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1.
M. A. A. Gadallah 《Journal of Arid Environments》2000,44(4):451
Three-week old soybean (Glycine max) plants were subjected to a factorial combination of four regimes of soil matric water potential (ψm=−0·03, −0·5, −1·0 and −1·5 MPa), two levels of supplementary Zn (O and 20 mgl−1) and two levels of foliar IAA application (O and 10 mgl−1). Under control conditions (no Zn, no IAA), increasing soil drying progressively retarded shoot and root growth (length and dry mass production), reduced leaf relative water content (RWC) and decreased the contents of chlorophyll (Chl) and shoot soluble sugars (SS), but increased soluble sugar content of roots and lowered osmotic water potential of shoots and roots (osmotic adjustment). Total free amino acid (TAA) content increased in shoots but decreased in roots whereas contents of soluble proteins (SP) decreased in shoots and roots. The effect of water stress was statistically significant (p<0·05) and had a major effect (as indicated by η2values) on leaf RWC, shoot and root dry masses and osmotic potential. Supplementary Zn improved root growth at all levels of stress and shoot growth under severe stress. Improvement of growth was positively correlated with the internal tissue Zn concentrations (r=0·91 and 0·86 for shoot and 0·94 and 0·82 for root length and dry mass respectively). Exogenous IAA raised (p<0·05) RWC, Chl, DM (slightly), root SS, and SP, whereas shoot TAA was lowered. Effects on root TAA and shoot SS were more complex: they were lowered at zero stress and raised under severe stress. IAA and Zn in combination had additive effects on Chl, growth and osmotic potential, but their combined effects on SP and TAA were more complex. It is concluded that the treatment of soybean plants grown under conditions of low soil water potentials and Zn deficiency with Zn and IAA solutions counteracted the deleterious effects of stress, especially at high stress levels, and helped stressed plants to grow successfully under these adverse unfavourable conditions. 相似文献
2.
A greenhouse experiment was conducted to investigate the effects of moderate (14 cm) vs. severe (7 cm) defoliation on tiller recruitment and mortality within the interior and on the perimeter of weeping lovegrass (Eragrostis curvula) tussocks. Tiller number per marked shoot within the interior was significantly greater in plants defoliated at 14-cm stubble height than at 7-cm stubble height (2·37 vs. 0·43, p<0·05) 28 weeks after defoliation; likewise, tiller number per marked shoot was also greater on the perimeter of tussocks in the higher stubble than the lower stubble defoliation treatment (5·10 vs. 2·03, p<0·05). Tiller natality increased significantly 4 weeks after defoliation except for tillers cut to 7-cm stubble height within the interior of tussocks where tiller natality reached a peak at 4·5 weeks after defoliation. During the later stages of canopy development, tiller numbers per marked shoot gradually declined as tiller mortality increased. Tillers began senescing 13 weeks after defoliation, and the senescence rate was 52% greater in the 7-cm stubble height treatment than in the 14-cm stubble height treatment (2·33 vs. 1·53, p<0·0001). Within the interior of tussocks, number of the marked tillers more than doubled under the 14-cm stubble height treatment, whereas the plants lost 57% of the monitored tillers under the 7-cm stubble height treatment. We concluded that the central dieback process in weeping lovegrass is accelerated by severe defoliation. 相似文献
3.
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
4.
The columnar cactus Polaskia chende, endemic to Central Mexico, occurs in the wild and in silviculturally managed populations where artificial selection for better edible fruits operates by sparing and favouring desirable phenotypes during vegetation clearance. Wild and managed populations were compared in morphology and reproductive biology to analyse if human selection has influenced phenotypic divergence, if it has modified breeding systems and if reproductive isolation exists between them. Fruits from managed populations were larger (6·36±0·17 cm3), heavier (19·62±1·32), sweeter (9·07±0·25 °Brix), and with thinner peel (2·09±0·13 mm) than those from wild populations (5·77±0·18 cm3, 15·73±0·85 g, 8·23±0·31 °Brix, and 2·58±0·14 mm, respectively). Both population types bloom synchronically, show diurnal anthesis, with bees as the most likely pollinators, and have breeding system predominantly self-incompatible. Spatial and temporal barriers to pollen exchange between wild and managed populations are unlikely, and morphological differences would be related with an ongoing process of artificial selection. 相似文献
5.
