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1.
Ryegrass uniformly labelled with 1 4C was allowed to decompose for 10 years under field conditions in a range of contrasting soils. The amount of organic matter already in a soil had no effect on the retention of labelled C by that soil, nor had a variation in soil pH of from 4.9 to 8.1. Decomposition was initially slower in a strongly acid soil (pH 3.7) but by the end of 5 years the difference between this soil and the others had almost disappeared. The more clay in a soil, the greater the retention of labelled C over the whole 10 year period; this was true of both strongly acid and near-neutral soils. More labelled organic matter was leached from a soil containing 7.6% clay than from one with 17.5% clay, but the amount thus lost was insufficient to account for the difference in retention of C by the two soils. The decomposition of labelled plant material was faster in bare soil than in soil growing grass but the ‘protection’ thus given to the labelled C by the growing grass ended when the grass was removed. In bare soil about one third of the labelled ryegrass C was left after one year but thereafter decomposition became very much slower and about one eighth of the labelled C still remained in the soil after 10 years. The decay curve can be represented by a two compartment model, in which about 70% of the ryegrass C decomposed by a first order process of half life 0.25 years and the remainder by a similar process of half-life 8 years.  相似文献   

2.
Plasmid transfer among isolates of Rhizobium leguminosarum bv. viciae in heavy metal contaminated soils from a long-term experiment in Braunschweig, Germany, was investigated under laboratory conditions. Three replicate samples each of four sterilized soils with total Zn contents of 54, 104, 208 and 340 mg kg−1 were inoculated with an equal number (1×105 cells g−1 soil) of seven different, well-characterized isolates of R. leguminosarum bv. viciae. Four of the isolates were from an uncontaminated control plot (total Zn 54 mg kg−1) and three were from a metal-contaminated plot (total Zn 340 mg kg−1).After 1 year the population size was between 106 and 107 g−1 soil, and remained at this level in all but the most contaminated soil. In the soil from the most contaminated plot no initial increase in rhizobial numbers was seen, and the population declined after 1 year to <30 cells g−1 soil after 4 years. One isolate originally from uncontaminated soil that had five large plasmids (no. 2-8-27) was the most abundant type re-isolated from all of the soils. Isolates originally from the metal-contaminated soils were only recovered in the most contaminated soil. After 1 year, four isolates with plasmid profiles distinct from those inoculated into the soils were recovered. One isolate in the control soil appeared to have lost a plasmid. Three isolates from heavy metal contaminated soils (one isolate from the soil with total Zn 208 mg kg−1 and two isolates from the soil with total Zn 340 mg kg−1) had all acquired one plasmid. Plasmid transfer was confirmed using the distinct ITS-RFLP types of the isolates and DNA hybridization using probes specific to the transferred plasmid. The transconjugant of 2-8-27 which had gained a plasmid was found in one replicate after 2 years of the most contaminated soil but comprised more than 50% of the isolates. A similar type appeared in a separate replicate of the most contaminated soil after 3 years and persisted in both of these soils until the final sampling after 4 years. After 2 years isolates were recovered from four of the soil replicates with the chromosomal type of 2-8-27 which appeared to have lost one plasmid, but these were not recovered subsequently.Isolate 2-8-27 was among the isolates most sensitive to Zn in laboratory assays, whereas isolate 7-13-1 showed greater zinc tolerance. Acquisition of the plasmid conferred enhanced Zn tolerance to the recipients, but transconjugant isolates were not as metal tolerant as 7-13-1, the putative donor. Laboratory matings between 2-8-27 and 7-13-1 in the presence of Zn resulted in the conjugal transfer of the same small plasmid from 7-13-1 to isolate 2-8-27 and the transconjugant had enhanced metal tolerance. Our results show that transfer of naturally-occurring plasmids among rhizobial strains is stimulated by increased metal concentrations in soil. We further demonstrate that the transfer of naturally-occurring plasmids is important in conferring enhanced tolerance to elevated zinc concentrations in rhizobia.  相似文献   

