Decomposition of emergent macrophyte roots and rhizomes in a northern prairie marsh

Dry mass, nitrogen and phosphorus content in belowground litter of four emergent macrophytes (Typha glauca Godr., Phragmites australis (Cav.) Trin., Scolochloa festucacea (Willd.) Link and Scirpus lacustris L.) were followed for 1.2 years in a series of experimental marshes, Delta Marsh, Manitoba. Litter bags containing roots and rhizome materials of each species were buried in unflooded soil, or soil flooded at three water depths (1–30, 31–60, > 60 cm). There were few differences in dry mass loss in unflooded or flooded soils, and depth of flooding also had little effect on decomposition rates. In the flooded sites, Scolochloa and Phragmites roots lost more mass (48.9–63.8% and 59.2–85.5%, respectively) after 112 days than Typha and Scirpus (36.3–43.6 and 37.0–47.2%, respectively). These differences continued through to the end of the study, except in the shallow sites where Scirpus roots lost more mass and had comparable mass remaining as Scolochloa and Phragmites. In the unflooded sites, there was little difference between species. All litters lost nitrogen (22.9–90.0%) and phosphorus (46.3–92.7%) during the first 112 days, then levels tended to remain constant. Decay rates for our belowground root and rhizome litters were comparable to published literature values for aboveground shoot litter of the same species, except for Phragmites roots and rhizomes which decomposed at a faster rate (−k = 0.0014−0.0032) than shoots (−k = 0.0003−0.0007, [van der Valk, A.G., Rhymer, J.M., Murkin, H.R., 1991. Flooding and the decomposition of litter of four emergent plant species in a prairie wetland. Wetlands 11, 1–16]).

weathering fur simulation

ACM SIGGRAPH; ACM SIGCHI

Land use and water quality response in the northern region of Changxing County

In this paper, taking the northern region of Changxing County for example, with ammonia nitrogen as a pollution assessment index, we used an improved export coefficient method for estimate polluting load of non-point source pollution (NSP) and the social pollution survey data in the study area to estimate point source pollution. By comparing the total pollution output and the national surface water environmental quality standards find that the whole study area achieves the second water quality standard. However, Jiapu Township exceeds the water quality standards seriously because of the superfluous point source pollution. The water quality of other Townships is good. Further analysis showed that different types of land use and proportions in the northern region of Changxing County have a significant impact on the non-point source pollution, the general law is farmland contributes the largest share of the non-point source pollution output, followed by residential area and bare land, besides, with the increase in the proportion of forest and the decrease of farmland and residential area, the non-point source pollution reduces gradually. © 2010 IEEE.

Radiolarian distribution in surface sediments of the northern and central South China Sea

Radiolarian distribution in surface sediments of 104 stations from northern and central South China Sea show that the abundance and diversity of radiolarians increase with the water depth and are related to radiolarian concentrations from the water column, diminished terrigenous input, variability in calcareous shell content and the rate of silica and carbonate dissolution in the deep sea. According to the appearances of individual species in surface sediments at particular depths, seven faunal boundaries distribution are recognized at water depths of 100, 450, 650, 1000, 1200, 1400 and 2500 m. Four radiolarian assemblages in the sediments were identified by applying clustering procedures. Geographic distributions of these four assemblages coincide with present-day hydrologic features of the surface waters in this area.

Phylogeography of the Northern Atlantic species Chondrus crispus (Gigartinales, Rhodophyta) inferred from nuclear rDNA internal transcribed spacer sequences

Eighteen isolates of the red algae Chondrus crispus were collected from Northern Atlantic sites, together with C. ocellatus, C. yendoi and C. pinnulatus from the North Pacific. The nuclear rDNA internal transcribed spacer (ITS) was sequenced and compared, spanning both the ITS regions and the 5.8S rRNA gene. Percentage of nucleotide variation for C. crispus ranged from 0.3% to 4.0%. Phylogenetic analyses were performed using maximum parsimony (MP), neighbor-joining (NJ) and minimum evolution methods. They showed that two main clades existed within the C. crispus samples examined and that suggested C. crispus had a single Atlantic origin. The clustering however did not follow the geographic origin. We hypothesized that the current distribution of C. crispus populations might be a result of three main factors: temperature boundaries, paleoclimate and paleoceanography. ITS data exhibited abundant molecular information not only for phylogeographical investigation but also for systematics studies.

