Volatilisation of aromatic hydrocarbons from soil: Part I,fluxes from coal tar contaminated surface soils     

BO Lindhardt  Thomas H. Christensen  Lizzi Andersen 《Water, air, and soil pollution》1996,89(1-2):129-146

The non-steady-state fluxes of aromatic hydrocarbons were measured in the laboratory from the surface of soils contaminated with coal tar. Four soil samples from a former gasworks site were used for the experiments. The fluxes were quantified for 11 selected compounds, 4 mono- and 7 polycyclic aromatic hydrocarbons, for a period of up to 8 or 16 days. The concentrations of the selected compounds in the soils were between 0.2 and 3,100 µg/g. The study included the experimental determination of the distribution coefficient of the aromatic hydrocarbons between the sorbed phase and the water under saturated conditions. The determined distribution coefficients showed that the aromatic hydrocarbons were more strongly sorbed to the total organic carbon including the coal tar pitch — by a factor of 8 to 25 — than expected for natural organic matter. The fluxes were also estimated using an analytical solution of the Fick's diffusion equation and assuming that the compounds diffused independently of each other and that instant equilibrium existed between the air, water and sorbed phases. A relatively good agreement was found between the predicted and the measured flux. The predicted fluxes were between 0.11 and 7.5 time the measured fluxes. The fluxes were overestimated for the monocyclic aromatic hydrocarbons and underestimated for 3-rings-PAHs.  相似文献   

Wood-inhabiting macrofungi in Danish beech-forests - conflicting diversity patterns and their implications in a conservation perspective     

Jacob Heilmann-Clausen  Morten Christensen 《Biological conservation》2005,122(4):633-642

Macrofungal diversity was investigated on 281 decaying beech trees distributed across 14 forests in Denmark, based on sporocarp inventories. Two aspects of diversity were considered, i.e., species richness per fallen tree and the incidence of red-listed species occurrence per tree. For both diversity measures the effects of both tree and site variables were tested. In total, 319 fungal species were identified, including 28 red-listed. Decay stage and wood volume were identified as key variables influencing species richness as well as red-listed species incidence. Red-listed species, however, showed a preference for more decayed trees than non red-listed species. Further, red-listed species incidence was found to be significantly higher on broken trees, compared to fallen trees with a distinct root-plate, indicating tree death cause to be important for some red-listed species. The relations between diversity measures and site variables were conflicting. Species richness per tree decreased with increasing maximum tree age and dead wood continuity, possibly a consequence of competitive exclusion of unspecialised opportunistic species in old-grown stands. For red-listed species the opposite trend was evident, and it is concluded that forest history may have fundamental effects on the community structure of wood-inhabiting fungi. Accordingly, simple species richness may be a misleading conservation measure if the aim is to conserve the most threatened aspects of forest biodiversity.  相似文献   

Release of ferulic acid from oat hulls by Aspergillus ferulic acid esterase and trichoderma xylanase   总被引：7，自引：0，他引：7  

Yu P  Maenz DD  McKinnon JJ  Racz VJ  Christensen DA 《Journal of agricultural and food chemistry》2002,50(6):1625-1630

Oat hulls, an agricultural byproduct, contain a relatively high amount of ferulic acid (FA; 4-hydroxy-3-methoxycinnamic acid), which is believed to be inhibitory to oat hull biodegradability by rumen microorganisms. In this paper, Aspergillus ferulic acid esterase (FAE) was investigated for its ability to release FA from oat hulls. The objectives were to determine the effects of particle size of oat hulls (ground to pass through 1 mm and 250 microm screens and a 100 microm sieve) on release of FA by FAE both in the presence and in the absence of Trichoderma xylanase. The results show that the release of FA by FAE was dependent upon the particle size of oat hulls (< or = 250 microm). In the absence of Trichoderma xylanase, little FA was released by FAE. In the presence of Trichoderma xylanase, there was a significant release of FA by FAE, indicating a synergistic interaction between FAE and Trichoderma xylanase on release of FA from oat hulls. These results indicate that FAE is able to break the ester linkage between FA and the attached sugar, releasing FA from oat hulls. This may leave the remainder of the polysaccharides open for further hydrolytic attack by rumen microorganisms. It is likely that removing FA from oat hulls could improve rumen biodegradability, thus improving the nutritional value of oat hulls.  相似文献   

