Gas Exchange and Epidermal Characteristics of Miscanthus Populations in Taiwan Varying with Habitats and Nitrogen Application

Seventeen clones of C₄ grass Miscanthus spp. collected from different climatic regions and elevations of Taiwan were transplanted in pots. 15–16 months after collection the plants received 0, 1, and 2 g of nitrogen fertiliser (N₀, N₁, and N₂, respectively) per pot. All the measurements were done 10–12 d after N application. The relationships between net photosynthetic rate (P _N) and photon flux density (PFD) showed a saturated curve, with PFD saturation at about 1 000 µmol m^–2 s^–1. The ranges of PFD saturated P _N (P _sat) for all the tested clones with N₀, N₁, and N₂ were 8–16, 11–18, and 12–21 µmol m^–2 s^–1, respectively. The clones from southern Taiwan, a tropical region, showed the highest P _sat, followed by the clones from northern Taiwan, a subtropical region, while those from mountainous area showed the lowest P _sat. The clones collected from southern Taiwan showed the highest frequency of stomata on the adaxial surface, and those collected from the high mountainous area showed the lowest frequency. Also the adaxial surface of leaves from the higher mountainous area had more wax deposited than the leaves from the lowland. Thus the low P _sat in mountain clones is limited by both stomatal and non-stomatal factors. Further, the lower leaf conductance and different epidermal characteristics of mountain clones might prevent excessive loss of heat through transpiration and provide production against ultraviolet-B radiation.     

Specific IgE and IgG4 antibodies to Japanese cedar pollen and total IgE antibody in lumbermen

Serum levels of specific IgE and IgG4 antibodies to Japanese cedar (Cryptomeria japonica) pollen and total IgE antibody in 75 lumbermen and in 53 male office workers at an urban establishment were measured by means of an enzyme linked immunosorbent assay (ELISA) and compared. No significant differences of specific IgE and IgG4 to cedar pollen and total IgE were found between the lumbermen and the office workers. There were no significant differences of incidence of cedar pollinosis and positive (greater than 100 FU/ml) rate of serum specific IgE between the two groups, though the lumbermen were exposed to dense concentrations of cedar pollen in their working area. In the lumbermen who showed positive values of specific IgE, the mean value of the specific antibody in Japanese cedar pollinosis lumbermen was significantly higher than that in symptom-free lumbermen, while no significant differences of serum level of specific IgG4 were found between the two groups.     

Patterns of stable S isotopes in a forested catchment as indicators for biological S turnover

Despite intensive biogeochemical research during the last thirty years, the relative importance of biological S turnover for the overall SO ₄ ^2– budget of forested catchments remains uncertain. The objective of the present study was (i) to gain new insight into the S cycle of theLehstenbach catchment (Northeastern Bavaria, Germany) through the analysis of stable isotopes of S and (ii) to differentiate between sites which are hot spots for SO ₄ ^2– reduction and sites where mineralization and adsorption/desorption processes are more important. The ³⁴S values and SO ₄ ^2– concentrations of soil solutions, throughfall and groundwater at four different sites as well as runoff of the catchment were measured. The relatively low variability of ³⁴S in throughfall and bulk precipitation was in contrast to the high temporal and spatial variability of ³⁴S in the soil solution. Sulfate in the soil solution of upland sites was slightly depleted in³⁴S compared to input values. This was most likely due to S mineralization. Sulfate in the soil solution from wetland soils was clearly enriched in³⁴S, indicating dissimilatory SO ₄ ^2– reduction. The observed spatial and temporal patterns of³⁴S turnover and SO ₄ ^2– concentrations might explain the overall balanced S budget of the catchment. At a time of decreasing anthropogenic deposition SO ₄ ^2– is currently released from upland soils. Furthermore, mineralization of organic S may contribute to SO ₄ ^2– release. Wetland soils in the catchment represent a sink for SO ₄ ^2– due to dissimilatory SO ₄ ^2– reduction.     

