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1.
Population density and species diversity of microfungal communities were investigated in the rhizosphere soil of the halophytic plant Zygophyllum qatarense inhabiting saline and nonsaline habitats of the arid desert environment of Bahrain. Unlike the nonsaline habitat which is situated in the physiographic zone of multiple escarpment and backslopes, the saline site is located in the coastal lowlands and is featured by high chloride content, electrical conductivity, total soluble salts and low organic matter. Soils of both habitats are sandy, slightly alkaline, poor in nutrient sources, low in water-holding capacity and mainly dominated by a salt-tolerant flora. Quantification of data for the recovery of fungi were based on colony identification and counts by a series of ten-fold dilutions plate method, using various natural, synthetic and selective media. A total of 2780 isolates, fluctuating between 25 and 1109 per sample, were recovered during the present study among all habitats, seasons and plant sizes. Grouping of these isolates has resulted in a maximum of 28 fungal taxa varied between 5 and 15 species, of which 24 were hyphomycetes, 3 ascomycetes and one was an unknown species. All the recorded species in this study, excluding the genus Fusarium, are newly reported from the arid terrestrial habitats of Bahrain. Of the encountered fungi,Cladosporium sphaerospermum was the most dominant and frequent genus, among all plant sizes, followed by Penicillium citrinam and Aspergillus fumigatus, a finding with consistent documented data from similar arid Sahara ecosystems. Examination of data, supported by analysis of relative density values, percentage recovery rates, polar ordination and diversity indices revealed that the nonsaline habitat during the dry period yielded the highest isolate frequency, species abundance, and diversity when compared with the saline habitat. Moreover, a progressive increase in colony occurrence and species diversity was equivalently associated with increment in plant size in the nonsaline habitat. Apparently, the vast majority (moderate to low occurrence class) of the reported species are rhizosphere indigenous saprophytic cellulose-decomposers, whilst the sparse taxa (high occurrence class), e.g. C. sphaerospermum, are regarded as thermo-osmotolerant. Comparison of species richness among samples suggests that small plants inhabiting nonsaline habitats during the wet and dry season were richest in species composition. It is proposed that inter- and intra-specific variation in fungal community between the above habitats reflect not only the influence of plant age and season but also extends to critical multi-soil edaphic and biotic factors involving essentially soil moisture, salinity and root growth dynamic and exudates.  相似文献   

2.
Restoration of palatable grasses on degraded rangelands dominated by unpalatable grasses in central Argentina is limited by low availability of seeds and safe sites for seedling establishment. The objective of our study was to determine how mechanical disturbance of unpalatable grasses (Stipa spp.) in combination with seeding of a palatable grass (Poa ligularis) influenced species composition in a degraded rangeland excluded from livestock grazing. In April 2001 10 blocks were uniformly distributed on a previously burned site dominated by unpalatable grasses, and treatments applied in 8 m×8 m experimental plots. Treatments were ‘disked and seeded’ and control (no disking, no seeding). Perennial plant cover and end-of-season standing crop, at species or species group level, were assessed in December 2002/2003 and in December 2004/2006, respectively. P. ligularis out-competed both tillers of unpalatable grasses that survived mechanical disturbance and seedlings of unpalatable grasses established after mechanical disturbance. The cover and end-of-season standing crop of unpalatable grasses was higher in the control than in the ‘disked and seeded’ treatment, whereas the cover and end-of-season standing crop of P. ligularis was higher in the latter than in the former treatment. Our results suggest that a rapid transition from a state dominated by unpalatable grasses to a state dominated by palatable grasses can be achieved by mechanical disturbance of unpalatable grasses in combination with seeding of palatable grasses in semiarid rangelands of central Argentina.  相似文献   

