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971.
In spite of their low concentrations in soil solutions, low–molecular weight organic substances (LMWOS) such as amino acids, sugars, and uronic acids play a major role in the cycles of C and N in soil. With respect to their low concentrations and to possible matrix interferences, their analysis in soil leachates is a challenging task. We established two HPLC (high‐performance liquid chromatography) methods for the parallel determination of amino acids and carbohydrates in soil leachates. The pre‐column derivatization of amino acids with an o‐phthaldialdehyde (OPA) mercaptoethanol solution yields quantitation limits between 0.03 and 0.44 µmol L–1 and SD values of <8.3% (n = 9). High‐performance anion‐exchange chromatography (HPAEC) on a Dionex CarboPac PA 20 column with a NaOH acetate gradient combined with pulsed amperometric detection (PAD) was used for the determination of carbohydrates. The calibration curves obtained for 11 carbohydrates showed excellent linearity over the concentration range from 0.02 to 50.0 mg L–1. Recovery studies revealed good results for all analytes (89%–108%). Interferences from Hg(II) salts and chloroform used for stabilization of the leachates did not occur with both chromatographic methods. The optimized method was successfully used for quantitative determinations of amino acids and carbohydrates in soil leachates. 相似文献
972.
针对NY/T 148-1990测定方法中,加活性炭目的是降低由于浸出土壤有机质所产生的颜色对有效磷测定结果的影响,但是却限制了土壤有效磷的批量测定,为此进行了不加活性炭条件下测定土壤有效磷的改进试验。试验结果表明,不加活性炭条件下,浸出土壤有机质所产生的颜色对土壤有效磷测定结果在测定误差范围内可以忽略不计;两种有效磷测定方法的平均值均在误差范围之内,但改进方法所测结果更接近于NY/T 148-1990标准值,测值间离散度低,稳定性强,且测定速度快、结果准确度及精密度高、成本低。 相似文献
973.
974.
Qingjie Wang Yuhua Bai Huanwen Gao Jin He Hao Chen R.C. Chesney N.J. Kuhn Hongwen Li 《Geoderma》2008,144(3-4):502-508
Data from a 16-year field experiment conducted in Shanxi, on the Chinese Loess Plateau, were used to compare the long-term effects of no-tillage with straw cover (NTSC) and traditional tillage with straw removal (TTSR) in a winter wheat (Triticum aestivum L.) monoculture. Long-term no-tillage with straw cover increased SOM by 21.7% and TN by 51.0% at 0–10 cm depth and available P by 97.3% at 0–5 cm depth compared to traditional tillage. Soil microbial biomass C and N increased by 135.3% and 104.4% with NTSC compared to TTSR for 0–10 cm depth, respectively. Under NTSC, the metabolic quotient (CO2 evolved per unit of MBC) decreased by 45.1% on average in the top 10 cm soil layer, which suggests that TTSR produced a microbial pool that was more metabolically active than under NTSC. Consequently, winter wheat yield was about 15.5% higher under NTSC than under TTSR. The data collected from our 16-year experiment show that NTSC is a more sustainable farming system which can improve soil chemical properties, microbial biomass and activity, and thus increase crop yield in the rainfed dryland farming areas of northern China. The soil processes responsible for the improved yields and soil quality, in particular soil organic matter, require further research. 相似文献
975.
