{\left/ {\vphantom {{\left( {{\text{A}} - \left( {{\text{L}}_1 - {\text{L}}_0 } \right)} \right)} {\left( {{{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} \mathord{\left/ {\vphantom {{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} 2}} \right. } 2}} \right)}}} \right. } {\left( {{{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} \mathord{\left/ {\vphantom {{\left( {{\text{L}}_1 + {\text{L}}_0 } \right)} 2}} \right. } 2}} \right)}} $ , where A is litterfall production during the month, L₀ is the standing litterstock at the beginning of the month and L₁ is the standing litterstock at the end of the month. Annual decomposition coefficients (k _L ) were similar in cocoa systems (0.221–0.227) but higher under secondary forests (0.354). Correlations between litter quality parameters and the decomposition coefficient showed nitrogen and lignin concentrations as well as ratios that include nitrogen are the best predictors of decomposition for the litters studied. Our results confirm the hypothesis that decomposition decreases following forest conversion to shaded cocoa systems because of litter quality changes and that decomposition rates correlate to litter quality differences between forest and cocoa ecosystems. The study also showed that standing litter pools and litterfall production in recently converted cocoa plantations are low compared to secondary forests or mature cocoa systems. Management strategies involving the introduction of upper canopy species during plantation development with corresponding replacement of tree mortality with diverse fast growing species will provide high quality and quantity litter resources.     

Utilization of cyclohexanone and related substances by a Nocardia sp.

A species of the genus Nocardia that could utilize cyclohexanone as a sole carbon source was isolated from soil. Cyclohexanone-grown cultures grew readily on cyclohexanol, cis, trans-cyclohexane-1,2-diol, cis-cyclohexane-1,2-diol, adipic acid and 2-hydroxycyclohexane-1-one without a noticeable lag period. The bacterium also grew on pimelic acid but only after a lag period of 4 days. Resting cell suspensions of cyclohexanone-grown cells were found to oxidize cyclohexanone, cyclohexanol, cyclohexane-1,2-dione, cis, trans-cyclohexane-1,2-diol and 2-hydroxycyclohexane-1-one at high \({\text{Q}}_{{\text{O}}_{\text{2}} }\) values. Evidence was obtained that indicated that the bacterium degraded cyclohexanone via 2-hydroxycyclohexane-1-one.     

Retention of Dissolved Inorganic Nitrogen by Foliage and Twigs of Four Temperate Tree Species

Nitrogen (N) retention by tree canopies is believed to be an important process for tree nutrient uptake, and its quantification is a key issue in determining the impact of atmospheric N deposition on forest ecosystems. Due to dry deposition and retention by other canopy elements, the actual uptake and assimilation by the tree canopy is often obscured in throughfall studies. In this study, ¹⁵N-labeled solutions ( $ ^{15} {\text{NH}}_{4}^{ + } $ and $ ^{15} {\text{NO}}_{3}^{ - } $ ) were used to assess dissolved inorganic N retention by leaves/needles and twigs of European beech, pedunculate oak, silver birch, and Scots pine saplings. The effects of N form, tree species, leaf phenology, and applied $ {\text{NO}}_{3}^{ - } $ to $ {\text{NH}}_{4}^{ + } $ ratio on the N retention were assessed. Retention patterns were mainly determined by foliar uptake, except for Scots pine. In twigs, a small but significant ¹⁵N enrichment was detected for $ {\text{NH}}_{4}^{ + } $ , which was found to be mainly due to physicochemical adsorption to the woody plant surface. The mean $ {{^{15} {\text{NH}}_{4}^{ + } } \mathord{\left/ {\vphantom {{^{15} {\text{NH}}_{4}^{ + } } {^{15} {\text{NO}}_{3}^{ - } }}} \right. \kern-0em} {^{15} {\text{NO}}_{3}^{ - } }} $ retention ratio varied considerably among species and phenological stadia, which indicates that the use of a fixed ratio in the canopy budget model could lead to an over- or underestimation of the total N retention. In addition, throughfall water under each branch was collected and analyzed for $ ^{15} {\text{NH}}_{4}^{ + } $ , $ ^{15} {\text{NO}}_{3}^{ - } $ , and all major ions. Net throughfall of $ ^{15} {\text{NH}}_{4}^{ + } $ was, on average, 20 times higher than the actual retention of $ ^{15} {\text{NH}}_{4}^{ + } $ by the plant material. This difference in $ ^{15} {\text{NH}}_{4}^{ + } $ retention could not be attributed to pools and fluxes measured in this study. The retention of $ ^{15} {\text{NH}}_{4}^{ + } $ was correlated with the net throughfall of K⁺, Mg²⁺, Ca²⁺, and weak acids during leaf development and the fully leafed period, while no significant relationships were found for $ ^{15} {\text{NO}}_{3}^{ - } $ retention. This suggests that the main driving factors for $ {\text{NH}}_{4}^{ + } $ retention might be ion exchange processes during the start and middle of the growing season and passive diffusion at leaf senescence. Actual assimilation or abiotic uptake of N through leaves and twigs was small in this study, for example, 1–5% of the applied dissolved ¹⁵N, indicating that the impact of canopy N retention from wet deposition on forest productivity and carbon sequestration is likely limited.     

