New donors and acceptors of nitrogen oxide as a potential therapeutical agents

The synthesis of new donors and acceptors of nitrogen oxide is described. New lipophilic nitronylnitroxyl radicals (NNR) that act as paramagnetic scavengers of nitrogen oxide are synthesized and characterized. The purity of the preparations is determined, and their structures are confirmed. The lipophilicity of the radicals is tested by ESR spectroscopy. The incorporation into lipid multilayers is shown to protect NNR from reduction in biological samples, while their ability to scavenge nitrogen oxide and form iminonitroxyl radicals is retained. A decreased rate of NNR reduction under these conditions substantially enhances their effectiveness as paramagnetic acceptors of nitrogen oxide in biological systems. The synthesis of a new hydrophilic NO donor, 3-bromo-3,4-dihydro-4,4-dimethyl-4-(2-pyridyl)-diazet-1,2-dioxide (DDpyr), is described. The constants of DDpyr decomposition in tris-HCl buffer (pH 7.5) and in DMSO are determined (4.5 x 10(-6) and 0.5 x 10(-6) s-1, respectively). A substantially higher rate of of DDpyr decomposition in buffer, compared with the decomposition rates determined previously for some diazetines, makes DDpyr a prospective candidate for the use in aqueous media. It is found in experiments on perfused rat caudal artery that DDpyr is an effective vasodilator. Intraperitoneal injection of DDpyr to hereditarily hypertensive rats (ISIAH line) at doses of 100-200 micrograms/kg body mass considerably diminishes their systolic arterial pressure.     

Seasonal variation of nitrogen transformations in the pelagial of selected nearshore waters of the Baltic Sea with emphasis on the particulate pool

Physical and chemical conditions, particulate matter and N-uptake were characterized at two sampling sites at the eastern German coast of the Baltic Sea (Pomeranian Bay) over the annual period of 1997 (February–November). The inshore sampling sites (5 m water depth) differed with respect to the potential influences of river run-off and salt water exchange (mean values of salinity: 7.05 and 8.72 PSU), respectively. The mean org-C_diss/org-C_part-ratios (4.9 and 12.6) fell in the same order of magnitude (1.0–12.6) as values of neighboring inshore waters, and increasing values reflect an enhancement of the trophic level. Beside differences of nitrogen concentrations (dissolved inorganic nitrogen: 1.8–23.8 and 0.9–9.9 mol l^–1), particulate nitrogen (4.30–41.01 and 2.69–9.08 mol l^–1) and absolute uptake of N-nutrients (mean sum of NH₄ ⁺, urea, NO₃ ^– uptake rates: 0.141 and 0.087 mol l^–1 h^–1), specific uptake of ¹⁵N-labelled nutrients (NH₄ ⁺, urea, NO₃ ^–) as well as the relationships between the measured variables characterize distinguishable inshore systems. The high variability at the shallow sampling sites prevents, however a simple resolution of the seasonal courses. Light dose could be identified as a potential key in order to describe long-term variations of N-uptake at the station with higher organic matter concentration (station KW), but phytoplankton development is better reflected in the seasonal course of N-uptake at the other station. Specific nitrogen uptake rates (NH₄ ⁺: 0.0009–0.0353 h^–1, urea: 0.0001–0.0137 h^–1, NO₃ ^–: 0.000004–0.0009 h^–1) and relative nitrogen preferences indicate extraordinary importance of reduced nitrogenous nutrients (NH₄ ⁺, urea) at both stations throughout the year.     

Carbon and nitrogen cycling in intertidal sediments near Doel,Scheldt Estuary

Carbon and nitrogen cycling in intertidal mud flat sediments in the Scheldt Estuary was studied using measurements of carbon dioxide, methane and nitrous oxide emission rates and pore-water profiles of CO₂, ammonium and nitrate. A comparison between chamber measured carbon dioxide fluxes and those based on CO₂ pore-water gradients using Fick's First law indicates that apparent diffusion coefficients are 2 to 28 times higher than bulk sediment diffusion coefficients based on molecular diffusion. Seasonal changes in gaseous carbon fluxes or CO₂ pore water concentrations cannot be used directly, or in a simple way, to determine seasonal rates of mineralization, because of marked seasonal changes in pore-water storage and exchange parameters.The annual amount of carbon delivered to the sediment is 42 mol m^–2, of which about 42% becomes buried, the remaining being emitted as methane (7%) or carbon dioxide (50%). Each year about 2.6 mol N m^–2 of particulate nitrogen reaches the sediment; 1.1 mol m^–2 is buried and 1.6 mol m^–2 is mineralized to ammonium. Only 0.42 mol m^–2 yr^–1 of the ammonium produced escapes from the sediments, the remaining being first nitrified (1.2 mol m^–2 yr^–1) and then denitrified (1.7 mol m^–2 yr^–1). Simple calculations indicate that intertidal sediments may account for about 14% and 30% of the total estuarine retention of nitrogen and carbon, respectively.     

