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91.
Omar SA 《Biodegradation》1998,9(5):327-336
Thirteen fungal species isolated from soil treated with pesticides were tested for their ability to mineralize and degrade three organophosphate insecticides currently used in Egypt (Cyolan®, Malathion® and Dursban®) in liquid media free from phosporus (P) and sulfur (S). All fungal species grew successfully on the culture media treated with the three used doses of insecticides (10, 50 and 100 ppm active ingredient) but the growth rate varied with the species, the insecticide and the doses. At 10 ppm level, insecticide degradation expressed in term of organic P mineralization (calculated as % of applied P) was the highest with all fungi tested. Organic P mineralization from pesticides was decreased by increasing the dose used to 50 and 100 ppm. The highest amount of P mineralized was observed with Cyolan® followed by Malathion® whilst P mineralization from Dursban® proceeded very slowly. Aspergillus terreus showed the greatest potential to mineralize organic P followed by A. tamarii, A. niger, Trichoderma harzianum and Penicillium brevicompactum whilst the remaining fungi only moderately mineralized the organic P component of the insecticides tested. Organic sulfur mineralization by the used fungal species paralleled, to some extent, organic P mineralization. The extracellular protein content of culture filtrates in the presence of various doses of insecticides was also decreased by increasing insecticide concentrations. The extracellular protein was significantly correlated with P and S mineralization (r = 0.89** and 0.64**, respectively) whilst correlation with cell dry mass was not significant (r = 0.03 and 0.003) suggesting a direct relationship between pesticide degradation and microbial protein production. The addition of P or S to the growth media enhanced extracellular protein excretion, and increased organic P and S mineralization by the most potent species tested (A. niger, A. tamarii, A. terreus and T. harzianum). This increment was significant in most cases, especially at the higher application rates. The relationship between extracellular protein excretion and organic P and S mineralization from insecticides was highly significant with the addition of inorganic phosphorus (r = 0.96** and 0.83**, respectively) or sulfur (r = 0.85** and 0.89**, respectively) to the growth media. 相似文献
92.
Chun Fang Shen Serge R. Guiot Sonia Thiboutot Guy Ampleman Jalal Hawari 《Biodegradation》1998,8(5):339-347
Microcosm tests simulating bioslurry reactors with 40% soilcontent, containing high concentrations of TNT and/or RDX,and spiked with either [14C]-TNT or[14C]-RDX were conducted to investigate the fate ofexplosives and their metabolites in bioslurry treatment processes.RDX is recalcitrant to indigenous microorganisms in soil andactivated sludge under aerobic conditions. However, soilindigenous microorganisms alonewere able to mineralize 15% of RDX to CO2 underanaerobic condition, and supplementation of municipal anaerobicsludge as an exogenous source of microorganismssignificantly enhanced the RDX mineralization to 60%. RDXmineralizing activity of microorganisms in soil and sludge wassignificantly inhibited by the presence of TNT. TNTmineralization was poor (< 2%) and was not markedlyimproved by the supplement ofaerobic or anaerobic sludge. Partitioning studies of[14C]-TNT in the microcosmsrevealed that the removal of TNTduring the bioslurry process was due mainly to thetransformation of TNT and irreversiblebinding of TNT metabolites onto soil matrix. In the case ofRDX under anaerobic conditions,a significant portion (35%) of original radioactivity wasalso incorporated into the biomass andbound to the soil matrix. 相似文献
93.
Plant Effects on Spatial and Temporal Patterns of Nitrogen Cycling in Shortgrass Steppe 总被引:6,自引:0,他引:6
Because of the water-limited nature and discontinuous plant cover of shortgrass steppe, spatial patterns in ecosystem properties
are influenced more by the presence or absence of plants than by plant type. However, plant type may influence temporal patterns
of nutrient cycling between plant and soil. Plants having the carbon-3 (C3) or carbon-4 (C4) photosynthetic pathway differ in phenology as well as other attributes that affect nitrogen (N) cycling. We estimated net
N mineralization rates and traced nitrogen-15 (15N) additions among plant and soil components during May, July, and September of 1995 in native plots of C3 plants, C4 plants, or mixtures of C3 and C4. Net N mineralization was significantly greater in C3 plots than in C4 plots during both July and September. C3 plots retained significantly more 15N in May than did mixed and C4 plots; these differences in
15N retention were due to greater 15N uptake by C3 plants than by C4 plants during May. There were no significant differences in total 15N retention among plant communities for July and September. Soil 15N was influenced more by presence or absence of plants than by type of plant; greater quantities of
15N remained in soil interspaces between plants than in soil directly under plants for July and September. Our results indicate
that plant functional type (C3 versus C4) can affect both the spatial and the temporal patterns of N cycling in shortgrass steppe. Further research is necessary to
determine how these intraseasonal differences translate to longer-term and coarser-scale effects of plants on N cycling, retention,
and storage.