Comparative studies on the photosynthetic responses of three freshwater phytoplankton species to temperature and light regimes

The photosynthetic responses of Microcystis aeruginosa, Scenedesmus obliquus, and Cyclotella meneghiniana to temperature and light regimes were investigated. M. aeruginosa had a higher specific growth rate at 30°C than at 14 and 20°C. Its specific growth rate was the maximum among the three species at 30°C. This suggests that M. aeruginosa could predominate in a water body having high temperature. When exposed to high light, M. aeruginosa showed lower maximal photosystem II (PSII) quantum yield (Φ_M), operational PSII quantum yield ( $ \Phi_{\text{M}}^{\prime } $ ), and active reaction centers per excited cross section (RC/CS_m) than S. obliquus and C. meneghiniana. Moreover, after 2?h low light recovery at 14°C and 20°C, the recovery of Φ_M, $ \Phi_{\text{M}}^{\prime } $ and RC/CS_m in M. aeruginosa were less than the other two species. This indicates that the capacity of high light adaptation of M. aeruginosa is the lowest among the studied species at 14–20°C. When exposed to high light, C. meneghiniana had higher Φ_M and $ \Phi_{\text{M}}^{\prime } $ lost and induced higher nonphotochemical quenching at 14–20°C. This suggests that C. meneghiniana developed a higher resistance to high light under low growth temperatures. M. aeruginosa showed the lowest light compensation point among these three species, which indicates that it could utilize low light more efficiently than the other two species. Cyclic electron flow around PSII may play a role in the photoprotective mechanism of all these three species.     

High resolution imaging to assess oilseed species?? root hair responses to soil water stress

An imaging method was developed to evaluate crop species differences in root hair morphology using high resolution scanners, and to determine if the method could also detect root hair responses to soil water availability. High resolution (1890 picture elements (pixels) cm^?1) desktop scanners were buried in containers filled with soil to characterize root hair development under two water availability levels (?63 and ?188?kPa) for canola (Brassica napus L. cv Clearwater), camelina (Camelina sativa L. Crantz cv Cheyenne), flax (Linum usitatissimum L. cv CDC Bethune), and lentil (Lens culinaris Medik. cv Brewer). There was notable effect of available moisture on root hair geometry (RHG). At ?188?kPa, length from the root tip to the root hair initiation zone decreased and root hair length (RHL) became more variable near the root hair initiation zone as compared to ?63?kPa. For the response of primary axial RHL, significant main effects were present for both water availability (P?<?0.05) and species (P?<?0.0001); lateral RHL showed a significant main effect for both water availability (P?<?0.05) and species (P?<?0.01) as well. For both primary axial and lateral root hair density (RHD), there was a significant effect of species (P?<?0.0001), but no significant response to water availability. No water availability x species interaction was present in any case. Low available water reduced RHL in both primary axial and lateral roots. The change in RHL due to water availability was most evident in canola and camelina. Additionally, those with greater RHL $ \left( {\text{canola} = \text{camelina} > \text{flax} = \text{lentil}} \right) $ had lower RHD $ \left( {\text{canola} = \text{camelina} < \text{flax} < \text{lentil}} \right) $ in primary axial roots and a similar trend was found in lateral RHL. Both water and species had a significant effect on primary axial root surface area (RSA) (P?<?0.05) but no significant effect was found for lateral RSA. For primary axial RSA the longest and most dense root hair had the greatest RSA. This novel approach to in situ rhizosphere imaging allowed observation of species differences in root hair development in response to water availability and should be useful in future studies of rhizosphere interactions and crop water and nutrient management.     