Neuronal apoptosis versus necrosis induced by glutamate or free radicals

The type of cell death encountered in neuronal cell cultures exposed to excitatory amino acids — such as glutamate, the major excitatory neurotransmitter in the central nervous system, or free radicals, such as nitric oxide (NO^.) and superoxide anoin (O2^{. –}), which react to form peroxynitrite (ONOO^–) — appears to depend on the intensity of the exposure and may involve two temporarily distinct phases. Following relatively fulminant insults, an initial phase of necrosis — associated with extreme energy depletion — may simply reflect the failure of neurons to carry out the default apoptotic death program used to efficiently dispose of aged or otherwise unwanted cells. Neurons recovering mitochondrial energy potential after an initial fulminant insult or following a more subtle inciting injury may subsequently undergo apoptosis, possibly associated with a factor released from mitochondria that triggers this death program. The maintenance of balanced energy production may be a decisive factor in detemining the degree, type, and progression of neuronal injury caused by excitotoxins and free radicals. Similar events could possibly occur in vivo after ischemia or other insults.     

The role of ammonium and nitrate retention in the acidification of lakes and forested catchments

The relative contribution of HN0₃ to precipitation acidity in eastern Canada has increased in recent years leading to some concern that the relative importance of NO^– ₃ deposition in acidification of terrestrial and aquatic ecosystems may increase. To gauge the extent of this impact, annual mass balances for N0^– ₃ and NH^{+ 4} were calculated for several forested catchments and lakes in Ontario. Retention of NH⁺ ₄ (R _NH4) by forested catchments was consistently high compared to retention of NO₃ ^– (R _NO3) which was highly variable. Retention of inorganic nitrogen was influenced by catchment grade and areal water discharge. In lakes, the reciprocals of retention of N0^– ₃ and NH⁺ ₄ were linearly related to the ratio of lake mean depth to water residence time (z/; equal to areal water discharge), and retention did not appear to be a function of degree of acidification of the lakes. Net N consumption-based acidification of lakes, defined as the ratio of annual NH; mass to N0^– ₃ mass consumption, was negatively correlated with / and N consumption-related acidification was most likely to occur when – was < 1.5 m yr^–1.If retention mechanisms are unaffected by changes in deposition, changes in deposition will still result in changes in surface water concentrations although the changes will be of similar proportions. Therefore, NO^– ₃ saturation should not be defined by concentrations alone, but should be defined as decreasing long-term, average NO^– ₃ retention in streams and lakes in response to long-term increases in NO^– ₃ deposition. Analysis o f survey data will be facilitated by grouping lakes and catchments according to similar characteristics.     

Effect of Single-Charged Anions of Different Nature on the DNA Molecule Conformation in Water–Salt Solutions

Methods of intrinsic viscosity () and beam flow birefringence were used to study the effects of some single-charged ions (F^–, Cl^–, Br^–, I^–, NO^– ₂, NO^– ₃, ClO^– ₄, SCN^–, CH₃COO^–) on the size and thermodynamic rigidity of a DNA molecule in aqueous solutions of sodium salts in a broad interval of ionic strength when temperature T is changed. It has been shown that the close interactions in a macromolecule and the resulting DNA persistent length a are independent of the type of the salt anion over the whole interval of . On the contrary, the specific volume of the DNA molecule in solution, proportional to the value, is quite sensitive to the anionic composition of the solvent, which is due to the effect of anions and their hydration on the long-range interactions in the macromolecule. The presence of polyatomic and halide anions is manifested differently in the value of DNA. Possible factors responsible for the observed effect and the role of structural alterations of water upon anion hydration are discussed.     

