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1.
Summary Creosobebush (Larrea tridentata) fine litter was treated with either the general biocide HgCl2 and CuSO4 or water (controls) and buried 5 cm beneath the soil surface in the northern Chihuahuan Desert. The treated litter showed significantly less mass loss than controls during the three month summer-autumn field study; controls lost about 20% of the original mass while treated litter lost less than 2%. In addition, the total nitrogen content of the control litter increased from an initial concentration of about 14.08 g kg-1 to 17.62 g kg-1 dry weight by the end of the study, while treated litter nitrogen content decreased to 13.30 g kg-1. Results suggest abiotic processes other than leaching have little effect on the decomposition of buried litter in this environment. 相似文献
2.
Summary The water balance of three different sized coexisting species of heteromyid rodents (Dipodomys merriami ca. 39 g;Perognathus fallax ca. 23 g;Perognathus longimembris ca. 9 g) was assessed while consuming two different diets (either wheat or hulled sunflower) at ambient temperatures of 15–30°C.
The metabolism of wheat as the sole food source was calculated to provide a greater metabolic water production (MWP) than
the consumption of sunflower seed because of their different composition. The state of water balance was assessed by measuring
urine concentrations and body weight maintenance on each diet at each temperature. Both measures showed that (i) all species
were able to maintain a more positive water on the higher MWP seed, (ii) for all species there was an ambient temperature
above which water balance could no longer be maintained, (iii) that this temperature was higher with the higher MWP food source
and (iv) water regulatory efficiency was negatively correlated with body mass.Dipodomys showed a reduced digestive efficiency compared toPerognathus. When presented with both seedsDipodomys showed no preference for either seed irrespective of the state of water balance whilst thePerognathus species showed a tendency for an increased preference for the high MWP food source at the higher ambient temperatures. The
ecological implications of these findings are discussed. 相似文献
3.
We examined the content and isotopic composition of nitrogen within soils of a juniper woodland and found that a cryptobiotic crust composed of cyanobacteria, lichens, and mosses was the predominant source of nitrogen for this ecosystem. Disturbance of the crust has resulted in considerable spatial variability in soil nitrogen content and isotopic composition; intercanopy soils were significantly depleted in nitrogen and had greater abundance of 15N compared to intra-canopy soils. Variations in the 15N/14N ratio for inter- and intra-canopy locations followed similar Rayleigh distillation curves, indicating that the greater 15N/14N ratios for inter-canopy soils were due to relatively greater net nitrogen loss. Coverage of cryptobiotic crusts has been reduced by anthropogenic activities during the past century, and our results suggest that destruction of the cryptobiotic crust may ultimately result in ecosystem degradation through elimination of the predominant source of nitrogen input. 相似文献
4.
Downward flux of water through roots (i.e. inverse hydraulic lift) in dry Kalahari sands 总被引:17,自引:0,他引:17
E.-D. Schulze M. M. Caldwell J. Canadell H. A. Mooney R. B. Jackson D. Parson R. Scholes O. E. Sala P. Trimborn 《Oecologia》1998,115(4):460-462
Downward transport of water in roots, in the following termed “inverse hydraulic lift,” has previously been shown with heat
flux techniques. But water flow into deeper soil layers was demonstrated in this study for the first time when investigating
several perennial grass species of the Kalahari Desert under field conditions. Deuterium labelling was used to show that water
acquired by roots from moist sand in the upper profile was transported through the root system to roots deeper in the profile
and released into the dry sand at these depths. Inverse hydraulic lift may serve as an important mechanism to facilitate root
growth through the dry soil layers underlaying the upper profile where precipitation penetrates. This may allow roots to reach
deep sources of moisture in water-limited ecosystems such as the Kalahari Desert.
Received: 1 January 1998 / Accepted: 1 April 1998 相似文献
5.
