Manipulating saltmarsh microtopography modulates the effects of elevation on sediment redox potential and halophyte distribution

1.Halophyte distributions on saltmarshes are strongly related to elevation in the tidal frame. However, collinearity between elevation, the consequent inundation regime, and sediment waterlogging/redox potential obscures the proximate causes of distribution patterns. We sought to distinguish the effects of elevation per se from those of waterlogging by manipulating microtopography. 2.We experimentally manipulated elevation by ±15 cm at locations that spanned the elevation ranges of three saltmarshes recently reactivated by managed coastal realignment. Experimental plots were initially cleared of any vegetation. Elevation and sediment redox potential were determined for each plot. We planted five perennial species (Armeria maritima, Atriplex portulacoides, Limonium vulgare, Plantago maritima and Triglochin maritima) in half of the plots, recording survival over four years, and monitored natural colonisation of the other plots. 3.Overall, redox potential increased with elevation. Sediments were more oxidising in raised plots and more reducing in lowered plots. Redox reductions in lowered plots were in line with those that would be predicted from the overall redox/elevation relationship, but increases in raised plots were greater than predicted from elevation alone. 4.Plant colonisation and survival was poorer in lowered plots and, for most species, improved in raised plots. This poorer colonisation and survival can, in part, be attributed to the concomitant alterations in redox potential and elevation in the tidal frame, but microtopographic manipulation also had substantial independent effects on plant performance, including on the survival of all planted species and the colonisation of Puccinellia maritima, Salicornia europaea agg. and Tripolium pannonicum. 5.Synthesis: Microtopography can have effects on sediment chemistry and plant performance similar in magnitude to those of overall tidal elevation. Understanding how its effects modulate the relationship between tidal elevation, redox and other environmental conditions helps clarify the abiotic factors that fundamentally determine halophyte colonisation and survival. These results support the use of topographic manipulation to enhance the diversity of created saltmarshes

Chandra Multiwavelength Project: Normal Galaxies at Intermediate Redshift

(abridged) We have investigated 136 Chandra extragalactic sources without broad optical emission lines, including 93 galaxies with narrow emission lines (NELG) and 43 with only absorption lines (ALG). Based on fx/fo, Lx, X-ray spectral hardness and optical emission line diagnostics, we have conservatively classified 36 normal galaxies (20 spirals and 16 ellipticals) and 71 AGNs. We found no statistically significant evolution in Lx/LB, within the limited z range. We have built log(N)-log(S), after correcting for completeness based on a series of simulations. The best-fit slope is -1.5 for both S and B energy bands, which is considerably steeper than that of the AGN-dominated cosmic background sources, but slightly flatter than the previous estimate, indicating normal galaxies will not exceed the AGN population until fx ~ 2 x 10-18 erg s-1 cm-2 (a factor of ~5 lower than the previous estimate). A group of NELGs appear to be heavily obscured in X-rays, i.e., a typical type 2 AGN. After correcting for intrinsic absorption, their X-ray luminosities could be Lx > 10^44 erg s-1, making them type 2 quasar candidates. While most X-ray luminous ALGs (XBONG - X-ray bright, optically normal galaxy candidates) do not appear to be significantly absorbed, we found two heavily obscured objects, which could be as luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+A galaxy candidates with strong Balmer absorption lines, but no [OII] line. The X-ray spectra of both galaxies are soft and one of them has a nearby close companion galaxy, supporting the merger/interaction scenario rather than the dusty starburst hypothesis.Comment: 31 pages, 9 figures, accepted for publication in ApJ (20 June 2006, v644), replaced with minor correction

Inflammatory monocytes require type I interferon receptor signaling to activate NK cells via IL-18 during a mucosal viral infection

The requirement of type I interferon (IFN) for natural killer (NK) cell activation in response to viral infection is known, but the underlying mechanism remains unclear. Here, we demonstrate that type I IFN signaling in inflammatory monocytes, but not in dendritic cells (DCs) or NK cells, is essential for NK cell function in response to a mucosal herpes simplex virus type 2 (HSV-2) infection. Mice deficient in type I IFN signaling, Ifnar(-/-) and Irf9(-/-) mice, had significantly lower levels of inflammatory monocytes, were deficient in IL-18 production, and lacked NK cell-derived IFN-gamma. Depletion of inflammatory monocytes, but not DCs or other myeloid cells, resulted in lower levels of IL-18 and a complete abrogation of NK cell function in HSV-2 infection. Moreover, this resulted in higher susceptibility to HSV-2 infection. Although Il18(-/-) mice had normal levels of inflammatory monocytes, their NK cells were unresponsive to HSV-2 challenge. This study highlights the importance of type I IFN signaling in inflammatory monocytes and the induction of the early innate antiviral response

Hard X-ray emitting Active Galactic Nuclei selected by the Chandra Multi-wavelength Project

We present X-ray and optical analysis of 188 AGN identified from 497 hard X-ray (f (2.0-8.0 keV) > 2.7x10^-15 erg cm^-2 s^-1) sources in 20 Chandra fields (1.5 deg^2) forming part of the Chandra Multi-wavelength Project. These medium depth X-ray observations enable us to detect a representative subset of those sources responsible for the bulk of the 2-8 keV Cosmic X-ray Background. Brighter than our optical spectroscopic limit, we achieve a reasonable degree of completeness (77% of X-ray sources with counter-parts r'< 22.5 have been classified): broad emission line AGN (62%), narrow emission line galaxies (24%), absorption line galaxies (7%), stars (5%) or clusters (2%). We find that most X-ray unabsorbed AGN (NH<10^22 cm^-2) have optical properties characterized by broad emission lines and blue colors, similiar to optically-selected quasars from the Sloan Digital Sky Survey but with a slighly broader color distribution. However, we also find a significant population of redder (g'-i'>1.0) AGN with broad optical emission lines. Most of the X-ray absorbed AGN (10^22<NH<10^24 cm^-2) are associated with narrow emission line galaxies, with red optical colors characteristically dominated by luminous, early type galaxy hosts rather than from dust reddening of an AGN. We also find a number of atypical AGN; for instance, several luminous AGN show both strong X-ray absorption (NH>10^22 cm^-2) and broad emission lines. Overall, we find that 81% of X-ray selected AGN can be easily interpreted in the context of current AGN unification models. Most of the deviations seem to be due to an optical contribution from the host galaxies of the low luminosity AGN.Comment: 26 pages; 13 figures (7 color); accepted for publication in the Astrophysical Journa