Uptake of sewage derived nitrogen by<Emphasis Type="Italic"> Ulva rigida</Emphasis> (Chlorophyceae) in Bahía Nueva (Golfo Nuevo,Patagonia, Argentine)

Uptake kinetics of nitrogen derived from sewage–seawater mixtures (2.5–20% v/v effluent) were determined in the laboratory for Ulva rigida (Chlorophyceae) native from Bahía Nueva (Golfo Nuevo, Patagonia, Argentine). In terms of nitrogen concentration, experimental enrichment levels varied between 53.7 and 362.3M of ammonium and between 0.77 and 6.21M of nitrate+nitrite. Uptake rates were fitted to the Michaelis–Menten equation, with the following kinetic parameters: ammonium: V_max = 591.2molg^–1h^–1, K _s=262.3M, nitrate+nitrite: V _max=12.9molg^–1h^–1, K _s=3.5M). Both nutrients were taken up simultaneously, but ammonium incorporation was faster in all cases. The results show a high capability of Ulva rigida to remove sewage-derived nitrogen from culture media. In the field, most of the nitrogen provided by the effluent would be tied up in algal biomass, supporting low nitrogen levels found at a short distance away from the source.     

Studies on structure activity relationship of some dihydroxy-4-methylcoumarin antioxidants based on their interaction with Fe(III) and ADP

Three dihydroxy-4-methylcoumarin (DHMC) derivatives, namely 7,8-DHMC, 6,7-DHMC and 5,7-DHMC alone and complexed with Fe (III) and ADP have been tested for their antioxidative potential. Chemical speciation studies and formation constants reveal the formation of strong DHMC–Fe–ADP (1:1:1) ternary complex. In vitro studies were done for their antioxidative property by scavenging the superoxide radicals (O ₂ ^– ) generated by xanthine + xanthine oxidase (XO) reaction. The IC₅₀ values for 7,8-DHMC, 6,7-DHMC and 5,7-DHMC and their ternary complexes with Fe (III)–ADP worked out to be 34.0 M, 62.0 M, 8.80 mM and 10.5, 11.5 and 148.5 M, respectively. The results indicate that O ₂ ^– scavenging potential of all the three DHMCs increased significantly after forming the ternary complex with Fe(III) and ADP. The structure activity relationship studies suggest that the introduction of hydroxyl group at 7th and 8th positions in the coumarins, irrespective of Fe(III)–ADP complexation, increases the antioxidative efficacy. No change in uric acid production in the reactions done for all studies further reveals that the coumarin derivatives and their complexes were the only causative factors for O ₂ ^– scavenging and not the suppression of the enzyme, xanthine oxidase.Published online: March 2005     

Epr detection of endogenous nitric oxide in postischemic heart using lipid and aqueous-soluble dithiocarbamate-iron complexes

Spin-trapping techniques combined with electron paramagnetic resonance (EPR) spectroscopy to measure nitric oxide (·NO) production were compared in the ischemic-reperfused myocardium for the first time, using both aqueous-soluble and lipophilic complexes of reduced iron (Fe) with dithiocarbamate derivatives. The aqueous-soluble complex of Fe and N-methyl-D-glucamine dithiocarbamate (MGD) formed MGD2-Fe-NO complex with a characteristic triplet EPR signal (a_N12.5 G and g_iso = 2.04) at room temperature, in native isolated rat hearts following 40 min global ischemia and 15 min reperfusion. Diethyldithiocarbamate (DETC) and Fe formed in ischemic-reperfused myocardium the lipophilic DETC2-Fe-NO complex exhibiting an EPR signal (g = 2.04 and g = 2.02 at 77K) with a triplet hyperfine structure at g. Dithiocarbamate-Fe-NO complexes detected by both trapping agents were abolished by the ·NO synthase inhibitor, N^G-nitro-L-arginine methyl ester. Quantitatively, both trapping procedures provi ded similar values for tissue ·NO production, which were observed primarily during ischemia. Postischemic hemodynamic recovery of the heart was not affected by the trapping procedure. (Mol Cell Biochem 175: 91–97, 1997)     

Interrelationships Between Nitrogen Supply and Photosynthetic Parameters in Vicia faba L.

