共查询到20条相似文献，搜索用时 31 毫秒
1.
Although arid environments are often considered among the least invaded terrestrial biomes, the impacts of exotic plant species can be severe and long lasting. Bromus rubens (red brome) is an exotic annual grass species in the Mojave Desert known to outcompete native plant species, alter habitat, and promote accumulation of fuel that contributes to increasing fire frequency and severity. We assessed longevity of the exotic B. rubens seeds in the soil by burying seeds at four depths (0, 2, 5, and 10 cm) and recovering seeds 6, 12, 18, and 24 months after burial. Seed viability was reduced with greater burial depth and greater time since burial. A relatively small proportion of seeds retained viability for two years, suggesting that while the B. rubens seed bank can be large, it is relatively short-lived. Although B. rubens apparently relies more on the annual production, dispersal, and germination of seeds than on a long-lived seed bank for its annual recruitment, the numerous seeds produced by individual plants indicate that even a small proportion of seeds remaining viable for more than a year can aid recruitment from the seed bank and is an important factor in understanding population dynamics. 相似文献
2.
We researched the soil seed bank dynamics of Thymus funkii subsp. funkii, a gypsovag shrub endemic to the southeastern Iberian Peninsula, to determine possible reasons for low recruitment in isolated populations growing on crusted gypsum soils. Recruitment-restriction hypotheses involving main factors in the seed bank dynamics were analysed, and a diagrammatic dynamics model drafted from a population perspective. Viable seed production averaged 362 per plant. Seed shadows resulting from primary dispersal were concentrated under the mother plant. There were two thyme-seed predators: coleopteran larvae (pre-dispersal phase) and Messor bouvieri ants (pre- and post-dispersal phases), which predated 16.4% and 3.8% of population yield, respectively. However, ants may simultaneously contribute to the spatial secondary dispersal, since they lost a small fraction of seeds they harvested. Seeds showed innate physiological dormancy to high summer temperatures, although this disappeared rapidly. The response of germination to other temperature × light conditions was wide and rapid. No permanent seed bank was detected in the soil. Seeds buried in the upper soil layer (2 cm) germinated highly and fast. In contrast, a significant fraction of seeds buried deeply (8 cm) remained viable for over one year. Germination in the field accounted for only 1.0% of the seed output, and seed death due to pathogen attack and aging was also low (3.0%). Seedling emergence was confined to autumn and showed a high correlation with total plant cover, irrespective of plant species. Seedling survival was very low. The small spatial correspondence between primary dispersal and seedling emergence patterns may reflect the importance of secondary dispersal in T. funkii seed bank dynamics. Hypotheses and consequences of such horizontal seed movements for conservation management are discussed. 相似文献
3.
S. Redondo-Gómez L. Andrades-MorenoR. Parra E. Mateos-NaranjoA.M. Sánchez-Lafuente 《Journal of Arid Environments》2011,75(3):309-312
Cyperus capitatus Vandelli (Cyperaceae) is distributed in coastal sandy habitats and mobile dunes of south Europe. Its seed germination ecology is not known, despite its potential to be used in re-vegetation projects. Laboratory experiments were conduced to assess the effects of salinity, light regime, cold stratification and burial on seed germination of this species. Overall, increasing salinity delayed germination, increased seed dormancy and mean time to germination (MTG), and reduced final germination percentage, inhibiting it completely above 1% of salinity; although it did not affect seed viability. C. capitatus seeds exhibited their greatest germination at levels between 0 and 1% in non-stratified seeds, and between 0 and 0.5% for stratified seeds. Thus, the effect of salt was greater for stratified seeds at 5 °C. Germination in light/darkness conditions was similar to that in full darkness. Finally, burial in sand of C. capitatus seeds appeared to have a significant effect on cumulative percentage of germination. Seeds buried at depths greater than 2 and 3 cm showed a lower germination success than those on sand surface or buried at shallower depths. Burial also affected the beginning and speed of seed germination. 相似文献
4.
