Temporal variation in precipitation chemistry on the shore of the Chesapeake Bay     

Thomas E. Jordan  David L. Correll  Donald E. Weller  Nancy M. Goff 《Water, air, and soil pollution》1995,83(3-4):263-284

We studied precipitation chemistry at the Rhode River on the western shore of the Chesapeake Bay. We sampled on an event basis, beginning in 1973 for some constituents in bulk precipitation. Beginning in 1981, we also sampled wet precipitation separately from bulk precipitation. In this report, we examine temporal variability of precipitation chemistry at different time scales. Several constituents showed long-term trends. In bulk precipitation, hydronium concentration increased by 27% of its mean concentration per decade, calcium by 67%, ammonium by 28%, and nitrate by 25%, while organic nitrogen decreased by 41%, organic phosphorus by 31%, and organic carbon by 16%. In wet precipitation, ammonium increased by 33% and calcium by 100%, while magnesium decreased by 78% per decade. Concentrations differed greatly among precipitation events, increasing as the volume of precipitation decreased and as the interval since the previous event increased. Most constituents also showed marked seasonal variation. We used a regression model to predict concentrations for each event from month, precipitation volume, and the time since the previous event. We evaluated how much of the interannual variability could be explained by these factors. The event-scale model accounted for almost half of the variability among annual means for ammonium, sodium, and magnesium in bulk precipitation, and for potassium in wet precipitation. This suggests that much of the interannual variability of concentrations may result from interannual variation in the temporal distribution of precipitation.  相似文献   

Coast live oak, Quercus agrifolia, susceptibility and response to goldspotted oak borer, Agrilus auroguttatus, injury in southern California     

Tom W. Coleman  Nancy E. Grulke  Miles DalyCesar Godinez  Susan L. SchillingPhilip J. Riggan  Steven J. Seybold 《Forest Ecology and Management》2011,261(11):1852-1865

Oak mortality is often associated with a complex of decline factors. We describe the morphological and physiological responses of coast live oak, Quercus agrifolia Née, in California to an invasive insect, the goldspotted oak borer (GSOB), Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), and evaluate drought as a potential inciting factor. Morphological traits of 356 trees were assessed and physiological traits of 70 of these were monitored intensively over one growing season. Morphological characteristics of tree health included crown thinning and dieback; bole staining resulting from larval feeding; density of GSOB adult exit holes; and holes caused by woodpecker feeding. These characteristics were used to rank GSOB infestation/injury into four classes, and taken together, they explained 87% of the variation in a principal component analysis. Drought stress on various size/age and infestation classes of Q. agrifolia was measured by assessing branchlet pre-dawn and solar noon xylem water potential, leaf cell turgor potential, and water use efficiency over one growing season. Both morphological and physiological traits were highly variable in mature and old growth trees. Early summer plant water status (branchlet xylem water potential and water use efficiency) was similar between uninfested and newly colonized trees, suggesting that GSOB are not pre-selecting drought-stressed Q. agrifolia for oviposition. By late summer, leaf water and cell turgor potentials were lower in infested than in uninfested mature trees, suggesting that GSOB infestation causes drought stress in these trees. Among the tree size/age classes, infested old growth trees exhibited the greatest change in water use efficiency over the growing season, and showed greater morphological injury symptoms of decline than infested mature trees. Morphological attributes of decline in Q. agrifolia associated with GSOB were correlated weakly with increasing physiological drought stress among infestation classes of trees. We propose that the collection of morphological responses of Q. agrifolia to GSOB described here can be used to monitor the future expansion of the GSOB distribution as well as the GSOB-induced decline of Q. agrifolia in California.  相似文献   

Mutations in a human ROBO gene disrupt hindbrain axon pathway crossing and morphogenesis     

Jen JC  Chan WM  Bosley TM  Wan J  Carr JR  Rüb U  Shattuck D  Salamon G  Kudo LC  Ou J  Lin DD  Salih MA  Kansu T  Al Dhalaan H  Al Zayed Z  MacDonald DB  Stigsby B  Plaitakis A  Dretakis EK  Gottlob I  Pieh C  Traboulsi EI  Wang Q  Wang L  Andrews C  Yamada K  Demer JL  Karim S  Alger JR  Geschwind DH  Deller T  Sicotte NL  Nelson SF  Baloh RW  Engle EC 《Science (New York, N.Y.)》2004,304(5676):1509-1513