3.
《自然地理学》2013,34(3):192-215
This work investigates the initial colonization on recent lahar deposits of the northeast slope of Popocatepetl volcano, Mexico, where 29 circular sample plots (1.57 m2) were established to determine the development stages of colonization in four types of habitats: 1997 lahar, 2001 lahar, margins, and terraces at the channel's bottom. Cluster analysis and the Sørensen Index were used to determine the floristic affinity of these lahars. Richness, frequency, percentage of species contribution, plant cover, density, and stem height were analyzed to determine the composition and structure of plant communities. The distribution of these variables reveals that the communities often have a simple internal structure; however, a relationship has already been established between changes in resilience and the age of the four lahars. Thus, floristic composition develops rapidly (1 sp. in terraces, 11 spp. in the margins, 29 spp. in the 2001 lahar, and 34 spp. in the 1997 lahar). Except for the 1997 lahar, however, structural characteristics are poorly developed in other incipient stages. As colonization advances, the affinity among the various components and sectors of the laharic deposits decreases, thus promoting the gradual incorporation of species found on the adjacent gorge slopes. The Principal Components Analysis used to identify other explanatory factors shows that of 15 variables studied, those associated with the morpho-sedimentology, the hydrovolcanic dynamics and stability of deposits (microtopography, thickness of the deposit, clast shapes, length of the deposit, depth of the gorge, and slope processes) explain a large percentage of variance. Only a few species (Lupinus campestris, Alchemilla procumbens and Penstemon gentianoides), are well adapted to poor soils and the effects of intense erosion caused by the flows.  相似文献   

4.
The aim of this work was to study the effect of controlling jarilla (Larreaspp.), nonforage shrubs for livestock, on two plant communities with different forage production in the arid mid-west of Argentina. Total vegetation cover, forage species cover and carrying capacity were determined during three growing seasons, for cleared and uncleared plots. At the end of the study, significant differences were found in theLarrea cuneifoliacommunity, where average forage species cover increased by 156% over the control, and greater carrying capacity (129%) was also obtained from the cleared treatment. No significant differences were found in theLarrea divaricatacommunity. Data lead us to recommend shrub control as an improvement practice only in areas with low forage species cover and poor carrying capacity.  相似文献   

5.
Shrub fertile islands are a common feature in arid ecosystems. To examine the effect of plant species on the spatial patterns of soil chemical and physical properties surrounding individual shrubs, two deciduous shrub species with different morphologies (Tamarix spp. and Haloxylon ammodendron Bge.) were studied at an oasis–desert ecotone in South Junggar Basin. Soil samples were collected under the shrub crown (canopy), at the vertically projected limit of shrub crown margin (periphery), and in the space between shrub crowns (interspace) at two depths, 0–10 and 10–20 cm, to analyze their physical and chemical properties. The results show that the fertile islands of Tamarix spp. are enriched with more soil nutrients (significantly higher, P<0.05; soil organic matter (SOM); total nitrogen (TN) and available nitrogen (AN); to a deeper depth (>20 cm) and in a larger area (beyond the canopied area) compared to that of H. ammodendron (significantly higher, P<0.05, soil nutrients detected only for AN; <20 cm in depth; smaller than the canopied area). Soil texture patterns surrounding the shrubs of the two species are even more different, with more coarse particles under the Tamarix spp. canopies compared to the interspace between shrubs but fewer under the H. ammodendron canopies compared to the interspaces. These variations are attributed to the difference in morphology of the two studied species: the Y-shaped crowns of H. ammodendron are less capable of capturing and maintaining litter under them than the hemispheroidal crowns of Tamarix spp., which leads to the less well developed fertile islands surrounding H. ammodendron shrubs.  相似文献   