Atmospheric deposition of nutrients to the North Atlantic Basin

Atmospheric chemical models are used to estimate the deposition rate of various inorganic oxides of nitrogen (NO_y), reduced nitrogen species (NH_x) and mineral dust to the North Atlantic Ocean (NAO). The estimated deposition of NO_y to the NAO (excluding the coastal ocean) and the Caribbean is 360 × 10⁹ Moles-N m^–2 yr^–1 (5.0 Tg N); this is equivalent to about 13% of the estimated global emission rate (natural and anthropogenic) and a quarter of the emission rate from sources in North America and Europe. In the case of NH_x, 258 Moles-N m^–2 yr^–1 (3.6 Tg N) are deposited to the NAO and the Caribbean; this is about 6% of the global continental emissions. There is relatively little data on the deposition rate of organic nitrogen species; nonetheless, this evidence suggests that concentrations and deposition rates are comparable to those for inorganic nitrogen.Because of anthropogenic emissions, the present-day deposition rate of NO_y to the NAO is about five times greater than pre-industrial times largely due to emissions from energy production and biomass burning. The present-day emissions of NH_x from continental anthropogenic sources are about four-to-five times greater than natural sources, mostly due to the impact of emissions from animal wastes associated with food production. Indeed, present-day emissions of NH_x from animal waste are estimated to be about 10 times greater than the pre-human era. The deposition rate of mineral dust to the NAO is about 170 Tg yr^–1; deposited with the dust (assuming average crustal abundances) is about 6 Tg yr^–1 of Fe and 0.2 Tg yr^–1 of P. Dust deposition in the NAO is almost completely attributable to transport from North African sources; a substantial fraction of the dust over the NAO is probably mobilized as a consequence of land use practices in arid regions and, consequently, it should be regarded as a pollutant.     

Losses of inorganic carbon and nitrous oxide from a temperate freshwater wetland in relation to nitrate loading

We studied the export of inorganic carbon and nitrous oxide (N₂O) from a Danish freshwater wetland. The wetland is situated in an agricultural catchment area and is recharged by groundwater enriched with nitrate (NO₃ ^–) (1000 M). NO₃ ^– in recharging groundwater was reduced (57.5 mol NO₃ ^– m^–2 yr^–) within a narrow zone of the wetland. Congruently, the annual efflux of carbon dioxide (CO₂) from the sediment was 19.1 mol C m^–2 when estimated from monthly in situ measurements. In comparison the CO₂ efflux was 4.8 mol C m^–2 yr^–1 further out in the wetland, where no NO₃ ^– reduction occurred. Annual exports of inorganic carbon in groundwater and surface water was 78.4 mol C m^–2 and 6.1 mol C m^–2 at the two sites, respectively. N₂O efflux from the sedimenst was detectable on five out of twelve sampling dates and was significantly (P < 0.0001) higher in the NO₃ ^– reduction zone (0.35–9.40 mol m^–2 h^–1, range of monthly means) than in the zone without NO₃ ^– reduction (0.21–0.41 mol m^–2 h^–1). No loss of dissolved N₂O could be measured. Total annual export of N₂O was not estimated. The reduction of oxygen (O₂) in groundwater was minor throughout the wetland and did not exceed 0.2 mol 0₂ m^–2yr^–1. Sulfate (SO₄ ^––) was reduced in groundwater (2.1 mol SO₄ ^–– m^–2 yr^–1) in the zone without NO₃ ^– reduction. Although the NO₃ ^– in our wetland can be reduced along several pathways our results strongly suggest that NO₃ ^– loading of freshwater wetlands disturb the carbon balance of such areas, resulting in an accelerated loss of inorganic carbon in gaseous and dissolved forms.     

Episodic sulphate export from wetlands in acidified headwater catchments: prediction at the landscape scale

Sulphate (SO ₄ ^–2 ) concentrations in 34 intensively measured Canadian Shield streams near the Dorset Research Centre, central Ontario, were used to test a hydrogeologic model that uses simple measures of wetland area and till depth to identify catchments that produce SO ₄ ^–2 pulses. Mean annual measured maximum SO ₄ ^–2 concentrations were significantly greater in shallow till (<1 m depth) catchments containing wetlands than catchments covered with deeper tills (>1 m depth) containing wetlands or catchments with no wetlands. Average maximum SO ₄ ^–2 concentrations in wetland catchments during years with dry summers were >20 mg/L in 19 of 20 catchments with average till depths of <1 m, whereas concentrations were <20 mg/L in 5 of 6 watersheds with average till depths of >1 m. Peaks in mean annual maximum SO ₄ ^–2 concentrations from wetland catchments with shallow till occurred during summers with rain fall 150–200 mm less than potential evaporation estimates. There were no significant differences in mean average annual SO ₄ ^–2 concentration among the different catchments during wet summers, with SO ₄ ^–2 concentrations ranging from 6 to 13 mg/L. These observations suggest that a large portion of the temporal and spatial variation in SO ₄ ^–2 chemistry and export can be predicted in headwater catchments of the Canadian Shield and perhaps in other landscapes where till depth influences upland-wetland hydrologic connections.     

