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31.
Elevated atmospheric carbon dioxide (CO2) has the potential to alter soil carbon (C) and nitrogen (N) cycling in arid ecosystems through changes in net primary productivity. However, an associated feedback exists because any sustained increases in plant productivity will depend upon the continued availability of soil N. We took soils from under the canopies of major shrubs, grasses, and plant interspaces in a Mojave Desert ecosystem exposed to elevated atmospheric CO2 and incubated them in the laboratory with amendments of labile C and N to determine if elevated CO2 altered the mechanistic controls of soil C and N on microbial N cycling. Net ammonification increased under shrubs exposed to elevated CO2, while net nitrification decreased. Elevated CO2 treatments exhibited greater fluxes of N2O–N under Lycium spp., but not other microsites. The proportion of microbial/extractable organic N increased under shrubs exposed to elevated CO2. Heterotrophic N2‐fixation and C mineralization increased with C addition, while denitrification enzyme activity and N2O–N fluxes increased when C and N were added in combination. Laboratory results demonstrated the potential for elevated CO2 to affect soil N cycling under shrubs and supports the hypothesis that energy limited microbes may increase net inorganic N cycling rates as the amount of soil‐available C increases under elevated CO2. The effect of CO2 enrichment on N‐cycling processes is mediated by its effect on the plants, particularly shrubs. The potential for elevated atmospheric CO2 to lead to accumulation of NH4+ under shrubs and the subsequent volatilization of NH3 may result in greater losses of N from this system, leading to changes in the form and amount of plant‐available inorganic N. This introduces the potential for a negative feedback mechanism that could act to constrain the degree to which plants can increase productivity in the face of elevated atmospheric CO2. 相似文献
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We explored whether the invasion of an exotic, nitrogen (N) fixing tree into native Hawaiian tropical forests has altered regional emissions of nitrous oxide (N2 O) and nitric oxide (NO), two atmospherically important trace gases produced by microorganisms in soils. Ecosystem processes, including nitrification and N-oxide emissions, were not affected by Morella faya (formerly Myrica faya ) invasion until it dominated the community with few native species in the overstory or understory. Remote-sensing estimates of upper-canopy leaf N concentration were strongly correlated to N-oxide emissions in ecosystems at the mesic-wet end of a precipitation gradient, where temperatures are warm, relatively constant, and N limits biological processes. In contrast, remotely sensed and field-based canopy chemistry was not related to N-oxide emissions in dry forest ecosystems where the seasonality of temperature and moisture exerted stronger control over soil gas fluxes. Thus, remote sensing of canopy N was useful for estimating the impact of M. faya on regional N-oxide emissions only in regions receiving >1800 mm rainfall annually. Our estimates of N-oxide emissions from M. faya are half as large and 35 times more precise than those made using traditional, plot-level methods of extrapolation. Over the 40 years since its first occurrence in wet forests of Hawai'i Volcanoes National Park, M. faya has increased N-oxide emissions 16-fold, with its effects most pronounced in summer and at the N-rich centers of dense, monospecific stands. 相似文献
34.
S ORENSTEIN T ZAHAVI D NESTEL R SHARON M BARKALIFA P G WEINTRAUB 《The Annals of applied biology》2003,142(3):341-348
Species from three subfamilies of Cicadellidae and one species of Cixiidae, all potential vectors of phytoplasmas, were trapped in vineyards over the course of two years. These insects were caught on yellow sticky traps during the spring; virtually none were trapped during the summer months. Molecular analysis (PCR) of selected samples of the leafhoppers and planthoppers for presence of phytoplasma DNA was conducted on most species. Neoaliturus fenestratus was the most abundant known vector species and was positive for stolbur (Stol) and aster yellows (AY) phytoplasma. Circulifer haematoceps complex, which were also positive for Stol and AY, were about 10‐fold fewer than N. fenestratus. Hyalesthes obsoletus, also a known phytoplasma vector, occurred in substantial numbers only late in the season when the vines and leaves were dehiscing and turning brown, but was positive for Stol and AY. A species whose vector status is unknown (Megophthalmus scabripennis) was also caught in large numbers and was shown, by PCR analysis, to be positive for AY. Other known vector species trapped included: Anaceratagallia laevis (positive for AY), Austroagallia sinuata, Dryodurades sp. (dlabolai?) (positive for AY), Macrosteles quadripunctulatus (positive for Stol), and Orosius orientalis. The spatial dispersion pattern of the four most abundant species were investigated by using Moran's spatial statistic; N. fenestratus and M. scabripennis showed significant spatial patterns, whereas C. haematoceps and H. obsoletus did not. 相似文献
35.
