Atmospheric nitrogen inputs and losses along an urbanization gradient from Boston to Harvard Forest,MA

Urbanization alters nitrogen (N) cycling, but the spatiotemporal distribution and impact of these alterations on ecosystems are not well-quantified. We measured atmospheric inorganic N inputs and soil leaching losses along an urbanization gradient from Boston, MA to Harvard Forest in Petersham, MA. Atmospheric N inputs at urban sites (12.3 ± 1.5 kg N ha^?1 year^?1) were significantly greater than non-urban (5.7 ± 0.5 kg N ha^?1 year^?1) sites with NH₄ ⁺ (median value of 77 ± 4 %) contributing thrice as much as NO₃ ^?. Proximity to urban core correlated positively with NH₄ ⁺ (R² = 0.57, p = 0.02) and total inorganic N inputs (R² = 0.61, p = 0.01); on-road CO₂ emissions correlated positively with NO ₃ ^? inputs (R² = 0.74, p = 0.003). Inorganic N leaching rates correlated positively with atmospheric N input rates (R² = 0.61, p = 0.01), but did not differ significantly between urban and non-urban sites (p > 0.05). Our empirical measurements of atmospheric N inputs are greater for urban areas and less for rural areas compared to modeled regional estimates of N deposition. Five of the nine sites had NO ₃ ^? leached that came almost entirely from nitrification, indicating that the NO₃ ^? in leachate came from biological processes rather than directly passing through the soil. A significant proportion (17–100 %) of NO ₃ ^? leached from the other four sites came directly from the atmosphere. Surprisingly, the four sites where atmospheric sources made up the largest proportion of leachate NO₃ ^? also had relatively low N leaching rates, suggesting that atmospheric N inputs added to terrestrial ecosystems can move to multiple sinks and losses simultaneously, rather than being lost via leaching only after abiotic and biotic sinks have become saturated. This study improves our understanding of atmospheric N deposition and leaching in urban ecosystems, and highlights the need to incorporate urbanization effects in N deposition models.     

A multi-environmental study of recent breeding progress on nitrogen use efficiency in wheat (Triticum aestivum L.)

Key message

By comparing 195 varieties in eight trials, this study assesses nitrogen use efficiency improvement in high and low nitrogen conditions in European winter wheat over the last 25 years.

Abstract

In a context where European agriculture practices have to deal with environmental concerns and nitrogen (N) fertiliser cost, nitrogen use efficiency (NUE) has to be improved. This study assessed genetic progress in winter wheat (Triticum aestivum L.) NUE. Two hundred and twenty-five European elite varieties were tested in four environments under two levels of N. Global genetic progress was assessed on additive genetic values and on genotype × N interaction, covering 25 years of European breeding. To avoid sampling bias, quality, precocity and plant height were added as covariates in the analyses when needed. Genotype × environment interactions were highly significant for all the traits studied to such an extent that no additive genetic effect was detected on N uptake. Genotype × N interactions were significant for yield, grain protein content (GPC), N concentration in straw, N utilisation, and NUE. Grain yield improvement (+0.45 % year^?1) was independent of the N treatment. GPC was stable, thus grain nitrogen yield was improved (+0.39 % year^?1). Genetic progress on N harvest index (+0.12 % year^?1) and on N concentration in straw (?0.52 % year^?1) possibly revealed improvement in N remobilisation. There has been an improvement of NUE additive genetic value (+0.33 % year^?1) linked to better N utilisation (+0.20 % year^?1). Improved yield stability was detected as a significant improvement of NUE in low compared to high N conditions. The application of these results to breeding programs is discussed.     

Combination of nitrogen deposition and ultraviolet-B radiation decreased litter decomposition in subtropical China

Aims

The interactive effects of enhanced nitrogen (N) deposition and ultraviolet-B (UV-B) radiation on litter decomposition are still unknown. The aims are to test whether the interactive effects of the two environmental factors on litter decomposition and nutrient loss are stronger than that of each factor alone.

Methods

Experiment included five treatments: elevated UV-B radiation (UV-B, 10 % enhancement), low N addition (N1, 30 kg N ha^?1 year^?1), high N addition (N2, 60 kg N ha^?1 year^?1), the two combined treatments of the two factors (UV-B+N1 and UV-B+N2), and an unmanipulated control.

