Nutrient Loading by Precipitation in the Maracaibo Lake Basin, Venezuela     

Jose A Morales  Ligbel Sanchez  Harvi Velasquez  Beatriz De Borrego  Marlene De Nava  Denis Portillo  Yulixis Cano  Angel Morillo  Ana Albornoz  Elsa Socorro 《Water, air, and soil pollution》2001,130(1-4):511-516

Nutrient content and pH of rain samples collected at nine sites during 1988-1996 were studied to determine the amounts of N, P and S added by precipitation over Maracaibo Lake basin. The basin is a wide depression occupied by Lake Maracaibo and extensive alluvial plains and delimited by a mountainous zone of variable physiolgraphic characteristics with different cattle ranching and industrial activities. Rain pHs averaged ≈ 4 to 6, individual samples occasionally reached as low as pH 3 in the south basin. NH₄ ⁺ levels were significantly higher (up to 2.6 mg/l NH₄-N) than NO₃ ^? plus NO₂ ^?. Phosphorus levels were low, ranging from undetectable to 1.5 mg/l. The amounts of inorganic N/ha/yr added ranged from ≈ 5.4 Kg in the north to ≈ 8 Kg in the south basin; around the lakeshore, it was estimated that ≈ 9.8–16.8 Kg TN/ha (≈ 55 % as organic-N) are annually deposited. The annual amounts of SO₄-S/ha added range from ≈ 10 to 13 Kg. The contribution of precipitation to P in the ecosystem is very small; ≈ 0.02 – 0.8 Kg of PO₄-P/ha/yr was added in basin. The results of this study show that precipitation represents a significant factor for the total nitrogen and sulfur loading to Maracaibo Lake Basin.  相似文献   

Study of nickel sorption onto biological sludges. possibilities for heavy metals removal treatments     

Jose Ignacio Lombrarna  Fernando Varona  Federico Mijangos 《Water, air, and soil pollution》1995,82(3-4):645-658

Nickel adsorption onto a sludge wasting from a biological aeration tank is described in this work. This procedure is planned as an alternative method for metal removal from industrial effluents containing heavy metals in low concentrations. Experimental results of equilibrium adsorption and laboratory equipment operation are reported. Equilibrium data of nickel adsorption were fitted to the Freundlich equation. On the basis of this equation, the effect of several parameters such us metal concentration, sludge concentration and metal dosing rate were tested. Nickel removal efficiency is about 80% in the most favourable cases. Aeration during metal-sludge contact was also tested but little enhancing in metal uptake was observed. This analysis can be used to define the best operation conditions in practical cases either for metal or organic matter removal.  相似文献   

Natural and human disturbances affect natural regeneration of Swietenia macrophylla: Implications for rainforest management     

Gabriel Gutiérrez-Granados  Veronica Juárez 《Forest Ecology and Management》2011,262(2):161-169

In this paper we document how changes in forest structure mediated by natural (hurricane) and human (logging) disturbances affect natural regeneration of Swietenia macrophylla via its effects on seed predation, germination, and early recruitment. Work was carried out in two ejidos within the Mayan zone of Quintana Roo, differing with regard to their exposure to the effect of the hurricane Dean 2008 (Naranjal Poniente; high hurricane impact) and Señor (with no evidence of hurricane effects). We experimentally set S. macrophylla seeds in both hurricane conditions and contrasting logging effects, in three treatments: (1) open access, (2) rodent and insect access and (3) rodent and insect exclusion. We measured three dependent variables: (i) number of seeds predated, (ii) number of seeds germinated and (iii) number of seedlings established. We found that the three variables measured were differentially affected by logging and hurricane Dean. Seed predation was higher in areas with hurricane effects; germination showed no differences, but early recruitment was differentially affected by the two conditions, via an increasing of herbivory and sun exposition. Both types of disturbances studied occurred periodically in Yucatan Peninsula and elsewhere in tropics, so it is necessary to implement specific actions in order to face changes in mahogany natural regeneration stocks, and supporting the future management of tropical forests.  相似文献   

Variant allometric scaling relationships between bud size and secondary shoot growth in <Emphasis Type="Italic">Quercus faginea</Emphasis>: implications for the climatic modulation of canopy growth     

Arben Q. Alla  J. Julio Camarero  Pilar Rivera  Gabriel Montserrat-Martí 《Annals of Forest Science》2011,68(7):1245-1254

• Introduction and statement of the research questions  

The relationships between primary and secondary growth in tree populations of contrasting climates are poorly understood. We tested the hypotheses that bud size and stem cross-sectional area are related through allometric relationship in shoots and that their scaling slopes change in response to climatic stress.  相似文献   

Characterization of the interaction between two food aroma components, alpha-pinene and ethyl butyrate, and ethylene-vinyl alcohol copolymer (EVOH) packaging films as a function of environmental humidity     

López-Carballo G  Cava D  Lagarón JM  Catalá R  Gavara R 《Journal of agricultural and food chemistry》2005,53(18):7212-7216

The ethylene-vinyl alcohol copolymers (EVOHs) are well-known high oxygen barrier materials that are being used successfully in the design of packaging structures for oxygen-sensitive food or pharmaceutical products. Recently, there has been increasing interest in using EVOH materials to provide a high barrier to organic compounds as a means to reduce food aroma scalping. However, the barrier function of this family of materials diminishes significantly in humid environments, and it is supposed that so does the organic vapor barrier. In this work, a new sorption-based method to characterize the interaction between food aroma and polymer films for packaging as a function of relative humidity is presented and is used to determine the barrier to ethyl butyrate and alpha-pinene of EVOH at 23 degrees C. The results show that although EVOH is an excellent barrier to food aroma when dry, a property that even improves at low relative humidity (RH), the solubility and diffusivity of the compounds tested increase dramatically with humidity at medium to high water activities. However, even in the worst case (100% RH), EVOH outperforms low-density polyethylene (LDPE) as a barrier to organic vapors at least 500,000-fold.  相似文献   