SHARON M. SWARTZ 《Journal of Zoology》1989,218(3):441-460
Biomechanical scaling of long bone joint surface areas was investigated in 13 species of anthropoid primates. It was proposed that joint surface areas should scale with positive allometry with respect to body size in order to maintain relatively constant safety factors for joints in small and large animals and that modifications from the overall pattern of scaling may be expected in the limb joints of species exhibiting specialized locomotor behaviours that radically alter limb loading. Within anthropoids, the brachiating primates, white-handed gibbons ( Hylobates lar ) and black-handed spider monkeys ( Ateles geoffroyi ), were used to test this hypothesis. Total joint surface areas were found to scale with significant positive allometry in 11 of 12 limb joints. The observed pattern of interspecific allometry supports the hypothesis that weight bearing is a major constraint on the design of joints. This positive interspecific allometry is reflected at the intraspecific level as well, with larger joints of larger species showing significant intraspecific scaling. Suspensory species showed no significant deviations from the overall anthropoid pattern, despite their reduced compressive loading of the limb joints, even after controlling for joint mobility. These results suggest that, while evolutionary changes in locomotor behaviour that produce significant increases in loading of a joint may be accompanied by selection for increased joint surface areas, adoption of locomotor repertoires that reduce limb loading may have no selective effect on joint morphology, and joint design in these cases will reflect the biomechanics of the ancestral locomotor condition. 相似文献
36.
MASAO TASAKA CAROLYN A. KAY SHARON M. SOMMERVILLE AROLINE E. GRANT ADRIAN S. TSANG 《Development, growth & differentiation》1986,28(5):471-482
Acid phosphatase–2, as characterized by gel electrophoresis under non-denaturing conditions, is a convenient marker for prestalk cells in Dictyostelium discoideum . We have purified this prestalk-specific enzyme and have examined its regulation during development. Under denaturing conditions, the enzyme has a molecular weight of 50,000 and an isoelectric point of 4.0. On the other hand, acid phosphatase-I have a Mr-55,000 polypeptide (AP1–55) and a minor Mr-50,000 polypeptide (AP1–50) and both have diffuse isoelectric point from 3.4 to 4.1. Using monoclonal antibodies directed against acid phosphatase-2 as probes, we showed that some acid phosphatase-2 are newly synthesized at slug stage and some are converted from AP1–50 which was synthesized during ealy development. 相似文献
37.
ARY A. HOFFMANN SHARON O'DONNELL 《Biological journal of the Linnean Society. Linnean Society of London》1992,47(2):147-159
Drosophila melanogaster were released at a field site and captured with two types of fruit pulp. When flies were rereleased they were more likely to be captured with the same type of fruit on which they were initially captured. Progeny reared in the laboratory tended to be attracted to the same type of fruit as their parents in field tests with two fruit combinations (lemon-orange, lemon-apple) but not a third combination (apple-orange). However, lines selected in the laboratory for increased attraction to apples or oranges over 15 generations differed in their response to these fruit types in the field. This indicates heritable variation for attraction to natural resources under field conditions. Simulations suggest that genotypes differed substantially in their responses to fruit resources. 相似文献
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STEPHEN D. PRINCE KONRAD J. WESSELS COMPTON J. TUCKER† SHARON E. NICHOLSON‡ 《Global Change Biology》2007,13(7):1308-1313
In semiarid regions the ratio of annual net primary production to precipitation, rain-use efficiency (RUE), has been used as an index of desertification. In a recent publication ( Hein & de Ridder, 2006 ) it was proposed that an incorrect understanding of the relationship between RUE and rainfall has led to a misinterpretation of the satellite record of desertification in the African Sahel. Here, we examine this suggestion and show that, contrary to Hein and de Ridder's statement, satellite studies of Sahelian RUE have reported increases, decreases, and constant values since 1981. Furthermore, we find that data do not support their proposal that RUE increases with rainfall, even in nondegraded areas. Hence we reject their corollary, that constant RUE is prima facie evidence of desertification. The fundamental difficulty with the use of RUE for detection of desertification remains, that is the difficulty of estimation of the RUE for nondegraded land at a regional scale. 相似文献
40.
Habitat variation,mutualism and predation shape the spatio‐temporal dynamics of tansy aphids 下载免费PDF全文
1. Spatially distributed resources can lead to the formation of metapopulations, where individual subpopulations are often small and can experience frequent local extinction events followed by recolonisation. An example of terrestrial metapopulations are specialised phytophagous insects on their patchily distributed host plants. 2. The present study investigated the population dynamics of a specialised aphid (Metopeurum fuscoviride) on its patchily distributed host plant (Tanacetum vulgare) and associated community of mutualistic ants and predators in a small‐scale field site. Furthermore, aphid habitat differences (plant size, C/N ratio, location and surrounding vegetation) were quantified, and seasonal timing and precipitation were considered. 3. Seasonal timing and precipitation both had effects on aphid colonisation, extinction events and aphid colony persistence. Towards the end of the season, and after higher precipitation, aphid colonisation events decreased and extinction events increased. Plant size and location as well as aphid within‐field dispersal determined the spatio‐temporal distribution of aphid colonies. 4. Mutualistic ants (Lasius niger and Myrmica rubra) increased the chance of establishment of aphid colonies. However, when M. rubra was tending, aphid colony persistence was reduced. Aphid persistence and extinction were dependent on aphid abundance, as a higher colony size reduced the probability of extinction by predation. 5. The results emphasise the importance of dispersal limitation, population growth and the presence of mutualists when studying the spatio‐temporal dynamics of tansy aphids, particularly in a small‐scale field site. 相似文献