The natural abundance15N/14N method was used to estimate the influence of silvicultural and P fertilization treatments on N accretion, N2fixation and N partitioning among tissues in a mature mesquiteProsopis glandulosavar.glandulosastand in Texas. The silvicultural treatments consisted of understory removal, herbicide treatment of brushy resprouts, thinning trees to single stems and 100 kg ha−1P fertilization. The trees had a mean basal diameter of 17·8 cm with 8 to 35 cm range. The stand was slow growing with the increase in dry matter ranging from 0·465 Mg ha−1year−1to 0·701 Mg ha−1year−1for the 8 years after the treatments were applied. N accretion after 8 years ranged from 3·1 kg ha−1year−1to 4·4 kg ha−1year−1.Due to the range in δ15N of the leaves, twigs, branches and trunk, we used the weighted (by biomass) average δ15N per tree in calculations of the percent N derived from N2fixation (%Ndfa). There was considerable variability in δ15N of the reference plants, i.e. from 3·3 to 5·9. In contrast there was low variability in the background δ15N of nearby soils (7·0±1·0). As the total above-ground biomass δ15N of a grass grown outside the influence of mesquite (7·8±0·58) had the same δ15N as the soil (7·5±1·0), we used the grass outside the influence of mesquite and the weighted tree mean δ15N to calculate % of N derived from N2fixation.The decrease in intraspecific competition by thinning multistemed trees to single stemmed trees was the only treatment that significantly (p= 0·0001) increased growth. Interspecific competition, i.e. understory removal, did not increase growth. There were no significant differences in total N production or N fixation among treatment means. The most striking result was the highly positive correlation between tree δ15N and total N per tree and biomass per tree (R2= 0·90,F= 164·4, df. = 18, mean square error (MSE) = 0·155,p= 0·0001). This implies that the younger trees colonizing infertile soils relied more heavily on N2fixation than larger trees which accumulated 1200 kg ha−1more N under their canopies. The percentage N derived from N2fixation ranged from 63 to 73% in the various treatments. Despite the high percentage of N derived from N2fixation, the N2fixation of the stand was very low, i.e. 1·98 to 2·80 kg N ha−1year−1, due to the low growth of the stand. We believe that comparisons of the whole tree weighted δ15N to background soil δ15N provides a more reasonable approach to estimate % N2fixation than comparisons of leaves of fixers and reference plants. 相似文献
6.
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
7.
The objectives of this study were to determine the composition, density and spatial distribution of the soil seed bank of woody species, as well as their regeneration pattern in two different land use systems, controlled (ranch) and open grazing, in an Acacia woodland of the Rift Valley in Ethiopia. We also compared the species composition of the soil seed bank and the above-ground vegetation to find out if differences exist in the soil seed bank and advance regeneration between the two land use systems. The germination requirements of seeds of the woody species were also investigated under laboratory conditions. Acacia senegal, Acacia seyal, Acacia tortilis, Dichrostacys cinerea and Balanites aegyptiaca were encountered in the above-ground vegetation in both systems. Seeds of only A. tortilis (90±32 seeds m−2) from the ranch, and A. senegal (5±3 seeds m−2) and A. tortilis (72±34 seeds m−2) from the open system were found in the soil seed bank along transects with patchy horizontal pattern. The two systems were not significantly different in density of soil seed banks of A. senegal andA. tortilis . Jaccard's similarity index showed that only a few woody species were common in the soil seed flora and above ground vegetation. However, all of the species accumulated seeds (58±43–331±130 seeds m−2) in/on the soil under the canopy. Very large numbers of seeds of A. tortilis (19382±9722 seeds m−2) and D. cinerea (1278±494 seeds m−2) were also found in barns. Most of the seeds recovered from the soil samples (60–80%) were found in the litter layer. Acid and mechanical scarification improved legume germination (36–99% and 60–99%, respectively) over boiling water (0–48%). Treatment means differed significantly for all the legumes (p<0·001) but not for Balanites. Height and diameter class distribution of regeneration of A. tortilis and D. cinerea in both systems and A. senegal in the open system had a negative exponential correlation (rs=−0·5, −0·25 and −0·86, respectively). A. seyal and B. aegyptiaca showed poor regeneration. Horizontal distribution of advance regeneration of all the species was patchy. Advance regeneration of A. seyal, A. tortilis and B. aegyptiaca were not significantly different, while that of A. senegal and D. cinerea were significantly different between the two systems. Poor representation of species in the soil seed bank along transects and in the different height and diameter classes may be attributed to the low density of mature trees as well as the mode and strategy of seed dispersal. Ungulate and wind dispersed species (e.g. A. senegal, A. tortilis and D. cinerea) were highly favoured. Patchiness in the distribution of seeds and advance regeneration was also a result of endozoochory. Dispersal of non-ungulate dispersed seeds (A. senegal, A. seyal and B. aegyptiaca) was restricted to the canopy zone. Piles of seeds ofA. tortilis and D. cinerea that were found in barns were a result of consumption of their pods by cattle. High concentration of seeds in the litter layer may be due to low soil disturbance and larger size of seeds. The height and diameter class distribution of A. senegal (in the open system), A. tortilis and D. cinerea also indicated that the species have good regeneration. Results from the germination tests indicated that seeds of the legumes require pre-sowing treatments to give a rapid, uniform and improved germination. Intervention through artificial regeneration should be employed to improve the density and regeneration capacity of those species with hampered regeneration at both systems. 相似文献
8.
