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1.
Nitrogen addition reduces soil respiration in a mature tropical forest in southern China 总被引:10,自引:0,他引:10
JIANGMING MO WEI ZHANG WEIXING ZHU† PER GUNDERSEN‡ YUNTING FANG DEJUN LI HUI WANG 《Global Change Biology》2008,14(2):403-412
Response of soil respiration (CO2 emission) to simulated nitrogen (N) deposition in a mature tropical forest in southern China was studied from October 2005 to September 2006. The objective was to test the hypothesis that N addition would reduce soil respiration in N saturated tropical forests. Static chamber and gas chromatography techniques were used to quantify the soil respiration, following four‐levels of N treatments (Control, no N addition; Low‐N, 5 g N m?2 yr?1; Medium‐N, 10 g N m?2 yr?1; and High‐N, 15 g N m?2 yr?1 experimental inputs), which had been applied for 26 months before and continued throughout the respiration measurement period. Results showed that soil respiration exhibited a strong seasonal pattern, with the highest rates found in the warm and wet growing season (April–September) and the lowest rates in the dry dormant season (December–February). Soil respiration rates showed a significant positive exponential relationship with soil temperature, whereas soil moisture only affect soil respiration at dry conditions in the dormant season. Annual accumulative soil respiration was 601±30 g CO2‐C m?2 yr?1 in the Controls. Annual mean soil respiration rate in the Control, Low‐N and Medium‐N treatments (69±3, 72±3 and 63±1 mg CO2‐C m?2 h?1, respectively) did not differ significantly, whereas it was 14% lower in the High‐N treatment (58±3 mg CO2‐C m?2 h?1) compared with the Control treatment, also the temperature sensitivity of respiration, Q10 was reduced from 2.6 in the Control with 2.2 in the High‐N treatment. The decrease in soil respiration occurred in the warm and wet growing season and were correlated with a decrease in soil microbial activities and in fine root biomass in the N‐treated plots. Our results suggest that response of soil respiration to atmospheric N deposition in tropical forests is a decline, but it may vary depending on the rate of N deposition. 相似文献
2.
The semiarid and arid zones cover a quarter of the global land area and support one‐fifth of the world's human population. A significant fraction of the global soil–atmosphere exchange for climatically active gases occurs in semiarid and arid zones yet little is known about these exchanges. A study was made of the soil–atmosphere exchange of CH4, CO, N2O and NOx in the semiarid Mallee system, in north‐western Victoria, Australia, at two sites: one pristine mallee and the other cleared for approximately 65 years for farming (currently wheat). The mean (± standard error) rates of CH4 exchange were uptakes of ?3.0 ± 0.5 ng(C) m?2 s?1 for the Mallee and ?6.0 ± 0.3 ng(C) m?2 s?1 for the Wheat. Converting mallee forest to wheat crop increases CH4 uptake significantly. CH4 emissions were observed in the Mallee in summer and were hypothesized to arise from termite activity. We find no evidence that in situ growing wheat plants emit CH4, contrary to a recent report. The average CO emissions of 10.1 ± 1.8 ng(C) m?2 s?1 in the Mallee and 12.6 ± 2.0 ng(C) m?2 s?1 in the Wheat. The average N2O emissions were 0.5 ± 0.1 ng(N) m?2 s?1 from the pristine Mallee and 1.4 ± 0.3 ng(N) m?2 s?1 from the Wheat. The experimental results show that the processes controlling these exchanges are different to those in temperate systems and are poorly understood. 相似文献
3.
JESPER RIIS CHRISTIANSEN LARS VESTERDAL INGEBORG CALLESEN BO ELBERLING INGER KAPPEL SCHMIDT PER GUNDERSEN 《Global Change Biology》2010,16(8):2224-2240
Water and nutrient fluxes for single stands of different tree species have been reported in numerous studies, but comparative studies of nutrient and hydrological budgets of common European deciduous tree species are rare. Annual fluxes of water and inorganic nitrogen (N) were established in a 30‐year‐old common garden design with stands of common ash (Fraxinus excelsior), European beech (Fagus sylvatica L.), pedunculate oak (Quercus robur), small‐leaved lime (Tilia cordata Mill.), sycamore maple (Acer pseudoplatanus) and Norway spruce (Picea abies [L.] Karst.) replicated at two sites in Denmark, Mattrup and Vallø during 2 years. Mean annual percolation below the root zone (mm yr?1±SE, n=4) ranked in the following order: maple (351±38)>lime (284±32), oak (271±25), beech (257±30), ash (307±69)? spruce (75±24). There were few significant tree species effects on N fluxes. However, the annual mean N throughfall flux (kg N ha?1 yr?1±SE, n=4) for spruce (28±2) was significantly larger than for maple (12±1), beech (11±1) and oak (9±1) stands but not different from that of lime (15±3). Ash had a low mean annual inorganic N throughfall deposition of 9.1 kg ha?1, but was only present at Mattrup. Annual mean of inorganic N leaching (kg ha?1 yr?1±SE, n=4) did not differ significantly between species despite of contrasting tree species mean values; beech (25±9)>oak (16±10), spruce (15±8), lime (14±8)? maple (1.9±1), ash (2.0±1). The two sites had similar throughfall N fluxes, whereas the annual leaching of N was significantly higher at Mattrup than at Vallø. Accordingly, the sites differed in soil properties in relation to rates and dynamics of N cycling. We conclude that tree species affect the N cycle differently but the legacy of land use exerted a dominant control on the N cycle within the short‐term perspective (30 years) of these stands. 相似文献
4.