Effect of selected soil factors on chlorosis of peanut plants grown in calcareous soils in Cyprus

In 1986 and 1987 surveys were conducted of 34 (1986) and 35 (1987) peanut (Arachis hypogaea L.) fields in which the plants showed various degrees of chlorosis. In the areas concerned, plant appearance was classified according to a chlorotic index and corresponding soil samples were taken and analysed for CaCO₃, pH, NO₃–N and DTPA-extractable Fe in 1986 and for CaCO₃, NO₃–N and active lime in 1987.Regression analyses showed that CaCO₃, active lime and NO₃–N were positively correlated, while DTPA-extractable Fe was negatively correlated, with the chlorosis problem. The critical levels above which plants were chlorotic were 20 to 25% CaCO₃ and 10% active lime. Plants began to be chlorotic when DTPA-extractable Fe was below 2.5 mg·kg^–1. The soil factors examined explained about 60% of the variability in plant chlorosis.     

Processes affecting the response of sulfate concentrations to clearcutting in a northern hardwood forest, Catskill Mountains, New York, U.S.A.

The effects of disturbance on the biogeochemical processes that affect the sulfur (S) cycle in forested ecosystems are important, but have been studied in only a few locations. In this investigation, the mechanisms that caused large decreases in stream SO ₄ ^2– concentrations after clearcutting a small forested catchment in the Catskill Mountains of southeastern New York in 1997 were identified through an examination of pH and SO ₄ ^2– concentrations in soil solutions, bulk deposition of SO ₄ ^2– in throughfall collectors, adsorbed SO ₄ ^2– concentrations in buried soil bags, and spatial variations in SO ₄ ^2– concentrations in shallow groundwater. The load of SO ₄ ^2– –S in stream water during the first 2 years after clearcutting was about 2 kg ha^–1 year^–1 less than the background value of 8–10 kg ha^–1 year^–1. The 10 and 19% decrease in net throughfall flux of SO ₄ ^2– –S during the 2nd and 3rd year after the clearcut, respectively, reflects reduced dry deposition of S after removal of the canopy, but this decrease accounts for 0 and 43%, respectively, of the decrease in SO ₄ ^2– load in streamflow for these 2 years. The pH of B-horizon soil water decreased from 4.5 to 4.0 within 8 months after the clearcut, and SO ₄ ^2– concentrations decreased from 45 µmol L^–1 to less than 20 µmol L^–1 during this time. A strong correlation between SO ₄ ^2– concentrations and pH values (r ² = 0.71, p < 0.01) in B-horizon soil water during the post-harvest period (1997–1999) reflects increased SO ₄ ^2– adsorption in response to soil acidification. Sulfate concentrations in groundwater from 21 spatially distributed wells were inversely related to a topographic index that served as a surrogate for soil wetness; thus, providing additional evidence that SO ₄ ^2– adsorption was the dominant cause of the decreased SO ₄ ^2– concentrations in the stream after clearcutting. These results are consistent with those from a 1985 whole-tree harvest at the Hubbard Brook Experimental Forest in New Hampshire in which increased SO ₄ ^2– adsorption resulting from decreased soil pH was the primary cause of decreased SO ₄ ^2– concentrations in stream water.     