The water status of Terminalia brownii seedlings was assessed in relation to incident microclimate and initial irrigation treatments, during establishment at Olorgesailie in the Rift Valley of Kenya. Experimental treatments involved incorporation of a water-absorbing polymer with the root systems of the plants during establishment, and repeated irrigation, in a factorial design. The maximum photosynthetically active radiation of over 2500 μmol/m2/s recorded during the first 9 days after outplanting was associated with air temperatures of up to 47·4°C, and leaf-to-air vapour pressure deficits (VPDs) of up to 8·04 kPa. Water potentials declined to a minimum of -3·7 MPa, 9 days after outplanting, indicating severe water deficits. Stomatal conductances were generally below 0·2 cm/s, reflecting a high degree of stomatal closure. However, conductances of over 1·3 cm/s were observed on the 6th day after outplanting, associated with VPDs below 1·5 kPa. These relatively high conductances were restricted to plants which had received irrigation; overall, irrigation was found to significantly increase stomatal conductance on three of the four measurement days. Although the application of synthetic polymers increased stomatal conductances on two of the measurement days, the effects were very slight (treated means 0·02-0·03 cm/s higher than controls). These results indicate the severity of the transplant shock in semi-arid sites for seedling water status, and imply that initial irrigation treatments are more likely to increase establishment rates of tree seedlings than application of synthetic polymers. 相似文献
9.
The profile distribution of total, diethylene triamine penta-acetic acid (DTPA)- and 0·1
HCl-extractable Fe and Mn were determined in 12 pedons formed on three contiguous sand dunes in the semi-arid savanna of Nigeria. The total Fe and Mn contents varied from 100 to 3750 and 40 to 11,375 μg g−1, respectively. Values of 0·1
HCl-extractable Fe and Mn varied from 8·0 to 123 and 1·5 to 43·5 μg g−1, respectively. The corresponding values of DTPA-extractable Fe and Mn were 4·5 to 16·0 and 1·0 to 38·8 μg g−1. Total Fe and Mn correlated significantly with clay in nearly all the dunes (p≤ 0·01) but were not significantly correlated with organic matter. The 0·1
HCl-extractable Mn had a positive significant correlation with soil pH (r= 0·58*) in Illela dunes but a negative significant correlation with pH in the Sangiwa dunes (r= −0·75***). The values of extractable Fe and Mn in the sand dune soils are above the critical limits reported in other literature, thus deficiencies of these micronutrients do not pose a problem to crop production in the study area. 相似文献
10.
The germination behaviour of five Helianthemum species (H. almeriense, H. appeninum, H. cinereum, H. hirtum, H. squamatum) has been studied under controlled conditions. Constant 15, 20 or 25 °C and alternating 25/15 °C temperature regimes and 16/8 h light/dark photoperiod conditions were used. Presowing treatments applied were manual scarification, boiling water, hot water, dry heat and sulphuric acid. Germination values recorded were final germination percentage and germination rate expressed as days to reach 50% of the final germination percentage (T50). Incubation temperature had no significant effect on final germination percentage for untreated seeds of the five Helianthemum species. However, variation due to temperature was significant for scarified seeds, with the lowest germination percentage attained at 25 °C. In all Helianthemum species studied, the highest germination percentages were obtained by manual scarification of seeds. Germination rate of scarified seeds decreased as germination temperature increased. The different presowing treatments investigated allowed some germination in some species, but none were any better than manual scarification. The high germination among most species studied, following mechanical rupture of the seed coat, shows that the mechanism of dormancy lies in the seed coat. The physical dormancy caused by impermeable seed-coat appears to be the main reason of poor germination of untreated seeds of Helianthemum species studied. 相似文献
11.
Uromastyx philbyi 《Journal of Arid Environments》1996,33(4):457-461
The standard metabolic rate ofUromastyx philbyiwas measured at 20–40 °C, using constant pressure manometric respirometers. Standard metabolic rate was mass-dependent. Values for the mass exponent ‘b’ ranged from 0·75 at 20 °C to 0·82 at 40 °C. Standard metabolic rate increased as temperature increased with high Q10values at low temperatures (20–25 °C). Low standard metabolic rates in this species are probably an adaptation to herbivory in hot desert environments. 相似文献
12.