Natural wetlands are critically important to global change because of their role in modulating atmospheric concentrations of CO2, CH4, and N2O. One 4‐year continuous observation was conducted to examine the exchanges of CH4 and N2O between three wetland ecosystems and the atmosphere as well as the ecosystem respiration in the Sanjiang Plain in Northeastern China. From 2002 to 2005, the mean annual budgets of CH4 and N2O, and ecosystem respiration were 39.40 ± 6.99 g C m?2 yr?1, 0.124 ± 0.05 g N m?2 yr?1, and 513.55 ± 8.58 g C m?2 yr?1 for permanently inundated wetland; 4.36 ± 1.79 g C m?2 yr?1, 0.11 ± 0.12 g N m?2 yr?1, and 880.50 ± 71.72 g C m?2 yr?1 for seasonally inundated wetland; and 0.21 ± 0.1 g C m?2 yr?1, 0.28 ± 0.11 g N m?2 yr?1, and 1212.83 ± 191.98 g C m?2 yr?1 for shrub swamp. The substantial interannual variation of gas fluxes was due to the significant climatic variability which underscores the importance of long‐term continuous observations. The apparent seasonal pattern of gas emissions associated with a significant relationship of gas fluxes to air temperature implied the potential effect of global warming on greenhouse gas emissions from natural wetlands. The budgets of CH4 and N2O fluxes and ecosystem respiration were highly variable among three wetland types, which suggest the uncertainties in previous studies in which all kinds of natural wetlands were treated as one or two functional types. New classification of global natural wetlands in more detailed level is highly expected. 相似文献
5.
Heather E. Weatherly Stephen F. Zitzer James S. Coleman John A. Arnone III 《Global Change Biology》2003,9(8):1223-1233
Rising atmospheric CO2 has been predicted to reduce litter decomposition as a result of CO2‐induced reductions in litter quality. However, available data have not supported this hypothesis in mesic ecosystems, and no data are available for desert or semi‐arid ecosystems, which account for more than 35% of the Earth's land area. The objective of our study was to explore controls on litter decomposition in the Mojave Desert using elevated CO2 and interannual climate variability as driving environmental factors. In particular, we sought to evaluate the extent to which decomposition is modulated by litter chemistry (C:N) and litter species and tissue composition. Naturally senesced litter was collected from each of nine 25 m diameter experimental plots, with six plots exposed to ambient [CO2] or 367 μL CO2 L?1 and three plots continuously fumigated with elevated [CO2] (550 μL CO2 L?1) using FACE technology beginning in April 1997. All litter collected in 1998 (a wet, or El Niño year; 306 mm precipitation) was pooled as was litter collected in 1999 (a dry year; 94 mm). Samples were allowed to decompose for 4 and 12 months starting in May 2001 in mesh litterbags in the locations from which litter was collected. Decomposition of litter produced under elevated CO2 and ambient CO2 did not differ. Litter produced in the wetter year showed more rapid initial decomposition (over the first 4 months) than that produced in the drier year (27±2% yr?1 or 7.8±0.7 g m?2 yr?1 for 1998 litter; 18±3% yr?1 or 2.2±0.4 g m?2 yr?1 for 1999 litter). C:N ratios of litter produced under elevated CO2 (wet year: 37±0.5; dry year: 42±2.5) were higher than those of litter produced under ambient CO2 (wet year: 34±1.1; dry year: 35±1.4). Litter production in the wet year (amb. CO2: 25.1±1.1 g m?2 yr?1; elev. CO2: 35.0±1.1 g m?2 yr?1) was more than twice as high as that in the dry year (amb. CO2: 11.6±1.7 g m?2, elev. CO2: 13.3±3.4 g m?2), and contained a greater proportion of Lycium pallidum and a lower proportion of Larrea tridentata than litter produced in the dry year. Decomposition, viewed across all treatments, decreased with increasing C:N ratios, decreased with increasing proportions of Larrea tridentata and increased with increasing proportions of Lycium pallidum and Lycium andersonii. Because litter C:N did not vary by litter production year, and CO2 did not alter decomposition or litter species/tissue composition, it is likely that the impact of year‐to‐year variation in precipitation on the proportion of key plant species in the litter may be the most important way in which litter decomposition will be modulated in the Mojave Desert under future rising atmospheric CO2. 相似文献
6.