H2 oxidation,O2 uptake and CO2 fixation in hydrogen treated soils

In many legume nodules, the H₂ produced as a byproduct of N₂ fixation diffuses out of the nodule and is consumed by the soil. To study the fate of this H₂ in soil, a H₂ treatment system was developed that provided a 300 cm³ sample of a soil:silica sand (2:1) mixture with a H₂ exposure rate (147 nmol H₂ cm^–3hr^–1) similar to that calculated exist in soils located within 1–4 cm of nodules (30–254 nmol H₂ cm^–3hr^–1). After 3 weeks of H₂ pretreatment, the treated soils had a K_m and V_max for H₂ uptake (1028 ppm and 836 nmol cm^–3 hr^–1, respectively) much greater than that of control, air-treated soil (40.2 ppm and 4.35 nmol cm^–3 hr^–1, respectively). In the H₂ treated soils, O₂, CO₂ and H₂ exchange rates were measured simultaneously in the presence of various pH₂. With increasing pH₂, a 5-fold increase was observed in O₂ uptake, and CO₂ evolution declined such that net CO₂ fixation was observed in treatments of 680 ppm H₂ or more. At the H₂ exposure rate used to pretreat the soil, 60% of the electrons from H₂ were passed to O₂, and 40% were used to support CO₂ fixation. The effect of H₂ on the energy and C metabolism of soil may account for the well-known effect of legumes in promoting soil C deposition.     

Exchange of N-gases at the Höglwald Forest – A summary

During 4 years continuous measurements of N-trace gas exchange were carried out at the forest floor-atmosphere interface at the Höglwald Forest that is highly affected by atmospheric N-deposition. The measurements included spruce control, spruce limed and beech sites. Based on these field measurements and on intensive laboratory measurements of N₂-emissions from the soils of the beech and spruce control sites, a total balance of N-gas emissions was calculated. NO₂-deposition was in a range of –1.6 –2.9 kg N ha^–1 yr^–1 and no huge differences between the different sites could be demonstrated. In contrast to NO₂-deposition, NO- and N₂O-emissions showed a huge variability among the different sites. NO emissions were highest at the spruce control site (6.4–9.1 kg N ha^–1 yr^–1), lowest at the beech site (2.3–3.5 kg N ha^–1 yr^–1) and intermediate at the limed spruce site (3.4–5.4 kg N ha^–1 yr^–1). With regard to N₂O-emissions, the following ranking between the sites was found: beech (1.6–6.6 kg N ha^–1 yr^–1) >> spruce limed (0.7–4.0 kg N ha^–1 yr^–1) > spruce control (0.4–3.1 kg N ha^–1 yr^–1). Average N-trace gas emissions (NO, NO₂, N₂O) for the years 1994–1997 were 6.8 kg N ha^–1 yr^–1 at the spruce control site, 3.6 kg N ha^–1 yr^–1 at the limed spruce site and 4.5 kg N ha^–1 yr^–1 at the beech site. Considering N₂-losses, which were significantly higher at the beech (12.4 kg N ha^–1 yr^–1) than at the spruce control site (7.2 kg N ha^–1 yr^–1), the magnitude of total gaseous N losses, i.e. N₂-N + NO-N + NO₂-N + N₂O-N, could be calculated for the first time for a forest ecosystem. Total gaseous N-losses were 14.0 kg N ha^–1 yr^–1 at the spruce control site and 15.5 kg N ha^–1 yr^–1 at the beech site, respectively. In view of the huge interannual variability of N-trace gas fluxes and the pronounced site differences in N-gas emissions it is concluded that more research is needed in order to fully understand patterns of microbial N-cycling and N-gas production/emission in forest ecosystems and mechanisms of reactions of forest ecosystems to the ecological stress factor of atmospheric N-input.     

Throughfall chemistry in a loblolly pine plantationunder elevated atmospheric CO2 concentrations

Accelerated tree growth under elevatedatmospheric CO₂ concentrations may influencenutrient cycling in forests by (i) increasingthe total leaf area, (ii) increasing the supplyof soluble carbohydrate in leaf tissue, and (iii) increasing nutrient-use efficiency. Here wereport the results of intensive sampling andlaboratory analyses of NH ₄ ⁺ , NO ₃ ^– , PO ₄ ^3– , H⁺, K⁺, Na⁺,Ca²⁺, Mg²⁺, Cl^–, SO ₄ ^2– , and dissolved organic carbon (DOC) in throughfallprecipitation during the first 2.5+ years of the DukeUniversity Free-Air CO₂ Enrichment (FACE)experiment. After two growing seasons, a largeincrease (i.e., 48%) in throughfall deposition of DOCand significant trends in throughfall volume and inthe deposition of NH ₄ ⁺ , NO ₃ ^– , H⁺, and K⁺ can be attributed to the elevatedCO₂ treatment. The substantial increase indeposition of DOC is most likely associated withincreased availability of soluble C in plant foliage,whereas accelerated canopy growth may account forsignificant trends toward decreasing throughfallvolume, decreasing deposition of NH ₄ ⁺ ,NO ₃ ^– , and H⁺, and increasing deposition of K⁺ under elevated CO₂. Despiteconsiderable year-to-year variability, there wereseasonal trends in net deposition of NO ₃ ^– ,H⁺, cations, and DOC associated with plant growthand leaf senescence. The altered chemical fluxes inthroughfall suggest that soil solution chemistry mayalso be substantially altered with continued increasesin atmospheric CO₂ concentrations in the future.     