3.
The fate of carbon (C) in grassland soils is of particular interest since the vast majority in grassland ecosystems is stored below ground and respiratory C‐release from soils is a major component of the global C balance. The use of 13C‐depleted CO2 in a 10‐year free‐air carbon dioxide enrichment (FACE) experiment, gave a unique opportunity to study the turnover of the C sequestered during this experiment. Soil organic matter (SOM), soil air and plant material were analysed for δ13C and C contents in the last year of the FACE experiment (2002) and in the two following growing seasons. After 10 years of exposure to CO2 enrichment at 600 ppmv, no significant differences in SOM C content could be detected between fumigated and non‐fumigated plots. A 13C depletion of 3.4‰ was found in SOM (0–12 cm) of the fumigated soils in comparison with the control soils and a rapid decrease of this difference was observed after the end of fumigation. Within 2 years, 49% of the C in this SOM (0–12 cm) was exchanged with fresh C, with the limitation that this exchange cannot be further dissected into respiratory decay of old C and freshly sequestered new C. By analysing the mechanistic effects of a drought on the plant‐soil system it was shown that rhizosphere respiration is the dominant factor in soil respiration. Consideration of ecophysiological factors that drive plant activity is therefore important when soil respiration is to be investigated or modelled.  相似文献   

4.
利用15NO3-标记法研究土壤微生物量氮的化学及生物有效性   总被引：5，自引：0，他引：5  
采用加入含15N的硝态氮培养方法标记了土壤微生物量氮 ,然后利用碱解扩散法测定了标记土壤有效氮含量 ,温室培养法评价了小麦对标记的土壤微生物量氮的吸收情况。结果表明 ,碱解扩散法对土壤微生物量固持的15N的提取比率 (即提取液中15N原子百分超 /土壤15N原子百分超 )在 1 47～ 2 83之间(平均 2 0 1 ) ,碱解氮中约有 3 0 1 %～ 61 6% (平均 42 9% )来自土壤微生物固持氮。植物体15N丰度在0 749%～ 1 1 62 %之间 ,明显高于15N的自然丰度 ,表明土壤微生物固持的15N在小麦生长期间发生释放 ,为植物利用。土壤微生物固持氮对植物的有效性比率 (植物地上部分15N原子百分超 /土壤15N原子百分超 )在 3 7～ 7 1之间。可见 ,土壤微生物量固持氮有较高的化学及生物有效性  相似文献   

5.
为比较入侵植物与本地植物对土壤微生态影响的差异, 探索外来植物入侵的土壤微生物学机制, 本研究通过同质园试验, 比较分析了2种入侵菊科植物(紫茎泽兰、黄顶菊)和2种本地植物(马唐、猪毛菜)对土壤肥力和微生物群落的影响, 并通过盆栽反馈试验验证入侵植物改变后的土壤微生物对本地植物旱稻生长的反馈作用。同质园试验结果表明: 2种入侵植物和2种本地植物分别对土壤微生态产生了不同的影响, 尤其是紫茎泽兰显著提高了土壤有效氮、有效磷和有效钾含量,紫茎泽兰根际土壤中有效氮含量为39.80 mg·kg-1,有效磷含量为48.52 mg·kg-1。磷脂脂肪酸指纹图谱结果表明, 2种入侵植物与2种本地植物相比, 较显著增加了土壤中放线菌数量, 而紫茎泽兰比其他3种植物显著增加了细菌和真菌数量。盆栽结果表明: 黄顶菊生长过的土壤灭菌后比灭菌前旱稻株高增加113%, 紫茎泽兰也使旱稻的株高增加17%。由以上结果可知, 紫茎泽兰和黄顶菊可能通过改变入侵地土壤的微环境, 形成利于其自身生长扩散的微生态环境从而实现其成功入侵。  相似文献   