Seedling recruitment in a semi-arid steppe: The role of microsite and post-dispersal seed predation 总被引：2，自引：0，他引：2
Grasslands dominated by Stipa tenacissima are important ecosystems in the arid and semiarid climates of western Mediterranean, where they have originated by degradation of open dry forests and shrublands. At present, although the level of exploitation in these ecosystems is very low, succession processes seem to have stopped. In this study, we explore the role of microsite and post-dispersal seed predation on the seedling emergence of two species from advanced successional stages (Rhamnus lycioides, Quercus coccifera), three species from degraded stages (Cistus clusii, Helianthemum violaceum, Anthyllis terniflora), and of the dominant species (Stipa tenacissima). Seeds of these species were sown in plots divided into two microsites: (i) under tussocks of S. tenacissima and (ii) in the bare soil between tussocks. Soil moisture was significantly higher in the tussock microsites. The interaction observed between microsite and time, reflected the slower drying process under tussocks. Seed predation was in general high and differed significantly between species but not between microsites. Q. coccifera was especially affected by predation. The only germination detected in gap areas was that of H. violaceum. The results pointed to a direct facilitative effect of tussock grass on the germination in R. lycioides (20.4±8.0%) and S. tenacissima (41.3±5.7%) while the corresponding figures for bare ground were 0%. These results suggest that the recovery of potential vegetation in this ecosystem is not possible or, at least, is very slow because the residual shrub patches do not generate a sufficient number of seeds able to disperse to favorable germination microsites. S. tenacissima may act as facilitator of seedling recruitment if there is a supply of diaspores. 相似文献
5.
We studied current recruitment failure of Dobera glabra, an important famine-food throughout the dryland parts of the Horn of Africa. The species has previously been found to have recalcitrant seeds, a strategy not common for plants in dryland areas. We experimentally tested (1) how germination capacity of D. glabra is affected by seed form, storage period and moisture under nursery conditions, and (2) how seed predation by vertebrate herbivore and seed exposure at germination site affect germination under field conditions in northern Afar rangelands, Ethiopia. D. glabra seeds that received either mulching or supplementary watering (3 days/week) had a higher germination success than controls. The seeds are probably desiccation sensitive since stored seeds had poor germination performance compared to fresh seeds. Seeds in the rangeland plots protected from herbivores had significantly higher germination success compared to open plots. Our findings demonstrate that seed predation and moisture limitation highly reduced the germinability of the recalcitrant D. glabra seeds, indicating that the species might have persisted due to past wetter periods and low herbivore density in dry environments. 相似文献
6.
Calligonum 《Journal of Arid Environments》2002,51(4):603
A greenhouse study was conducted to determine the effects of sand burial on seed germination and seedling emergence of ten Calligonum L. species. The results suggested that the deeper the seeds in sand, the lower and slower their germination and seedling emergence. Seedling emergence occurred from a maximum depth of 12 cm with most seedlings emerging from 2 and 4 cm depths. The percent seedling emergence, number of days of first emergence, percent seed germination and percent of dormant seeds were significantly affected by different species and burial depth. There was a significant positive correlation between the number of days to first emergence and burial depth. Both mean percent germination and percent seedling emergence were negatively correlated with depth significantly for each species. 相似文献
7.
HOU Yurong KE Mei WEI Peng LAN Jiyong LI Chao KANG Shuai KAYRAT Aldeyarhan WANG Lu 《资源与生态学报(英文版)》2022,13(2):312-318
The mining of placer iron ore greatly influences the surrounding desert grassland. In Agdala Town, Qinghe County, Xinjiang, the soil seed bank is severely damaged, and the utilization and productivity of desert grasslands are almost zero, which seriously affects the safety of the ecological environment and the development of local animal husbandry. It is very important to supplement soil seed banks to enhance the species composition of desert grasslands after ecological restoration. In this study, the effects of the seed bank, species composition, and seed burial depth on the seedling emergence rate at placer iron ore site before and after artificial seed bank replenishment were compared using the germination tray method. The original soil seed bank in the study area contained only four species, which were all annual plants. The dominant species were Salsola ruthenica and Corispermum orientale, and the soil seed bank density was very small. The emergence regularity of the soil seed bank was closely related to water content, and the emergence of annual vegetation was explosive. Seed burial depth affected the emergence rate of perennial grass, and we determined that a burial depth of 0-5 cm was the most effective for emergence. This indicates that seedling emergence of artificially supplemented soil seed bank can be completed within 7 days if the sowing depth is appropriate; sowing depths greater than 5 cm affect seed germination. These findings provide a basis for selecting species to populate large areas. 相似文献
8.