Mechanisms of Cl− uptake through brush border membranes isolated from the posterior intestine of the freshwater trout,Oncorhynchus mykiss,R.

Summary This paper presents a study of the mechanisms of Cl^– transport through the brush border membranes of the posterior part of the intestine in the freshwater trout, Oncorhynchus mykiss. The mechanisms for Cl^– transport in the posterior intestine are distinct from those in the middle intestine; an inwardly directed pH gradient stimulates Cl^– uptake by bursh border membrane vesicles, indicating a Cl^–/OH^– exchange. A pH-regulated Cl^– conductance is present, which is not activated at normal intracellular pH. Cl^– uptake is stimulated by an outwardly directed HCO ₃ ^– gradient revealing the presence of a Cl^–/HCO ₃ ^– exchange but, conversely, Cl^– is not exchanged against SO ₄ ^2- . In addition, carbonic anhydrase activities have been detected in both the intracellular and extracellular leaflets of the bursh border membranes which favour the establishment of a bicarbonate gradient. A model of Cl^– transport mechanisms through the brush-border membranes of the posterior intestine of the freshwater trout is proposed.Abbreviations BBM brush border membrane - CA carbonic anhydrase - EGTA ethylene-bis(oxyethylenenitrilo)tetra-acetic acid - FW fresh water - Hepes N-2-hydroxy-ethyl-piperazine-N'-2-ethanesulphonic acid - Mes 2-(N-morpholino)ethane sulphonic acid - SITS 4-acetamido-4-isothiocyanostilbene-2,2-disulphonic acid - TEA triethanolamine - TMA tetramethylammonium - TRIS tris(hydroxymethyl)aminomethane     

Effect of tree distance on N2O and CH4-fluxes from soils in temperate forest ecosystems

Complete annual cycles of N₂O and CH₄ flux in forest soils at a beech and at a spruce site at the Höglwald Forest were followed in 1997 by use of fully automatic measuring systems. In order to test if on a microsite scale differences in the magnitude of trace gas exchange between e.g. areas in direct vicinity of stems and areas in the interstem region at both sites exist, tree chambers and gradient chambers were installed in addition to the already existing interstem chambers at our sites. N₂O fluxes were in a range of –4.6–473.3 g N₂O-N m^–2 h^–1 at the beech site and in a range of –3.7–167.2 g N₂O-N m^–2 h^–1 at the spruce site, respectively. Highest N₂O emissions were observed during and at the end of a prolonged frost period, thereby further supporting previous findings that frost periods are of crucial importance for controlling annual N₂O losses from temperate forests. Fluxes of CH₄ were in a range of +10.4––194.0 g CH₄ m^–2 h^–1 at the beech site and in a range of –4.4––83.5 g CH₄ m^–2 h^–1 at the spruce site. In general, both N₂O-fluxes as well as CH₄-fluxes were higher at the beech site. On a microsite scale, N₂O and CH₄ fluxes at the beech site were highest within the stem area (annual mean: 49.6±3.3 g N₂O-N m^–2 h^–1; –77.2±3.1 g CH₄ m^–2 h^–1), and significantly lower within interstem areas (18.5±1.4 g N₂O-N m^–2 h^–1; –60.2±1.8 g CH₄ m^–2 h^–1). Significantly higher values of total N, C and pH in the organic layer, as well as increased soil moisture, especially in spring, in the stem areas, are likely to contribute to the higher N₂O fluxes within the stem area of the beech. Also for the spruce site, such differences in trace gas fluxes could be demonstrated to exist (mean annual N₂O emission within (a) stem areas: 9.7±0.9 g N₂O-N m^–2 h^–1 and (b) interstem areas: 6.2±0.6 g N₂O-N m^–2 h^–1; mean annual CH₄ uptake within (a) stem areas: –26.1±0.6 g CH₄ m^–2 h^–1 and (b) interstem areas: –38.4±0.8 g CH₄ m^–2 h^–1), though they were not as pronounced as at the beech site.     

