塔克拉玛干沙漠南缘柽柳和胡杨水势季节变化研究

对塔克拉玛干沙漠南缘的柽柳和胡杨生长周期内的清晨水势和水势日变化的连续野外测定表明,两种植物在整个生长期内均未出现明显的水分亏缺.清晨水势的季节变化幅度不大,正午水势有不同程度的降低;一次性人工灌溉对植物水分状况没有明显影响.采伐利用方式不影响植物的水分状况.地下水是柽柳和胡杨生存与生长的先决条件.维持该区域地下水位的基本稳定是保证该区域柽柳和胡杨恢复重建的重要前提.     

The demographic costs of nectar production in the desert perennial Prosopis glandulosa (Mimosoideae): a modular approach

Nectar production in angiosperms is considered to represent a reproductive cost, and has been associated with a decrease in fruit set or an overall decrease in the energetic budget of the plant. Populations of Prosopis glandulosa var. torreyana (honey mesquite) are a suitable system to evaluate the demographic costs of nectar production, as populations are composed of a 1:1 proportion of nectarful to nectarless individuals. The study was carried out in a population of 404 individuals of Prosopis g1andulosa var. torreyana found in an area with differing water availability in the Southern Chihuahuan Desert. The possible costs of nectar production were assessed on 1212 shoots of the honey mesquite that were tagged in 1994 and followed until 1998. We used two methods of analysis to describe the effect of nectar production on modular population dynamics: matrix analysis and log-xlinear models. Water availability and the varying environmental conditions affected plant growth, but nectar production did not have an effect on the demographic parameters we measured. The values of λ did not differ between nectar morphs and the only important effects we detected were the year to year variation in precipitation and microclimate differences at each site. Furthermore, the elasticity of each demographic process (growth, fecundity, retrogression and stasis) between nectar morphs did not differ. The log-linear models suggested a similar pattern but could discriminate the importance of each factor (nectar morph, year and site) on module fate. We were not able to detect a demographic cost of nectar production in the honey mesquite. The absence of a demographic response could be due to the negligible cost of producing nectar for this species or that the resources allocated for growth are different from those allocated for reproduction. Our results suggest that the modular fates of mesquites are mainly determined by environmental factors. This revised version was published online in August 2006 with corrections to the Cover Date.     

From plains to inselbergs: species in special habitats as indicators for climate change?

Aim This study proposes a process to select plant species that would provide suitable candidates for monitoring climate change impacts in areas where complete biological inventories are lacking. Location Inselberg floras of nine inselberg landscapes (i.e. isolated mountains) in the arid Desert and Nama Karoo biome in Namibia were analysed to develop a selection process. Methods Data from detailed field surveys were summarized to determine species only occurring on inselberg habitats (i.e. inselberg specialists). Detrended correspondence analysis and a step‐by‐step selection process based on species distribution patterns were used to determine species occurring on inselbergs beyond their zonal distribution ranges. Results The systematic selection process initially identified 88 plant species. Based on field observations and published sources eliminating species (1) with a wide distribution elsewhere, (2) distribution influenced by local effects and (3) for which their status of knowledge of distribution was clearly inadequate, this list was further reduced to 25 species. This included southern species occurring on inselbergs likely beyond their zonal distribution, such as Adenolobus garipensis, Aloe dichotoma and Euphorbia gummifera, as well as savanna and escarpment species at their western zonal distribution edge (e.g. Cordia sinensis, Commiphora glaucescens and Moringa ovalifolia). Main conclusions The step‐by‐step selection process proposed in this study to assist with the selection of indicators for climate change provides an objective tool in areas where biodiversity coverage is not adequate and little is known about physiology, growth and reproductive patterns of individual species. As such it introduces a method for preliminary screening of species, but will require further input based on field observations and expert knowledge.     

Plant distribution and dispersal mechanisms at the Hassayampa River Preserve, Arizona, USA

This study focuses on the relationships between plant dispersal syndromes and plant distributions at the community scale. Species composition and cover are reported from 29 10 × 20-m vegetation plots along five topographic cross-sections in the riparian zone of the Hassayampa River Preserve, Arizona. We find that spatial patterns of dispersal guilds vary within the flood plain of this semiarid region river. Our main results are: (1) wind-dispersed species are fairly evenly distributed at all elevations and distances from the river, whereas cover of animal-dispersed species increases with elevation above, and at greater distances from, the river; (2) wind-dispersed species are proportionally more abundant in the pioneer Populus–Salix community, whereas plants in the late-seral Prosopis community are predominantly animal-dispersed; (3) most of the species classified as obligate-wetland and facultative-wetland are wind-dispersed, whereas facultative-upland and obligate-upland species are mostly animal-dispersed; and (4) there are significantly fewer wind-dispersed species in areas of high total vegetation cover. These results may reflect successional patterns resulting from periodic flooding. Low areas close to the river flood more frequently and with greater intensity than areas farther from the river. Many pioneer species that establish in disturbed areas are wind-dispersed. Over successional time, pioneer species cede to more drought tolerant species that are predominantly animal-dispersed.     