J. M. Jesus C. S. C. Calheiros P. M. L. Castro M. T. Borges 《International journal of phytoremediation》2014,16(4):334-346
High salinity wastewaters have limited treatment options due to the occurrence of salt inhibition in conventional biological treatments. Using recirculating marine aquaculture effluents as a case study, this work explored the use of Constructed Wetlands as a treatment option for nutrient and salt loads reduction. Three different substrates were tested for nutrient adsorption, of which expanded clay performed better. This substrate adsorbed 0.31 mg kg?1 of NH4 +?N and 5.60 mg kg?1 of PO4 3??P and 6.9 mg kg?1 dissolved salts after 7 days of contact. Microcosms with Typha latifolia planted in expanded clay and irrigated with aquaculture wastewater (salinity 2.4%, 7 days hydraulic retention time, for 4 weeks), were able to remove 94% NH4 +?N (inlet 0.25 ± 0.13 mg L?1), 78% NO2 ??N (inlet 0.78 ± 0.62 mg L?1), 46% NO3 ??N (inlet 18.83 ± 8.93 mg L?1) whereas PO4 3??P was not detected (inlet 1.41 ± 0.21 mg L?1). Maximum salinity reductions of 52% were observed. Despite some growth inhibition, plants remained viable, with 94% survival rate. Daily treatment dynamics studies revealed rapid PO4 3??P adsorption, unbalancing the N:P ratio and possibly affecting plant development. An integrated treatment approach, coupled with biomass valorization, is suggested to provide optimal resource management possibilities. 相似文献
7.
BAOZHANG CHEN NICHOLAS C. COOPS T. ANDY BLACK RACHHPAL S. JASSAL JING M. CHEN MARK JOHNSON 《Global Change Biology》2011,17(3):1442-1460
This study investigated how nitrogen (N) fertilization with 200 kg N ha?1 of urea affected ecosystem carbon (C) sequestration in the first‐postfertilization year in a Pacific Northwest Douglas‐fir (Pseudotsuga menziesii) stand on the basis of multiyear eddy‐covariance (EC) and soil‐chamber measurements before and after fertilization in combination with ecosystem modeling. The approach uses a data‐model fusion technique which encompasses both model parameter optimization and data assimilation and minimizes the effects of interannual climatic perturbations and focuses on the biotic and abiotic factors controlling seasonal C fluxes using a prefertilization 9‐year‐long time series of EC data (1998–2006). A process‐based ecosystem model was optimized using the half‐hourly data measured during 1998–2005, and the optimized model was validated using measurements made in 2006 and further applied to predict C fluxes for 2007 assuming the stand was not fertilized. The N fertilization effects on C sequestration were then obtained as differences between modeled (unfertilized stand) and EC or soil‐chamber measured (fertilized stand) C component fluxes. Results indicate that annual net ecosystem productivity in the first‐post‐N fertilization year increased by~83%, from 302 ± 19 to 552 ± 36 g m?2 yr?1, which resulted primarily from an increase in annual gross primary productivity of~8%, from 1938 ± 22 to 2095 ± 29 g m?2 yr?1 concurrent with a decrease in annual ecosystem respiration (Re) of~5.7%, from 1636 ± 17 to 1543 ± 31 g m?2 yr?1. Moreover, with respect to respiration, model results showed that the fertilizer‐induced reduction in Re (~93 g m?2 yr?1) principally resulted from the decrease in soil respiration Rs (~62 g m?2 yr?1). 相似文献
8.