Role of SO4 adsorption and desorption in the long-term S budget of a coniferous catchment on the Canadian Shield

The hypothesis that SO₄ desorption can explain apparent long term net SO₄-S losses (5 kg·ha^–1·yr^–1 on average) at the Lake Laflamme catchment from 1982 to 1991 is examined. Field observations show that SO₄ concentrations in the soil solution are strongly buffered during percolation through the Bf horizon. In the Bf horizon, SO₄ exchange reactions between the adsorbed and aqueous compartments are rapid (hours). Most (60%) of the adsorbed SO₄ may be readily desorbed with deionized water. These observations and the presence of an important adsorbed SO₄-S reservoir in the Bf horizon (113 kg·ha^–1) as compared with annual wet SO₄-S deposition (7 kg·ha^–1), suggest that on the short-term, adsorption and desorption reactions can control dissolved SO₄ concentration in the Bf horizon. To examine whether SO₄ adsorption/desorption could explain long-term SO₄-S losses by the catchment, an aggregated Langmuir isotherm for the Bf horizon was used to calculate the catchment's resilience to changing SO₄-S loads. The results indicate that the soil should adjust rapidly (within 4 years) to changing SO₄-S loads and that SO₄ desorption alone cannot explain long-term net SO₄-S losses. Other possibilities, such as an underestimation of dry deposition or the weathering of S-bearing minerals also appear unlikely. Our results suggest a net release of SO₄-S from the soil organic S reservoirs (1230 kg·ha^–1) present in the catchment.     

Oral immunotherapy with transgenic rice seed containing destructed Japanese cedar pollen allergens,Cry j 1 and Cry j 2, against Japanese cedar pollinosis

Transgenic rice accumulating the modified major Japanese cedar pollen allergens, Cryptomeria japonica 1 (Cry j 1) and Cryptomeria japonica 2 (Cry j 2), which were deconstructed by fragmentation and shuffling, respectively, in the edible part of the seed was generated by transformation of a good‐tasting rice variety, ‘Koshihikari’. These modified cedar pollen antigens were deposited in ER‐derived protein bodies (PB‐I), which are suitable for delivery to the mucosal immune system in gut‐associated lymphoid tissue when orally administered because antigens bioencapsulated in PB‐I are resistant against hydrolysis by intestinal enzymes and harsh environments. Mice fed transgenic seeds daily for three weeks and then challenged with crude cedar pollen allergen showed marked suppression of allergen‐specific CD4⁺ T‐cell proliferation, IgE and IgG levels compared with mice fed nontransgenic rice seeds. As clinical symptoms of pollinosis, sneezing frequency and infiltration of inflammatory cells such as eosinophils and neutrophils were also significantly reduced in the nasal tissue. These results imply that oral administration of transgenic rice seeds containing the structurally disrupted Cry j 1 and Cry j 2 antigens, serving as universal antigens, is a promising approach for specific immunoprophylaxis against Japanese cedar pollinosis.     

Ambrosia elatior (L.) in Hungary (1989–1990)

Summary Weeds and among themAmbrosia are probably the most important vascular plants related to pollinosis in Hungary. Sampling was carried out in central (Budapest) and in southern (Paks, Szeged) Hungary. The results of two years (1989–1990) of aerobiological study onAmbrosia airborne pollen are reported. The highest percentage of airborne pollen was found in the mid-August to mid-September period, having a good correlation with clinical data on pollinosis. The implications of these results are considered in the context of forecasting and prevention of seasonal ragweed pollinosis.     

The production and utilization of nitric oxide by a new,denitrifying strain of Pseudomonas aeruginosa

When a new strain of Pseudomonas aeruginosa was grown aerobically and then transferred to anaerobic conditions, cells reduced NO ₃ ^– quantitatively to NO ₂ ^– in NO ₃ ^– -respiration. In the absence of nitrate, NO ₂ ^– was immediately reduced to NO or N₂O but not to N₂ indicating that NO ₂ ^– -reductase but not N₂O-reductase was active. The formation of the products NO or N₂O depended on the pH in the medium and the concentration of NO ₂ ^– present. When P. aeruginosa was grown anaerobically for at least three davs N₂O-reductase was also active. Such cells reduced NO to N₂ via N₂O. The new strain generated a H⁺-gradient and grew by reducing N₂O to N₂ but not by converting NO to N₂O. For comparison, Azospirillum brasilense Sp7 showed the same pattern of NO-reduction. In contrast, Paracoccus denitrificans formed 3.5 H⁺/NO during the reduction of NO to N₂O in oxidant pulse experiments but could not grow in the presence of NO. Thus the NO-reduction pattern in P. denitrificans on one side and P. aeruginosa and A. brasilense on the other was very different. The mechanistic implications of such differences are discussed.     