6.
Analysis of raudhas vegetation in central Saudi Arabia   总被引：2，自引：0，他引：2  
The present study analyses the vegetation of three raudhas in central Saudi Arabia (Kharj, Khuraim and Binban). Seventy-five stands were examined and the martrix of 68 species × 75 stands, based on species cover data, was classified using TWINSPAN and ordinated using DECORANA. Eleven vegetation groups were generated: one dominated byHammada elegansand five dominated byAcaciaspp. (A. iraquensis, A. elatior, A. seyal, A. tortilis-Ziziphus spina-christi-Rhazya strictaandA. abyssinica). TheAcaciaspp. communities represent the climax stage of the xerophytic vegetation in Saudi Arabia and have, in most cases, high species cover and low species diversity. Another five groups are dominated, fully or partly, by species that often inhabit disturbed areas (Prosopis juliflora, Heliotropium bacciferum-Tamarix arabica-Prosopis juliflora-Pulicaria crispa, Ziziphus spinsa-christi-Lagonychium farctum-Alhagi maurorum-Cynodon dactylon, Salsola imbricataandBassia eriophoria-Chloris virgata-Zygophyllum coccineum-Seidlitzia rosmarinus). Many of these groups have low species cover and relatively high species diversity. The effects of environmental factors and human impact on species diversity and abundance of these communities were assessed.  相似文献   

7.
Soil disturbance is a wildlife habitat management tool that retards succession and promotes early seral vegetation. Our objective was to determine responses of two invasive herbaceous species (Pennisetum ciliare and Salsola iberica) and native perennial grasses to disking on different soils. Two 10 ×40 m plots were delineated within each of 4 blocks on Ramadero loams and 4 blocks on Delmita fine sandy loams. On Delmita soils, canopy cover of P. ciliare, S. iberica, and native perennial grasses averaged across all years was not affected by disking (ANOVA, P>0.05). On Ramadero soils, P. ciliare canopy cover was similar (Tukey's, P>0.05) on control and disked plots for the first 4 years post-disturbance, but P. ciliare cover was 10-fold greater (Tukey's, P=0.02) the 5th year after disking on disked versus control plots. On Ramadero soils, S. iberica canopy cover averaged across all years was 221 times greater (ANOVA, P=0.05) on disked plots than on control plots. Disking did not affect native perennial grass canopy cover. Land managers should consider soil series when disking for wildlife management, as disking disturbance may exacerbate exotic plant ingress and establishment on certain soils.  相似文献   

8.
A prescribed burn resulted in significant decreases in canopy cover of the grasses: Bouteloua eriopoda, Sporobolus flexuosus, and Aristida purpurea. One year post-burn, basal cover of B. eriopoda remained significantly lower in burned patches than in unburned areas but there were no differences in basal cover of the other perennial grasses. Only one species of the 14 summer annual species occurred in both burned and unburned plots. There were six species of spring annuals in burned patches but no spring annuals in the unburned grassland ten months post-burn. Fire killed 100% of the snakeweed shrubs (Gutierrezia sarothrae), 77% of the Ephedra torreyana shrubs, and 36% of the Yucca elata. All mesquite shrubs that were top-killed by fire, resprouted one month post-burn. Fire had no effect on abundance and species richness of rodents. There were fewer wolf spider, Geolycosa spp. burrows in burned areas than in unburned grassland. The area and volume of soil in termite galleries and sheeting were significantly larger in the unburned grassland than in the burned areas.  相似文献   

9.
In the semi-arid steppe rangelands of Central Turkey, Festuca valesiaca and Thymus sipyleus ssp rosulans have become the dominant species on degraded pastures. We hypothesized that decreases in species richness and abundance are correlated with increasing prevalence of these two species. Therefore, our objectives were to determine whether there are patterns in examined vegetation; how dominant species contribute to these patterns; and how patterns differ between grazed and ungrazed vegetation. We determined that protection from grazing increased species richness. Grazing significantly changed composition through decreasing total plant, forb, grass and F. valesiaca covers, while substantially increasing T. sipyleus cover. Topography, soil and grazing appear to impact the dominance of plant communities where F. valesiaca and T. sipyleus prevail. These two dominant species had a significant effect in shaping vegetation patterns. Based on regression analysis, alterations in species richness with changes in cover of forbs and shrubs were evident, and spatial heterogeneity of F. valesiaca and T. sipyleus indicated unstable vegetative patterns in heavily grazed pastures and successional changes in protected pastures. Our study results identify F. valesiaca and T. sipyleus as indicator species of vegetation suppression in condition assessments of degraded steppe rangelands.  相似文献   