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
9.
Biological invasions are a major threat for natural ecosystems. Deserts are characterized by their scarce, highly variable rainfall and thus considerably susceptible to invasions, especially by annual plants that can quickly capitalize sporadic rainfall events. In this study we evaluated the potential of an invasive winter-annual species native to the Mediterranean region (Schismus barbatus) to invade a summer-rainfall desert in the Central-Northern Monte Phytogeographical Province, Argentina, where the native annual flora is mainly composed of summer species. We recorded the number of germinated seeds from soil samples collected in four seasons (during one year) coinciding with four important life-stages of Schismus (pre-germination, post-germination I and II and post-dispersal), and contrasted our results with data obtained from the literature. Almost 33,000 Schismus seeds were estimated to germinate per m2, and about 90% percent of them germinated from samples collected in the pre-germination stage. Compared to deserts in USA and Australia, where Schismus has been a successful invader, the density of germinated seeds we observed was especially high even though the amount of rainfall for the vegetative period of Schismus was considerable lower. Our results suggest that S. barbatus has a great invasive potential in the Central-Northern Monte. The low number of annual plant populations that are able to compete for highly variable cool-season rains may be a key feature determining the invasibility of these deserts during the winter. 相似文献
10.
Joshua tree (Yucca brevifolia) is a charismatic symbol of the Mojave Desert. Despite its familiarity, we know little about the reproduction of this species, including mechanisms of seed dispersal. Here we examine mechanisms of seed dispersal and resulting seed fate. We experimentally tracked fruit and seed removal and followed the fates of Joshua tree seeds using radioactive tracers. The majority of Joshua tree fruits monitored were taken directly from the tree canopy by white-tailed antelope squirrels, and seeds and fruits on the soil surface were quickly removed by animals. Rodents given seeds labeled with scandium-46 cached them between 0.1 cm and 4.1 cm deep. Seedling emergence was most common for seeds planted 1 cm deep, whereas seeds placed on the soil surface seldom germinated. Wind dispersal is unlikely because fruits and seeds lack adaptations for wind dispersal; wind speeds required to move Joshua tree seeds and fruits across the soil surface were higher than those typically found in the Mojave Desert. Further, rodents removed most seeds before abiotic burial was possible. We conclude that most Joshua tree seeds are dispersed by scatter hoarding by rodents, and that caches made by rodents are suitable sites for seedling emergence. 相似文献
11.
We assessed reasons for rare recruitment in Acacia peuce, an Australian arid zone tree, by testing recruitment-limitation hypotheses relating to seed bank inputs and losses. Viable seed occurred in low density in the soil (<1 seed m2) whereas freshly produced seed was non-dormant and germination was high and fast, indicating small rain events can deplete seed banks without providing sufficient moisture for seedling survival. Seed bank seed had lower viability than fresh seed. Insect predation of seed was negligible but seed pod production and seed number/pod were low. Thus, seed bank accumulation is limited by low inputs and continual high seed losses through germination and potentially seed death. No seed shadow effect under adult canopies was found, but dispersal beyond existing stands was negligible. Seed dispersal from parent plants occurred by wind movement of unopened pods whereas the resident ant fauna did not transport seed. Microsite parameters strongly influenced horizontal distribution of buried seed, with all seed being retrieved from vegetated sandy mounds. Overall, we found that seedling recruitment is likely to be confined to large above average rainfall events because the species is unlikely to maintain a seed bank in below-average and average rainfall phases. 相似文献
12.
13.