We determined for Vicia faba L the influence of nitrogen uptake and accumulation on the values of photon saturated net photosynthetic rate (P _Nmax), quantum yield efficiency (), intercellular CO₂ concentration (C _i), and carboxylation efficiency (C _e). As leaf nitrogen content (N_L) increased, the converged onto a maximum asymptotic value of 0.0664±0.0049 mol(CO₂) mol(quantum)^–1. Also, as N_L increased the C _i value fell to an asymptotic minimum of 115.80±1.59 mol mol^–1, and C _e converged onto a maximum asymptotic value of 1.645±0.054 mol(CO₂) m^–2 s^–1 Pa^–1 and declined to zero at a N_L-intercept equal to 0.596±0.096 g(N) m^–2. fell to zero for an N_L-intercept of 0.660±0.052 g(N) m^–2. As N_L increased, the value of P _Nmax converged onto a maximum asymptotic value of 33.400±2.563 mol(CO₂) m^–2 s^–1. P _N fell to zero for an N_L-intercept of 0.710±0.035 g(N) m^–2. Under variable daily meteorological conditions the values for N_L, specific leaf area (_L), root mass fraction (R_f), P _Nmax, and remained constant for a given N supply. A monotonic decline in the steady-state value of R_f occurred with increasing N supply. _L increased with increasing N supply or with increasing N_L.     

Nitrogen fixation by periphyton and plankton on the Amazon floodplain at Lake Calado

Nitrogen fixation by periphyton and plankton was measured on the Amazon flood-plain using the acetylene reduction method calibrated with¹⁵N-N₂. The average ratio (± SD) of moles C₂H₄ reduced per mole N₂-N fixed was 3.4 ± 0.7, similar to other studies. Periphyton and plankton had high rates of light-dependent nitrogen fixation, with dark nitrogen fixation averaging 26% of the average rates in the light. The average daily (24 h) rates for periphyton nitrogen fixation in 1989 and 1990 were 1.79 and 0.51 mmol N₂-N·m^–2·d^–1 respectively, which are comparable to summer rates in many temperate cyanobacterial assemblages. Nitrogen fixation was depressed at N0₃ ^– concentrations as low as 0.5 M, and was below detection limits at concentrations of 4 M, which occurred during periods of river flooding. Planktonic nitrogen fixation rates were high (0.5–0.8 mmol N₂-N·m^–2·d^–1) during the high-water and drainage phases of the annual hydrograph when the floodplain waters were draining towards the river (low NO₃ ^–), but rates were undetectable (< 0.05 mmol N₂-N·m^–2·d^–1) when there was river flooding (high NO₃ ^–). Nitrogen fixation by periphyton and plankton in 1989–1990 accounted for approximately 8% of previously reported total annual nitrogen inputs to the floodplain at Lake Calado.     

Long-term effects of CO2 enrichment and temperature increase on a temperate grass sward

Perennial ryegrass swards were grown in large containers on a soil and were exposed during two years to elevated (700 L L^-1) or ambient atmospheric CO₂ concentration at outdoor temperature and to a 3 °C increase in air temperature in elevated CO₂. The nitrogen nutrition of the grass sward was studied at two sub-optimal (160 and 530 kg N ha^-1 y^-1) and one non-limiting (1000 kg N ha^-1 y^-1) N fertilizer supplies. At cutting date, elevated CO₂ reduced by 25 to 33%, on average, the leaf N concentration per unit mass. Due to an increase in the leaf blade weight per unit area in elevated CO₂, this decline did not translate for all cuts in a lower N concentration per unit leaf blade area. With the non-limiting N fertilizer supply, the leaf N concentration (% N) declined with the shoot dry-matter (DM) according to highly significant power models in ambient (% N=4.9 DM^-0.38) and in elevated (%N=5.3 DM^-0.52) CO₂. The difference between both regressions was significant and indicated a lower critical leaf N concentration in elevated than in ambient CO₂ for high, but not for low values of shoot biomass. With the sub-optimal N fertilizer supplies, the nitrogen nutrition index of the grass sward, calculated as the ratio of the actual to the critical leaf N concentration, was significantly lowered in elevated CO₂. This indicated a lower inorganic N availability for the grass plants in elevated CO₂, which was also apparent from the significant declines in the annual nitrogen yield of the grass sward and in the nitrate leaching during winter. For most cuts, the harvested fraction of the plant dry-matter decreased in elevated CO₂ due, on average, to a 45–52% increase in the root phytomass. In the same way, a smaller share of the plant total nitrogen was harvested by cutting, due, on average, to a 25–41% increase in the N content of roots. The annual means of the DM and N harvest indices were highly correlated to the annual means of the nitrogen nutrition index. Changes in the harvest index and in the nitrogen nutrition index between ambient and elevated CO₂ were also positively correlated. The possible implication of changes in the soil introgen cycle and of a limitation in the shoot growth potential of the grass in elevated. CO₂ is discussed.Abbreviations 350 outdoor climate - 700 outdoor climate +350 L L^-1[CO₂] - 700+ outdoor climate +350 L L^-1 (CO₂) and +3 °C - N-- low N fertilizer supply - N+ high N fertilizer supply - N++ non-limiting N fertilizer supply - DM dry-matter     