Aggregate strength and mechanical behaviour of a sandy loam soil under long-term fertilization treatments   总被引：4，自引：0，他引：4  

L.J. Munkholm  P. SchjØnning  K. Debosz  H. E. Jensen  & B.T. Christensen 《European Journal of Soil Science》2002,53(1):129-137

Current concern for soil quality has stimulated research on soil biological and chemical properties. In contrast, the mechanical behaviour of soil is somewhat neglected. We have examined the effects on soil mechanical properties of more than 100 years of contrasting fertilization employing three treatments from the Askov long‐term experiment: UNF (unfertilized), NPK (mineral fertilized) and AM (animal manured). We have measured tensile strength of aggregates when air‐dry and when adjusted to ?10, ?30 and ?100 kPa pressure potential. Four aggregate size classes were investigated (1–2, 2–4, 4–8 and 8–16 mm diameter). Soil fragmentation was characterized in the field using a drop‐shatter test. Bulk soil strength was determined in the field using a shear vane and a torsional shear box. Soil texture, pH, cation exchange capacity and microbial biomass were measured. The unfertilized soil has little soil organic matter and microbial biomass and is dense. Its aggregates were strong when dry and weak when wet. In contrast, the manured soil had strong aggregates when wet and rather weak ones when dry. The NPK soil generally had intermediate properties. The differences between the soils when dry seem to be related to differences in dispersible clay content, whereas the differences when wet are related to differences in the amount of organic binding and bonding material. The optimal water content for tillage as well as the tolerable range in water content was largest in the manured soil and smallest in the unfertilized soil. Our results indicate that soil mechanical properties should be measured over a range of water regimes to determine the effects of various long‐term fertilization treatments.  相似文献   

Solid-phase microextraction of volatile compounds from the chopped leaves of three species of Eucalyptus     

Zini CA  Zanin KD  Christensen E  Caramão EB  Pawliszyn J 《Journal of agricultural and food chemistry》2003,51(9):2679-2686

Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography and ion-trap mass spectrometry has been used to identify biogenic volatile organic compounds present in the headspace of chopped leaves of Eucalyptus (E.) dunnii, E. citriodora, and E. saligna. A simple HS-SPME method entailing 30 min of extraction at 30 degrees C was developed for this purpose. Thirty compounds were identified in the headspace of 60 juvenile chopped Eucalyptus leaves, and another 30 were tentatively identified. The presence of compounds such as (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMNT), (E,E)-alpha-farnesene, (E,E,E)-3,7,11,15-tetramethyl-1,3,6,10,14-hexadecapentaene (TMHP), beta-caryophyllene, alpha-humulene, germacrene D, and beta-cubebene in the headspace of the leaves but not in the essential oils from the same Eucalyptus trees and information about the infochemical roles of some of these compounds in other living plant systems suggest they might play a bioactive role in Eucalyptus leaves.  相似文献   

HPLC determination of chlorophyll and carotenoid pigments in processed green pea cultivars (Pisum sativum L.)     

Edelenbos M  Christensen LP  Grevsen K 《Journal of agricultural and food chemistry》2001,49(10):4768-4774