Results

The annual decomposition rates under combination of UV-B and N addition significantly decreased compared with that under UV-B and N additions for Pinus massoniana, and did also compared with that under UV-B but did not significantly differ with N additions for Cyclobalanopsis glauca. Negative effects of N additions alone on lignin degradation and P loss were partly offset but negative effect on N loss was further amplified when was combined with UV-B.

Conclusions

The combination of N deposition and UV-B radiation on litter decomposition and nutrient loss was significantly different from that of each factor alone without a general response pattern of decomposition, and was regulated by litter chemistry.     

Biomass and Genotype × Environment Interactions of Populus Energy Crops in the Midwestern United States

Using Populus feedstocks for biofuels, bioenergy, and bioproducts is becoming economically feasible as global fossil fuel prices increase. Maximizing Populus biomass production across regional landscapes largely depends on understanding genotype × environment interactions, given broad genetic variation at strategic (genomic group) and operational (clone) levels. A regional network of Populus field tests was established in the Midwest USA in 1995, 1997, and 2000 to assess relative productivity of 187 clones grown at Westport, Minnesota (45.7° N, 95.2° W); Waseca, Minnesota (only 2000; 44.1° N, 93.5° W); Arlington, Wisconsin (43.3° N, 89.4° W); and Ames, Iowa (42.0° N, 93.6° W). We evaluated biomass potential throughout plantation development and identified clones with yield substantially greater than commercial controls (Eugenei, NM6). For each site, biomass ranges (Mg ha^?1 year^?1) of the best six clones were: Westport: 2.3 to 3.9 (5 years), 8.0 to 10.1 (8 years), and 8.9 to 11.3 (10 years); Waseca: 10.4 to 13.4 (7 years); Arlington: 5.1 to 7.1 (3 years), 14.8 to 20.9 (6 years), and 16.1 to 21.1 (8 years); and Ames: 4.3 to 5.3 (4 years), 11.1 to 20.9 (7 years), and 14.3 to 24.5 (9 years). Mean biomass of the best three clones was 1.4 to 2.7 times greater than controls as trees developed at Westport (1995, 1997) and Waseca 2000. Genotype × environment interactions governed biomass production, with clone–mean rank correlations across sites ranging from 0.29 to 0.81. We identified generalist genotypes (e.g. Crandon, NC14105, NM2) with elevated biomass across the region and specialists (e.g. 7300501, 80X01015, and NC14103) with exceptional biomass at specific locations.     

Sex-specific carbon and nitrogen partitioning under N deposition in Populus cathayana

Key message

Females of Populus cathayana allocated increased N to soluble proteins, while males keep N allocation pattern unchanged under N enrichment.

Abstract

In our study, Populus cathayana as a model species is employed to detect the sex-specific responses in growth, photosynthetic nitrogen (N) use efficiency (PNUE), carbon (C) and N partitioning when exposed to 0, 7.5 and 15 g N m^?2 year^?1 on the basis of local N deposition level. Our results showed that females had higher responses in photosynthesis and growth than males when exposed to N deposition, and also exhibited higher PNUE than males when exposed to high level of N deposition, suggesting that plasticity in the females may enhance the capacity of young seedlings to acquire resources. Moreover, we found that females mainly allocated increased N to soluble proteins and detergent-soluble proteins, but not to cell-wall proteins, while males maintained original partitioning pattern of N and also accumulated excessive N in the form of free amino acids. Females also allocated more fraction of leaf N to carboxylation (P _C), bioenergetics (P _B), and then more fraction of leaf N to all components of photosynthetic machinery (P _T) than males under high level of N deposition. Such sex-specific N allocation strategy may correlate with sex-related PNUE. These results indicated that there is a higher critical N demand in females, and females could use N nutrient more efficiently than males under high N deposition. We also found that higher shift from starch to soluble sugars, such as sucrose, occurred in females than in males under N enrichment. By contrast, excessive accumulation of starch and non-structural carbohydrate in females relative to males was observed under control conditions, which might inhibit female photosynthesis rate. Accordingly, we suggested that the different leaf C and N partitioning patterns could explain the sex-specific responses in growth. Therefore, females may obtain advantageous position in the process of intraspecific competition when exposed to high level of N deposition because they have higher light capture (total leaf area) ability and utilization efficiency (PNUE) than the males that confer the ability for fast growth and thus are likely to be more responsive to N enrichment. Our results suggested that it could be important to look at the stronger growth response of the females over the males under N enrichment at both the leaf and the plant scale.     