Response of an agricultural soil to pentachlorophenol (PCP) contamination and the addition of compost or dissolved organic matter 总被引:1,自引:0,他引:1
Rosalia Scelza Maria Antonietta Rao Liliana Gianfreda 《Soil biology & biochemistry》2008,40(9):2162-2169
The response of a fresh, agricultural soil when contaminated with pentachlorophenol (PCP) and supplemented with compost (C) or dissolved organic matter (DOM) was studied in the laboratory. The concentration of PCP and the changes in various functionally related properties (i.e. microbial biomass, basal respiration, soil hydrolase and oxidoreductase activity) were measured over 150 d. Variations in the main physical and chemical properties of the soils were also monitored. Two different doses of compost (C1 = 0.27% and C2 = 0.83%, corresponding to 10 and 30 t ha−1, respectively) or DOM (D1 = 0.07% and D2 = 0.2%) equivalent to the carbon content of the two compost doses C1 and C2 were used and the following five systems were investigated: soil (S), soil–compost (S-C1 and S-C2) and soil–DOM (S-D1 and S-D2). PCP concentrations declined progressively and significantly with time. This effect was most pronounced for the soils amended with the lower compost dose C1 (S-C1) and with the two DOM (S-D1 and S-D2) amounts. Significantly reduced amounts of PCP were extracted after its 500-d residence in the various systems. Higher amounts of the residual PCP were extracted from the humic acids (HA), fulvic acids (FA) and humin–mineral (HU) fractions of the 500 d aged samples than from the same unfractionated samples, indicating that the residual PCP preferentially accumulated in the organic fractions of soil. The soil showed an endogenous microbial activity as indicated by basal respiration, microbial biomass and all the enzymatic activities tested (dehydrogenase, glucosidase, phosphatase, arylsulphatase and urease). Addition of the PCP severely depressed some of the tested biochemical properties suggesting an inhibitory effect on microbial activity. Conversely, higher basal respiration, and similar β-glucosidase and phosphatase activities were measured in comparison with the controls. No significant effects were observed following the addition of two doses of the compost or the DOM. Fungal colonies belonging to the taxonomic group of Ascomycetes and identified as Byssochlamys fulva developed with time in all the PCP-contaminated samples. Growth of B. fulva in vitro in the presence of PCP showed that the isolate was tolerant to 12.5 and 25 mg l−1 PCP and degraded 20% of its initial concentration in 8 d. Overall, the results indicate that many complex processes occurred in the contaminated soil and combinations of these determined the response to PCP contamination. The sorption of PCP to the soil matrix (which increased with time) and its degradation/transformation by indigenous soil microbial activity were likely involved. Both the processes appeared to be favoured by the presence of dissolved organic matter. 相似文献
976.
977.
Eric Paterson Barry Thornton Andrew J. Midwood Shona M. Osborne Allan Sim Pete Millard 《Soil biology & biochemistry》2008,40(9):2434-2440
Plants link atmospheric and soil carbon pools through CO2 fixation, carbon translocation, respiration and rhizodeposition. Within soil, microbial communities both mediate carbon-sequestration and return to the atmosphere through respiration. The balance of microbial use of plant-derived and soil organic matter (SOM) carbon sources and the influence of plant-derived inputs on microbial activity are key determinants of soil carbon-balance, but are difficult to quantify. In this study we applied continuous 13C-labelling to soil-grown Lolium perenne, imposing atmospheric CO2 concentrations and nutrient additions as experimental treatments. The relative use of plant- and SOM-carbon by microbial communities was quantified by compound-specific 13C-analysis of phospholipid fatty acids (PLFAs). An isotopic mass-balance approach was applied to partition the substrate sources to soil respiration (i.e. plant- and SOM-derived), allowing direct quantification of SOM-mineralisation. Increased CO2 concentration and nutrient amendment each increased plant growth and rhizodeposition, but did not greatly alter microbial substrate use in soil. However, the increased root growth and rhizosphere volume with elevated CO2 and nutrient amendment resulted in increased rates of SOM-mineralisation per experimental unit. As rhizosphere microbial communities utilise both plant- and SOM C-sources, the results demonstrate that plant-induced priming of SOM-mineralisation can be driven by factors increasing plant growth. That the balance of microbial C-use was not affected on a specific basis may suggest that the treatments did not affect soil C-balance in this study. 相似文献
978.