Cys-92, Cys-95, and the C-terminal 12 residues of the Vibrio harveyi ferric uptake regulator (Fur) are functionally inessential

Ferric uptake regulator (Fur) is a global regulator involved in multiple aspects of bacterial life. The gene encoding the Vibrio harveyi Fur (Fur(vh)) was cloned from a pathogenic V. harveyi strain isolated from diseased fish. Furvh shares 77% overall sequence identity with the Escherichia coli Fur (Fur(Ec)) and could complement a mutant of Fur(Ec). Like Fur(Ec), Fur(Vh), possesses two cysteine residues at positions 92 and 95, yet unlike Fur(Ec), in which these cysteine residues constitute part of the metal ion coordination site and hence are vital to the repressor activity, C92 and C95 of Fur(Vh) proved to be functionally inessential. Further study identified a Vibrio Fur signature sequence, which is preserved in all the ten Vibrio Fur proteins that have been discovered to date but in none of the non-vibrio Fur proteins. Site-directed and random mutation analyses of the signature residues, the cysteine residues, and seven highly charged amino acid residues indicated that D9, H32, C137, and K138 of Fur(vh) are functionally important but D9, C137, and K138 can be replaced by more than one functional substitutes. Systematic deletion analysis demonstrated that the C-terminal 12 residues of Fur(Vh) are functionally inessential. These results (i) indicated that the activation mechanism, or certain aspects of which, of Fur(Vh) is possibly different from that of Fur(Ec); and (ii) suggested that it is not very likely that the C-terminal 12 residues play any significant role in the activation or stability of Fur(Vh); and (iii) provided insights into the potential function of the local structure involving C137 and K138.

Molecular analysis of the fur (ferric uptake regulator) gene of a pathogenic Edwardsiella tarda strain

The gene encoding the Edwardsiella tarda ferric uptake regulator (Fur(Et)) was cloned from a pathogenic E. tarda strain isolated from diseased fish. Fur(Et) shares 90% overall sequence identity with the Escherichia coli Fur (Fur(Ec)) and was able to complement the mutant phenotype of a fur(Ec)-defective E. coli strain. Mutational analysis indicated that C92S and C95S mutations inactivated Fur(Et) whereas E112K mutation resulted in a superactive Fur(Et) variant. Fur(Et) negatively regulated its own expression; interruption of this regulation impaired bacterial growth, altered the production of certain outer membrane proteins, and attenuated bacterial virulence.

Tectonic Evolution and Dynamics of Deepwater Area of Pearl River Mouth Basin, Northern South China Sea

Quantitative studies on the evolution and dynamics of the deepwater area of Pearl River Mouth basin (PRMB) were carried out based on the latest geological and seismic data. The study area is generally in an extensional state during the Cenozoic. The major extension happened in the earlier syn-rift stages before 23 Ma and the extension after 23 Ma is negligible. Two rapid subsidence periods, 32-23 Ma and 5.3-2.6 Ma, are identified, which are related to the abrupt heat decay during margin breakup and the collision between the Philippine Sea plate and the Eurasian plate, respectively. The strongest crustal thinning in the Baiyun (sic) sag may trigger the syn-rift volcanism along the weak faulted belt around the sag. The Cenozoic tectonic evolution of the study area could be divided into five stages: rifting (similar to 50-40 Ma), rift-drift transition (similar to 40-32 Ma), early post-breakup (similar to 32-23 Ma), thermal subsidence (similar to 23-5.3 Ma) and neotectonic movement (similar to 5.3-0 Ma).

Modern changes of tidal troughs among the radial sand ridges in northern Jiangsu coastal zone

Using satellite images taken on different dates, GIS analysis of aerial photos, bathymetric maps and other field survey data, tidal troughs and major sand ridges in the northern Jiangsu coastal area were contrasted. The results show that there have been three types of movement or migration of tidal trough in this area: (1) Periodic and restricted, this type of trough usually developed along the beaches with immobile gully head as a result of the artificial dams and the swing range increased from gully head to the low reaches, so they have been obviously impacted by human activity and have longer swing periods; (2) Periodic and actively, this kind of trough, which swung with a fast rate and moved periodically on sand ridges, were mainly controlled by the swings of the host tidal troughs and hydrodynamic forces upon tidal sand ridge and influenced slightly by human constructions; (3) Steadily and slowly, they are the main tidal troughs with large scale and a steady orientation in this area and have slow lateral movement. The differences in migration mode of tidal trough shift result in different rates of migration and impact upon tidal sand ridges. Lateral accumulation on current tidal trough and deposition on abandoned tidal troughs are the two types of sedimentation of the tidal sand ridges formation. The whole radial sand ridge was generally prone to division and retreat although sand ridges fluctuated by the analysis of changes in talwegs of tidal troughs and shorelines of sand ridges.