Plant and soil responses of an alpine steppe on the Tibetan Plateau to multi-level nitrogen addition

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.     

Stable carbon and nitrogen isotope ratios of Eucalyptus and Acacia species along a seasonal rainfall gradient in Western Australia

Key message

Eucalyptus and Acacia species were surprisingly similar with respect to variations in δ ¹³ C, δ ¹⁵ N. Both genera respond with speciation and associated changes in leaf structure to drought.

Abstract

Stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) in leaves of eucalypts (Corymbia and Eucalyptus) and Acacia (and some additional Fabaceae) species were investigated together with specific leaf area (SLA), leaf nitrogen (N) and leaf phosphorous (P) concentration along a north–south transect through Western Australia covering winter- and summer-dominated rainfall between 100 and 1,200 mm annually. We investigated 62 eucalypts and 78 woody Fabaceae species, mainly of the genus Acacia. Leaf δ¹³C values of Eucalyptus and Acacia species generally increased linearly with latitude from ?29.5 ± 1.3 ‰ in the summer-dominated rainfall zone (15°S–18°S) to about ?25.7 ± 1.1 ‰ in the winter-dominated rainfall zone (29°S–31°S). δ¹⁵N increased initially with southern latitudes (0.5 ± 1.6 ‰ at 15°S; 5.8 ± 3.3 ‰ at 24–29°S) but decreased again further South (4.6 ± 3.5 ‰ at 31°S). The variation in δ¹³C and δ¹⁵N was probably due to speciation of Eucalyptus and Acacia into very local populations. There were no species that were distributed over the whole sampling area. The variation in leaf traits was larger between species than within species. Average nitrogen concentrations were 11.9 ± 1.05 mg g^?1 in Eucalyptus, and were 18.7 ± 4.1 mg g^?1 in Acacia. Even though the average nitrogen concentration was higher in Acacia than Eucalyptus, δ¹⁵N gave no clear indication for N₂ fixation in Acacia. In a multiple regression, latitude (as a surrogate for rainfall seasonality), mean rainfall, leaf nitrogen concentration, specific leaf area and nitrogen fixation were significant and explained 69 % of the variation of δ¹³C, but only 36 % of the variation of δ¹⁵N. Higher nitrogen and phosphorus concentration could give Acacia an advantage over Eucalyptus in arid regions of undefined rainfall seasonality.     

Urban influences on the nitrogen cycle in Puerto Rico

Anthropogenic actions are altering fluxes of nitrogen (N) in the biosphere at unprecedented rates. Efforts to study these impacts have concentrated in the Northern hemisphere, where experimental data are available. In tropical developing countries, however, experimental studies are lacking. This paper summarizes available data and assesses the impacts of human activities on N fluxes in Puerto Rico, a densely populated Caribbean island that has experienced drastic landscape transformations over the last century associated with rapid socioeconomic changes. N yield calculations conducted in several watersheds of different anthropogenic influences revealed that disturbed watersheds export more N per unit area than undisturbed forested watersheds. Export of N from urban watersheds ranged from 4.8 kg ha^?1 year^?1 in the Río Bayamón watershed to 32.9 kg ha^?1 year^?1 in the highly urbanized Río Piedras watershed and 33.3 kg ha^?1 year^?1 in the rural-agricultural Río Grande de Añasco watershed. Along with land use, mean annual runoff explained most of the variance in fluvial N yield. Wastewater generated in the San Juan Metropolitan Area receives primary treatment before it is discharged into the Atlantic Ocean. These discharges are N-rich and export large amounts of N to the ocean at a rate of about 140 kg ha^?1 year^?1. Data on wet deposition of inorganic N ( $\hbox{NH}_{4}^{+}+\hbox{NO}_{3}^{-}Anthropogenic actions are altering fluxes of nitrogen (N) in the biosphere at unprecedented rates. Efforts to study these impacts have concentrated in the Northern hemisphere, where experimental data are available. In tropical developing countries, however, experimental studies are lacking. This paper summarizes available data and assesses the impacts of human activities on N fluxes in Puerto Rico, a densely populated Caribbean island that has experienced drastic landscape transformations over the last century associated with rapid socioeconomic changes. N yield calculations conducted in several watersheds of different anthropogenic influences revealed that disturbed watersheds export more N per unit area than undisturbed forested watersheds. Export of N from urban watersheds ranged from 4.8 kg ha⁻¹ year⁻¹ in the Río Bayamón watershed to 32.9 kg ha⁻¹ year⁻¹ in the highly urbanized Río Piedras watershed and 33.3 kg ha⁻¹ year⁻¹ in the rural-agricultural Río Grande de A?asco watershed. Along with land use, mean annual runoff explained most of the variance in fluvial N yield. Wastewater generated in the San Juan Metropolitan Area receives primary treatment before it is discharged into the Atlantic Ocean. These discharges are N-rich and export large amounts of N to the ocean at a rate of about 140 kg ha⁻¹ year⁻¹. Data on wet deposition of inorganic N () suggest that rates of atmospheric N deposition are increasing in the pristine forests of Puerto Rico. Stationary and mobile sources of NO _x (NO+NO₂) and N₂O generated in the large urban centers may be responsible for this trend. Comprehensive measurements are required in Puerto Rico to quantitatively characterize the local N cycle. More research is required to assess rates of atmospheric N deposition, N fixation in natural and human-dominated landscapes, N-balance associated with food and feed trade, and denitrification.     