The abandonment of cultivated wetland soil increased the contents of light fraction organic matter (LFOM), heavy fraction
organic matter (HFOM) and soil organic matter (SOM). The LFOM and HFOM content increased to 13.3 g kg−1 and 62.4 g kg−1 after 5 years whereas they were 8.4 and 47.9 g kg−1 after 9 years of cropping, respectively. Fourteen years after abandonment, HFOM content increased to 104.3 g kg−1. LFOM was positively correlated with HFOM (p < 0.001). A Langmuir equation was used to calculate the highest HFOM value. The value for the natural wetland soil was closed
to this theoretical value (140.8 g kg−1). After 14 years of abandonment, the HFOM maximum (HFOMMax) value was lower than the equilibrium value suggesting that a further increase in HFOM can occur after abandonment. Assuming
a linear accumulation (3.87 Mg C ha−1yr−1), it would take approximately 24 years after the abandonment to reach the HFOMMax value. 相似文献
979.
Mechanisms of real and apparent priming effects and their dependence on soil microbial biomass and community structure: critical review 总被引:6,自引:1,他引:5
The number of studies on priming effects (PE) in soil has strongly increased during the last years. The information regarding
real versus apparent PE as well as their mechanisms remains controversial. Based on a meta-analysis of studies published since
1980, we evaluated the intensity, direction, and the reality of PE in dependence on the amount and quality of added primers,
the microbial biomass and community structure, enzyme activities, soil pH, and aggregate size. The meta-analysis allowed revealing
quantitative relationships between the amounts of added substrates as related to microbial biomass C and induced PE. Additions
of easily available organic C up to 15% of microbial biomass C induce a linear increase of extra CO2. When the added amount of easily available organic C is higher than 50% of the microbial biomass C, an exponential decrease
of the PE or even a switch to negative values is often observed. A new approach based on the assessment of changes in the
production of extracellular enzymes is suggested to distinguish real and apparent PE. To distinguish real and apparent PE,
we discuss approaches based on the C budget. The importance of fungi for long-term changes of SOM decomposition is underlined.
Priming effects can be linked with microbial community structure only considering changes in functional diversity. We conclude
that the PE involves not only one mechanism but a succession of processes partly connected with succession of microbial community
and functions. An overview of the dynamics and intensity of these processes as related to microbial biomass changes and C
and N availability is presented. 相似文献
980.
Evolution of soil chemical properties in the past 50 years in the Tai Lake Region, China 总被引:1,自引:0,他引:1
Hui Wang Yuan-hua Dong De-cheng Li B. Velde Qiong An Zhong-xiang Guo Qi-dong Zuo 《Soil & Tillage Research》2008,100(1-2):54-59
The Tai Lake Region (TLR) is traditionally an ecologically sustainable agricultural area due to the intensive application of traditional organic fertilizer. However in the past 50 years, agricultural management practices such as fertilizer usage and cropping systems changed this situation. In order to investigate how these changes affected soil chemical properties and ultimately the sustainability of agriculture production, a case study was conducted in Taicang County in the TLR. It was found that soil organic carbon (SOC) content significantly decreased from 22.8 g kg−1 in 1959 to 12.9 g kg−1 in 1981 while soil total nitrogen (TN) increased significantly from 1.2 g kg−1 in 1959 to 1.6 g kg−1 in 1981 due to the application of mineral fertilizer especially N fertilizer nearly entirely replacing of traditional organic fertilizer, and then both slightly increased to 14.0 g kg−1 and 1.7 g kg−1, respectively in 2004. Soil total phosphorus (TP), total potassium (TK), and available K (AK) contents showed little changes from 1981 to 2004 but soil available P (AP) content increased significantly from 7 mg kg−1 in 1981 to 26 mg kg−1 in 2004. The changes of soil properties from 1959 to 1981 were attributed to the changes of fertilizer usage and the changes of soil properties from 1981 to 2004 were attributed to the changes of cropping systems and fertilizer application, particularly vegetable production which resulted in the significant changes of fertilizer usage. 相似文献