Chlorophyll and carotenoid pigments from six cultivars of processed green peas (Avola, Tristar, Rampart, Turon, Bella, and Greenshaft) were extracted with 100% acetone and analyzed by reversed-phase HPLC. A total of 17 pigments were identified in the pea cultivars including 8 xanthophylls ((all-E)-neoxanthin, (9'Z)-neoxanthin, (all-E)-violaxanthin, neochrome, (all-E)-lutein epoxide, (all-E)-lutein, neolutein B, neolutein A), 4 chlorophyll b related compounds (chlorophyll b derivative, chlorophyll b, chlorophyll b', and pheophytin b), 4 chlorophyll a related compounds (chlorophyll a derivative, chlorophyll a, chlorophyll a', and pheophytin a), and (all-E)-beta-carotene. The efficiency of different extraction procedures using 100% acetone showed that initial extraction followed by three reextractions without holding time between gave a higher extraction yield than no reextraction and 30 or 60 min holding time. All six cultivars contained the same pigments, but the concentration of each pigment varied significantly. On average of the two years, the chlorophyll a concentration varied from 4800 to 7300 microg/100 g fresh weight, the chlorophyll b concentration from 2100 to 2800 microg/100 g fresh weight, the (all-E)-lutein concentration from 1200 to 1900 microg/100 g fresh weight, and the (all-E)-beta-carotene concentration from 300 to 490 microg/100 g fresh weight in the processed pea cultivars. These differences in pigment concentration between the investigated cultivars are discussed in relation to maturity, product color and nutritional quality.  相似文献   

Wheat and barley straw decomposition under field conditions: Effect of soil type and plant cover on weight loss,nitrogen and potassium content     

Bent T. Christensen 《Soil biology & biochemistry》1985,17(5):691-697

The decomposition of wheat and barley straw buried in a coarse sand and a sandy loam soil was followed under field conditions using chopped straw enclosed in mesh bags. The straw was buried at 10 cm depth in early autumn. Plots were either kept fallow or covered in plants during the summer and autumn following straw burial. Samples were recovered on 10 dates over 15 months and were analyzed for weight loss, C, N and K content. Results obtained were corrected for organic matter and nutrients introduced to the straw by soil entering the mesh bags. Soil temperatures and soil moisture contents were determined.The plant cover reduced soil temperatures, soil moisture contents and straw weight loss rates during the summer. The overall weight loss pattern was similar for the two straw types. In both soils, the straw showed an initial weight loss of 30% during the first month after burial. After 6 months (spring), the straw had lost about 50% of its weight. The weight loss then proceeded faster in fallow than in the planted plots. Seasonal changes in weight loss rates were relatively small. The absolute weight loss rates, determined by a simple linear regression model, ranged from 0.10% day^?1in planted plots of the coarse sand to 0.17% day^?1 in uncovered plots of the sandy loam. For planted plots, weight losses after 15 months of exposure were 67% in the coarse sand and 78% in the sandy loam. Corresponding values for fallowed plots were 75 and 92%, respectively.Initial straw N contents differed, but overall N dynamics was less influenced by straw type than by soil type. In the sandy loam, net immobilization began just after straw burial and reached a maximum in the spring, where 3 mg N g^?1 initial straw was immobilized. The N release was more rapid in fallowed than in planted plots. In the coarse sand, N was initially leached from the straw, and the immobilization of N was less extensive than in the sandy loam. Further, the release of N from the straw was grossly similar in fallowed and planted plots. For all treatments, the net release of N from the straw began when the C-to-N ratio was between 28 and 35.Most of the straw K content was leached during the first month after straw burial. Subsequent straw K content was not affected by initial K content or plant cover.  相似文献   

Mineralisation of <Superscript>15</Superscript>N-labelled sheep manure in soils of different texture and water contents     

Ingrid?K.?ThomsenEmail author  Per?Schj?nning  Bent?T.?Christensen 《Biology and Fertility of Soils》2003,37(5):295-301