Y. Olvera-Carrillo I. Méndez M.E. Sánchez-Coronado J. Márquez-Guzmán V.L. Barradas P. Huante A. Orozco-Segovia 《Journal of Arid Environments》2009,73(4-5):414-420
We studied in Opuntia tomentosa the effect of plant shade (orientation and distance), and the place where the seeds remained before germination. Seeds were collected in 1998 and a) sown immediately on soil (non-buried seeds), b) stored in the laboratory and sown on soil during the 1999 rainy season (control) or c) buried after collection (under the shade of a tree, a rock and in an open space), exhumed 7 months later and sown in 1999 (exhumed seeds). Seeds were sown under or outside the shade of several trees; or on the northern, eastern and western sides of a 14-m-tall tree. In 1999, germination was high in all samples, but the control seeds had delayed germination. After two rainy seasons, non-buried seeds had the lowest germination rate. Germination was not affected by the distance from the tree. Outside of the plant's shade, germination was low. Germination was affected more by the environmental heterogeneity than by the individual plant shade. Germination probabilities were the highest at 16–19 °C; field germination was zero at 20.6 °C. Seed polymorphism and microenvironmental heterogeneity spread germination across two rainy seasons creating a permanent seed bank. 相似文献
14.
Variations in spatial and temporal availability of fruits and seeds in oases are important not only for animal seeking resources, but also for palm population dynamics. We explored spatial association patterns between avian frugivores and blue fan palms in two natural palm patches of Baja California. Spatial patterns were analyzed at the individual tree and at 2 ha patches. We evaluated seed predation by vertebrates and invertebrates, and vertebrate seed dispersal around palms. Birds responded to fruit aggregation at the individual tree and the patch scales, but responses varied between patches. Palm fruit variables—the quantity and the phenological phase—and avian visits showed strong spatial aggregation and association at both scales in one patch, but not in the other. The intensities of seed predation and seed dispersal were significantly higher directly below palms than at >3 m away from them. Patches differed in the intensity of seed predation around palms and in the diversity of mammalian dispersers, but not in the intensity of seed dispersal. Blue fan palms function as important resources' focuses for a great number of animals that use palm oases as corridors, bringing seeds as they move and connecting isolated populations of palms. 相似文献
15.
Seeds of many arid habitat plants have a water-impermeable coat and can germinate only after being scarified. Bruchine seed beetles are important parasites of legume seeds in these environments, but their effect on germination can be unpredictable. Beetles deplete seed resources and can kill the embryo but also scarify seeds. We investigated the effects of a generalist parasite, Stator limbatus, on the germination and growth of two common legumes in the Sonoran desert, catclaw acacia (Acacia greggii) and blue paloverde (Parkinsonia florida). Feeding damage from a single larva greatly increased germination of paloverde but not acacia. This benefit was reduced if seeds were attacked by multiple larvae. Beetle-damaged seeds of both hosts germinated more quickly than did control seeds. Infestation by beetles reduced seedling size, though effects were greater for paloverde than for acacia. Our results demonstrate that the effect of S. limbatus can be highly host-specific. In addition, beetle infestation may enhance or reduce seedling recruitment, depending on the availability of other scarifying agents and the number of larvae per seed. Such contingencies make it difficult to predict the net effect of seed beetles on efforts to control invasive legume hosts or establish native hosts during aridland restoration. 相似文献
16.
Soils of arid regions of Central Asia contain salts of different types that may differentially affect seed germination and plant development. We studied effect of NaCl, Na2SO4, 2NaCl + KCl + CaCl2 and 2Na2SO4+K2SO4+MgSO4 on germination of Kochia prostrata and Kochia scoparia seeds under a range of concentrations from 0.5 to 5% and at two constant temperature regimes +22 °C and +6 °C. The observed salt tolerance limit of germination at constant temperature +22 °C for both species was 5-6%, while at low temperature (+6 °C) this limit was 2%. The salt tolerance of young plants (before flowering) was 3% for NaCl. Low concentrations of sulfuric and mixed salts had a stimulating effect on seed germination in K. prostrata. Despite similarity of salt-tolerance limits the studied species showed a significant difference in seed recovery ability, i.e. the ability of ungerminated, salt-soaked seeds to germinate after transfer to fresh water. K. scoparia demonstrated a full germination recovery after seed transfer to distilled water while K. prostrata showed only a partial recovery. 相似文献
17.
