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Prosopis ruscifolia, with its 15 cm long spines, has spread onto vast areas of Argentine grazing lands and formed dense impenetrable stands. We examined grafting the highly respected Prosopis alba (algarrobo blanco) onto Prosopis ruscifolia (vinal) rootstock, with the objective of converting undesirable stands of vinal into desirable stands of P. alba. This grafting experiment examined five dates and three light treatments (full-sunlight, half-shade and ‘tent’ treatment 30×40 cm black plastic shade). The full-sun, half-shade and tent treatments gave 2·4±2·02, 6·0±1·22 and 6·6±0·99 (mean±95% confidence interval) successful grafts out of 10, respectively. Future work should evaluate grafting of P. ruscifolia coppice resprouts with P. alba scions, after the P. ruscifolia trees have been harvested for fuelwood or lumber. EliteP. alba clones are now available for use in grafting. 相似文献
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Field and laboratory studies were conducted during the period May 1993–April 1994 on the cocoons and hatchlings ofAporrectodea calignosa(Savigny 1826), a common earthworm found in Benghazi, Libya. Cocoon production started in August 1993 and continued until April 1994. A positive correlation between soil moisture (r=0.74;p< 0.05) and cocoon production, and a negative one between soil temperature (r=−0.85;p< 0.05) on cocoon production were found. Mean incubation time was 47 days. Some cocoons contained a single worm (single hatchling) whereas the majority of them (68%) contained two, the first hatchling and second hatchling. The rate of change of body mass (F=2.18;p>0.05) and the average body mass (F=1.25;p>0.05) of the single, first and second hatchlings were similar. 相似文献
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Prosopis 《Journal of Arid Environments》1995,30(4)
Canker and tip-dieback diseases have been found in field and greenhouse plantings ofProsopisbeing examined in agroforestry trials in South Texas. Several fungal species were associated with the field cankers, most notably aLasiodiplodiaand aPestalotiopsis. In the greenhouse, a tip-dieback as well as a canker disease that began at pruning cuts on the stock plants was seen.Pestalotiopsiswas most commonly isolated from these plants. Isolated cultures of theLasiodiplodiaand thePestalotiopsistogether with several other often associated fungi, (includingAlternariaFusarium) were tested for pathogenicity on young mesquite plants. OnlyLasiodiplodiaandPestalotiopsisproduced cankers under the conditions tested when spores were applied using wound inoculation techniques.Pestalotiopsisrequired high wound inoculation techniques.Pestalotiopsisrequired high humidity and proved much less damaging compared toLasiodiplodia, which closely mimicked the field symptoms. Benlate was found to give the greatest growth inhibition of these fungal pathogens inin vitrofungicide tests. 相似文献
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Ian F. Snowball 《Geophysical Journal International》1997,130(3):704-716
The intensity of rotational remanent magnetization (RRM) acquired by single-domain greigite at a rotation frequency of 5 rps was combined with measurements of anhysteretic remanent magnetization (ARM) to calculate the effective biasing field ( Bg ) that produced the RRM. Samples of single-domain greigite had Bg values between -137 and -84 μT, and a MDFRRM of c. 80 mT. By contrast, a suite of natural and synthetic ferrimagnetic iron oxide samples, including single-domain magnetite and y Fe3 O4 tape particles, acquired Bg values between -3 and -14 μT, and MDFRRM ranged between 43 and 68 mT (when RRM was acquired). Multidomain magnetite did not acquire a RRM. Bg values at 5 rps were calculated from previously published data for magnetite particles of different grain sizes, which revealed a minimum Bg value of -24 μT and a MDFRRM of 57 mT for the finest fraction (0.2-0.8 μm in diameter). In a geological example, measurements of Bg and MDFRRM were used to detect the presence of greigite in a 4 m long Late Weichselian sediment core. Variations in inclination, declination and the intensity of the natural remanent magnetization (NRM) correlate with changes in magnetic mineralogy. 相似文献
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Neobuxbaumia tetetzo 《Journal of Arid Environments》1996,32(4):395-405
A supposed hybrid population betweenNeobuxbaumia tetetzoandCephalocereus columna-trajani(Cactaceae) in a semi-arid ecosystem at Zapotitlán de La Salinas, in the Mexican State of Puebla, was investigated by analysing number of ribs, number of areoles per cm and number of branches. Tests for equality of means using the Games and Howell method and Stepwise Discriminant Analysis, indicated that the number of ribs and number of areoles per cm supported our hypothesis for the existence of these naturally occurring hybrids, which are intermediate and distinct from the parental species. Other qualitative characteristics which distinguished hybrids and parental species are highlighted, and the possible meaning of the phenomenon is discussed. 相似文献