Selective feeding by larval dytiscids (Coleoptera:Dytiscidae) and effects of fish predation on upper littoral zone macroinvertebrate communities of arctic lakes

Carbon and nitrogen stable isotopic data from the primary producers in mangrove ecosystems are needed to investigate trophic links and biogeochemical cycling. Compared with other mangrove species (e.g. Rhizophora mangle) very few measurements have been conducted on the white mangrove, Laguncularia racemosa. The carbon and nitrogen stable isotopic and elemental compositions of L. racemosa were analyzed and compared from Florida and Belize. ¹³C values of L. racemosa from Florida (mean = –26.4) were slightly higher than those from Twin Cays, Belize (mean = -27.4), which may be due to higher salinity in some parts of the Florida site. There was no difference between the ¹⁵N values from L. racemosa from these two sites (Florida mean = 0.6; Belize mean = 0.3), which are indicative of nitrogen derived from nitrogen fixation in a planktonic marine system. However, higher ¹⁵N values from L. racemosa at Man of War Cay in Belize (11.4 and 12.3), which is fertilized by roosting marine birds (14.0), illustrate that L. racemosa can sensitively reflect alternative nitrogen sources. Although the isotopic data could not distinguish between Avicennia germinans, R. mangle and L. racemosa in Belize the L. racemosa had considerably higher C/N ratios (46.5 – 116.1) compared with the Florida samples (42.2 – 76.0) or the other mangrove species. Unlike some previous findings from R. mangle, substrate characteristics (e.g. salinity, NH₄ ⁺, and H₂S) were not related to the isotopic or elemental composition of L. racemosa. ¹³C, ¹⁵N and C/N were analyzed for ecosystem components from L. racemosa habitats at Twin Cays, including other plants (e.g. R. mangle, A. germinans and seagrass), detritus, microbial mats and sediments. Results from mass-balance calculations show that mangrove detritus composes very little of the sediment, which is principally composed of microbial biomass (80 – 90%). Detritus at some sites is also influenced by sources other than that from L. racemosa, including seagrass leaves.     

Plankton and hydrochemistry of Lake Futalaufquen (Patagonia,Argentina) during the growing season

Plankton communities and hydrochemistry of an oligotrophic lake occupying a glacial valley in Argentinian Patagonia (42 °49S; 71 °43W) were studied. Monthly samples at three stations integrated from 0 to 50 m and stratified samples at the site of maximum depth, were taken during the growing season. Transparency was always controlled by glacial silt, and not by phytoplankton. Lake water belongs to the calcium-bicarbonate type, with low conductivity (24 µS cm^–1), and poor buffering capacity. Forty-five phytoplankton taxa were found. Mean phytoplankton density was 49 cells ml^–1 and mean biomass 69 µg l^–1. N:P relationships, inorganic nitrogen exhaustion in the photic layer, and correlations between nutrients and phytoplankton density suggests nitrogen as the main limiting factor. Fifteen zooplankton species were found. Mean zooplankton density was 12.2 ind. l^–1 and mean biomass 22.9 µg l^–1. Diatoms and Boeckellidae were the dominant planktonic groups. Morphometry and hydrological factors were responsible for horizontal heterogeneity in phytoplankton and chemical variables.     