Effect of source germplasm and season on the in vivo haploid induction rate in tropical maize     

Aida Z. Kebede  Baldev S. Dhillon  Wolfgang Schipprack  Jose L. Araus  Marianne Bänziger  Kassa Semagn  Gregorio Alvarado  Albrecht E. Melchinger 《Euphytica》2011,180(2):219-226

For in vivo production of doubled haploid (DH) lines in maize, the rate of haploid induction is of crucial importance. Maternal haploid induction depends primarily on the inducer used as a pollinator. However, the source germplasm used as a maternal parent and the environmental conditions for induction may also influence haploid induction and these aspects have not been examined in tropical maize so far. The objectives of our study were to (i) monitor the variation for haploid induction rate (HIR) among diverse source germplasm in tropical maize, (ii) determine the relative importance of general (GCA) and specific (SCA) combining abilities for HIR, and (iii) investigate the influence of summer and winter seasons and genotype × season interactions on this trait. Ten inbreds were mated in a half diallel design. The resulting 45 F₁ single crosses were pollinated with the haploid inducer hybrid RWS × UH400 during the summer 2008 and winter 2009 seasons in a lowland tropical environment in Mexico. HIR of the single crosses averaged over seasons ranged from 2.90 to 9.66% with an overall mean of 6.74%. Mean HIR was significantly (P < 0.01) higher during the winter (7.37%) than summer season (6.11%). Significant (P < 0.01) variation was observed due to GCA effects of parental inbreds of single crosses but not for SCA, GCA × season and SCA × season interactions. Our study underpins that a higher HIR in tropical maize can be obtained by selecting appropriate source germplasm and undertaking pollination under favorable environmental conditions.  相似文献   

A map of the interactome network of the metazoan C. elegans   总被引：1，自引：0，他引：1  

Li S  Armstrong CM  Bertin N  Ge H  Milstein S  Boxem M  Vidalain PO  Han JD  Chesneau A  Hao T  Goldberg DS  Li N  Martinez M  Rual JF  Lamesch P  Xu L  Tewari M  Wong SL  Zhang LV  Berriz GF  Jacotot L  Vaglio P  Reboul J  Hirozane-Kishikawa T  Li Q  Gabel HW  Elewa A  Baumgartner B  Rose DJ  Yu H  Bosak S  Sequerra R  Fraser A  Mango SE  Saxton WM  Strome S  Van Den Heuvel S  Piano F  Vandenhaute J  Sardet C  Gerstein M  Doucette-Stamm L  Gunsalus KC  Harper JW  Cusick ME  Roth FP  Hill DE  Vidal M 《Science (New York, N.Y.)》2004,303(5657):540-543

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The crystal structure of a sodium galactose transporter reveals mechanistic insights into Na+/sugar symport     

Faham S  Watanabe A  Besserer GM  Cascio D  Specht A  Hirayama BA  Wright EM  Abramson J 《Science (New York, N.Y.)》2008,321(5890):810-814

Membrane transporters that use energy stored in sodium gradients to drive nutrients into cells constitute a major class of proteins. We report the crystal structure of a member of the solute sodium symporters (SSS), the Vibrio parahaemolyticus sodium/galactose symporter (vSGLT). The approximately 3.0 angstrom structure contains 14 transmembrane (TM) helices in an inward-facing conformation with a core structure of inverted repeats of 5 TM helices (TM2 to TM6 and TM7 to TM11). Galactose is bound in the center of the core, occluded from the outside solutions by hydrophobic residues. Surprisingly, the architecture of the core is similar to that of the leucine transporter (LeuT) from a different gene family. Modeling the outward-facing conformation based on the LeuT structure, in conjunction with biophysical data, provides insight into structural rearrangements for active transport.  相似文献   

Diet drives convergence in gut microbiome functions across mammalian phylogeny and within humans     

Muegge BD  Kuczynski J  Knights D  Clemente JC  González A  Fontana L  Henrissat B  Knight R  Gordon JI 《Science (New York, N.Y.)》2011,332(6032):970-974

Coevolution of mammals and their gut microbiota has profoundly affected their radiation into myriad habitats. We used shotgun sequencing of microbial community DNA and targeted sequencing of bacterial 16S ribosomal RNA genes to gain an understanding of how microbial communities adapt to extremes of diet. We sampled fecal DNA from 33 mammalian species and 18 humans who kept detailed diet records, and we found that the adaptation of the microbiota to diet is similar across different mammalian lineages. Functional repertoires of microbiome genes, such as those encoding carbohydrate-active enzymes and proteases, can be predicted from bacterial species assemblages. These results illustrate the value of characterizing vertebrate gut microbiomes to understand host evolutionary histories at a supraorganismal level.  相似文献   

Fast readout of object identity from macaque inferior temporal cortex   总被引：1，自引：0，他引：1  

Hung CP  Kreiman G  Poggio T  DiCarlo JJ 《Science (New York, N.Y.)》2005,310(5749):863-866

Understanding the brain computations leading to object recognition requires quantitative characterization of the information represented in inferior temporal (IT) cortex. We used a biologically plausible, classifier-based readout technique to investigate the neural coding of selectivity and invariance at the IT population level. The activity of small neuronal populations (approximately 100 randomly selected cells) over very short time intervals (as small as 12.5 milliseconds) contained unexpectedly accurate and robust information about both object "identity" and "category." This information generalized over a range of object positions and scales, even for novel objects. Coarse information about position and scale could also be read out from the same population.  相似文献