We assessed the geographic distribution of Tillandsia lomas in northern Chile, from Arica (18°20′S) to the Loa river (21°25′S) and discussed the factors that might potentially underlie the observed patterns. We carried out extensive field survey complemented with aerial surveys and analysis of specimens deposited in herbaria. We detected over 30 Tillandsia stands most of which corresponded to the species Tillandsia landbeckii and can be grouped in 10 large systems. Other two species were also detected Tillandsia marconae and Tillandsia virescens, both of which show a restricted distribution in the area. Our results provide evidence on the wide distribution of Tillandsia lomas in northern Chile and its association with fog corridors. 相似文献
13.
Variation in growth, physiology and ionic relations patterns of Allenrolfea occidentalis, a perennial halophyte of dry habitats, was studied under field conditions from May 1996 to November 1997. An A. occidentalis community has a characteristic soil pH of 7·3–8·3. During the two years, the population was exposed to great variations in soil salinity, from 29 to 146 dS m−1, and soil moisture, ranging from drought (9·2%) to wet (19%). The salt concentrations were significantly higher in the surface soil layers than in the subsurface layers. Seasonal changes in dry weight are directly related to soil salinity stress. Allenrolfea occidentalis had greater growth and biomass production under saline conditions. Na+and Cl−ions were accumulated in plant tissues in much greater amounts than K+, Ca2+, and Mg2+. Soil salinities were significantly reduced at the end of the growing season. Water potentials of the shoots decreased significantly with increasing salinity. The plant (Fv/Fmratio) was more affected by salinity and irradiation levels during the summer period. 相似文献
14.
Extraction and characterization of mucilage in Opuntia spp. 总被引：1，自引：0，他引：1
The cactus pear (Opuntia ficus indica) mucilage is an interesting ingredient for the food industry because of its viscosity properties. We studied the conditions for the extraction and precipitation of the plants mucilage. Extraction conditions were: pad/water ratios (1:51:7), extraction temperature, (40±2 and 16±2 °C) and extraction time (4, 8 and 16 h). For the precipitation of the mucilage two types of alcohol (ethanol and isopropyl alcohol) and two water/alcohol ratios (1:3 and 1:4) were used.No differences were found in any of the measured variables among the different extraction or precipitation methods.The average mucilage yield after drying was 1.48% based on fresh weight (f.w.) and 19.4% based on dry weight (d.w.).The dried mucilage had in average 5.6% moisture; 7.3% protein; 37.3% ash; 1.14% nitrogen; 9.86% calcium and 1.55% of potassium. The colour analysis showed a high L* value and the chromatic co-ordinates were in the yellow-greenish spectrum.The use of isopropyl alcohol is recommended in ratio 1:3, since its commercial value is lower in comparison with ethanol. 相似文献
15.
Robyn Adams 《Journal of Arid Environments》1999,43(4):437
The effects of temperature, water stress, hydration–dehydration cycles and seed priming on the germination of Callitris verrucosa and Callitris preissii, two Australian semi-arid coniferous tree species, were investigated. Optimum germination occurred at 18°C, with a minimum germination time of 8–9 days for both species. At this temperature, germination was inhibited at osmotic potentials lower than −1·0 MPa, but the capacity to germinate at low osmotic stress increased as the temperature decreased. Seed priming and hydration–dehydration cycles did not reduce seed viability, and Callitris seeds appear to retain the physiological changes induced by short-term hydration, as the time to the onset of germination was decreased to about 3 days. The capacity of Callitris seeds for incremental germination is likely to increase overall germination success in a low rainfall environment. 相似文献
16.
Vegetation, microclimate, seedling frequency, freezing tolerance, and cold acclimation were compared for seedlings of Artemisia tridentata collected from 1775, 2175, and 2575 m elevation in the eastern Sierra Nevada, California. Data were used to test the hypothesis that ecotypic differences in stress physiology are important for seedling survival along gradients from desert to montane ecosystems. The vegetation canopy cover and A. tridentata seedling frequency were greatest at 2575 m, compared to 1775 and 2175 m. Snow cover ameliorated temperatures near the soil surface for part of the winter and depth varied across elevations. Freezing tolerance was compared for seedlings maintained in growth chambers at day/night air temperatures of 25°C/15°C. The temperature at which electrolyte leakage and Photosystem II function (FV/FM) from leaves were half-maximum was approximately −13·5°C for leaves of seedlings from all three elevations. Shifting day/night air temperatures from 25°C/15°C to 15°C/5°C initiated about 1·5° of acclimation by plants from all three altitudes, with seedlings from the highest elevation exhibiting the greatest acclimation change. Measurements of ambient air and canopy temperatures at the three elevations indicated that wintertime average low temperatures were consistent with the measured degree of freezing tolerance. At small spatial scales used in this study, pollen and seed dispersal between study sites may have precluded resolution of ecotypic differences. Patterns of freezing tolerance and cold acclimation may depend on a combination of mesoclimate and microclimate temperatures, canopy cover, snow depth, and snow melt patterns. 相似文献
17.