6.
Nuclear magnetic resonance (NMR) spectra were obtained for solid samples of whole soils from three long–term field sites at Rothamsted Experimental Station, UK. In all sites, soil organic matter content was either increasing or decreasing due to contrasted long–continued treatments. Two soils were from Highfield, one from under old grassland (47 g organic C kg?1) and one from an area kept as bare fallow following ploughing of grass 21 years previously (14 g organic C kg?1). Three soils were taken from Broadbalk, two from plots within the Broadbalk Continuous Wheat Experiment which had received no fertilizer or animal manure annually for 148 years (7 and 27 g organic C kg?1, respectively) and one from Broadbalk Wilderness, wooded section (38 g organic C kg?1). Broadbalk Wilderness was arable until 1881 and has reverted to deciduous woodland in the subsequent 110 years. Two soils were from Geescroft, one from an arable field (9 g organic C kg?1) and one from Geescroft Wilderness (35 g organic C kg?1) which began reversion to deciduous woodland at the same time as Broadbalk Wilderness but is now acid (pH = 4.2) in contrast to Broadbalk which is calcareous (pH = 7.3). Solid–state 13C NMR spectra were obtained on a 300–MHz instrument using cross polarization (CP) and magic angle spinning (MAS). All samples exhibited peaks in the following spectral regions: 0–45 ppm (alkyl), 45–60 ppm (methoxyl, carbohydrate and derivatives), 60–110 ppm (carbohydrates and derivatives, C–α of peptides), 110–160 ppm (aromatics) and 160–185 ppm (carboxyl groups and derivatives). Within the spectrum of a specific sample it was not possible to determine the relative proportions of soil organic carbon in the different forms identified because a range of factors can potentially alter the relative areas of peaks in different regions of the spectrum. However, from a comparison of relative peak areas within a set of soils from a given site, differing only in organic matter content, information can be deduced regarding the forms of C that are more or less subject to change in response to land use or management. At all sites carbohydrate C appears to be the form that is most subject to change, suggesting that it is an ‘active’ fraction compared with the other forms. It was greatest where organic matter inputs were greatest (due to inputs of farmyard manure or reversion to woodland) and declined relative to other forms following ploughing of old grassland. Alkyl C increased as total C accumulated but did not decline relative to other forms following ploughing of grass. One reason for the non–quantitative nature of the soil 13C CPMAS spectra was a short (approximately 1 ms) component of the rotating–frame TI relaxation time for H nuclei (T1pH). This problem was not overcome by acquiring data at – 60°C. In principle, solid–state spectra of soils obtained by direct polarization (i.e. without CP) might produce quantitative results, but the low C content of most mineral soils (10–50 g C kg?1) precludes this, given current instrumentation.  相似文献   

7.
Soil microbial activity in opencast coal mine restorations   总被引：6，自引：0，他引：6  
Abstract. A number of restored areas, a soil store and undisturbed areas on opencast coal mine sites, all of similar soil type, were sampled. The microbiological activity (dehydrogenase assay), nitrogen mineralization and nitrifying potentials and physico-chemical characteristics of the soils were determined. Dehydrogenase activities ranged from 140 to 580 μg TPF g-1 24 h-1 in undisturbed control soils, whereas the disturbed soils had activities of 10 to 220 μg g-1 24 h-1, with the smallest activities being recorded in the stored and most recently reinstated soil, indicating that disturbance has depressed microbial activity. Nitrogen mineralization potential was significantly affected by disturbance, with a value of 18 to 26 μg inorganic N g-1 21 d-1 in the soil store and 38 μg-1 21 d-1 in a soil reinstated for six months, although the values were less than this in soils reinstated for up to six years. Nitrifying potential was not significantly less in the stored soils, being within the range of 60 to 135 μg nitrate N formed g-1 soil 21 d-1, which was similar to that found in the undisturbed control soil. The water-holding capacity was less in the stored soil than the undisturbed controls, and was significantly less in soil reinstated for 1.5 to 2.5 years, being only 65% of the undisturbed value (0.66 g water g-1 soil). Ammonium content of the soil store was one hundred fold larger in the soil store than in the controls (0.6 to 1.7 μg ammonium N g-1). The carbon contents in the control soils ranged from 4.5 to 7.2%, whereas the stored and reinstated soils had generally less amounts ranging from 1.6 to 5.8%. There was a significant and positive correlation between water-holding capacity and nitrifying potential. The implications for long-term restoration are discussed.  相似文献   

8.
Counter-diffusion coefficients of Rb86 and Sr89 counter diffusing against H+ ions were measured in Dundee silt loam and Sharkey clay soils at differing soil bulk-densities. The cation exchange complex of each soil was saturated with either Rb+, Sr++, or H+ and washed free of salts before making diffusion measurements. The water content of the soil on an oven-dry weight basis was maintained at a constant value for all bulk-densities; 14.2 and 28.0 per cent for the Dundee and Sharkey soils respectively. These moisture contents correspond to a tension of 2/3 bar for sieved soil. The diffusion coefficients were dependent upon concentration. Average counter-diffusion coefficients were calculated and related to soil bulk-density. Soil compaction of Dundee silt loam had little or no effect upon the counter diffusion of Rb86. The average counter-diffusion coefficients of Sr89 in Dundee silt loam and Sharkey clay were significantly and linearly related to bulk-density; as bulk-density increased the average counter-diffusion coefficients increased. The average counter-diffusion coefficients were approximately 0.5–0.75 of the corresponding self-diffusion coefficients measured previously in these soils. The applicability of counter- and self-diffusion data to practical field problems are discussed.  相似文献   

