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111.
The effect of CO2 concentration on plant growth and the size of the rhizosphere denitrifier population was investigated for ryegrass grown at 3 different soil pH values (pH 4.3, 5.9 and 7.0). Soil microcosms were planted with ryegrass and maintained under constant growth conditions at either ambient (450ppm) or elevated (720ppm) CO2 concentration. At harvest, the rhizosphere soil was collected and subjected to a potential denitrification assay to provide an estimate of the size of the denitrifier population present. Ryegrass dry matter production varied across the pH range studied and contrary to other studies, elevated CO2 concentration did not consistently increase growth. Plant growth was reduced by ≈ 35% and 23% at pH 4.3 and pH 5.9, respectively, under elevated CO2 concentration. At pH 7.0, however, plant growth was increased by ≈ 45% under elevated CO2. Potential denitrification rates within the rhizosphere followed a similar pattern to plant growth in the different treatments, suggesting that plant growth and the size of denitrifier population within the rhizosphere are coupled. This study investigates the relationship between plant growth and rhizosphere denitrification potential, thereby providing an estimate of the size of the denitrifier population under increased CO2 concentration and soil pH. 相似文献
112.
113.
Agricultural fields are an important anthropogenic source of atmospheric nitrous oxide (N2O) and nitric oxide (NO). Although many field studies have tested the effectiveness of possible mitigation options on N2O and NO emissions, the effectiveness of each option varies across sites due to environmental factors and field management. To combine these results and evaluate the overall effectiveness of enhanced‐efficiency fertilizers [i.e., nitrification inhibitors (NIs), polymer‐coated fertilizers (PCFs), and urease inhibitors (UIs)] on N2O and NO emissions, we performed a meta‐analysis using field experiment data (113 datasets from 35 studies) published in peer‐reviewed journals through 2008. The results indicated that NIs significantly reduced N2O emissions (mean: ?38%, 95% confidential interval: ?44% to ?31%) compared with those of conventional fertilizers. PCFs also significantly reduced N2O emissions (?35%, ?58% to ?14%), whereas UIs were not effective in reducing N2O. NIs and PCFs also significantly reduced NO (?46%, ?65% to ?35%; ?40%, ?76% to ?10%, respectively). The effectiveness of NIs was relatively consistent across the various types of inhibitors and land uses. However, the effect of PCFs showed contrasting results across soil and land‐use type: they were significantly effective for imperfectly drained Gleysol grassland (?77%, ?88% to ?58%), but were ineffective for well‐drained Andosol upland fields. Because available data for PCFs were dominated by certain regions and soil types, additional data are needed to evaluate their effectiveness more reliably. NIs were effective in reducing N2O emission from both chemical and organic fertilizers. Moreover, the consistent effect of NIs indicates that they are potent mitigation options for N2O and NO emissions. 相似文献
114.
A spectrophotometric method for simultaneous analysis of glycine and lysine is proposed by application of neural networks on the spectral kinetic data. The method is based on the reaction of glycine and lysine with 1,2-naphthoquinone-4-sulfonate (NQS) in slightly basic medium. On the basis of the difference in the rate between the two reactions, these two amino acids can be determined simultaneously in binary mixtures. Feed-forward neural networks have been trained to quantify considered amino acids in mixtures under optimum conditions. In this way, a one-layer network was trained. Sigmoidal and linear transfer functions were used in the hidden and output layers, respectively. Linear calibration graphs were obtained in the concentration range of 1 to 25microgml(-1) for glycine and 1 to 19microgml(-1) for lysine. The analytical performance of this method was characterized by the relative standard error. The proposed method was applied to the determination of considered amino acids in synthetic samples. 相似文献
115.
Metabolism of ammonia (NH3) and hydroxylamine (NH2OH) by wild-type and a nitrite reductase (nirK) deficient mutant of Nitrosomonas europaea was investigated to clarify the role of NirK in the NH3 oxidation pathway. NirK-deficient N. europaea grew more slowly, consumed less NH3, had a lower rate of nitrite (NO2
−) production, and a significantly higher rate of nitrous oxide (N2O) production than the wild-type when incubated with NH3 under high O2 tension. In incubations with NH3 under low O2 tension, NirK-deficient N. europaea grew more slowly, but had only modest differences in NH3 oxidation and product formation rates relative to the wild-type. In contrast, the nirK mutant oxidized NH2OH to NO2
− at consistently slower rates than the wild-type, especially under low O2 tension, and lost a significant pool of NH2OH–N to products other than NO2
− and N2O. The rate of N2O production by the nirK mutant was ca. three times higher than the wild-type during hydrazine-dependent NO2
− reduction under both high and low O2 tension. Together, the results indicate that NirK activity supports growth of N. europaea by supporting the oxidation of NH3 to NO2
− via NH2OH, and stimulation of hydrazine-dependent NO2
− reduction by NirK-deficient N. europaea indicated the presence of an alternative, enzymatic pathway for N2O production. 相似文献
116.