The influence of nitrogen concentration and ammonium/nitrate ratio on N-uptake,mineral composition and yield of citrus

In short-term water culture experiments with different ¹⁵N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH₄ ⁺ at a higher rate than NO₃ ^–. Maximum NO₃ ^– uptake by the whole plant occurred at 120 mg L^–1 NO₃ ^–-N, whereas NH₄ ⁺ absorption was saturated at 240 mg L^–1 NH₄ ⁺-N. ¹⁵NH₄ ⁺ accumulated in roots and to a lesser degree in both leaves and stems. However, ¹⁵NO₃ ^– was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH₄ ⁺ (15–60 mg L^–1 N) to nutrient solutions containing 120 mg L^–1 N as ¹⁵N labeled nitrate reduced ¹⁵NO₃ ^– uptake. Maximum inhibition of ¹⁵NO₃ ^– uptake was about 55% at 2.14 mM NH₄ ⁺ (30 mg L^–1 NH₄ ⁺-N) and it did not increase any further at higher NH₄ ⁺ proportions.In a long-term experiment, the effects of concentration and source of added N (NO₃ ^– or NH₄ ⁺) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH₄ ⁺ versus NO₃ ^– nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO₃ ^–-N:NH₄ ⁺-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L^–1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO₃ ^– or NH₄ ⁺ as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO₃ ^–-N/NH₄ ⁺-N ratio. With increasing proportions of NH₄ ⁺ in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH₄ ⁺, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO₃ ^–-N:NH₄ ⁺-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH₄ ⁺ in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO₃ ^–:NH₄ ⁺ ratio.     

Influence of cis-[Re2GABA2Cl4]Cl2 on the antioxidant defense system parameters of normal human blood

The effect of the rhenium complex cis-[Re₂GABA₂Cl₄]Cl₂ on the antioxidant parameters of normal human blood in vitro have been studied. The results suggest that the complex influences various enzymes in the cascade of reactions utilizing active oxygen metabolites. However, the manifestation of this activity varies over the studied concentration range of the complex in the preincubation medium (10^–12-10^–4 M), so the effects appear to be concentration-dependent. The largest differences in antioxidant parameters in comparison with control were observed for the concentrations 10^–8, 10^–5, and 10^–4 M. Thus, correlations between the peroxidation level, superoxide dismutase (SOD) activity, antioxidant factor (F), and indexes of resistance of erythrocytes for hemolysis (TR) were found.     

Quantification of N2-fixation and survival of inoculated diazotrophs associated with roots of Kallar grass

White clover plants were grown for 97 days under two temperature regimes (20/15°C and 8/5°C day/night temperatures) and were supplied with either small amounts (a total of 80 mg N pot^–1) of ammonium (NH ₄ ⁺ ) or nitrate (NO ₃ ^– ) nitrogen, or received no mineral N and relied on N₂ fixation. Greatest growth and total leaf area of clover plants occurred in N₂ fixing and NO ₃ ^– -fed plants grown at 20/15°C and poorest growth occurred in NH ₄ ⁺ -fed plants grown at 8/5°C. Nodule mass per plant was greater at 8/5°C due to increased nodule numbers rather than increased dry weight per nodule. This compensated to some extent for the reduced N₂-fixing activity per unit dry weight of nodule tissue found at the low growth temperature up to 116 d after sowing, but thereafter both activity per nodule dry weight and activity per plant were greater at the low temperature. Highest nitrate reductase activity (NRA) per g fresh weight and total activity per leaf, petiole or root occurred in NO ₃ ^– -fed plants at 8/5°C. Low growth temperature resulted in a greater partitioning of total plant NRA to the roots of NO ₃ ^– -fed plants. The results are considered in relation to the use of N fertiliser in the spring under field conditions.