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E. Mndez 《Journal of Arid Environments》2007,68(4):678-682
The germination response of Denmoza rhodacantha (Salm-Dyck) Britton & Rose to seed scarification and different calcium concentrations was analysed. Both scarified and unscarified seeds were treated with two different calcium concentrations (1.74 or 6.36 meq l−1 calcium sulfate in distilled water). All treatments were conducted under a constant temperature (30 °C), and a photoperiodic regime of 12 h light and 12 h dark. Germination was initiated significantly sooner (3.6 days), and the rate of final germination was significantly higher (90.8%), for scarified seeds treated with a solution of 6.36 meq l−1 Ca compared with all other treatments (9.0–11.4 days and 3.6–6.8%, respectively). There were no significant differences among the treatments for the time in which 50% of final germination occurred (6.9–13.6 days). The results suggest that both factors, scarification and calcium concentration, favor germination of Denmoza seeds. 相似文献
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Prosopis pallida H.B.K. is one of the most economically and ecologically important tree species in the arid and semi-arid lands of the American continent. Sections of P. pallida were used to describe its wood anatomy and to determine whether annual rings were visible or not. Results showed that P. pallida has well-differentiated annual growth rings and is therefore suitable for dendrochronological studies. Tree ring chronologies correlate well with precipitation events related to El Niño Southern Oscillation phases. A master chronology for the northern area of Peru was built with these data, and some physiological derivations from the anatomy of P. pallida wood are discussed. 相似文献
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In the field of phylogenetic analyses, the rbcL gene encoded large subunit Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco, EC4.1.1.39), which plays a crucial role in the process of photosynthesis for most terrestrial plants, has been considered to be conserved; however, recent controversy regarding rbcL conservation has appeared since it was proposed to be under natural selection within all principal lineages of land plants. In this study, by examining the variation of DNA and protein sequences among 17 species in the family Tamaricaceae, three nonsynonymous mutations were identified to be under positive selection. The favored sites were located in the alph-helix domains of Rubisco, with decreased hydrophobicity and increased entropy, which could facilitate CO2 penetration into the active site of Rubisco. We also found that the expression level of rbcL in different genotypes of Reaumuria soongarica shifted in response to various stresses such as drought, temperature, salt, and light. This study not only sheds light on the functional/structural features of Rubisco in the evolution scenarios from C3-like into C4 in Tamaricaceae but also provides useful information on directing genetic performance to enhance photosynthesis efficiency of desert plants for sustaining fragile desert ecosystems; furthermore, it promotes the ability to cope with desert aridification and global warming. 相似文献
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A field experiment was conducted to examine the effects of large-scale climatic changes on biomass and biomass allocation in Leymus chinensis on an 11 longitude gradient along the North-east China Transect (NECT) in 2000. Ten sites, selected for plant sampling along the gradient, experienced approximately uniform theoretical radiation, but differed in precipitation and geographical elevation. The total biomasses, vegetative shoot biomass and reproductive shoot biomass of the species increased from the west to the east with the decrease of aridity or the increase of precipitation, but that of rhizome biomass decreased in the spatial ranging from 116° to 120° E. Vegetative shoot biomass allocation increased from the west to the east along the gradient; rhizome allocations, however, dropped significantly. Unlike those of rhizome and vegetative shoot, reproductive shoot biomass allocations at the two ends were remarkably lower than that in the middle of the gradient. In general, the total and component biomass and their allocations showed strong correlation with precipitation or aridity index along the gradient. 相似文献
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Ari Ben-Menahem 《Geophysical Journal International》1982,70(2):535-537
Summary An extension of the Love-Larmor theory to a low-loss unelastic earth model, leads to the surprisingly simple approximation
where τs = 447.4 sidereal day is the static wobble period, τR = 306 sidereal day is the rigid-earth wobble period and τw = 433 sidereal day is the observed Chandler period. Q W , Q μ are the respective average Q values of the wobble and the Earth's mantle at τW . The known numerical factor F is only slightly dependent on the Earth structure. 相似文献
