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排序方式: 共有684条查询结果,搜索用时 15 毫秒
651.
Matthew S. Kendall John D. Christensen Christopher Caldow Michael Coyne Christopher Jeffrey Mark E. Monaco Wendy Morrison Zandy Hillis‐Starr 《水产资源保护:海洋与淡水生态系统》2004,14(2):113-132
- 1. A necessary component of implementing a successful marine reserve is the quantification of the biological resources that fall under its protection. Without such an initial assessment, the future effects of the reserve on the local habitat and biotic community cannot be quantified and will remain the subject of debate.
- 2. This study provides such a baseline assessment of fish diversity and habitat types within a recently enlarged marine reserve. Buck Island Reef National Monument, US Virgin Islands, was recently enlarged from approximately 4 km2 to over 76 km2. Areas of sand, seagrass, and hard‐bottom under protection were increased from 0.29 km2, 0.47 km2, and 1.96 km2 to 2.70 km2, 2.89 km2, and 18.30 km2 respectively when the Monument was expanded. A 53 km2 area of pelagic/deep‐water habitat with unknown bottom type is now also protected by the Monument.
- 3. Visual counts of fish within 25×4 m2 transects conducted during the day were used to assess fish community structure and habitat utilization patterns. Species richness, diversity, assemblage structure, and fish density were evaluated and compared among sand, seagrass, and hard‐bottom habitats. Hard‐bottom sites had over twice the mean species richness and diversity as sand and seagrass sites, and several times greater mean fish density.
- 4. Quantification of the fish community in pelagic and deep‐water habitats within the reserve is recommended to provide a more comprehensive assessment of the offshore areas of the reserve. Fish numbers, size, and diversity outside the reserve boundaries must also be evaluated to allow quantification of the effects of the marine reserve on the adjacent fish communities.
652.
653.
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
654.
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
655.
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
656.
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
657.
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
658.
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
659.
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
660.
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