Diversification patterns of pebble-mimic dragons are consistent with historical disruption of important habitat corridors in arid Australia 总被引:2,自引:2,他引:0
Shoo LP Rose R Doughty P Austin JJ Melville J 《Molecular phylogenetics and evolution》2008,48(2):528-542
The pebble-mimic dragon lineage of Tympanocryptis is widely distributed in the stony, or ‘gibber’, deserts of Australia but is noticeably absent from intersecting areas of sand deserts. Past fluctuations in the extent and configuration of sandy desert habitat barriers are likely to have been an import factor promoting genetic differentiation in this group. We sequenced a 1400 bp region of mitochondrial DNA and a 1400 bp nuclear gene (RAG-1) to investigate phylogeographic structuring of species of pebble-mimic dragons. Our topology indicates an early split in this lineage between eastern and western parts of the arid zone that probably dates to the mid-Miocene. This split corresponds directly with large expanses of contemporary sandy habitat in the form of Great Sandy and Great Victoria Deserts. Our data indicate that this biogeographic barrier established very early on in the development of the arid zone and has persisted to present. Additional genetic structuring in the absence of recognized barriers suggests that an expanded view of potential habitat barriers in the arid zone is required. 相似文献
6.
The purpose of this paper was to analyze the diversity patterns of Cactaceae at a global scale, to identify those countries
where conservation actions should be performed. In order to do this, the species richness and the number of endemic species
for 34 American countries were determined. With these data, the relationship between the total number of species or the number
of endemic species and the area of the countries were analyzed. In addition, a complementarity analysis was conducted to determine
the most important countries for cactus conservation. Results showed that Mexico had the highest number of total and endemic
species followed by Argentina, Bolivia, Brazil, and Peru, among others. There was a significant positive relationship between
both, the total and endemic species, and the area of the countries. Despite this fact, the cactus diversity in Mexico, Argentina,
Peru, Bolivia, Chile, and Costa Rica was higher than expected according to their area. Further, these countries also presented
the highest proportions of endemic species. The complementarity analysis indicated that 24 countries are necessary to preserve
all cactus species. However, 94% of all species could be preserved with only 10 countries. Considering the diversity patterns
and the complementarity analysis, three important groups for cactus conservation were identified: (1) Mexico, Argentina, Peru,
Bolivia, Chile, and Costa Rica, (2) Paraguay and Cuba, and (3) Brazil and USA. Conservation efforts should be focused on these
countries in order to preserve cactus diversity. 相似文献
7.
Marc Le Romancer Mélusine Gaillard Claire Geslin Daniel Prieur 《Reviews in Environmental Science and Biotechnology》2007,6(1-3):17-31
The tolerance limits of extremophiles in term of temperature, pH, salinity, desiccation, hydrostatic pressure, radiation,
anaerobiosis far exceed what can support non-extremophilic organisms. Like all other organisms, extremophiles serve as hosts
for viral replication. Many lines of evidence suggest that viruses could no more be regarded as simple infectious “fragments
of life” but on the contrary as one of the major components of the biosphere. The exploration of niches with seemingly harsh
life conditions as hypersaline and soda lakes, Sahara desert, polar environments or hot acid springs and deep sea hydrothermal
vents, permitted to track successfully the presence of viruses. Substantial populations of double-stranded DNA virus that
can reach 109 particles per milliliter were recorded. All these viral communities, with genome size ranging from 14 kb to 80 kb, seem to
be genetically distinct, suggesting specific niche adaptation. Nevertheless, at this stage of the knowledge, very little is
known of their origin, activity, or importance to the in situ microbial dynamics. The continuous attempts to isolate and to
study viruses that thrive in extreme environments will be needed to address such questions. However, this topic appears to
open a new window on an unexplored part of the viral world.
Marc Le Romancer and Mélusine Gaillard contributed equally to this work. 相似文献
8.
Quantitative effects of vegetation cover on wind erosion and soil nutrient loss in a desert grassland of southern New Mexico,USA 总被引:3,自引:0,他引:3
Wind is a key abiotic factor that influences the dynamics of arid and semiarid systems. We investigated two basic relationships
on vegetation manipulation (grass cover reduction) plots at the Jornada Experimental Range in southern New Mexico: (1) wind
erosion rates (horizontal mass flux and dust emission) versus vegetative cover, and (2) nutrient loss versus vegetative cover.