9.
麦鱼套作改良滨海盐土的研究   总被引：1，自引：0，他引：1       下载免费PDF全文
从１９８８年开始，进行沿海滩涂盐土大面积以囤蓄雨水为主，回龙水灌溉辅的养鱼改良强度盐渍化土的试验，当其含盐量降至一定的数值后，脱盐速率明显下降。在此基础上，从１９９０年开始，又建立了麦鱼套作新的种养殖模式，并瑟其它中度以下盐渍土种植大麦的传统种植制度和目前的大面积蓄淡养鱼改土的利用方式进行比较试验。  相似文献   

10.
Minesoils are characterized by low soil organic matter and poor soil physicochemical environment. Mine soil reclamation process has potential to restore soil fertility and sequester carbon (C) over time. Soil organic C (SOC) pool and associated soil properties were determined for reclaimed minesoils under grass and forest landuses of varied establishment year. Three grassland sites of 30, 9, and 1 years after reclamation (G30, G9, and G1) and two forest sites, 11 years after reclamation (RF) and undisturbed stand of 40 years (UF), were selected within four counties (Morgan, Muskingum, Noble, and Coshocton) of southeastern Ohio. Soil bulk density (BD) of reclaimed forest (RF) soil was significantly higher than undisturbed forest (UF) soils within 10–40 cm soil depth profile. Reclamation process increased soil pH from slightly acidic to alkaline and decreased the soil EC in both landuses. Among grassland soils, significant changes in SOC and total soil N contents were observed within 0–10 cm soil depth. SOC contents of G30 (29.7 Mg ha−1) and G9 (29.5 Mg ha−1) were significantly higher than G1 soils (9.11 Mg ha−1). Soil N content was increased from G1 (0.95 Mg ha−1) to G9 (2.00 Mg ha−1) site and then the highest value was found under G30 (3.25 Mg ha−1) site within 0–10 cm soil depth. UF soils had significantly higher SOC and total N content than RF soils at 0–10 and 10–20 cm soil depths. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
A combination of radiocarbon (14C) dating and biomarker analyses of the aliphatic hydrocarbons in soil lipids is proposed as a novel and improved method for studying the environmental history of peaty soils. The radiocarbon concentration of unfractionated bulk organic matter, hydrolysed soil residues and two lipid fractions (the aliphatic hydrocarbons and carboxylic acids) recovered from a stagnohumic gley soil, were compared using AMS (accelerator mass spectrometry) and radiometric 14C dating techniques. The radiocarbon ages recorded by the aliphatic hydrocarbon fractions were consistently older than those measured from the unfractionated soil, and were in most cases older than the residues remaining after acid hydrolysis. This pattern was observed at three different depths in the soil profile. The apparent age difference between the hydrocarbon fraction and its unfractionated substrate increased with depth. An abundance of long–chain n–alkanes, similar to those found in higher plant waxes, characterized the aliphatic hydrocarbon fraction from the deepest soil (at 21.5–24.5–cm depth). The radiocarbon age of this basal organic component (13470± 170 years bp ) indicated that it derived from the initial re–establishment of vegetation on the local deglaciated landscape with the onset of the Windermere Interstadial (c. 14000–13000 14C years bp ). Bulk organic detritus within the basal horizon dated at some 3000 years younger, and presumably as a result of the downward penetration and retention of some mobile organic residues produced later in the development of the soil profile. The survival and apparent stratigraphical stability of these recoverable aliphatic hydrocarbons provides the opportunity, via the development of AMS dating, to measure an unambiguous radiocarbon age for the origin of organic residues retained in soils and sediments.  相似文献   