沙生濒危物种霸王的高频植株再生研究 总被引：3，自引：3，他引：0
实验选用霸王无菌苗的茎尖、子叶、下胚轴和胚根作为材料,研究霸王不同外植体的离体培养技术。结果表明,霸王茎尖是诱导丛生芽的良好外植体,而子叶、下胚轴和胚根是诱导愈伤组织的良好外植体;霸王茎尖的最适增殖培养基是:MS+6-BA 5.0 mg·L-1+NAA 1.0 mg·L-1;最适生根培养基是:MS+IAA 1.5 mg·L-1;最适愈伤组织诱导培养基是:MS+6-BA 1.0 mg·L-1或MS+6-BA 1.0 mg·L-1+NAA 0.5 mg·L-1。沙质基质为霸王组培苗过渡的最佳基质。 相似文献
18.
Factors affecting temporal and spatial variations of growth were studied in cirio, a succulent often surpassing 10 m in height. Measurements were obtained for intervals of 3–93 years at 14 sites in Baja California. Height tended to be asymptotic but total plant length (i.e. including all succulent stems) increased in linear relation to trunk diameter. Growth in length showed an overall average of 4·6 cm year−1 but ranged from 0·3–16·7 cm year−1 (annualized from data for intervals >34 year). Most of the variation was among individuals, but some differences between sites were also significant. Growth was clearly and strongly related to size only for individuals less than 1 m in height. Repeated measures on the same individuals showed that the autocorrelation of growth was about 0·8 between intervals of 3 or more years. Differences among individuals were related to physiographic position, the presence of caliche and the density of neighboring plants, which together explained 43% of the variation. We discuss the implications of these results for age estimates, indicators of site quality and studies of similar plants. 相似文献
19.
David R. Gaylord Franklin F. Foit Jr. Jeffrey K. Schatz Angela J. Coleman 《Journal of Arid Environments》2001,47(4):403
Sedimentary deposits from the Smith Canyon dune field, south-central Columbia Basin, Washington, U.S.A. document climatically-influenced Late Pleistocene and Holocene aeolian and fluvial deposition in a region impacted by glacial outburst floods and tephra falls. The depositional history is summarized by five environmentally distinctive and climatically sensitive sedimentary units (temporal limits estimated): Unit 1 (c. 15·5–8 ka), pedogenically altered glacial outburst flood and minor aeolian silt and clay; Unit 2 (c. 8–6·9 ka), fluvial and minor aeolian sand; Unit 3 (c. 6·9–6·8 ka), flood-induced fluvial sand with gravel-sized tephra clasts; Unit 4 (c. 6·8–3·9 ka), aeolian dune sand; Unit 5 (c. 3·9 ka to present), pedogenically altered, stabilized dune sand. Estimated age ranges are based on stratigraphic position, tephrochronology, and correlation with temporally constrained strata from elsewhere in the region. 相似文献
20.
Effects of salinity, temperature and light on germination of invasive Prosopis juliflora (Sw.) D.C. 总被引：1，自引：1，他引：1
Effects of salinity, temperature, light and their interactions on the rate and final percentage of germination were evaluated for the invasive shrub Prosopis juliflora, grown under arid environmental conditions of the United Arab Emirates (UAE). Seeds that were not treated with NaCl germinated well in a wide range of temperatures and in both full light and complete dark. Seed germination decreased significantly with the increase in both NaCl concentration and temperature. Optimal germination percentage occurred at 25 °C. The inhibitory effect of high salinity on final germination percentage was greater at 40 °C than at 15 and 25 °C. Germination was completely inhibited in 400 mM NaCl at 40 °C and in 600 mM NaCl at 25 °C. However, germination rate was significantly greater at 40 °C than at 15 and 25 °C in lower salinities and the reverse was true at higher salinities. Germination in light was significantly greater than in the dark at lower salinity levels and high temperature. 相似文献