10.
We quantified soil nutrients and biological crust cover (bryophytes and lichens) under the canopies of three species of Mojave Desert shrubs and in interspaces between shrubs at three elevations to determine the effects of shrub species, soil crust, and elevation on islands of soil fertility. Means of pH, organic matter, total Kjeldahl nitrogen, nitrogen mineralization, and gravimetric soil moisture are significantly greater in soils under Ambrosia dumosa (Gray) Payne, Larrea tridentata Cov., and Coleogyne ramosissima Torr. than soils from adjacent interspace microhabitats. Although soil moisture and soil organic matter increase by a factor of 1.5 from the low elevation to the high elevation site, the ratio of shrub to interspace concentrations, or the difference in mean soil variables between shrubs and interspaces, is effectively constant and independent of elevation. Total bryophyte and lichen cover is relatively low (24.5%), however, there are 11 species of bryophytes and two species of lichens distributed across three elevations with the highest species richness and cover at the low-elevation site. Bryophyte and lichen cover is correlated with silt but is not related, consistently, to soil nutrients. Overall, the balance of processes controlling spatial aggregation of soil nutrients under shrubs is remarkably insensitive to potential differences in organic inputs among elevations, shrub species, and soil crust surfaces.  相似文献   

11.
Grazing effects on patchy dryland vegetation in northern Patagonia   总被引：1，自引：0，他引：1  
In this study the spatial patterns and dynamics of vegetation patches along a grazing gradient in the steppe ofLarrea divaricataandStipaspp. in NE Patagonia (Argentina) are described. A general effect of grazing is the reduction of total plant cover resulting from the decrease in cover of perennial grasses (Stipa speciosa, Poa ligularis, Stipa tenuis) and some tall shrubs (Chuquiraga hystrix, Bougainvillea spinosa, Lycium chilense). Dwarf shrubs (Nassauvia fueguianaandJunellia seriphioides) increase their cover under medium and/or high grazing pressures. Plant species are spatially grouped into patches which alternate with areas of bare soil. Eleven types of vegetation patch differing in the dominant plant functional type or species, floristic richness and size were identified with different relative frequency along the grazing gradient. Based on these results, it is postulated that grazing forces the replacement of large patches dominated by tall shrubs with high species richness, byLarrea divaricatapatches or small dwarf shrub patches with low species richness and the extinction of grass patches. This results from: (1) disruption of local balances of species deletions and additions; (2) fragmentation of large patches; and (3) formation of new vegetation patches. These changes lead to differing plant spatial organization and heterogeneity along the grazing gradient which may be described by characteristic arrays of vegetation patches.  相似文献   

12.
放牧强度对科尔沁沙地沙质草地植被的影响   总被引：5，自引：3，他引：2  
为了研究科尔沁沙地沙质草地在不同放牧强度下植被特征的变化规律,比较了围封、中度放牧、重度放牧3种条件下的植被盖度、群落组成、物种多样性、地上/地下生物量和凋落物量等植被特征的变化特征。结果表明:(1)围封、中度放牧和重度放牧沙质草地的优势植物均为一年生植物,但围封和中度放牧中多年生禾本科植物优势度高于重度放牧,重度放牧沙质草地一年生植物所占优势度最大;(2)放牧强度对沙质草地植被盖度、地上生物量及凋落物量有显著影响。随着放牧强度的增加,植被盖度、地上生物量和凋落物量均降低;(3)围封、中度放牧和重度放牧沙质草地物种丰富度及多样性差异均不显著;(4)放牧强度和土壤深度及其交互作用均能影响地下生物量。随着放牧强度的增加,总的地下根系生物量减小。而重度放牧草地中, 3个土壤深度间地下根系生物量差异不显著。放牧改变了沙质草地植物群落的组成、极大降低了植被盖度和生产力;尤其是重度放牧急剧增加了一年生植物的优势、且对浅层根分布的减少影响最大。  相似文献   