12.
Radionuclide fallout during nuclear accidents on the land may impair the atmosphere, contaminate farmland soils and crops, and can even reach the groundwater. Previous research focused on the field distribution of deposited radionuclides in farmland soils, but details of the amounts of radionuclides in the plough layer and the changes in their proportional distribution in the soil profile with time are still inadequate. In this study, a lysimeter experiment was conducted to determine the vertical migration of 137Cs and 60Co in brown and aeolian sandy soils, collected from the farmlands adjoining Shidaowan Nuclear Power Plant(NPP) in eastern China, and to identify the factors influencing their migration depths in soil. At the end of the experiment(800 d), >96% of added 137Cs and 60Co were retained in the top 0–20 cm soil layer of both soils;very little 137Cs or 60Co initially migrated to 20–30 cm, but their amounts at this depth increased with time. The migration depth of 137Cs was greater in the aeolian sandy soil than in the brown soil during 0–577 d, but at the end of the experiment, 137Cs migrated to the same depth(25 cm) in both soils. Three phases on the vertical migration rate(v) of 60Co in the aeolian sandy soil can be identified: an initial rapid movement(0–355 d, v = 219 ± 17 mm year-1), followed by a steady movement(355–577 d, v = 150 ± 24 mm year-1) and a very slow movement(577–800 d, v = 107 ± 7 mm year-1). In contrast, its migration rate in the brown soil(v = 133 ± 17 mm year-1) was steady throughout the 800-d experimental period. The migration of both 137Cs and 60Co in the two soils appears to be regulated by soil clay and silt fractions that provide most of the soil surface area, soil organic carbon(SOC), and soil pH, which were manifested by the solid-liquid distribution coefficient of 137Cs and 60Co. The results of this study suggest that most 137Cs and 60Co remained within the top layer(0–20 cm depth) of farmland soils following a simulated NPP accident, and little reached the subsurface(20–30 cm depth). Fixation of radionuclides onto clay minerals may limit their migration in soil, but some could be laterally distributed by soil erosion and taken up by crops, and migrate into groundwater in a high water table level area after several decades.Remediation measures, therefore, should focus on reducing their impact on the farmland soils, crops, and water.  相似文献   

13.
蔡祖聪 《土壤学报》2003,40(2):239-245
用15N分别标记尿素和KNO3,研究了淹水条件下 ,黄泥土和红壤性水稻土的无机氮转化过程及尿素和KNO3对氮素转化过程的影响。结果表明 ,淹水条件下 ,土壤中存在15NH 4 的成对硝化和反硝化过程。红壤性水稻土15NH 4 硝化只检测到15NO- 2 ,但有反硝化产物15N2 生成 ,因此 ,很可能存在着好气反硝化过程。15NO- 3浓度的下降符合一级反应方程 ,黄泥土的速率常数几乎是红壤性水稻土的 1 0倍。反硝化过程和DNRA过程共同参与15NO- 3的还原。加入尿素提高土壤pH ,增加黄泥土DNRA过程对反硝化过程的基质竞争能力 ,但反硝化过程仍占绝对优势。加入尿素或KNO3改变土壤pH是导致对无机氮转化影响有所不同的主要原因 ,浓度的作用较为次要。  相似文献   

14.
One of the characteristics of soils located within the cores of stockpile storage mounds at opencast mine sites is their accumulation of ammonium-nitrogen. Two areas of restored land were constructed from soil stockpiled for 3 years; one consisted of mound-surface (‘aerobic zone’) soil, and the other of deeply buried (‘anaerobic zone’) soil. In that constructed from mound-surface soil, concentrations of both ammonium- and nitrate-nitrogen remained fairly stable throughout the first 6 months of restoration at about 12–20 μg g?1, but in the site constructed from deeply buried soil, concentrations of ammonium-N decreased from an initial high of 160 to 14 μg N g?1 soil after 14 weeks, and increased again to 42 μg N g?1 soil by week 29. In contrast, concentrations of nitrate-nitrogen at the latter site increased from an initial 9 μg to a maximum recorded level of 77 μg N g?1 soil by week 14, before subsiding to 9 μg N g?1 soil by week 29. Nitrate was considered to have been lost from the restored soils by a combination of leaching and denitrification, as no vegetation was established at these sites. After a short-term stimulation following restoration, soil microbial biomass levels remained fairly constant, though soils (up to 3 years after restoration) were characterized by a very small ratio of biomass C: organic C.  相似文献   