Third-Order Nonlinear Optical Response of Layered Composites Materials Containing Gold Nanoparticles

Nonlinear third-order susceptibility \(\chi _{\text {eff}}^{(3)}\) of composites materials having alternated layers of dielectric and plasmonic nanostructures of gold nanoparticles was theoretically studied using the effective medium theory and the degenerate electron gas model. Real and imaginary parts of χeff(3) for the proposed composite material were calculated for the spectral region around the plasmon resonance of gold nanoparticles. The results reveal an enhanced nonlinear optical response compared with the obtained one for individual layers, as well as a reversal signal of \(\chi _{\text {eff}}^{(3)}\) for different volume fraction conditions.     

Longitudinal distribution of nitrate δ15N and δ18O in two contrasting tropical rivers: implications for instream nitrogen cycling

The longitudinal variations in the nitrogen (δ¹⁵N) and oxygen (δ¹⁸O) isotopic compositions of nitrate (NO₃ ^?), the carbon isotopic composition (δ¹³C) of dissolved inorganic carbon (DIC) and the δ¹³C and δ¹⁵N of particulate organic matter were determined in two Southeast Asian rivers contrasting in the watershed geology and land use to understand internal nitrogen cycling processes. The $ \delta^{15} {\text{N}}_{{{\text{NO}}_{3} }} $ became higher longitudinally in the freshwater reach of both rivers. The $ \delta^{18} {\text{O}}_{{{\text{NO}}_{3} }} $ also increased longitudinally in the river with a relatively steeper longitudinal gradient and a less cultivated watershed, while the $ \delta^{18} {\text{O}}_{{{\text{NO}}_{3} }} $ gradually decreased in the other river. A simple model for the $ \delta^{15} {\text{N}}_{{{\text{NO}}_{3} }} $ and the $ \delta^{18} {\text{O}}_{{{\text{NO}}_{3} }} $ that accounts for simultaneous input and removal of NO₃ ^? suggested that the dynamics of NO₃ ^? in the former river were controlled by the internal production by nitrification and the removal by denitrification, whereas that in the latter river was significantly affected by the anthropogenic NO₃ ^? loading in addition to the denitrification and/or assimilation. In the freshwater-brackish transition zone, heterotrophic activities in the river water were apparently elevated as indicated by minimal dissolved oxygen, minimal δ¹³C_DIC and maximal pCO₂. The δ¹⁵N of suspended particulate nitrogen (PN) varied in parallel to the $ \delta^{15} {\text{N}}_{{{\text{NO}}_{3} }} $ there, suggesting that the biochemical recycling processes (remineralization of PN coupled to nitrification, and assimilation of NO₃ ^?-N back to PN) played dominant roles in the instream nitrogen transformation. In the brackish zone of both rivers, the $ \delta^{15} {\text{N}}_{{{\text{NO}}_{3} }} $ displayed a declining trend while the $ \delta^{18} {\text{O}}_{{{\text{NO}}_{3} }} $ increased sharply. The redox cycling of NO₃ ^?/NO₂ ^? and/or deposition of atmospheric nitrogen oxides may have been the major controlling factor for the estuarine $ \delta^{15} {\text{N}}_{{{\text{NO}}_{3} }} $ and $ \delta^{18} {\text{O}}_{{{\text{NO}}_{3} }} $ , however, the exact mechanism behind the observed trends is currently unresolved.     

Disturbances on a Wooded Raised Bog—How Windthrow, Bark Beetle and Fire Affect Vegetation and Soil Water Quality?

