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1.
A sampler for collection of interstitial water from wetland sediments is described. It differs from other sampling devices because it does not have to be filled with solution to facilitate diffusion, it does not have to be removed from the wetland to collect samples, and it can be used to draw repeated samples over time from identical locations. The device facilitates in situ measurement of a wide range of abiotic parameters such as electrical conductivity, redox potential, and pH in wetland sediments. The device has application in ecological investigations of sediment-borne wildlife diseases, studies of benthic invertebrates, measurement of nutrient exchange, and other aspects of wetland ecology. 相似文献
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The influence of subterranean termites on the hydrological characteristics of a Chihuahuan desert ecosystem 总被引:4,自引:0,他引:4
Summary Rainfall simulation at an average intensity of 124 mm·h-1 was used to compare infiltration and run off on arid areas where subterranean termites had been eliminated four years prior to the initiation of the study (termite free) with adjacent areas populated by subterranean termites (termites present). Infiltration rates on termite free plots with less than 5% perennial plant cover were significantly lower 51.3±6.8 mm·h-1 than rates on comparable termites present plots 88.4±5.6 mm·h-1. On plots centered on Larrea tridentata shrubs, there were no differences in infiltration rates with or without termites. Plots with shrub cover had the highest infiltration rates 101±6 mm·h-1. Highest run-off volumes were recorded from termite free <5% grass cover plots and the lowest from plots with shrubs. There were no differences in suspended sediment concentrations from termites present and termite free plots. Average bed load concentration was more than three times greater from termite free, <5% cover plots than from termites present, <5% cover plots.The reduction in infiltration, high run-off volumes and high bedloads from termite free areas without shrub cover is related to increased soil bulk density resulting from the collapse of subterranean galleries of the termites that provide avenues of bulk flow into the soil. Subterranean termites affect the hydrology of Chihuahuan desert systems by enhancing water infiltration and retention of top soil. The presence of a shrub canopy and litter layer cancels any effect of subterranean termites on hydrological parameters. Since approximately 2/3 of the area is not under shrub canopies, subterranean termites are considered to be essential for the maintenance of the soil water characteristics that support the present vegetation. 相似文献
3.
A simple procedure for obtaining useful narrow-pH-range ampholytes from inexpensive laboratory-synthesized ampholytes by preparative isoelectric focusing in Pevikon is described. The narrow range ampholytes prepared in this way are comparable to commercial ampholyte preparation as judged by conductivity, buffer capacity, pH gradient formation, and resolving power. These inexpensive narrow-range ampholytes are particularly well suited to preparative isoelectric focusing applications requiring large quantities of ampholytes. 相似文献
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Chronic photoinhibition in seedlings of tropical trees 总被引:1,自引:0,他引:1
Seedlings of five canopy species of tropical trees from Costa Rica and Puerto Rico were grown in full shade (midday range of photosynthetic photon flux density [PPFD], 100–140 μmol m?2 s?1), partial shade (midday PPFD, 400–600 μmol m?2 s?1) and full sun (midday PPFD, 1 500–1 800 μmol m?2 s?1) for 3 months. The species were Ochroma lagopus (Bombacaceae), a pioneer species; Inga edulis (Fabaceae), found in secondary forest; and Dipteryx panamensis (Fabaceae), Hampea appendiculata (Malvaceae), and Manilkara bidentata (Sapotaceae), three species characteristic of primary forest. After the plants were placed in the dark overnight, chlorophyll fluorescence characteristics were measured for recently expanded and mature leaves. The ratio of variable fluorescence to maximum fluorescence (Fv/Fm) was used to estimate the degree of chronic photoinhibition. Only individuals of one species, Dipteryx panamensis, showed significant depression of Fv/Fm after long-term exposure to full sun. The depression was highly correlated with quantum yield of O2 evolution which also declined after exposure to full sun. The decline may have been related to foliar N concentration. Although all plants were supplied with ample nutrients, foliar N did not increase significantly for Dipteryx seedlings in full sun, whereas it did for Ochroma and Inga. Leaf age affected Fv/Fm only in the cases of Manilkara, where it was slightly lower in recently expanded leaves, and of Dipteryx where it interacted with the effects of light regime. We conclude that chronic photoinhibition is not common in seedlings of canopy trees of tropical rain forests except when availability of mineral nutrients may be limiting. 相似文献
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Summary Among a group of 31 ts- yeast mutants screened electrophoretically for heat-sensitive synthesis of each stable RNA species, only mutant ts351 failed to accumulate 25S RNA at 36°C. Pulse-labeling experiments at 36°C showed that 35S and 27S precursor RNA and mature 18S r-RNA molecules are synthesized by ts351 cells but that 25S and 5.8S RNA species are not made and new 60S ribosomal sub-units are not assembled. The mutant is blocked at a specific point in r-RNA processing: the cutting of 27S to form 25S and 5.8S r-RNA. 相似文献
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Bishwo N. Adhikari John P. Hamilton Marcelo M. Zerillo Ned Tisserat C. André Lévesque C. Robin Buell 《PloS one》2013,8(10)
The kingdom Stramenopile includes diatoms, brown algae, and oomycetes. Plant pathogenic oomycetes, including Phytophthora, Pythium and downy mildew species, cause devastating diseases on a wide range of host species and have a significant impact on agriculture. Here, we report comparative analyses on the genomes of thirteen straminipilous species, including eleven plant pathogenic oomycetes, to explore common features linked to their pathogenic lifestyle. We report the sequencing, assembly, and annotation of six Pythium genomes and comparison with other stramenopiles including photosynthetic diatoms, and other plant pathogenic oomycetes such as Phytophthora species, Hyaloperonospora arabidopsidis, and Pythium ultimum var. ultimum. Novel features of the oomycete genomes include an expansion of genes encoding secreted effectors and plant cell wall degrading enzymes in Phytophthora species and an over-representation of genes involved in proteolytic degradation and signal transduction in Pythium species. A complete lack of classical RxLR effectors was observed in the seven surveyed Pythium genomes along with an overall reduction of pathogenesis-related gene families in H. arabidopsidis. Comparative analyses revealed fewer genes encoding enzymes involved in carbohydrate metabolism in Pythium species and H. arabidopsidis as compared to Phytophthora species, suggesting variation in virulence mechanisms within plant pathogenic oomycete species. Shared features between the oomycetes and diatoms revealed common mechanisms of intracellular signaling and transportation. Our analyses demonstrate the value of comparative genome analyses for exploring the evolution of pathogenesis and survival mechanisms in the oomycetes. The comparative analyses of seven Pythium species with the closely related oomycetes, Phytophthora species and H. arabidopsidis, and distantly related diatoms provide insight into genes that underlie virulence. 相似文献
10.
Evolution, interactions, and biological networks 总被引:2,自引:0,他引:2