Received 8 December 1997; accepted 6 May 1998. 相似文献
94.
Osteoblasts in culture can differentiate into mature mineralizing osteoblasts when stimulated with osteogenic agents. Clinical trials and in vivo animal studies suggest that specific polyunsaturated fatty acids (PUFAs) may benefit bone health. The aim of this study was to investigate whether arachidonic acid (AA) and docosahexaenoic acid (DHA) affect osteogenesis in osteoblasts and the transdifferentiation into adipocytes. Results from this study show that long‐term exposure to AA inhibited alkaline phosphatase (ALP) activity in these cells, which might be prostaglandin E2 (PGE2)‐mediated. DHA exposure also inhibited ALP activity which was evident after both short‐ and long‐term exposures. The mechanism whereby DHA inhibits ALP activity is not clear and needs to be investigated. Although long‐term exposure to PUFAs inhibited ALP activity, the mineralizing properties of these cells were not compromised. Furthermore, PUFA exposure did not induce adipocyte‐like features in these cells as evidenced by the lack of cytoplasmic triacylglycerol accummulation. More research is required to elucidate the cellular mechanisms of action of PUFAs on bone. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
95.
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97.
98.
Daniel Obrist 《Biogeochemistry》2007,85(2):119-123
Plants accumulate significant amounts of atmospheric mercury (Hg) in aboveground biomass, likely sequestering over 1,000 Mg
of atmospheric Hg every year. This large mercury uptake could be strong enough to affect tropospheric Hg levels and might
be partially responsible for seasonal variations in atmospheric Hg observed at Mace Head, Ireland. The fluctuations of Hg
concentrations coincide temporally with the annual oscillation of carbon dioxide (CO2) in the Northern Hemisphere, which is a result of seasonal growth of vegetation. Therefore, declining Hg concentrations in
spring and summer may be attributed in part to plant uptake of atmospheric Hg. Further, the increase of Hg concentrations
during non-active vegetation periods might partially be due to plant-derived Hg emitting back to the atmosphere during carbon
mineralization. The implications of these propositions are that past and future changes in biomass productivity and organic
carbon pools may have had—and may continue to have—significant effects on atmospheric Hg levels. Specifically, large losses
in soil and biomass carbon pools in the last 150 years could have contributed significantly to observed increases in atmospheric
Hg pollution. The roles of vegetation and terrestrial carbon pools should receive detailed consideration on how they might
attenuate or exacerbate atmospheric Hg pollution. 相似文献
99.
Herbivores influence nutrient cycling and primary production in terrestrial plant communities. However, both empirical and
theoretical studies have indicated that the mechanisms by which herbivores influence nutrient availability, and thus their
net effects on primary production, might differ between time scales. For a grassland in southeast England, we show that the
effects of rabbits on primary production change over time in a set of grazed plots paired with exclosures ranging from 0 to
14 years in age. Herbivore exclusion decreased net aboveground primary production (APP) in the short term, but increased APP
in the long term. APP was closely correlated with N mineralization rates in both grazed and ungrazed treatments, and accumulation
of litter within the grazing exclosures led to higher N mineralization rates in exclosures in the long run. Rabbit grazing
did not influence litter quality. The low contrast in palatability between species and the presence of grazing-tolerant plants
might prevent rabbits from favoring unpalatable plant species that decompose slowly, in contrast to results from other ecosystems.
Our results indicate that it is essential to understand the effects on N cycling in order to predict the effect of rabbit
grazing on APP. Rabbits might decrease N mineralization and APP in the long term by increasing losses of N from grasslands. 相似文献
100.
Simulating the effects of N availability, straw particle size and location in soil on C and N mineralization 总被引:2,自引:0,他引:2
Predicting the C and N mineralization of straw added to soil is important for forecasting subsequent soil N availability during
and between crop growth cycles. The decomposition module of the STICS model, parameterized under optimal conditions, was used
to predict straw decomposition in sub-optimal conditions, i.e. when contact between soil and residue was poor (due to large
size residues or surface placement) or when mineral N availability was restricted. The data used in the simulations were obtained
from published studies of effects of residue size, location and N availability on C and N mineralization from straw under
controlled laboratory conditions. We selected studies in which the dynamics of C and N mineralization were measured simultaneously.
The dynamics of straw mineralization could be well predicted by the model under optimal conditions with standard parameter
values as derived from measured C/N ratios of the residues, but not under sub-optimal conditions which required a new parameterization. A good fit could be obtained
on these treatments by a marked reduction in the rate constants of residue and microbial biomass decomposition and a marked
increase in the microbial biomass C/N ratio. Our results show the need to include in decomposition models routines for simulating effects of spatial heterogeneity
of residue distribution, different particle sizes and limiting N availability. 相似文献