4-[18F]Fluoro-N-methyl-N-(propyl-2-yn-1-yl)benzenesulfonamide ([18F]F-SA): a versatile building block for labeling of peptides, proteins and oligonucleotides with fluorine-18 via Cu(I)-mediated click chemistry

Cu(I)-mediated [3+2]cycloaddition between azides and alkynes has evolved into a valuable bioconjugation tool in radiopharmaceutical chemistry. We have developed a simple, convenient and reliable radiosynthesis of 4-[¹⁸F]fluoro-N-methyl-N-(propyl-2-yn-1-yl)benzenesulfonamide ([ ¹⁸ F]F-SA) as a novel aromatic sulfonamide-based click chemistry building block. [ ¹⁸ F]F-SA could be prepared in a remotely controlled synthesis unit in 32 ± 5 % decay-corrected radiochemical yield in a total synthesis time of 80 min. The determined lipophilicity of [ ¹⁸ F]F-SA (logP = 1.7) allows handling of the radiotracer in aqueous solutions. The versatility of [ ¹⁸ F]F-SA as click chemistry building block was demonstrated by the labeling of a model peptide (phosphopeptide), protein (HSA), and oligonucleotide (L-RNA). The obtained radiochemical yields were 77 % (phosphopeptide), 55–60 % (HSA), and 25 % (L-RNA), respectively. Despite the recent emergence of a multitude of highly innovative novel bioconjugation methods for ¹⁸F labeling of biopolymers, Cu(I)-mediated click chemistry with [ ¹⁸ F]F-SA represents a reliable, robust and efficient radiolabeling technique for peptides, proteins, and oligonucleotides with the short-lived positron emitter ¹⁸F.     

Increased nitrogen deposition alleviated the adverse effects of drought stress on <Emphasis Type="Italic">Quercus variabilis</Emphasis> and <Emphasis Type="Italic">Quercus mongolica</Emphasis> seedlings

The plasticity response of Quercus variabilis and Quercus mongolica seedlings to combined nitrogen (N) deposition and drought stress was evaluated, and their performance in natural niche overlaps was predicted. Seedlings in a greenhouse were exposed to four N deposition levels (0, 4, 8, and 20 g N m^?2 year^?1) and two water levels (80 and 50 % field-water capacity). Plant traits associated with growth, biomass production, leaf physiology, and morphology were determined. Results showed that drought stress inhibited seedling performance, altered leaf morphology, and decreased fluorescence parameters in both species. By contrast increased N supply had beneficial effects on the nutritional status and activity of the PSII complex. The two species showed similar responses to drought stress. Contrary to the effects in Q. mongolica, N deposition promoted leaf N concentration, PSII activity, leaf chlorophyll contents, and final growth of Q. variabilis under well-watered conditions. Thus, Q. variabilis was more sensitive to N deposition than Q. mongolica. However, excessive N supply (20 g N m^?2 year^?1) did not exert any positive effects on the two species. Among the observed plasticity of the plant traits, plant growth was the most plastic, and leaf morphology was the least plastic. Therefore, drought stress played a primary role at the whole-plant level, but N supply significantly alleviated the adverse effects of drought stress on plant physiology. A critical N deposition load around 20 g N m^?2 year^?1 may exist for oak seedlings, which may more adversely affect Q. variabilis than Q. mongolica.     