The quantity, composition, and spatial dispersion of seed banks can greatly affect community dynamics. While seed banks of hot deserts have been studied extensively, little is known about seed banks in cold deserts, in particular the relationship between the seed bank and the aboveground vegetation. We investigated the relationship between the seed bank and aboveground vegetation and the effect of microhabitat (shrub interspace or beneath shrub) and aboveground community phase (high or low perennial bunchgrass cover) on the seed bank of a Great Basin Desert sagebrush community. The seed bank and aboveground vegetation differed in their most dominant species, resulting in moderately dissimilar species compositions as determined by Sørensen's similarity index and Bray–Curtis distance. In contrast, comparing the seed bank species composition to the aboveground vegetation structure (functional groups) using non-metric multidimensional scaling (NMDS) revealed a correspondence between the two communities. Shrub seed densities were higher beneath shrubs. Neither microhabitat nor community phase explained variation in total seed density or species richness. Therefore, our measures of the aboveground vegetation did not influence seed density across functional groups or species richness, and the similarity between the seed bank and aboveground vegetation varied depending on the aboveground organizational level used in comparisons. 相似文献
18.
M.F. Ramos-Ordoñez M.C. Arizmendi 《Journal of Arid Environments》2011,75(9):757-762
Parthenocarpy (production of seedless fruits) is a characteristic associated with a strategy to reduce seed predation by birds and to increase the attractiveness to frugivorous birds. Red cuajiote (Bursera morelensis) is an endemic tree species of Mexico that produces seeded and parthenocarpic fruits. The purpose of this work was to examine whether parthenocarpy is a factor that increases the number of bird visits to trees and if it is a strategy to diminish seeds predation by granivorous birds. We made field observations to determine the relation between the number of bird visits and fruit removal rate, to the total number of parthenocarpic fruits produced, and the number of birdpredated fruits to the number and proportion of parthenocarpic fruits in the trees. We found that in trees with a bigger amount of parthenocarpic fruits, both frugivoruos and granivorous birds made more visits; we then suggested that parthenocarpic fruits can act like a signal of attraction by means of a density and coloration effect. Also, we found that in trees with bigger proportions of parthenocarpic fruit, predation by granivorous birds is smaller. Parthenocarpy has an adaptative value for B.morelensis increasing bird visitation and reducing seed predation in the Tehuacan Valley. 相似文献
19.
The purpose of our study was to better understand seed germination ecology of the spring annual short-lived Olimarabidopsis pumila, which grows in the Gurbantonggut Desert, China. Seeds underwent after-ripening at 4, 20 ± 2 (room temperature) and 30 °C. After dormancy was broken, germination capacity was a function of temperature and presence of light. For the temperature range studied (4–30 °C), germination capacity was significantly higher between 15 and 25 °C than at temperatures above or below them. Alternating temperatures of 20/10, 25/10 and 25/15 °C were favorable for germination. Although GA3 did promote dark germination of seeds, GA3 did not replace light for germination. Seeds germinated to >75% if light exposure time was over 8 h and temperature and moisture conditions were favorable. Seeds were able to germinate at relatively low water potentials (83% at ?0.41 MPa), but decreasing water potentials produced detrimental effects on germination percentage and rate. Thus, dormancy characteristics and germination behavior of O. pumila seeds ensure that germination occurs in the desert only when soil moisture conditions are favorable for seedling establishment and survival. 相似文献
20.
Seasonal variation of the soil seed bank of grasses in central Argentina as related to grazing and shrub cover 总被引：1，自引：0，他引：1
The objectives of this research were to (a) study seasonal variation of the seed bank of grasses in two areas with different grazing history, (b) analyse the effect of the presence of shrubs on the seed bank and (c) study seed viability and dormancy in buried seeds of Piptochaetium napostaense and Stipa tenuis. The seed density of grasses was in general low and showed seasonal variation. Most of the grasses showed maximum seed density in December when seed dispersal occurs. Shrub cover did not show a marked influence in seed accumulation. The relatively high number of damaged seeds suggests that predation may be an important factor in seed bank dynamics in the Caldenal. Seeds of dominant perennial forage grasses showed dormancy that could explain, at least in part, persistence of these species in spite of periodical disturbance. 相似文献