Irene Schaffner Stefan Hofbauer Michael Krutzler Katharina F. Pirker Marzia Bellei Gerhard Stadlmayr Georg Mlynek Kristina Djinovic‐Carugo Gianantonio Battistuzzi Paul G. Furtmüller Holger Daims Christian Obinger 《Molecular microbiology》2015,96(5):1053-1068
It is demonstrated that cyanobacteria (both azotrophic and non‐azotrophic) contain heme b oxidoreductases that can convert chlorite to chloride and molecular oxygen (incorrectly denominated chlorite ‘dismutase’, Cld). Beside the water‐splitting manganese complex of photosystem II, this metalloenzyme is the second known enzyme that catalyses the formation of a covalent oxygen–oxygen bond. All cyanobacterial Clds have a truncated N‐terminus and are dimeric (i.e. clade 2) proteins. As model protein, Cld from Cyanothece sp. PCC7425 (CCld) was recombinantly produced in Escherichia coli and shown to efficiently degrade chlorite with an activity optimum at pH 5.0 [kcat 1144 ± 23.8 s?1, KM 162 ± 10.0 μM, catalytic efficiency (7.1 ± 0.6) × 106 M?1 s?1]. The resting ferric high‐spin axially symmetric heme enzyme has a standard reduction potential of the Fe(III)/Fe(II) couple of ?126 ± 1.9 mV at pH 7.0. Cyanide mediates the formation of a low‐spin complex with kon = (1.6 ± 0.1) × 105 M?1 s?1 and koff = 1.4 ± 2.9 s?1 (KD ~ 8.6 μM). Both, thermal and chemical unfolding follows a non‐two‐state unfolding pathway with the first transition being related to the release of the prosthetic group. The obtained data are discussed with respect to known structure–function relationships of Clds. We ask for the physiological substrate and putative function of these O2‐producing proteins in (nitrogen‐fixing) cyanobacteria. 相似文献
9.
TIM J. CLOUGH JANET E. BERTRAM ROBERT R. SHERLOCK ROBERT L. LEONARD BARBARA L. NOWICKI† 《Global Change Biology》2006,12(2):352-363
There is considerable uncertainty in the estimates of indirect N2O emissions as defined by the Intergovernmental Panel on Climate Change's (IPCC) methodology. Direct measurements of N2O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N2O budget. The objectives of this research were to measure the N2O fluxes from a spring‐fed river, relate these fluxes to the dissolved N2O concentrations and NO3‐N loading of the river, and to try to define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N2O L?1. River NO3‐N and dissolved N2O concentrations ranged from 2.5 to 5.3 mg L?1 and 0.4 to 1.9 μg N2O‐N L?1, respectively, with N2O saturation reaching 404%. Floating headspace chambers were used to sample N2O fluxes. N2O‐N fluxes were significantly related to dissolved N2O‐N concentrations (r2=0.31) but not to NO3‐N concentrations. The N2O‐N fluxes ranged from 38 to 501 μg m?2 h?1, averaging 171 μg m?2 h?1 (±SD 85) overall. The measured N2O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N2O present in the groundwater that fed the river. 相似文献
10.
TIM J. CLOUGH JANET E. BERTRAM ROBERT R. SHERLOCK ROBERT L. LEONARD BARBARA L. NOWICKI† 《Global Change Biology》2006,12(3):477-488
There is considerable uncertainty in the estimates of indirect N2O emissions as defined by the intergovernmental panel on climate change's (IPCC) methodology. Direct measurements of N2O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N2O budget. The objectives of this research were to measure the N2O fluxes from a spring‐fed river, relate these fluxes to the dissolved N2O concentrations and NO3‐N loading of the river, and to try and define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N2O L?1. River NO3‐N and dissolved N2O concentrations ranged from 2.5 to 5.3 mg L?1 and 0.4 to 1.9 μg N2O‐N L?1, respectively, with N2O saturation reaching 404%. Floating headspace chambers were used to sample N2O fluxes. N2O‐N fluxes were significantly related to dissolved N2O‐N concentrations (r2=30.6) but not to NO3‐N concentrations. The N2O‐N fluxes ranged from 38–501 μg m?2 h?1, averaging 171 μg m?2 h?1 (±SD 85) overall. The measured N2O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N2O present in the groundwater that fed the river. 相似文献
11.
