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991.
Zhang D.Cao M.Li Y.Wang S.Hao P.Feng Z. 《应用与环境生物学报》2018,(6):1301-1306
It is of great significance to ability to obtain new natural products with diverse activities through the study of soil microorganisms. However, less than 1% of the total soil microorganisms can be cultured under laboratory conditions, thus limiting the discovery of new compounds. Metagenomics, by which the genomic DNA of soil microorganisms can be extracted and expressed in heterologous hosts, provides a new approach for the functional study of soil microorganisms. Natural halides have good bioactivities, including antibacterial and antitumor activities. Halogenases play an important role in biosynthesis, and introducing bioactivities of halogenated compounds. To investigate the potential of halogenated compounds production from soil microorganisms, a soil metagenomic library was screened by PCR for clones harboring reduced flavin adenine dinucleotide (FADH2) - dependent halogenase genes. Sixty-five positive clones were identified from the library, and the amino acid sequences of halogenase genes within the positive clones were analyzed. Phylogenetic analyses revealed that more than 85% of these genes were separated from known halogenases to form new clades in the phylogenetic tree; moreover the soilderived halogenases showed high diversity. By further biosynthetic gene analysis of the positive clones, a new type I polyketide biosynthetic gene sequence was identified, which is probably related to the biosynthesis of the halogenated type I polyketide. In conclusion, novel and diverse halogenase genes were identified on sixty-five metagenomic clones using a sequence-driven metagenomic approach, laying a foundation for the further discovery of novel natural halides biosynthetic gene clusters and halides. © 2018 Science Press. All rights reserved. 相似文献
992.
Weichuan Qiao Rong Li Tianhao Tang Achuo Anitta Zuh 《Frontiers of Environmental Science & Engineering》2021,15(2):20
993.
Effects of Stonewalled Terracing Techniques on Soil-Water Conservation and Wheat Production Under Mediterranean Conditions 总被引:2,自引:0,他引:2
A field plot experiment was conducted in the Palestinian Autonomous Areas to study the effect of stonewalled terracing on soil and water conservation as compared to the nonterraced areas. Effects of the wheat canopy were considered as a second treatment. The experiment was undertaken over a period of two seasons (2000 and 2001). The results of the experiment found that the mean soil erosion was significantly lower (P < 0.05) in the terraced plots than in those that were nonterraced (182 kg/ha and 3525 kg/ha during the first season, 1769 kg/ha and 5057 kg/ha during the second season for terraced and nonterraced plots, respectively). A similar trend was observed with respect to runoff in areas under the same treatments. The wheat canopy showed lower, but not significant runoff and erosion in most of the cases for both seasons. Due to better soil and water conservation, the terraced plots obtained significantly higher total plant dry matter than nonterraced plots (1570 and 630 kg/ha in 2000, 2545 and 889 kg/ha in 2001 for terraced and nonterraced treatment, respectively). The runoff coefficient was 20% and 4% for the nonterraced and terraced plots, respectively. Rainstorms with intensity ≥4 mm/hand rainfall ≥10 mm are more likely to cause runoff and erosion. 相似文献
994.
Tijuana Childhood Lead Risk Assessment Revisited: Validating a GIS Model with Environmental Data 总被引:3,自引:0,他引:3
The objective of this research was to determine the spatial distributions of childhood lead poisoning and soil lead contamination
in urban Tijuana. The Bocco–Sanchez model of point-source emissions was evaluated in terms of validity and reliability. We
compared the model's predicted vulnerable populations with observed cases of childhood lead poisoning in Tijuana, identified
fixed point sources in the field, and analyzed 76 soil samples from 14 sites. The soil lead results were compared to the blood
lead analyses performed on Tijuana children whose blood lead levels were ≥10 μg/dL, who reported that they did not use lead-glazed
ceramics for cooking or storing food (n = 63). Using GIS, predicted vs observed risk areas were assessed by examining spatial patterns, including the distribution of cases
per designated risk area. Chi-square analysis of expected vs observed values did not differ significantly at the p = 0.02 level, showing that the model was strikingly accurate in predicting the distribution of subjects with elevated blood lead.
Results reveal that while point sources are significant, other sources of lead exposure are also important. The relative public
health risk from exposure to lead in an urban setting may be assessed by distinguishing among sources of exposure and associating
concentrations to blood lead levels. The results represent an iterative approach in environmental health research by linking
environmental and human biomarker lead concentrations and using these results to validate an environmental model of risk to
lead exposure. 相似文献
995.