In order to investigate the effect of soil water and texture on C and N mineralisation of applied organic matter, sheep manure was sandwiched between two halves of intact soil cores and incubated at 20°C. The soils contained 10.8% (L1), 22.4% (L3) and 33.7% (L5) clay, respectively, and were drained to seven different matric potentials in the range -15 to -1,500 hPa. Evolution of CO₂-C was determined during 4 weeks of incubation. Contents of NO₃^--N, ¹⁵N and microbial biomass N were determined at the end of the incubation. The net release of CO₂-C from the manure (estimated as the difference between soils with and without manure) and the total CO₂-C evolution from soils with manure was not related to soil water content. Most CO₂-C evolved from manure-amended soils in the least clayey L1 soil. The manure caused immobilisation of soil NO₃^--N but the soil matric potential had no major effects on the net NO₃^--N production. Less than 1% of the manure ¹⁵N was found as NO₃^--N at the end of the incubation. When unamended, the sandy L1 soil held the least N in microbial biomass but the largest increases in biomass N caused by manure application were found in this soil. Despite the higher increases in microbial biomass N in the L1 soil, the total content of microbial biomass N in soils with manure application peaked in the most clayey soil (L5). The recovery of manure ¹⁵N at the end of the incubation ranged from 89% to 102%. The variation in ¹⁵N recovery was not related to soil clay content nor to soil matric potential. The experimental set-up was designed to mimic field conditions where manure is left as a discrete layer surrounded by structurally intact soil. In this situation the soil clay content and the soil water level appeared to have little influence on the C and N turnover in the manure layer.  相似文献   

Distribution of protozoa in scots pine mycorrhizospheres     

Sari Timonen  Søren Christensen 《Soil biology & biochemistry》2004,36(7):1087-1093

The distribution of heterotrophic flagellates, naked amoebae, testate amoebae and ciliates was investigated in habitats created by Scots pine-Paxillus involutus and -Suillus bovinus ectomycorrhizospheres. The protozoa living on plant and fungal surfaces preferred the non-mycorrhizal pine roots over mycorrhizal roots or external mycelium. The testate amoebae were more abundant on external mycelium than on mycorrhizae regardless of the mycorrhizal fungal species. Numbers of protozoa were higher in the different habitats provided by S. bovinus mycorrhizospheres when compared with P. involutus mycorrhizospheres. Interestingly, the quality of the bacterial flora as food for the protozoa was affected by the mycorrhizal fungi even in the soils adjacent to non-mycorrhizal root tips of pine. These results demonstrate that mycorrhizal fungi create habitats differently suitable for protozoa living in boreal forest soil.  相似文献   

Early decomposer assemblages of soil organisms in litterbags with vetch and rye roots     

Slavka Georgieva  Søren Christensen  Henning Petersen 《Soil biology & biochemistry》2005,37(6):1145-1155

The assemblages of microbial (bacteria and fungi), microfaunal (protozoa and nematodes) and mesofaunal (microarthropods) populations were studied in decomposing root residues from hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) in a litterbag field experiment. Litterbags containing vetch or rye root residues were buried in soil at the same day as either vetch or rye winter catch crops were incorporated into the field soil from which the materials were gathered. The litterbags were sampled after 6 weeks in the field. In vetch, bacterial and fungal biomasses were similar whereas fungi dominated microbial biomass in rye. The biomass of the bacterial consuming fauna dominated by nematodes and microarthropods was similar to the biomass of bacteria in vetch as opposed to in rye where bacterivore biomass was lower than bacterial biomass. This suggests a much higher bacterial production in vetch compared to rye. Furthermore, in vetch dauer larvae of bacteria feeding nematodes prevailed, which is also a sign of high bacterial production followed by food shortage for the bacterivores. Bacterivorous and predatory nematodes with capability of consuming protozoa showed an inverse relationship to flagellated protozoa. This suggests that these nematodes controlled the protozoan biomass constituting a lower fraction of the bacterivore biomass in vetch compared to in rye. Such intraguild predator-prey relationship is therefore indicated for microbivorous organisms among bacterivorous and predatory nematodes (the intraguild predator) protozoa (the intraguild prey) and bacteria (the common prey). The much higher fungal biomass in rye than in vetch litterbags was not reflected in the biomass of the fungal feeders. Due to the generally lower intrinsic rate of increase of the fungivores, as well as of the omnivores and predators, in comparison with the bacterial feeders, they were not able to generate dense populations at this early stage of decomposition.  相似文献