Plant and soil responses of an alpine steppe on the Tibetan Plateau to multi-level nitrogen addition 总被引:2,自引:0,他引:2
Yongwen Liu Xu-Ri Xingliang Xu Da Wei Yinghong Wang Yuesi Wang 《Plant and Soil》2013,369(1-2):515-529
Background
Although plant growth in alpine steppes on the Tibetan Plateau has been suggested to be sensitive to nitrogen (N) addition, the N limitation conditions of alpine steppes remain uncertain.Methods
After 2 years of fertilization with NH4NO3 at six rates (0, 10, 20, 40, 80 and 160 kg N ha?1 yr?1), the responses of plant and soil parameters as well as N2O fluxes were measured.Results
At the vegetation level, N addition resulted in an increase in the aboveground N pool from 0.5?±?0.1 g m?2 in the control plots to 1.9?±?0.2 g m?2 in the plots at the highest N input rate. The aboveground C pool, biomass N concentration, foliar δ15N, soil NO3 ?-N and N2O flux were also increased by N addition. However, as the N fertilization rate increased from 10 kg N ha?1 yr?1 to 160 kg N ha?1 yr?1, the N-use efficiency decreased from 12.3?±?4.6 kg C kg N?1 to 1.6?±?0.2 kg C kg N?1, and the N-uptake efficiency decreased from 43.2?±?9.7 % to 9.1?±?1.1 %. Biomass N:P ratios increased from 14.4?±?2.6 in the control plots to 20.5?±?0.8 in the plots with the highest N input rate. Biomass N:P ratios, N-uptake efficiency and N-use efficiency flattened out at 40 kg N ha?1 yr?1. Above this level, soil NO3 ?-N began to accumulate. The seasonal average N2O flux of growing season nonlinearly increased with increased N fertilization rate and linearly increased with the weighted average foliar δ15N. At the species level, N uptake responses to relative N availability were species-specific. Biomass N concentration of seven out of the eight non-legume species increased significantly with N fertilization rates, while Kobresia macrantha and the one legume species (Oxytropics glacialis) remained stable. Both the non-legume and the legume species showed significant 15N enrichment with increasing N fertilization rate. All non-legume species showed significant increased N:P ratios with increased N fertilization rate, but not the legume species.Conclusions
Our findings suggest that the Tibetan alpine steppes might be N-saturated above a critical N load of 40 kg N ha?1 yr?1. For the entire Tibetan Plateau (ca. 2.57 million km2), a low N deposition rate (10 kg N ha?1 yr?1) could enhance plant growth, and stimulate aboveground N and C storage by at least 1.1?±?0.3 Tg N yr?1 and 31.5?±?11.8 Tg C yr?1, respectively. The non-legume species was N-limited, but the legume species was not limited by N. 相似文献12.
1. The release of total phosphorus (TP) and nitrogen (N in ammonium) was measured for the five most abundant fish species (>85% of biomass) in Mouse and Ranger Lakes, two biomanipulated, oligotrophic lakes in Ontario. 2. The specific release rate of both nutrients was significantly related to fish mass; log10 TP release rate (μg h?1) = 0.793 (±0.109) [log10 wet mass (g)] + 0.7817 (±0.145), and log10 N release rate (μg h?1) = 0.6946 (±0.079) [log10wet mass (g)] + 1.7481 (±0.108). 3. When fish nutrient release was standardized for abundance (all populations, 1993–95) and epilimnetic volume, fish were estimated to contribute 0.083 (±0.061) μg TP L?1 day?1, and 0.41 (±0.17) μg N L?1 day?1 in Mouse L., and 0.062 (±0.020) μg TP L?1 day?1 and 0.31 (±0.08) μg N L?1 day?1 in Ranger L. 4. In comparison, concurrent rates of total planktonic P regeneration were 1.02 (±0.45) μg L?1 day?1 (Mouse L.) and 0.85 (±0.19) μg L?1 day?1 (Ranger L.). Fish represented 8% of planktonic P release in Mouse L. and 7% in Ranger L. 5. Fish dry mass had mean elemental body compositions of 39.3% carbon, 10.9% nitrogen, and 4.0% phosphorus (all fish combined), with a mean molar C : N : P ratio of 27 : 6 : 1. This comprised about 55% and 23% of the total epilimnetic particulate P and N respectively. 6. Turnover times of P and N in fish were approximately 103 and 48 days respectively. In comparison, planktonic turnover times of particulate P in Mouse and Ranger Lakes were 4.3 and 4.4 days respectively. Given their high P content and low turnover rates, fish appear to be important P sinks in lakes. 相似文献
13.