Sources,fates, and impacts of nitrogen inputs to terrestrial ecosystems: review and synthesis

The relative importance of nitrogen inputs from atmospheric deposition and biological fixation is reviewed in a number of diverse, non-agricultural terrestrial ecosystems. Bulk precipitation inputs of N (l–l2 kg N ha^–1 yr^–1) are the same order of magnitude as, or frequently larger than, the usual range of inputs from nonsymbiotic fixation (< 1=" –=" 5=" kg=" n=">^–1 yr^–1), especially in areas influenced by industrial activity. Bulk precipitation measurements may underestimate total atmospheric deposition by 30–40% because they generally do not include all forms of wet and dry deposition. Symbiotic fixation generally ranges from 10–160 kg N ha^–1 yr^–1) in ecosystems where N-fixing species are present during early successional stages, and may exceed the range under unusual conditions.Rates of both symbiotic and nonsymbiotic fixation appear to be greater during early successional stages of forest development, where they have major impacts on nitrogen dynamics and ecosystem productivity. Fates and impacts of these nitrogen inputs are important considerations that are inadequately understood. These input processes are highly variable in space and time, and few sites have adequate comparative information on both nitrogen deposition and fixation.

Redox control of proton transfers in membrane b-type cytochromes: an absorption and resonance Raman study on bis(imidazole) and bis(imidazolate) model complexes of iron-protoporphyrin

Optical absorption spectra and resonance Raman (RR) spectra, obtained with Soret excitation, are reported for bis(imidazole) and bis(imidazolate) complexes of iron(II)- and iron(III)-protoporphyrin IX, prepared in aqueous conditions. Perdeuteration experiments on the axial ligands permitted the assignment of the symmetric Fe-(ligand)₂ stretching mode of Fe[x]PP(L)₂ to RR bands at 203 (x = II; L = ImH), 212 (x = II; L = Im^–), 201 (x = III; L = ImH) and 226 cm^–1 (x = III; L = Im^–). These frequency differences indicate a strengthening of the axial bonds when the imidazole deprotonations occur. The larger difference observed for the ferric derivatives reflects the stronger -donor capability of the Im^– anion for iron(III) over iron(II). For the ferrous derivatives, the frequencies of several skeletal porphyrin modes (₄, ₁₀, ₁₁ and ₃₈) are downshifted by 2–10 cm^–1 upon deprotonation of the ligands. This effect corresponds to an increased back-bonding from the metal atom to the porphyrin ring when the axial ligand decreases its -acid strength. Bringing further support to this interpretation, an inverse linear relationship is established between the frequencies of (Fe(Il)-L₂) and ₁₁. This correlation is expected to monitor the overall H-bonding state of histidine ligands of reduced cytochromes b. On the other hand, absorption measurements have characterized large pK_a differences for the sequential imidazole ionizations of Fe[x]PP(ImH)₂ in aqueous cetyltrimethylammonium bromide (9.0 and 10.8 for x = 111; 13.0 and 14.1 for x = II). These titrations show that Fe(II)PP(Im^–)₂ and Fe(III)PP(ImH)₂ are good proton-acceptor and proton-donor, respectively, and suggest a model by which heme, located in a favorable environment inside a cytochrome, could couple a cycle of electron transfer with a proton transfer. Based on sequence data and structural models, it is further proposed that, in several membrane cytochromes b (b, b ₆, b ₅₅₉), a positively charged amino acid residue and an imidazolate ligand of the ferriheme could form an ion pair involved in a redox control of proton transfer.Abbreviations RR resonance Raman - EPR electron paramagnetic resonance - PP protoporphyrin IX - ImH imidazole - Im^– imidazolate - Im* imidazole or imidazolate - 1MeIm 1-methylimidazole - HisH histidine - His^– histidinate - CTABr cetyltrimethylammonium bromide - NaDS sodium dodecylsulphate - VLP very low potential - LP low potential - HP high potential     

Fluxes of nitrous oxide and methane from drained peatlands following forest clear-felling in southern Finland