Pinus rotundata dominated peatbog (?ofinka Nature Reserve) in the T?eboň Basin, Czech Republic, was affected by “natural” disturbances: wind damage (1984), followed by a bark beetle attack, and fire (1994, 2000). Phytosociological relevés were used to document vegetation. Soil water chemistry was compared in three differently affected stands: (1) an undisturbed Pinus rotundata bog forest, (2) a windthrow – bark beetle affected stand and (3) a site burned by wildfire in 2000. The species composition of the windthrow – bark beetle affected sites and the undisturbed P. rotundata bog forest differed mainly in the shrub and tree layers. Burned sites were partly colonized by anemochorous species (e.g. Taraxacum sp. div.) that disappeared within two or three years after colonization. Bare peat was colonized by bryophytes (e.g. Marchantia polymorpha and Funaria hygrometrica) typical of the disturbed sites, and by Polytrichum sp. div. and Aulacomnium palustre. Most plant species characteristic of the P. rotundata bog forest occurred at the burned sites eight years after the fire, but in different abundances. The edificator of the former community—P. rotundata—was mostly absent. Compared with windthrow followed by the bark beetle attack, fire promoted rapid expansion of Molinia caerulea. Soil water in both the undisturbed P. rotundata bog forest and the windthrow – bark beetle affected sites had a similar composition: very low pH values, high P concentrations, low concentrations of cations (Ca²⁺, Mg²⁺and K⁺) and inorganic nitrogen. The concentrations of soluble reactive phosphorus (SRP) and ${\text{NH}}_4^ + - {\text{N}}$ were negatively correlated with the groundwater table. Total P, SRP and ${\text{NH}}_4^ + - {\text{N}}$ concentrations in the soil water at the burned site were by one order of magnitude higher than those in the P. rotundata bog forest, while concentrations of K⁺, Mg²⁺ and Ca²⁺ were only about two times higher. High concentrations of P and N in the soil water found three years after the fire indicated a long-term elevated nutrient content in the soil water.     

Weeds influence soil bacterial and fungal communities

Background and aims

Vineyards harbour a variety of weeds, which are usually controlled since they compete with grapevines for water and nutrients. However, weed plants may host groups of fungi and bacteria exerting important functions.

Methods

We grew three different common vineyard weeds (Taraxacum officinalis, Trifolium repens and Poa trivialis) in four different soils to investigate the effects of weeds and soil type on bacterial and fungal communities colonising bulk soil, rhizosphere and root compartments. Measurements were made using the cultivation-independent technique Automated Ribosomal Intergenic Spacer Analysis (ARISA).

Results

Weeds have a substantial effect on roots but less impact on the rhizosphere and bulk soil, while soil type affects all three compartments, in particular the bulk soil community. The fungal, but not the bacterial, bulk soil community structure was affected by the plants at the late experimental stage. Root communities contained a smaller number of Operational Taxonomic Units (OTUs) and different bacterial and fungal structures compared with rhizosphere and bulk soil communities.

Conclusions

Weed effect is localised to the rhizosphere and does not extend to bulk soil in the case of bacteria, although the structure of fungal communities in the bulk soil may be influenced by some weed plants.     

Interaction of ascorbate with photosystem I

Ascorbate is one of the key participants of the antioxidant defense in plants. In this work, we have investigated the interaction of ascorbate with the chloroplast electron transport chain and isolated photosystem I (PSI), using the EPR method for monitoring the oxidized centers \( {\text{P}}_{700}^{ + } \) and ascorbate free radicals. Inhibitor analysis of the light-induced redox transients of P₇₀₀ in spinach thylakoids has demonstrated that ascorbate efficiently donates electrons to \( {\text{P}}_{ 7 0 0}^{ + } \) via plastocyanin. Inhibitors (DCMU and stigmatellin), which block electron transport between photosystem II and Pc, did not disturb the ascorbate capacity for electron donation to \( {\text{P}}_{700}^{ + } \) . Otherwise, inactivation of Pc with CN^? ions inhibited electron flow from ascorbate to \( {\text{P}}_{700}^{ + } \) . This proves that the main route of electron flow from ascorbate to \( {\text{P}}_{700}^{ + } \) runs through Pc, bypassing the plastoquinone (PQ) pool and the cytochrome b ₆ f complex. In contrast to Pc-mediated pathway, direct donation of electrons from ascorbate to \( {\text{P}}_{700}^{ + } \) is a rather slow process. Oxidized ascorbate species act as alternative oxidants for PSI, which intercept electrons directly from the terminal electron acceptors of PSI, thereby stimulating photooxidation of P₇₀₀. We investigated the interaction of ascorbate with PSI complexes isolated from the wild type cells and the MenB deletion strain of cyanobacterium Synechocystis sp. PCC 6803. In the MenB mutant, PSI contains PQ in the quinone-binding A₁-site, which can be substituted by high-potential electron carrier 2,3-dichloro-1,4-naphthoquinone (Cl₂NQ). In PSI from the MenB mutant with Cl₂NQ in the A₁-site, the outflow of electrons from PSI is impeded due to the uphill electron transfer from A₁ to the iron-sulfur cluster F_X and further to the terminal clusters F_A/F_B, which manifests itself as a decrease in a steady-state level of \( {\text{P}}_{700}^{ + } \) . The addition of ascorbate promoted photooxidation of P₇₀₀ due to stimulation of electron outflow from PSI to oxidized ascorbate species. Thus, accepting electrons from PSI and donating them to \( {\text{P}}_{700}^{ + } \) , ascorbate can mediate cyclic electron transport around PSI. The physiological significance of ascorbate-mediated electron transport is discussed.     