西北干旱荒漠区种子植物科的区系分析

西北干旱荒漠区分布有种子植物82科、484属、1704种,优势现象明显,优势科11个,它们是菊科、豆科、禾本科、藜科,十字花科、蓼科,莎草科、毛莨科、蔷薇科、唇形科和百合科;表征科8个,它们是香蒲科,麻黄科,柽柳科、蒺藜科,胡颓子科、藜科、眼子菜科和蓼科。地理成分多样,其中以世界广布成分为主,共37科,占总科数的45.12%,其次为温带成分（包括热带至温带,亚热带至温带,温带,温带至寒带）,共有31科,占总科数的37.80%,热带成分,热带致亚热带成分较少,共14科,占总科数的17.07%。这些反映出植物的分布与本地区气候相适应的特点。     

Calcareous nannofossil biostratigraphy and paleoecology of the Cretaceous–Tertiary transition in the central eastern desert of Egypt

The Gebel Qreiya and nearby Wadi Hamama sections of the central Eastern Desert are among the most complete K/T boundary sequences known from Egypt. The two sections were analyzed spanning an interval from l.83 Myr below to about 3 Myr above the K/T boundary. A 1-cm-thick red clay layer at the K/T boundary at Gebel Qreiya contains an Ir anomaly of 5.4 ppb. The high-resolution study and well-preserved nannoflora provide good age control and the first quantitative records of calcareous nannofossil assemblages for paleoecological interpretations across the K/T transition in Egypt. Four zones (Micula murus, Micula prinsii, NP1, and NP2) were distinguished and correlated with other nannofossil and planktonic foraminiferal zonations that are broadly applicable for the eastern Tethys region. Latest Maastrichtian assemblages are abundant and diverse, though Cretaceous species richness progressively decreased across the K/T boundary. Dominant species include Arkhangelskiella cymbiformis, Micula decussata and Watznaueria barnesae, with high abundance of dissolution-resistant M. decussata reflecting periods of high environmental stress. Thoracosphaera blooms mark the K/T boundary and are followed by an acme of the opportunistic survivor Braarudosphaera bigelowii, the first appearance of the new Tertiary species Cruciplacolithus primus, and an acme of Coccolithus cavus/pelagicus. These successive abundance peaks provide the basis for subdivision of the Early Danian Zones NP1 and NP2 into five subzones. Correlation of selected nannofossil taxa from the Egyptian sections with those from various onshore marine and deep-sea sections provides insights into their paleoenvironmental and paleoecological affinities.     

Plant communities of a Central Namib inselberg landscape

Abstract. Three granite inselbergs and six dolerite dykes and their surroundings were investigated in the Central Namib, at the interface between the Namib Desert and Nama Karoo biomes. The main objectives of this study included a phytoso‐ciological interpretation of the described plant communities, explanation of the correlation of the communities with environmental variables and quantification of the relative contribution of different types of variables to structuring plant communities. Nine grassland and shrubland plant communities were recognized, largely organized according to general habitat, elevation, size of inselberg and geology. Soil properties, often thought to play an important role in arid environments, showed no clear patterns in the level of analyses used in this study. Other environmental parameters of importance in arid mountain habitats, such as slope aspect and angle, also played a minor role. The main implications of the study are: 1. Central Namib inselbergs, particularly granite domes, harbour diverse plant communities, often with species from neighbouring higher rainfall areas, and are thus of high conservation value. 2. The poor contribution of environmental variables in this study, which are conventionally used in field studies of plant community – environment relationships, may demand a critical review of additional parameters to be included when analysing plant community – environment relations in arid environments. In particular between‐season variation, phytogeographic aspects and the heterogeneity of microhabitats, often contained within a plant community, need to be taken into account.     

Classification and ordination of plant communities of the Naukluft Mountains,Namibia

Abstract. To determine the relationship between vegetation and environmental parameters in a desert‐savanna ecotone, vegetation in the Naukluft Mountains of Namibia (southern Africa) was described and analysed in terms of environmental parameters determining the observed patterns. 12 plant communities, largely characterized by low shrubs, were described on the basis of a classification. Through ordination altitude, clay, potassium content of the substrate and, to a lesser extent, habitats were identified as underlying environmental factors determining the composition of these plant communities. The edaphic parameters showed some correlation with subsurface geology, but microclimatic conditions, water availability and level of disturbance appeared to override the effect of nutrient composition provided by different substrate. Communities of conservation importance, such as plant communities composed of Karoo shrubs, are prevalent on the mountain plateau, presenting an isolated outpost of Nama Karoo vegetation. The transitional status between desert and savanna, remnant patches of Nama Karoo and the high habitat diversity mark the importance of this high altitude area for biodiversity conservation.