Drainage of waterlogged sites has been part of the normal forestry practice in Fennoscandia, the Baltic countries, the British Isles and in some parts of Russia since the early 20^th century, and currently, about 15 million hectares of peatlands and other wetlands have been drained for forestry purposes. The rate of forest clear-felling on drained peatlands will undergo a rapid increase in the near future, when a large number of these forests approach their regeneration age. A small-scale pilot survey was performed at two nutrient-rich and old peatland drainage areas in southern Finland to study if forest clear-felling has significant impacts on the exchange of nitrous oxide (N₂O) and methane (CH₄) between soil and atmosphere. The average N₂O emissions from the two drainage areas during three growing seasons following clear-felling were 945 and 246 g m^–2 d^–1. The corresponding CH₄ fluxes were –0.07 and –0.52 mg m^–2 d^–1. Clear-felling had impacts on the environmental factors known to affect the N₂O and CH₄ fluxes of peatlands, i.e. clear-felling raised the water table level and increased the peat temperature. However, no substantial changes in the fluxes of CH₄ following clear-felling were observed. The results concerning N₂O indicated a potential for increased emissions following clear-felling of drained peatland forests, but further studies are needed for a critical evaluation of the impacts of clear-felling on the fluxes of CH₄ and N₂O.     

Application of N-15 dilution for simultaneous estimation of nitrification and nitrate reduction in soil-water columns

Nitrification and denitrification rates were estimated simultaneously in soil-floodwater columns of a Crowley silt loam (Typic Albaqualfs) rice soil by an¹⁵N isotopic dilution technique. Labeled NO ₃ ^– was added to the floodwater of soil-water columns, half were treated with urea fertilizer. The (NO ₃ ^– +NO ₂ ^– )–N and (NO ₃ ^– +NO ₂ ^– )–N concentrations in the floodwater were measured over time and production and reduction rates for NO ₃ ^– calculated. Nitrate reduction in the urea amended columns averaged 515 mol N m^–2h^–1 and nitrification averaged 395 mol N m^–2h^–1 over the 35–153 d incubation. The nitrification rate for 4–19 d sampling period (1,560 mol N m^–2h^–1) in the urea amended columns was almost 9 times greater than the reduction rate (175 mol N m^–2h^–1) over the same period. Without the addition of urea the NO ₃ ^– production rate averaged 32 mol N m^–2h^–1 and reduction 101 mol N m^–2h^–1.     

Influence of inorganic microelements on the production of camptothecin with suspension cultures of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis>

The effects of eight microelements (I^–, BO₃ ^3–, MoO₄ ^2–, Co²⁺, Cu²⁺, Mn²⁺, Fe²⁺, Zn²⁺) on the biosynthesis of camptothecin and the growth of suspension cultures of Camptotheca acuminata were studied. The increase of I^– to 25 M l^–1, Cu²⁺ to 1 M l^–1, Co²⁺ to 2 M l^–1 and MoO₄ ^2– to 10 M l^–1 in Murashige and Skoog (MS) medium resulted in 1.66, 2.84, 2.53 and 2.04 times higher of camptothecin yield than that in standard MS medium respectively. Combined treatment of I^– (25 M l^–1), Cu²⁺ (1 M l^–1), Co²⁺ (2 M l^–1) and MoO₄ ^2– (10 M l^–1) lead to improve cell dry weight, camptothecin content, and camptothecin yield to 30.56 g l^–1, 0.0299%, and 9.15 mg l^–1, respectively, which were 20.2, 208.9 and 273.8% increment respectively when compared with those of control.     

Freezing tolerance and avoidance in high tropical Andean plants: Is it equally represented in species with different plant height?

Summary CO₂ assimilation in relation to light intensity and the relationship between leaf nitrogen and phosphorus concentrations and CO₂ assimilation in 14 species of ecologically important Zimbabwean trees were examined. Eight of the species are members of the Fabaceae (Leguminosae). In the majority of Zimbabwean climax woodlands, the dominant trees are non-nodulating members of the sub-family Caesalpinioideae. The species examined have higher light saturation points (>700 mol m^–2 s^–1) than woody species from temperate areas; one species, Acacia nigrescens, did not reach saturation at photon fluxes greater than 1500 mol m^–2 sec^–1. Higher leaf nitrogen content was found to correlate positively with higher CO₂ assimilation rates (r=0.85; P0.0003); there was no correlation between leaf phosphorus content and CO₂ uptake rates. There were no significant differences between sites in terms of leaf nitrogen or phosphorus content, but the mean photosynthetic rate at one of the sites (Chizedzi) was lower. Taxa from the nodulating legumes were found to have higher leaf nitrogen contents (309.1±SD 22 mmol m^–2) than those of the non-nodulating species (239±33); the lowest nitrogen contents were found in nonleguminous trees (179±42), with the exception of Ziziphus mucronata. This species may form an association with an N₂-fixing actinomycete.