In this study we consider a multiple comparison of several treatments with a control based on multivariate normal response in clinical trials. Specifically we construct a step down procedure by referring to Dunnett and Tamhane (1991). Furthermore we formulate the all-pairs power by using the recursive formula derived by Hayter and Tamhane (1991) and Dunnett, Horn and Vollandt (2001). Finally we compare the step down procedure with the single step procedure proposed by Nakamura and Imada (2005) in terms of some numerical examples regarding the power of the test. 相似文献
117.
Effects of substratum on the diversity and stability of ammonia-oxidizing communities in a constructed wetland used for wastewater treatment 总被引:2,自引:0,他引:2
AIM: To study the relationship between the nature of the substratum and the diversity and stability of the ammonia-oxidizing microbial community in a constructed wetland for the treatment of wastewaters. METHODS AND RESULTS: Samples have been taken the year around from sections of the wetland filled with different substrata. When present, the root zones of the helophyte Phragmites australis were also sampled. The diversity of the ammonia-oxidizing community was established by a coupled PCR-DGGE method based on the 16s rRNA gene. Averaged over the seasons, no large differences in community composition were observed between the different substrata, although the section with zeolite always showed the highest frequencies of bands belonging to ammonia-oxidizing bacteria of the beta-subclass of the Proteobacteria. Only sequences related to the Nitrosospira lineage were detected. Averaged again over the seasons, the section with zeolite was also most constant with respect to the potential ammonia-oxidizing activity. CONCLUSIONS: Although the ammonia-oxidizing communities did not differ significantly between the different sections of the constructed wetland, the characteristics of zeolite were most appropriate to accommodate a stable and active community of ammonia-oxidizing bacteria. The presence of the helophyte had no effect on the diversity and stability of the ammonia-oxidizing community. SIGNIFICANCE AND IMPACT OF THE STUDY: It has been shown that substrata used in constructed wetlands made no distinction between ammonia-oxidizing strains in relation to attachment. However, zeolite had the best performance with respect to activity over the seasons. 相似文献
118.
Macinnis ML 《Behavioural processes》2007,75(2):182-187
The goal was to determine whether rats time filled and empty intervals of equal duration differently. Each of five rats was trained for 50 sessions on an instrumental appetitive head entry procedure in which food was available (primed) every 120 s. On "empty" cycles, 30s prior to the next food prime, a 0.5-s pulse of white noise was presented. On "filled" cycles, 30s prior to the next food prime, white noise came on and stayed on until food was delivered. The two types of cycles were presented with equal probability. The results showed that the rats timed both the food-to-food interval and the stimulus-to-food interval. A comparison of the response gradients on filled and empty cycles following stimulus presentation showed better temporal discrimination on filled cycles. The results were modeled using a Packet theory of timing, with a linear averaging rule to combine the temporal information provided by the stimulus and food. The model fits to the individual response gradients were evaluated with a Turing test. 相似文献
119.
In this study, the inhibitory effect of TCE on nitrification process was investigated with an enriched nitrifier culture.
TCE was found to be a competitive inhibitor of ammonia oxidation and the inhibition constant (K
I
) was determined as 666–802 μg/l. The TCE affinity for the AMO enzyme was significantly higher than ammonium. The effect of
TCE on ammonium utilization was evaluated with linearized plots of Monod equation (e.g., Lineweaver–Burk, Hanes–Woolf and
Eadie–Hofstee plots) and non-linear least square regression (NLSR). No significant differences were found among these data
evaluation methods in terms of kinetic parameters obtained. 相似文献
120.
West Coast prairies in the US are an endangered ecosystem, and effective conservation will require an understanding of how
changing climate will impact nutrient cycling and availability. We examined how seasonal patterns and micro-heterogeneity
in edaphic conditions (% moisture, total organic carbon, % clay, pH, and inorganic nitrogen and phosphorus) control carbon,
nitrogen, and phosphorus cycling in an upland prairie in western Oregon, USA. Across the prairie, we collected soils seasonally
and measured microbial respiration, net nitrogen mineralization, net nitrification, and phosphorus availability under field
conditions and under experimentally varied temperature and moisture treatments. The response variables differed in the degree
of temperature and moisture limitation within seasons and how these factors varied across sampling sites. In general, we found
that microbial respiration was limited by low soil moisture year-round and by low temperatures in the winter. Net nitrogen
mineralization and net nitrification were never limited by temperature, but both were limited by excessive soil moisture in
winter, and net nitrification was also inhibited by low soil moisture in the summer. Factors that enhanced microbial respiration
tended to decrease soil phosphorus availability. Edaphic factors explained 76% of the seasonal and spatial variation in microbial
respiration, 35% of the variation in phosphorus availability, and 29% of the variation in net nitrification. Much of the variation
in net nitrogen mineralization remained unexplained (R
2 = 0.19). This study, for the first time, demonstrates the complex seasonal controls over nutrient cycling in a Pacific Northwest
prairie. 相似文献