Soil carbon fractions in grasslands respond differently to various levels of nitrogen enrichments

Background and Aims

Soil contains many different C fractions which have diverse physical and chemical compositions. Examining these differential soil C fractions in response to N enrichment is helpful for better understanding soil C changes under the predominantly increasing N deposition. In this study, we used a field N addition experiment in a grassland to explore the effects of various N enrichment levels on soil C fractions.

Methods

We conducted a field manipulative experiment which used a Latin square design with six N addition levels of 0, 2, 4, 8, 16 and 32 g N m^?2 year^?1 since 2003 in a semiarid grassland in northern China. Soil samples were collected in August (when plants have the greatest biomass), 2011. We measured C and N concentrations in soil light fraction, microbial biomass, extractable organic matter, heavy fraction, and total soil C and N.

Results

The results showed that total soil C and N, and heavy fraction C and N were not significantly affected by N addition after 9 years of treatments. In contrast, different N enrichment levels changed soil light fraction C and N, ranging from 4.3 to 27.7 % and 3.3–30.0 %, respectively. Moreover, both light fraction C and N had a nonlinear relationship with N addition rates, and the threshold for N-induced change in light fraction C and N was near 16 g N m^?2 year^?1 in this semiarid grassland. Increases of soil light fraction C and N primarily resulted from changes in biotic (N-stimulated aboveground biomass) and abiotic (soil temperature, moisture and pH) factors under N enrichment. Soil microbial biomass exponentially declined with increasing N, but extractable organic C showed a positive linear response to N enrichment rates. Changes in microbial biomass C and extractable organic C were primarily due to the reduced soil pH under N addition.

Conclusions

Our findings suggest that various soil C fractions differentially respond to elevated N, because different sets of biotic and abiotic factors regulate those fractions under N enrichment.     

Simulated nitrogen deposition significantly suppresses the decomposition of forest litter in a natural evergreen broad-leaved forest in the Rainy Area of Western China

Background and aims

Litter, an essential component of forest ecosystems, plays an important role in maintaining soil fertility, sequestering carbon (C) and improving soil biodiversity. However, litter decomposition is affected by increased nitrogen (N) deposition. Numerous reports have presented N deposition experiments in different forest ecosystems to investigate the effects of N deposition on litter decomposition, but the effects remain unclear, especially in ecosystems receiving increasingly higher levels of ambient N deposition. To address this gap, we performed a litterbag experiment to understand the effects of increasing N deposition on the litter decomposition process in natural evergreen broad-leaved forest in the Rainy Area of Western China.

Methods

A 2-year field litter decomposition experiment was conducted using the litterbag method. Four levels of N deposition were established: control (CK; 0 kg·N·ha^?1·year^?1), low N deposition (LN; 50 kg·N·ha^?1·year^?1), medium N deposition (MN; 150 kg·N·ha^?1·year^?1), and high N deposition (HN; 300 kg·N·ha^?1·year^?1). The simulated N depositions ranged from 50% to 320% of the ambient rate of wet N deposition.

Results

Simulated N deposition significantly increased the remaining mass, C, N, lignin and cellulose of the litter. The LN treatment decreased the remaining phosphorus (P); conversely, the HN treatment increased it. In the late stage of the study period, the mass remaining was positively closely correlated to the lignin and cellulose remaining during the decomposition process.

Conclusions

Simulated N deposition significantly suppressed the litter decomposition in the natural evergreen broad-leaved forest, despite the high rate of ambient N deposition, and the inhibitory effects increased with the N deposition levels. The suppressive effect of N deposition on litter decomposition may be primarily explained by the inhibition of lignin and cellulose degradation by the exogenous inorganic N. With ongoing N deposition in future, N deposition may have a potentially significant impact on C and N cycles in such forest ecosystems.

     

Potential for Production of Perennial Biofuel Feedstocks in Conservation Buffers on the Coastal Plain of Georgia,USA