15.
利用15N同位素标记方法,研究在两种水分条件即60％和90％ WHC下,添加硝酸盐(NH4NO3,N 300 mg kg-1)和亚硝酸盐(NaNO2,N 1 mg kg-1)对中亚热带天然森林土壤N2O和NO产生过程及途径的影响.结果表明,在含水量为60％ WHC的情况下,高氮输入显著抑制了N2O和NO的产生(p＜0.01);但当含水量增为90％ WHC后,实验9h内抑制N2O产生,之后转为促进.所有未灭菌处理在添加NO2-后高氮抑制均立即解除并大量产生N2O和NO,与对照成显著差异(p＜0.01),在60％ WHC条件下,这种情况维持时间较短(21 h),但如果含水量高(90％ WHC)这种情况会持续很长时间(2周以上),说明水分有效性的提高和外源NO2-在高氮抑制解除中起到重要作用.本实验中N2O主要来源于土壤反硝化过程,而且加入未标记NO2-后导致杂合的N2O(14N15NO)分子在实验21 h内迅速增加,表明这种森林土壤的反硝化过程可能主要是通过真菌的“共脱氮”来实现,其贡献率可多达80％以上.Spearman秩相关分析表明未灭菌土壤NO的产生速率与N2O产生速率成显著正相关性(p＜0.05),土壤含水量越低二者相关性越高.灭菌土壤添加NO2-能较未灭菌土壤产生更多的NO,但却几乎不产生N2O,表明酸性土壤的化学反硝化对NO的贡献要大于N2O.  相似文献   

16.
Our aim was to study the effects of C (as glucose and artificial rhizodeposits) on S immobilization, in relation to microbial biomass‐S and soil arylsulphatase (ARS) activity, in contrasting soils (a calcareous and an acid brown soil). The glucose‐C and artificial rhizodeposit‐C with or without cysteine were added at six rates (0, 100, 200, 400, 600 and 800 mg kg?1 soil) to the two soils and then incubated with Na235SO4 for 1 week prior to analysis. The percentages of 35S immobilized increased when C as glucose and rhizodeposit (without cysteine) were added to both soils. With cysteine‐containing rhizodeposit, the percentages of 35S immobilized remained relatively stable (23.5% to 29.9%) in the calcareous soil, but decreased in the acid brown soil (52.7% to 31.5%). For both soils, cysteine‐containing rhizodeposit additions showed no significant correlation between immobilized‐35S and microbial biomass‐35S, suggesting that microorganisms immobilized cysteine‐S preferentially instead of 35S from the tracer (Na235SO4). In the calcareous soil, a positive and significant correlation was found between ARS activity and microbial biomass‐35S (r = 0.85, P < 0.05) when glucose was added. We also saw this correlation in the acid brown soil when rhizodeposit‐C without cysteine was added (r = 0.90, P < 0.05). Accordingly, the results showed the presence of extracellular arylsulphatase activity of 48.7 mg p‐nitrophenol kg?1 soil hour?1 in the calcareous soil and of 27.0 mg p‐nitrophenol kg?1 soil hour?1 in the acid brown soil.  相似文献   

17.
A phenanthrene-degrading bacterial strain Pseudomonas sp. GF3 was examined for plant-growth promoting effects and phenanthrene removal in soil artificially contaminated with low and high levels of phenanthrene (0, 100 and 200 mg kg−1) in pot experiments. Low and high phenanthrene treatments significantly decreased the growth of wheat. Inoculation with bacterial strain Pseudomonas sp. GF3 was found to increase root and shoot growth of wheat. Strain GF3 was able to degrade phenanthrene effectively in the unplanted and planted soils. Over a period of 80 days the concentration of phenanthrene in soil in which wheat was grown was significantly lower than in unplanted soil (p<0.05). At the end of the 80-d experiments, 62.2% and 42.3% of phenanthrene had disappeared from planted soils without Pseudomonas sp. GF3 when the phenanthrene was added at 100 and 200 mg kg−1 soil, respectively, but 84.8% and 70.2% of phenanthrene had disappeared from planted soils with the bacterial inoculation. The presence of vegetation significantly enhances the dissipation of phenanthrene in the soil. There was no significant difference in soil polyphenol oxidase activities among the applications of 0, 100 and 200 mg kg−1 of phenanthrene. However, the enzyme activities in planted and unplanted soils inoculated with the strain Pseudomonas sp. GF3 were significantly higher than those of non-inoculation controls. The bacterial isolate was also able to colonize and develop in the rhizosphere soil of wheat after inoculation.  相似文献   