Whendee L. Silver rew W. Thompson Megan E. McGroddy Ruth K. Varner† Jadson D. Dias‡ Hudson Silva†‡ Patrick M. Crill† Michael Keller§ 《Global Change Biology》2005,11(2):290-306
Fine root dynamics have the potential to contribute significantly to ecosystem‐scale biogeochemical cycling, including the production and emission of greenhouse gases. This is particularly true in tropical forests which are often characterized as having large fine root biomass and rapid rates of root production and decomposition. We examined patterns in fine root dynamics on two soil types in a lowland moist Amazonian forest, and determined the effect of root decay on rates of C and N trace gas fluxes. Root production averaged 229 (±35) and 153 (±27) g m?2 yr?1 for years 1 and 2 of the study, respectively, and did not vary significantly with soil texture. Root decay was sensitive to soil texture with faster rates in the clay soil (k=?0.96 year?1) than in the sandy loam soil (k=?0.61 year?1), leading to greater standing stocks of dead roots in the sandy loam. Rates of nitrous oxide (N2O) emissions were significantly greater in the clay soil (13±1 ng N cm?2 h?1) than in the sandy loam (1.4±0.2 ng N cm?2 h?1). Root mortality and decay following trenching doubled rates of N2O emissions in the clay and tripled them in sandy loam over a 1‐year period. Trenching also increased nitric oxide fluxes, which were greater in the sandy loam than in the clay. We used trenching (clay only) and a mass balance approach to estimate the root contribution to soil respiration. In clay soil root respiration was 264–380 g C m?2 yr?1, accounting for 24% to 35% of the total soil CO2 efflux. Estimates were similar using both approaches. In sandy loam, root respiration rates were slightly higher and more variable (521±206 g C m2 yr?1) and contributed 35% of the total soil respiration. Our results show that soil heterotrophs strongly dominate soil respiration in this forest, regardless of soil texture. Our results also suggest that fine root mortality and decomposition associated with disturbance and land‐use change can contribute significantly to increased rates of nitrogen trace gas emissions. 相似文献
14.
R. J. RITCHIE 《Plant, cell & environment》1996,19(11):1307-1316
Synechococcus R-2 (PCC 1942) actively accumulates sulphate in the light and dark. Intracellular sulphate was 1.35 ± 0.23 mol m?3 (light) and 0.894 ± 0.152 mol m?3 (dark) under control conditions (BG-11 media: pHo, 7.5; [SO42?]o, 0.304 mol m?3). The sulphate transporter is different from that found in higher plants: it appears to be an ATP-driven pump transporting one SO42?/ATP [ΔμSO42?i,o=+ 27.7 ± 0.24 kJ mol?1 (light) and + 24 ± 0.34 kj mol?1 (dark)]. The rate of metabolism of SO42?at pHo, 7.5 was 150 ± 28 pmol m?2 s?1 (n = 185) in the light but only 12.8 ± 3.6 pmol m?2 s?1 (n = 61) in the dark. Light-driven sulphate uptake is partially inhibited by DCMU and chloramphenicol. Sulphate uptake is not linked to potassium, proton, sodium or chloride transport. The alga has a constitutive over-capacity for sulphate uptake [light (n= 105): Km= 0.3 ± 0.1 mmol m?3, Vmax, = 1.8 ± 0.6 nmol m?2 s?1; dark (n= 56): Km= 1.4 ± 0.4 mmol m?3, Vmax= 41 ± 22 pmol m?2 s?1]. Sulphite (SO32?) was a competitive inhibitor of sulphate uptake. Selenate (SeO42?) was an uncompetitive inhibitor. 相似文献
15.
Taichi Fujii Ken Terao Maiko Tsuda Shinichi Kitamura Takashi Norisuye 《Biopolymers》2009,91(9):729-736
The z‐average mean‐square radius of gyration 〈S2〉z, the particle scattering function P(k), the second virial coefficient, and the intrinsic viscosity [η] have been determined for amylose tris(phenylcarbamate) (ATPC) in methyl acetate (MEA) at 25°C, in ethyl acetate (EA) at 33°C, and in 4‐methyl‐2‐pentanone (MIBK) at 25°C by light and small‐angle X‐ray scattering and viscometry as functions of the weight‐average molecular weight in a range from 2 × 104 to 3 × 106. The first two solvents attain the theta state, whereas the last one is a good solvent for the amylose derivative. Analysis of the 〈S2〉z, P(k), and [η] data based on the wormlike chain yields h (the contour length or helix pitch per repeating unit) = 0.37 ± 0.02 and λ?1 (the Kuhn segment length) = 15 ± 2 nm in MEA, h = 0.39 ± 0.02 and λ?1 = 17 ± 2 nm in EA, and h = 0.42 ± 0.02 nm and λ?1 = 24 ± 2 nm in MIBK. These h values, comparable with the helix pitches (0.37–0.40 nm) per residue of amylose triesters in the crystalline state, are somewhat larger than the previously determined h of 0.33 ± 0.02 nm for ATPC in 1,4‐dioxane and 2‐ethoxyethanol, in which intramolecular hydrogen bonds are formed between the C?O and NH groups of the neighbor repeating units. The slightly extended helices of ATPC in the ketone and ester solvents are most likely due to the replacement of those hydrogen bonds by intermolecular hydrogen bonds between the NH groups of the polymer and the carbonyl groups of the solvent. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 729–736, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com 相似文献
16.