With global increases in the production of cellulosic biomass for fuel, or “biofuel,” concerns over potential negative effects of using land for biofuel production have promoted attention to concepts of agricultural landscape design that sustainably balance tradeoffs between food, fuel, fiber, and conservation. The Energy Independence Security Act (EISA) of 2007 mandates an increase in advanced biofuels to 21 billion gallons in 2022. The southeastern region of the USA has been identified as a contributor to meeting half of this goal. We used a GIS-based approach to estimate the production and N-removal potential of three perennial biofeedstocks planted as conservation buffers (field borders associated with riparian buffers, and grassed waterways) on the Coastal Plain of Georgia, USA. Land cover, hydrology, elevation, and soils data were used to identify locations within agricultural landscapes that are most susceptible to runoff, erosion, and nutrient loss. We estimated potential annual biomass production from these areas to be: 2.5–3.5 Tg for giant miscanthus (Miscanthus?×?giganteus), 2–8.6 Tg for “Merkeron” napier grass (Pennisetum purpureum), and 1.9–7.5 Tg for “Alamo” switchgrass (Panicum virgatum). When production strategies were taken into consideration, we estimated total biomass yield of perennial grasses for the Georgia Coastal Plain at 2.2–9.4 Tg year^?1. Using published rates of N removal and ethanol conversion, we calculated the amount of potential N removal by these systems as 8100–51,000 Mg year^?1 and ethanol fuel production as 778–3296 Ml year^?1 (206 to 871 million gal. US).     

Oxidation and reduction of sulfite contribute to susceptibility and detoxification of SO2 in Populus × canescens leaves

Key Message

The critical level for SO ₂ susceptibility of Populus × canescens is approximately 1.2 μL L ^?1 SO ₂ . Both sulfite oxidation and sulfite reduction and assimilation contribute to SO ₂ detoxification.

Abstract

In the present study, uptake, susceptibility and metabolism of SO₂ were analyzed in the deciduous tree species poplar (Populus × canescens). A particular focus was on the significance of sulfite oxidase (SO) for sulfite detoxification, as SO has been characterized as a safety valve for SO₂ detoxification in herbaceous plants. For this purpose, poplar plants were exposed to different levels of SO₂ (0.65, 0.8, 1.0, 1.2 μL L^?1) and were characterized by visible injuries and at the physiological level. Gas exchange parameters (stomatal conductance for water vapor, CO₂ assimilation, SO₂ uptake) of the shoots were compared with metabolite levels (sulfate, thiols) and enzyme activities [SO, adenosine 5′-phosphosulfate reductase (APR)] in expanding leaves (80–90 % expanded). The critical dosage of SO₂ that confers injury to the leaves was 1.2 μL L^?1 SO₂. The observed increase in sulfur containing compounds (sulfate and thiols) in the expanding leaves strongly correlated with total SO₂ uptake of the plant shoot, whereas SO₂ uptake rate was strongly correlated with stomatal conductance for water vapor. Furthermore, exposure to high concentration of SO₂ revealed channeling of sulfite through assimilatory sulfate reduction that contributes in addition to SO-mediated sulfite oxidation to sulfite detoxification in expanding leaves of this woody plant species.     

2-Phenylpyridine ruthenacycles as effectors of glucose oxidase activity: inhibition by RuII and activation by RuIII

Cyclometalated Ru^II derivatives of 2-phenylpyridine (Hphpy) [Ru(phpy)(bpy)₂]Cl (1a) and [Ru(phpy)(phen)₂]Cl (1b) (bpy is 2,2′-bipyridine, phen is 1,10-phenanthroline) behave as noncompetitive inhibitors of glucose oxidase from Aspergillus niger in the enzyme-catalyzed oxidation of d-glucose by O₂ into the corresponding lactone at pH 5.0 and 25 °C. The enzymatic activity has been measured by monitoring the O₂ consumption. The inhibition constants K _i are 0.036 and 0.017 M for 1a and 1b, respectively, indicating that 1b inhibits the enzymatic activity more efficiently than 1a. The well-known coordination compound [Ru(bpy)₃]Cl₂ (2) behaves, in contrast, as a competitive inhibitor, with K _i = 0.018 M under the same conditions. The monophasic consumption of O₂ in the case of 1a, 1b, and 2 is replaced by a distinct two-phase kinetics in the presence of the cyclometalated Ru^III compound [Ru(phpy)(bpy)₂]Cl₂ (3), which was obtained from 1a in the presence of a large excess of H₂O₂ and the iron TAML activator. Interestingly, the rates of the first and the second phases are influenced by 3 in a different way. The rate of the first phase is noticeably higher in the presence of Ru^III, although the dependence is nonmonotonic and maximal acceleration is observed at the lowest loadings of 3. The rate of the second phase decreases monotonically on increasing the concentration of the ruthenium complex in solution. The nonmonotonic action of 3 was confirmed by using the doubly cyclometalated Ru^III derivative [Ru(phpy)₂(bpy)]Cl. The diverse rate variations induced by 3 accounted for acceleration by Ru^III of the O₂ reduction by the reduced form of glucose oxidase during the first phase, which ceases after the enzymatic reduction of Ru^III to the Ru^II species, the latter behaving similarly to 1a as the inhibitor of the enzyme.     