Metabolism and thermoregulation in desert and montane grasshoppers

Temperature regulation and oxygen consumption were examined in two species of grasshoppers: Melanoplus sanguinipes from cold alpine tundra at elevation 3,800 m, and Trimerotropis pallidipennis from hot desert habitats at elevation 250 m. Both species utilized behavioral thermoregulation to keep body temperature (T _b ) more constant than environmental temperatures (T _e ) during the day. The difference in average T _b in the two species was much less than the difference in T _e 's. Microclimate measurements indicate that temperature regulation is not difficult for M. sanguinipes, but T. pallidipennis must restrict activity for much of the day to avoid heat stress and can easily overheat if it moves into sunlit areas. Oxygen consumption ( \(\dot V{\text{O}}_{\text{2}} \) ) at average T _b and total daily energy expenditures are higher in M. sanguinipes than in T. pallidipennis, as is the Q₁₀ for \(\dot V{\text{O}}_{\text{2}} \) . These differences may be related to different strategies for energy utilization and predator avoidance.     

Relative CO2/NH3 Permeabilities of Human RhAG, RhBG and RhCG

Mammalian glycosylated rhesus (Rh) proteins include the erythroid RhAG and the nonerythroid RhBG and RhCG. RhBG and RhCG are expressed in multiple tissues, including hepatocytes and the collecting duct (CD) of the kidney. Here, we expressed human RhAG, RhBG and RhCG in Xenopus oocytes (vs. H₂O-injected control oocytes) and used microelectrodes to monitor the maximum transient change in surface pH (ΔpH_S) caused by exposing the same oocyte to 5 % CO₂/33 mM HCO₃ ^? (an increase) or 0.5 mM NH₃/NH₄ ⁺ (a decrease). Subtracting the respective values for day-matched, H₂O-injected control oocytes yielded channel-specific values (*). $({\Updelta {\text{pH}}_{\text{S}}^{*} })_{{{\text{CO}}_{ 2} }}$ and $({ - \Updelta {\text{pH}}_{\text{S}}^{*} })_{{{\text{NH}}_{ 3} }}$ were each significantly >0 for all channels, indicating that RhBG and RhCG—like RhAG—can carry CO₂ and NH₃. We also investigated the role of a conserved aspartate residue, which was reported to inhibit NH₃ transport. However, surface biotinylation experiments indicate the mutants RhBG_D178N and RhCG_D177N have at most a very low abundance in the oocyte plasma membrane. We demonstrate for the first time that RhBG and RhCG—like RhAG—have significant CO₂ permeability, and we confirm that RhAG, RhBG and RhCG all have significant NH₃ permeability. However, as evidenced by $({\Updelta {\text{pH}}_{\text{S}}^{*} })_{{{\text{CO}}_{ 2} }} /({ - \Updelta {\text{pH}}_{\text{S}}^{*} })_{{{\text{NH}}_{ 3} }}$ values, we could not distinguish among the CO₂/NH₃ permeability ratios for RhAG, RhBG and RhCG. Finally, we propose a mechanism whereby RhBG and RhCG contribute to acid secretion in the CD by enhancing the transport of not only NH₃ but also CO₂ across the membranes of CD cells.