Ventilation frequency (FV) in motionless common sole Solea solea was measured before and after a startling stimulus in normoxia and in hypoxia (15% air saturation). Startling reduced FV in normoxia (from mean ±s.e. 41 ± 3·3 beats min?1 to near zero, i.e. 2·0 ± 1·8 beats min?1) and in hypoxia (from mean ±s.e. 80 ± 4·4 to 58·8 ± 12·9 beats min?1). It is suggested that the maintenance of high FV in hypoxia may increase the probability of detection by predators compared to normoxia. 相似文献
17.
L. Zhang D.‐M. Xiong B. Li Z.‐G. Zhao W. Fang K. Yang Q.‐X. Fan 《Zeitschrift fur angewandte Ichthyologie》2012,28(1):82-86
The 96‐h LC50 (median lethal concentration, LC50) tests were conducted using four different sizes of yellow catfish Pelteobagrus fulvidraco to provide primary information on the sensitivity of this species to elevated ammonia and/or nitrite, and to determine if the sensitivity is mediated by size under the same conditions. The results showed that 96‐h LC50 of fish weighing 0.034 ± 0.002, 0.296 ± 0.049, 3.52 ± 0.95 and 32.96 ± 5.75 g to total ammonia nitrogen‐N was 24.96, 35.85, 47.44 and 68.79 mg L?1, respectively; un‐ionized ammonia nitrogen‐N was 0.34, 0.49, 0.65 and 0.94 mg L?1 in test conditions of pH 7.42 and 23°C; and that nitrite nitrogen‐N was 69.06, 97.23, 133.61 and 196.05 mg L?1 in test conditions of pH 7.58 and 23°C, respectively. The NOEL (No Observable Effect Level) of fish (body weight from 0.03 to 30 g) to ammonia and nitrite was 2.25–6.22 mg L?1 total ammonia nitrogen‐N, 0.03–0.10 mg L?1 un‐ionized ammonia nitrogen‐N in test conditions of pH 7.42 and 23°C, and 6.27–17.68 mg L?1 nitrite nitrogen‐N in test conditions of pH 7.58 and 23°C, respectively. These results indicate that the susceptibility of this fish to total ammonia or nitrite was reduced with increasing size, and that a dose‐dependent relationship might exist between them. The 96‐h LC50 and NOEL of different sizes of fish to total ammonia, un‐ionized ammonia and nitrite would be important to know for water quality standards in yellow catfish aquaculture. 相似文献
18.
Nadine Summa Tanja Soldatovi Lutz Dahlenburg ivadin D. Bugari Rudi van Eldik 《Journal of biological inorganic chemistry》2007,12(4):461-475
A set of three oxaliplatin derivatives containing 1,2-trans-R,R-diaminocyclohexane (dach) as a spectator ligand and different chelating leaving groups X–Y, viz., [Pt(dach)(O,O-cyclobutane-1,1-dicarboxylate)], or Pt(dach)(CBDCA), [Pt(dach)(N,O-glycine)]+, or Pt(dach)(gly), and [Pt(dach)(N,S-methionine)]+, or Pt(dach)(l-Met), where l-Met is l-methionine, were synthesized and the crystal structure of Pt(dach)(gly) was determined by X-ray diffraction. The effect of
the leaving group on the reactivity of the resulting Pt(II) complexes was studied for the nucleophiles thiourea, glutathione
(GSH) and l-Met under pseudo-first-order conditions as a function of nucleophile concentration and temperature, using UV–vis spectrophotometric
techniques. 1H NMR spectroscopy was used to follow the substitution of the leaving group by guanosine 5′-monophosphate (5′-GMP2−) under second-order conditions. The rate constants indicate for all reactions a direct substitution of the X–Y chelate by
the selected nucleophiles, thereby showing that the nature of the chelate, viz., O–O (CBDCA2−), N–O (glycine) or S–N (l-Met), respectively, plays an important role in the kinetic and mechanistic behavior of the Pt(II) complex. The k
1 values for the reaction with thiourea, l-Met, GSH and 5′-GMP2− were found to be as follows (103
k
1, 37.5 °C, M−1 s−1): Pt(dach)(CBDCA) 61 ± 2, 21.6 ± 0.1, 23 ± 1, 0.352 ± 0.002; Pt(dach)(gly) 82 ± 3, 6.2 ± 0.2, 37 ± 1, 1.77 ± 0.01; Pt(dach)(l-Met) (thiourea, GSH) 62 ± 2, 24 ± 1. The activation parameters for all reactions studied suggest an associative substitution
mechanism.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
Effects of seasonality,transport pathway,and spatial structure on greenhouse gas fluxes in a restored wetland