Dominant species, functional assemblages and frequency of equilibrium phases in late summer phytoplankton assemblages in Hungarian small shallow lakes

Late summer phytoplankton associations were studied qualitatively and quantitatively in 80 Hungarian lakes altogether (mostly shallow salt lakes, reservoirs, oxbows, gravel pit lakes). Equilibrium phases sensu Sommer et al. (1993) were found only in 17 lakes. Most of them were under some kind (high salt content or very low level of nutrients) of stress factor. It is concluded that environmental stress forces phytoplankton communities towards equilibrium. No relationship between occurrence of equilibria and trophic state was found. Species number of non-equilibrated lakes was almost three times as high as those in equilibrium. Of the 31 recently described (Reynolds et al., 2002) phytoplankton assemblages most of those were recognized that are likely to occur in shallow lakes. Separation of a functional group W _S from W2 for Synura dominated lakes is suggested. It seemed also necessary to raise a group (Y _Ph) for lakes dominated by Phacotus. Sorting of Dinophyta species into different already described functional groups is desirable.     

MiR-34a promotes Fas-mediated cartilage endplate chondrocyte apoptosis by targeting Bcl-2

Seven organorhenium pentylcarbonate compounds (PC1–PC7) have been synthesized. DNA-binding studies of the PC-series compounds using electronic spectroscopy and gel electrophoresis suggest that the compounds presumably bind to DNA in an intercalative mode. The intrinsic binding constants for PC4, PC6, and PC7 were found to be 1.6 × 10⁴, 3.9 × 10⁴, and 4.2 × 10⁴ M^?1, respectively. The X-ray structure determinations and density functional theory calculations indicate that the polypyridyl ligands in the compounds are nearly planar facilitating DNA binding through an intercalation mechanism. Cytotoxicity studies of 10 µM pentylcarbonate compounds against HTB-12 human astrocytoma brain cancer cells were studied for 48 h. It was observed that each of the pentylcarbonate compounds is active against the cancer cells. However, under analogous conditions, CRL-2005 rat astrocyte normal brain cells are not affected significantly.     

Nitrous oxide emissions during the non-rice growing seasons of two subtropical rice-based rotation systems in southwest China

Background and aims

High nitrous oxide (N₂O) emissions may occur during the non-rice growing season of Chinese rice-upland crop rotation systems. However, our understanding of N₂O emission during this season is poor due to a scarcity of available field N₂O measurements.

Methods

Using the static manual chamber-GC technique, seasonal N₂O emissions during the non-rice growing season were simultaneously measured at two adjacent rice-wheat and rice-rapeseed fields in southwest China for three consecutive annual rotation cycles (May 2005 to May 2008).

Results

Compared to the control, N fertilizer applications significantly enhanced soil N₂O emissions from both wheat and rapeseed systems. Seasonal cumulative N₂O fluxes from wheat systems were on average 2.6 kg N ha^?1 for the recommended practice (RP [150 kg N ha^?1]) and 5.0 kg N ha^?1 for the conventional practice (CP [250 kg N ha^?1]). Lower N₂O emissions were observed from the adjacent rapeseed systems. Average cumulative seasonal N₂O fluxes from rapeseed were 1.5 and 2.2 kg N ha^?1 for the RP and CP treatments, respectively. The first 3 weeks after N fertilization were the “hot moment” of N₂O emissions for both the wheat and rapeseed systems. The lowest yield-scaled N₂O fluxes for wheat were obtained at the RP treatment (mean: 0.81 kg N Mg^?1) while for rapeseed the CP treatment produced the lowest yield-scaled fluxes (mean: 0.79 kg N Mg^?1). On average, the direct N₂O emission factors (EF_d) for the wheat system (1.76 %) were over two times higher than for the rapeseed system (0.73 %).

Conclusions

Intercropping of rapeseed tends to result in lower N₂O emissions than wheat for rice-upland crop rotation systems of southwest China, indicating that either the N fertilization or the cropping system need to be considered not only for improving the estimate of regional and/or national N₂O fluxes but also for proposing the climate-smart agricultural management practice to reduce N₂O emissions from agricultural soils.