18.
[14C] and [35S]labeled lignosulfonates (LS) or [14C]labeled coniferyl alcohol dehydropolymer (DHP) were aerobically incubated in soil for 17 weeks. Respiratory 14CO2 was compared with that from DHP or that from [U14C]cellulose. Less CO2 was released from ring and side chain carbons of LS than from DHP, though similar amounts of CO2 were released from the methoxyl groups of both compounds. After incubation, the soil samples were exhaustively extracted with water and then with a sodium pyrophosphate-NaOH solution. The water solubility of the originally completely-soluble LS carbons was greatly decreased by incubation, and a large portion of the extracted 35S was detected as sulfate. The pyrophosphate extract was separated into humic and fulvie acids. The humic acid from soils incubated with LS contained low 35S activity and a similar 14C activity to that from soils incubated with DHP. The fulvic acid from the soils incubated with LS contained higher amounts of 14C (and 35S) than that of the soils incubated with DHP. More side chain 14C activity than other 14C activity was found in both, the water extract and the fulvic acid from soils incubated with LS. The high 35S together with the high side chain 14C activity probably indicates an elimination of the side chain carbons together with sulfonic acid groups. Anaerobic incubation of soil with LS or DHP promoted breakdown and incorporation of LS and DHP into humus much less than aerobic incubation. The possible reduction in potential pollution from lignosulfonates due to the observed transformations in soil are discussed.  相似文献   

19.
The Rothamsted long‐term field experiments, started more than 150 years ago, provide unique material for the study of carbon turnover in subsoils. Total organic C, 14C and 13C were measured on soil profiles taken from these experiments, before and after the thermonuclear bomb tests of the mid‐20th century. Four contrasting systems of land management were sampled: land cultivated every year for winter wheat; regenerating woodland on acid soil; regenerating woodland on calcareous soil; and old grassland. The mean radiocarbon ages of all the pre‐bomb samples from cultivated land were 1210 years (0–23 cm), 2040 years (23–46 cm), 3610 years (46–69 cm) and 5520 years (69–92 cm). Bomb radiocarbon derived from thermonuclear tests was present throughout the profile in all the post‐bomb samples, although below 23 cm the amounts were small and the pre‐ and post‐bomb radiocarbon measurements were often not significantly different. Values of δ13C increased down the profile, from ?26.3‰ (0–23 cm layer, mean of all measurements) to ?25.2‰ for the 69–92 cm layer. The C/N ratios decreased with depth in virtually all of the profiles sampled. Excluding the surface (0–23 cm) soils from the old grassland, the hyperbola m = 152.1 ? 2341/(1 + 0.264n) gave a close fit to the radiocarbon data from all depths, all sampling times and all sites, where n is the organic C content of the soil, in t ha?1, and m is the radiocarbon content of the soil, in Δ14C units, corrected for expansion or contraction of soil layers with time. The aberrant grassland soils almost certainly contained coal: one of them was shown by 13C‐NMR to contain 0.82% coal C. In Part 2 (this issue) of this pair of papers, these radiocarbon and total C measurements are used to develop and test a new model for the turnover of organic C in subsoils.  相似文献   

20.
Changes in phosphorus (P) during soil development are central to the understanding of labile P for plant productivity and soil P management. We used NaOH‐EDTA extraction with 31P nuclear magnetic resonance spectroscopy (31P NMR), sequential P fractionation, and general soil chemical characterization to better our understanding of P dynamics within two chronosequences (Manawatu and Reefton) and one Basalt maturity sequence under original native vegetation. With time, orthophosphate and orthophosphate monoesters tended to increase with organic C to a maximum of about two‐thirds of NaOH‐EDTA‐extractable P in young soils (16 000 years in the Reefton chronosequence), but gradually declined thereafter to about one‐third of NaOH‐EDTA‐extractable P in the oldest soils (130 000 years old). This coincided with a depletion of P from primary minerals (e.g. apatite) and readily available P for plant production. This depletion of inorganic P resulted in a greater reliance on organic P cycling via mineralization, hence the depletion of the normally recalcitrant monoester‐P pool. Concomitantly, the build‐up of labile P species (diesters and pyrophosphate) and scyllo‐ over myo‐inositol hexakisphosphate occurred as soils developed, and might be attributed to microbial activity, including scavenging for P. This work highlights the importance of organic P cycling during pedogenesis.  相似文献   

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