The mechanisms controlling axon guidance are of fundamental importance in understanding brain development. Growing corticospinal and somatosensory axons cross the midline in the medulla to reach their targets and thus form the basis of contralateral motor control and sensory input. The motor and sensory projections appeared uncrossed in patients with horizontal gaze palsy with progressive scoliosis (HGPPS). In patients affected with HGPPS, we identified mutations in the ROBO3 gene, which shares homology with roundabout genes important in axon guidance in developing Drosophila, zebrafish, and mouse. Like its murine homolog Rig1/Robo3, but unlike other Robo proteins, ROBO3 is required for hindbrain axon midline crossing.  相似文献   

The global circulation of seasonal influenza A (H3N2) viruses     

Russell CA  Jones TC  Barr IG  Cox NJ  Garten RJ  Gregory V  Gust ID  Hampson AW  Hay AJ  Hurt AC  de Jong JC  Kelso A  Klimov AI  Kageyama T  Komadina N  Lapedes AS  Lin YP  Mosterin A  Obuchi M  Odagiri T  Osterhaus AD  Rimmelzwaan GF  Shaw MW  Skepner E  Stohr K  Tashiro M  Fouchier RA  Smith DJ 《Science (New York, N.Y.)》2008,320(5874):340-346

Antigenic and genetic analysis of the hemagglutinin of approximately 13,000 human influenza A (H3N2) viruses from six continents during 2002-2007 revealed that there was continuous circulation in east and Southeast Asia (E-SE Asia) via a region-wide network of temporally overlapping epidemics and that epidemics in the temperate regions were seeded from this network each year. Seed strains generally first reached Oceania, North America, and Europe, and later South America. This evidence suggests that once A (H3N2) viruses leave E-SE Asia, they are unlikely to contribute to long-term viral evolution. If the trends observed during this period are an accurate representation of overall patterns of spread, then the antigenic characteristics of A (H3N2) viruses outside E-SE Asia may be forecast each year based on surveillance within E-SE Asia, with consequent improvements to vaccine strain selection.  相似文献   

Careers in science. More women in science     

Handelsman J  Cantor N  Carnes M  Denton D  Fine E  Grosz B  Hinshaw V  Marrett C  Rosser S  Shalala D  Sheridan J 《Science (New York, N.Y.)》2005,309(5738):1190-1191

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Seeding and propagation of untransformed mouse mammary cells in the lung     

Podsypanina K  Du YC  Jechlinger M  Beverly LJ  Hambardzumyan D  Varmus H 《Science (New York, N.Y.)》2008,321(5897):1841-1844

The acquisition of metastatic ability by tumor cells is considered a late event in the evolution of malignant tumors. We report that untransformed mouse mammary cells that have been engineered to express the inducible oncogenic transgenes MYC and Kras(D12), or polyoma middle T, and introduced into the systemic circulation of a mouse can bypass transformation at the primary site and develop into metastatic pulmonary lesions upon immediate or delayed oncogene induction. Therefore, previously untransformed mammary cells may establish residence in the lung once they have entered the bloodstream and may assume malignant growth upon oncogene activation. Mammary cells lacking oncogenic transgenes displayed a similar capacity for long-term residence in the lungs but did not form ectopic tumors.  相似文献   

Neuroscience. When is a word not a word?     

McIntosh AR  Lobaugh NJ 《Science (New York, N.Y.)》2003,301(5631):322-323

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Economics. When a commodity is not exactly a commodity     

Folbre N 《Science (New York, N.Y.)》2008,319(5871):1769-1770

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A proposal for a Decade of the Mind initiative     

Albus JS  Bekey GA  Holland JH  Kanwisher NG  Krichmar JL  Mishkin M  Modha DS  Raichle ME  Shepherd GM  Tononi G 《Science (New York, N.Y.)》2007,317(5843):1321

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Deletion of Trpm7 disrupts embryonic development and thymopoiesis without altering Mg2+ homeostasis     

Jin J  Desai BN  Navarro B  Donovan A  Andrews NC  Clapham DE 《Science (New York, N.Y.)》2008,322(5902):756-760

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