13.
The present study provides an analysis of soil, vegetation types as well as structure and species distribution in 19 sites in El-Qaa plain along the Gulf of Suez (south Sinai, Egypt), and focuses on the environmental factors that control the species distribution. A total of 203 species belonging to 39 families of the vascular plants are recorded. Asteraceae, Fabaceae, Chenopodiaceae and Poaceae are the largest families. Grasses constitute only 9% of the recorded species, while the woody perennials (shrubs and sub-shrubs) are highly dominated (46%). Therophytes and chamaephytes are the most frequent, denoting a typical desert life-form spectrum. Floristic composition in the different geomorphologic landscape units showed differences in species richness. The highest mean species richness of 19.7±1.7 is recorded in the wadi channels. The lowest species richness values are recorded in the coastal shore and playas (6.0±1.4) and in the alluvial fans (mean of 8.4±1.6 species). Chorological analysis revealed that 46% of the studied species are uniregional, being native to the Saharo-Arabian region. On the other hand, about 50% of the recorded species are biregional and pluriregional, extending their distribution all over the Saharo-Arabian, Sudano-Zambezian, Irano-Turanian and Mediterranean regions. Classification of the vegetation is analysed using two-way indicator species analysis (TWINSPAN) techniques resulted in the recognition of five vegetation groups, each of definite vegetation and soil characters, and could be linked to a specific geomorphologic unit. Capparis spinosa var. spinosa occupied the terraces, Cornulaca monacantha, Convolvulus lanatus and Deverra tortuosa inhabited the alluvial plains, Launaea nudicaulis and Artemisia judaica characterized the wadi channels, Acacia tortilis subsp. raddiana and Leptadenia pyrotechnica characterized the alluvial fans and Tamarix nilotica, Zygophyllum album and Nitraria retusa on the playas and the coastal shore. Ordination techniques as detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA) are used to examine the relationship between the vegetation and studied soil parameters. Nine soil variables are included: electrical conductivity, pH, calcium carbonate, gypsum, organic matter, gravel, fine soil fractions and soil saturation percentage. Analysis with DCA gave results similar to CCA, suggesting that there is a relatively high correspondence between vegetation and soil factors. DCA axis 1 showed significant positive correlation with CaCO3, pH, soil saturation and organic matter, and interpreted as a calcium carbonate—soil saturation gradient. DCA axis 2 showed significant correlation with pH, gypsum and electric conductivity, and interpreted as an electric conductivity—gypsum gradient. Application of CCA indicated that soil surface sediment, CaCO3, soil saturation, pH and organic matter are the main operating edaphic gradients in the area. These gradients are related closely to the first three canonical axes, and accounted for 67% of the species–environment relationship among the sites.  相似文献   

14.
The spatial heterogeneity of resources in desert and semi-arid shrubland appears to be important in determining higher soil bacteria abundance around plants than in soil without plant cover. Thus, these bacterial communities could be important contributors to nutrient cycling in arid ecosystems. Bacterial diversity from Chilean sclerophyllous matorral was determined by Terminal Restriction Fragment Length Polymorphism (T-RFLP). Soil samples associated with the actinorhizal plant Colletia hystrix, non-actinorhizal plants and interspace soil without plant cover, were collected in May and October. The non-actinorhizal and interspace soil differed significantly in their potassium content in May and pH in October. The T-RFLP analysis revealed differences in the bacterial community structure from the different habitats. The soil bacterial communities associated with plants were the most similar, whereas the interspace soil community differed in both sampling times. The factors that best explained the groupings were potassium and pH. The greatest diversity was observed in the interspace soil. The Microbial Community Analysis showed a significant proportion of T-RFs identified as Firmicutes and Proteobacteria. Likewise, spatial and temporal differences were observed in the main groups' abundance. The dominance of Firmicutes suggests that the sclerophyllous matorral could be a different ecosystem to other arid and semi-arid soils with respect to the bacterial community structure.  相似文献   