where τ
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G. M. Brown 《Geophysical Journal International》1986,86(2):467-473
Summary. Analysis of geomagnetic data has shown that the superposed northward magnetic field, which reduces the S q ( H ) amplitude at northern mid-latitude stations on Abnormal Quiet Days, and increases the amplitude at stations on the equatorward side of the S q focus, builds up in amplitude over four to five days before the AQD occurs, and subsides over a similar period after the AQD. It is inferred indirectly that the azimuthal component By of the interplanetary magnetic field varies similarly. Data for the opposite meridian show that the imposed field reverses to a southward direction at lower latitudes. The inferred currents to account for these fields are believed to flow in the ionosphere, but to arise from magnetospheric electric fields induced by the solar wind-transported IMF. 相似文献
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KATHY J. LICHT WENDY L. CUNNINGHAM JOHN T. ANDREWS EUGENE W. DOMACK ANNE E. JENNINGS 《Polar research》1998,17(2):203-216
To compare north and south polar marine paleoenvironments over the last 30,000 years, comparable chronological (radiocarbon) records must be developed and refined. Many areas in the polar regions do not preserve marine carbonates (foraminifera, mollusks), and thus age determinations, of necessity, are based on the acid-insoluble organic (AIO) fraction of the sediment. Although AIO ages are problematic and rarely used in the Arctic, they provide reasonable and consistent chronologies for the Ross Sea, Antarctica. AIO dates are meaningful in the Ross Sea because there are relatively high levels of productivity, good preservation of marine biogenic material in the sediment, and little input of terrigenous sediment and old/dead carbon. Event stratigraphy based upon proxy records of biogenic silica and δ13 C can be used to assess the reliability of the AIO dates and surface age corrections. Reconstructed time-series of changes in the biogenic silica content of cores from the western Ross Sea show apparent similarities with the 'classic'deglacial climate sequence of the northern North Atlantic. Once the absolute ages of the antarctic AIO dates are constrained by independently dated records to validate surface age corrections, it will be possible to directly compare the timing of events such as ice-rafting events in the sedimentary record. 相似文献
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The alien grass Bromus tectorum dominates stable annual-plant communities that have replaced native shrub-perennial grass communities over much of the semi-arid western United States. We conducted field competition experiments between B. tectorum and a native grass, Elymus elymoides, on two sites to determine the effects of B. tectorum competition on perennial grasses, and the role of B. tectorum competition in the stability of B. tectorum-dominated communities. B. tectorum competition acting on seedling-stage E. elymoides plants greatly reduced first-year relative growth rates and biomass which, in turn, reduced second-year survival, biomass, and flowering. However, B. tectorum competition acting on older E. elymoides plants had much less effect, which may help to explain why intact perennial-plant communities are resistant to B. tectorum invasion. At the drier site, direct effects of B. tectorum competition were less, but competition and drier habitat combined to produce greater E. elymoides mortality. 相似文献
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M. Thiam S.A. AtteynineS. Traoré J.-M. DuplantierD. Maurel B. Sicard 《Journal of Arid Environments》2011,75(11):998-1007
Following the southward shift of rainfall isolines in the Sahel at the end of the 1960s, Gerbillus nigeriae appeared in northern Senegal in the mid-1990s, and two resident Gerbillidae (Taterillus pygargus and Taterillus gracilis) subsequently declined. We investigated the causal role of the capacity to conserve water in such climate-related shifts in the distribution of these Gerbillidae by comparing the effects of a water-poor diet on the water-efflux rate (W−out) of freshly trapped adults pre-acclimatized to a water-rich diet. During the 12-day period of water restriction in all species, 30-50% of individuals became hyperactive and showed greater weight loss and higher W−out than the remaining inactive individuals. Such emergence of migratory strategists within populations could accelerate the expansion of G. nigeriae. On a water-poor diet, T. gracilis showed a lower capacity to conserve water (higher W−out) than T. pygargus and G. nigeriae, in both inactive (W−out = 44.5 ± 1.8 vs 29.6 ± 0.8 vs 27.4 ± 0.7 ml kg−0.82.day−1, respectively) and hyperactive individuals (W−out = 60.4 ± 1 vs 45.4 ± 0.7 vs 44 ± 0.8 ml kg−0.82.day−1, respectively). We propose that the capacity to conserve water accounted for both expansion of G. nigeriae and decline of T. gracilis, whereas competition between T. pygargus and G. nigeriae could account for the decline of T. pygargus. 相似文献