In the semiarid Horqin sandy land of northern China, establishment of artificial sand-fixing shrubs on desertified sandy lands is an effective measure to control desertification and improve the regional environment. Caragana microphylla Lam. and Artemisia halodendron Turcz. ex Bess. are two of the dominant native shrub species, which are adapted well to windy and sandy environments, and thus, are widely used in revegetation programs to control desertification in Horqin region. To assess the effects of artificially planting these two shrub species on restoration of desertified sandy land, soil properties and plant colonization were measured 6 years after planting shrubs on shifting sand dunes. Soil samples were taken from two depths (0–5 cm and 5–20 cm) under the shrub canopy, in the mid-row location (alley) between shrub belts, and from nonvegetated shifting sand dune (as a control). Soil fine fractions, soil water holding capacity, soil organic C and total N have significantly increased, and pH and bulk density have declined at the 0–5-cm topsoil in both C. microphylla and A. halodendron. At the 5–20 cm subsurface soil, changes in soil properties are not significant, with exception of bulk density and organic C concentration under the canopy of A. halodendron and total N concentration under the canopy of C. microphylla. Soil amelioration processes are initiated under the shrub canopies, as higher C and N concentrations were found under the canopies compared with alleys. At the same time, the establishment of shrubs facilitates the colonization and development of herbaceous species. A. halodendron proved to have better effects in fixing the sand surface, improving soil properties, and restoring plant species in comparison to C. microphylla. 相似文献
996.
RESEARCH: Managing Mountainous Degraded Landscapes After Farmland Abandonment in the Central Spanish Pyrenees 总被引:1,自引:0,他引:1
Genista scorpius. Under a dense shrub cover both runoff and sediment yield are strongly controlled. As the shrub cover becomes open, sediment
yield and runoff increase greatly. A dense herbaceous cover yields high runoff coefficients but moderate soil losses. From
the results obtained, the possibility of abandoned field reclamation by means of selective clearing of scrub is discussed. 相似文献
997.
Carlos Garcia Teresa Hernandez Ascension Barahona Francisco Costa 《Environmental management》1996,20(1):133-141
Twenty-one severely eroded soils of SE Spain (Torriorthent xeric soils) were studied. These soils form a fragile system characterized
by soils with a low density of plant cover (<5%), are loamy and occur in a semiarid climate. The soils formerly were used
for agricultural purposes but were abandoned at least 15 years ago. These eroded soils had a low total organic carbon content,
and their humic substances, humic acid carbon, and carbohydrates were lower compared with soils that had never been cultivated
(natural soils). The variables in which the effects of erosion were particularly noted were those related with the active
organic matter (respiration and water-soluble organic matter). Those eroded soils with higher salt content showed lower organic
matter and carbohydrate contents. Only total nitrogen was correlated with the carbon fractions in the eroded soils. 相似文献
998.
含丰富藻类的河流由于藻类的光合作用与呼吸作用导致水中的溶解氧变化十分复杂且昼夜的变幅很大。使生化需氧量BOD_5的模拟所需采用的BOD_5—DO耦合模型的求解十分困难。本文根据在绵远河与石亭江的实际研究中采用了罗宾斯模型并作了合理的简化。利用藻类在夜间只有呼吸作用的特点进行溶解氧平衡计算以确定模型参数。在水质模拟中对模拟值与实测值作了比较,可看出模拟精度较好,因此本方法是适用和可取的。 相似文献
999.
Ground flora trampling studies: Five years after closure 总被引:8,自引:1,他引:8
Trampling as an ecological factor is a major concern of the management of park, forest, nature preserves, and wilderness areas
as recreational resources. Of particular importance to the management concept of carrying capacity is the relative resistance
of native plant communities, to trampling and the resilience or the capacity of impacted communities to recover. This information
can be used by management to establish seasonal use limits to prevent irreversible degradation of these resources. The purpose
of this study was to follow the recolonizaton of experimental trail surfaces barren of vegetative cover and hiked at three
levels of use intensity. Results of this study indicate that soil compaction as measured by soil penetration resistance increased
progressively with use level while the total number of species, species diversity, and dominant index scores declined. A major
finding was that the greatest degree of change occurred at the first level of hiking, indicating that major floristic measures
were most affected by the least amount of hiking. Recolonization of impacted areas that received 100 trampling passes as measured
by plant cover, dominant indices, floristic dissimilarity, and species diversity was similar to areas receiving four and eight
times more trampling, despite major differences in soil penetration resistance. These data suggest limited use delivered at
one time can be as damaging as increasing levels of use delivered at over time. 相似文献
1000.
Robert H. Webb H. Craig Ragland William H. Godwin Oennis Jenkins 《Environmental management》1978,2(3):219-233
The effects of off-road vehicles (ORVs) on the physical and chemical properties of 6 soil series were measured at Hollister Hills State Vehicular Recreation Area in central California. Accelerated soil erosion and the alteration of surface strength, bulk density, soil moisture, temperature, and soil nutrients were quantified to gain an insight into the difficulty of revegetating altered, or modified, areas.Erosion is severe at Hollister Hills, particularly in coarse grained soils on steep slopes. Erosion displaced 0.5 and 3.0 metric tons per square meter on 2 trails on gravelly sandy loam, and 0.3 metric tons/m2 from a trail on sandy loam. The surface strength and bulk density increased while the soil moisture decreased in gravelly sandy loam, coarse sandy loam, sandy loam, and clay. Clay loam had an increased surface strength with variably increased bulk density and no decrease in soil moisture. Diurnal temperature fluctuations increased and organic material and soil nutrients decreased in soil modified by vehicles.These property changes increase the erosion potential of the soil, impede germination of seedlings, and slow natural revegetation. Management methods in ORV-use areas should include planning trails by prior application of the universal soil loss equation and soil surveys, trail closure before complete loss of the soil mantle, and revegetation of closed areas. 相似文献