15.
呼伦贝尔沙质草甸草原洼地植物群落变化分析   总被引：1，自引：0，他引：1  
选择呼伦贝尔沙质草甸草原上的干洼地,采用系统取样方法对不同微地貌部位的植物群落变化进行研究。发现,草原区微地貌变化对生境异质性的控制作用明显。在洼地中旱生植物和旱生植物占优势,中旱生植物在阴(N)坡和下坡位或坡底占优势,旱生植物在阳(S)坡最占优势。下坡位或坡底的多年生植物比例最高,其次是阴(N)坡和中坡位,上坡位和阳(S)坡最少。洼地内出现了12个不同类型的群落。同一坡向的植被覆盖度、地上生物量、草层高度呈现下坡位＞中坡位＞上坡位的趋势。主要物种的重要值波动很大,表明洼地内的地形因子分配不均匀。SW上坡位植物群落特征各项指标均出现低值,导致局部恶劣环境的微地貌产出部位,与风蚀坑集中分布区耦合。表明SW坡上部风蚀沙漠化的高发生率与该微地貌部位植被发育差有关。  相似文献   

16.
将轮台天山南麓山前平原中下部自北至南分为4个地貌带:洪水剥蚀带、溢出带、三角洲带及两河交汇区带。并以土壤电导作为积盐程度的指标,分析了天山南麓山前平原4个地貌带土壤盐的分布特征:溢出带和三角洲带土壤盐分含量高,两端洪水剥蚀带和两河交汇区带盐分含量低。物种多样性及物种组成分析结果表明,自北至南物种多样性及物种数量都在下降,洪水剥蚀带主要为柽柳群落、琵琶柴群落,溢出带主要为柽柳群落、盐节木群落、盐角草群落,三角洲带及两河交汇区均为柽柳群落。通过相关性分析,土壤盐分与群落物种多样性相关性不显著。但是,土壤盐渍化的变化明显影响到植物群落物种组成的变化、群落类型的空间分布和演替。  相似文献   

17.
古尔班通古特沙漠植被与环境关系分析   总被引：2，自引：0，他引：2  
The Gurbantunggut Desert is the largest stable and semi-stable sand desert in China, yet few data exist on vegetation pattern and species-environment relationships for these diverse desert landscapes. The sand dunes of the survey area are mainly of the longi- tudinal form from north to south, but checkerboard-shaped and honeycomb-shaped forms are also present, with the height of 10-50 m. We measured vegetation and soil data on north-south transects and compared them with vegetation and soil data on east-west transects. Analysis revealed that the varying trend and strength of the species diversity, dominance and cover of the plant communities in the longitudinal and transverse directions across the landscape are significantly different. The results of CCA ordination show that the microhabitats of soil organic matter （OM）, soil salts （TS）, sorting index （ σ ）, topsoil water-content （SM） and pH relate to the differences in vegetation observed as differences in species assemblage from salt-intolerant ephemerals, micro-subshrubs and subshrubs to salt-tolerant shrubs and micro-arbors. The terrain （alt.） and soil texture （the contents of Mz and Ф 1） affect the spatial differentiation of many species. However, this spatial differentiation is not so marked on transects running longitudinally with the landscape, in the same direction as the dunes. The species of the desert vegetation have formed three assemblages under the action of habitat gradients, relating to three sections running transversely across the landscape, at right angles to the direction of the dune crests. In the mid-east section of the study area the topography is higher, with sand-lands or dune-slopes with coarse particles. Here the dominant vegetation comprises shrubs and subshrubs of Seriphidium santofium and Ephedra distachya, with large numbers of ephemeral and ephemeroid plants of Senecio subdentatus, and Carex physodes in spring and summer. On the soil of the dune-slopes in the mid-west of the study area, with coarse partic  相似文献   