The results indicate that wind erosion rates and nutrient loss by dust emission are strongly affected by plant cover; however,
the importance of shrubs and grasses in reducing dust flux may not be equal. The dramatic increase of wind erosion between
75% grass cover reduction and 100% grass cover reduction suggests that sparsely distributed mesquites are relatively ineffective
at reducing wind erosion and nutrient loss compared to grasses. Comparisons of nutrients between surface soils and wind blown
dust indicate that aeolian transport is a major cause for the loss of soil nutrients in susceptible environments. We found
that increased aeolian flux over three windy seasons (March 2004–July 2006) removed up to 25% of total organic carbon (TOC)
and total nitrogen (TN) from the top 5 cm of soil, and about 60% of TOC and TN loss occurred in the first windy season (March–July
2004). The balance between net loss of nutrients by aeolian processes and the addition of nutrients by biotic processes changed
from negative (net loss) to positive (net accumulation) between 50% grass cover reduction and 25% grass cover reduction. The
estimated lifetime of surface soil TOC and TN of about 10 years on the plot with 100% grass cover reduction indicates that
impacts of wind erosion on soil resources can occur on very short timescales. 相似文献
9.
Phylogeography and species boundaries of the western North American Nightsnake (Hypsiglena torquata): revisiting the subspecies concept 总被引:4,自引:3,他引:1
Mulcahy DG 《Molecular phylogenetics and evolution》2008,46(3):1095-1115
The subspecies concept has received considerable debate throughout the past century. Subspecies were originally used to delineate potential incipient species, but were later employed to simply capture geographical variation. There is a recent trend to eliminate the trinomial in light of new evidence. Discrete, diagnosable lineages are elevated to specific status, while those that show clinal variation and/or appear to represent ecological pattern classes are placed in synonymy with the parent species and the subspecific epithets are disregarded. Here, I examine the species boundaries of nightsnakes (Hypsiglena torquata) using standard phylogeographic methods and mtDNA data from 178 individuals. Previously, seventeen subspecies of H. torquata were described. In this study, I recognize six species in what was previously considered H. torquata: one is novel, two were previously recognized subspecies, while the remaining three are wide-spread, polymorphic lineages, composed of multiple subspecies. I make the case to maintain the subspecific lineages in these wide-ranging species because they are geographically cohesive, morphologically discrete, and may represent incipient species within each complex, which have not yet achieved speciation. These subspecies are maintained, not only pending future investigations, but because they provide a useful identity for the taxonomy of this diverse lineage. 相似文献
10.
We consider three case studies of long-term plant population dynamics in Makhtesh Ramon erosion cirque in the central Negev desert of Israel. We show that rainfall is the major driving variable in this system, and that it creates large temporal and spatial variation in plant species diversity and vegetation community composition. This variability makes it extremely difficult to distinguish `signal' (= pattern in vegetation) from `noise' (random spatial and temporal variance). Our long-term vegetation studies in permanent plots arranged along the length of the cirque, initiated in 1990 and continuing, show that there is high spatial and temporal variance in plant species' incidences and abundances. This is particularly true of annual plant species. However, using pairs of fenced and unfenced plots arranged along the major abiotic gradient, altitude (which mirrors changes in rainfall), we were able to tease apart the effects of variance in rainfall and herbivory. We found significant negative effects of herbivory by the re-introduced Asiatic wild ass (Equus hemionus) on plant cover and on vegetation community composition. In a study of the effects of herbivory by dorcas gazelles (Gazella dorcas) on the lily Pancratium sickenbergeri, we found that there was little inter-annual fluctuation in lily population size in two sand dunes in Makhtesh Ramon in spite of the high percentage of lilies that is removed by the gazelles and the almost complete herbivory of flowers by these herbivores. This result indicates that the dune lily populations may be maintained by dispersal of seed from other lily populations elsewhere in Makhtesh Ramon where gazelles are rare or absent. 相似文献