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Gavin McNicol Cove S. Sturtevant Sara H. Knox Iryna Dronova Dennis D. Baldocchi Whendee L. Silver 《Global Change Biology》2017,23(7):2768-2782
Wetlands can influence global climate via greenhouse gas (GHG) exchange of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Few studies have quantified the full GHG budget of wetlands due to the high spatial and temporal variability of fluxes. We report annual open‐water diffusion and ebullition fluxes of CO2, CH4, and N2O from a restored emergent marsh ecosystem. We combined these data with concurrent eddy‐covariance measurements of whole‐ecosystem CO2 and CH4 exchange to estimate GHG fluxes and associated radiative forcing effects for the whole wetland, and separately for open‐water and vegetated cover types. Annual open‐water CO2, CH4, and N2O emissions were 915 ± 95 g C‐CO2 m?2 yr?1, 2.9 ± 0.5 g C‐CH4 m?2 yr?1, and 62 ± 17 mg N‐N2O m?2 yr?1, respectively. Diffusion dominated open‐water GHG transport, accounting for >99% of CO2 and N2O emissions, and ~71% of CH4 emissions. Seasonality was minor for CO2 emissions, whereas CH4 and N2O fluxes displayed strong and asynchronous seasonal dynamics. Notably, the overall radiative forcing of open‐water fluxes (3.5 ± 0.3 kg CO2‐eq m?2 yr?1) exceeded that of vegetated zones (1.4 ± 0.4 kg CO2‐eq m?2 yr?1) due to high ecosystem respiration. After scaling results to the entire wetland using object‐based cover classification of remote sensing imagery, net uptake of CO2 (?1.4 ± 0.6 kt CO2‐eq yr?1) did not offset CH4 emission (3.7 ± 0.03 kt CO2‐eq yr?1), producing an overall positive radiative forcing effect of 2.4 ± 0.3 kt CO2‐eq yr?1. These results demonstrate clear effects of seasonality, spatial structure, and transport pathway on the magnitude and composition of wetland GHG emissions, and the efficacy of multiscale flux measurement to overcome challenges of wetland heterogeneity. 相似文献
20.
Nitrous oxide fluxes from corn fields: on-farm assessment of the amount and timing of nitrogen fertilizer 总被引:5,自引:0,他引:5
B. L. MA T. Y. WU N. TREMBLAY† W. DEEN‡ M. J. MORRISON N. B. MCLAUGHLIN E. G. GREGORICH G. STEWART‡ 《Global Change Biology》2010,16(1):156-170
Nitrogen fertilization is considered as an important source of atmospheric N2O emission. A seven site‐year on‐farm field experiment was conducted at Ottawa and Guelph, ON and Saint‐Valentin, QC, Canada to characterize the affect of the amount and timing of N fertilizer on N2O emission in corn (Zea mays L.) production. Using the static chamber method, gas samples were collected for 28‐days after preplant and 28‐days after sidedress fertilization at the seven site‐year, resulting in 14 monitoring periods. For both methods of fertilization, peak N2O flux and cumulative emission increased with the amount of N applied, with rates ranging from 30 to 900 μg N m?2 h?1. Depending on N amount and time of application, cumulative emission varied from 0.05 to 2.42 kg N ha?1, equivalent to 0.03% to 1.45% of the N fertilizer applied. Differences in N2O emission peaks among fertilizer treatments were clearly separated in 13 out of 14 monitoring periods. Total N2O emissions may have been underestimated compared with annual monitoring in 10 out of the 49 cases because the monitoring period ended before N2O efflux returned to the baseline level. The flux of N2O was negligible when soil mineral N in the 0–15 cm layer was < 20 mg N kg?1. While rainfall stimulated emission, soil temperature > 15 °C was likely the driving force responsible for the higher levels of N2O found for sidedress than preplant application methods. However, caution must be taken when interpreting these later results as preplant fertilization may have continuously stimulated N2O emissions after the 28‐days monitoring period, especially in situations where N2O effluxes have not fallen back to their baseline levels. Increasing fertilizer rates from 90 to 150 kg N ha?1 resulted in slight increases in yields, but doubled cumulative N2O emissions. 相似文献