18.
A field experiment was conducted to test the hypothesis that competitive interactions affect demographic responses of desert dune annuals to gradients in sand stability. The experiment was based on a three-way factorial design with two types of neighbor treatments (complete neighbor removalvs. control), two types of habitats (stablevs. unstable sands) and two species which characterize sandy areas of the western Negev Desert (Neurada procumbensandBromus fasciculatus). Each of the eight treatment/habitat/species combinations was characterized by three demographic variables: seedling survival to reproduction, fruit number per reproductive plant and fruit number per seedling. All of these variables exhibited significant interactions between the effects of neighbor removal and habitat type, indicating that neighbor conditions were important in determining the observed patterns of demographic variation. Moreover, while plants ofNeurada procumbensgrowing without neighbors suffered more mortality on unstable sands, conspecific plants growing at natural density conditions suffered more mortality on stable sands. In the case ofBromus fasciculatus, individuals growing in the absence of competitive effects produced more fruits on stable sands, but conspecific plants growing at natural density conditions exhibited higher fruit production on unstable sands. These findings indicate that competitive effects not only modify, but may even reverse demographic responses of desert dune annuals to gradients in sand stability. Based on these results and evidence from two other studies it is suggested that seed dispersal from abiotically favorable into less favorable habitats may increase fitness of desert annuals by reducing the average effect of competition.  相似文献   

19.
Li  Wei  Li  Xiaoyan  Huang  Yongmei  Wang  Pei  Zhang  Cicheng 《地理学报(英文版)》2019,29(9):1507-1526

In many arid ecosystems, vegetation frequently occurs in high-cover patches interspersed in a matrix of low plant cover. However, theoretical explanations for shrub patch pattern dynamics along climate gradients remain unclear on a large scale. This context aimed to assess the variance of the Reaumuria soongorica patch structure along the precipitation gradient and the factors that affect patch structure formation in the middle and lower Heihe River Basin (HRB). Field investigations on vegetation patterns and heterogeneity in soil properties were conducted during 2014 and 2015. The results showed that patch height, size and plant-to-patch distance were smaller in high precipitation habitats than in low precipitation sites. Climate, soil and vegetation explained 82.5% of the variance in patch structure. Spatially, R. soongorica shifted from a clumped to a random pattern on the landscape towards the MAP gradient, and heterogeneity in the surface soil properties (the ratio of biological soil crust (BSC) to bare gravels (BG)) determined the R. soongorica population distribution pattern in the middle and lower HRB. A conceptual model, which integrated water availability and plant facilitation and competition effects, was revealed that R. soongorica changed from a flexible water use strategy in high precipitation regions to a consistent water use strategy in low precipitation areas. Our study provides a comprehensive quantification of the variance in shrub patch structure along a precipitation gradient and may improve our understanding of vegetation pattern dynamics in the Gobi Desert under future climate change.

  相似文献   

20.
测定了荒漠地区超旱生小灌木红砂在3种生境(山前荒漠、山前戈壁和中游戈壁)下的叶片水分状态、抗氧化酶活性及渗透调节物质含量,以探讨荒漠植物在不同生境下的生理生化特征及对荒漠极端环境的适应机制。结果表明:在3种生境下,红砂叶片相对含水量和叶片水势随着土壤含水量的下降而下降,叶绿素含量随着土壤含水量的下降而升高。随着生境土壤干旱的加剧,超氧化物歧化酶(SOD)及过氧化物酶(POD)活性逐渐升高,而过氧化氢酶活性下降。在土壤含水量较少的戈壁生境,渗透调节物质含量上升。SOD和POD活性的升高是红砂抵御干旱环境的主要抗氧化保护机制;渗透调节在红砂叶片适应干旱胁迫的过程中发挥着重要作用,高的渗透调节能力使红砂在水分不足的条件下维持较低的渗透势,有利于植物吸水,从而增强其耐旱性。  相似文献   

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