Hybridization-differentiation is a major pathway of speciation and the active force of plant evolution, including homoploid speciation without change of chromosome numbers. Effective isolation between parental species and their hybrid derivatives plays an essential role in homoploid speciation for stabilizing a newly formed species. Studies of isolation mechanisms will facilitate our understanding of the speciation process. The genus Elymus of Triticeae (Poaceae) includes ca. 150 polyploid species with different genomes, viz. the S_tH, S_tY, S_tHY, S_tPY, and S_tWY from different origins, providing an ideal group for studying mechanisms of polyploid and homoploid speciation. There are about 30 tetraploid species containing the S_tY genomes distributed in temperate Asia and the eastern margin of Europe. In order to study genomic relationships of the S_tY Elymus species, samples representing 26 species collected from Western through Eastern Asia were extensively hybridized with each other. Meiotic pairing at metaphaseI of the intra- and interspecific hybrids was analyzed, which revealed a significant differentiation pattern in homology of the S_tY genomes among Elymus species studied. Species from the same regions, e.g. within eastern or western Asia, shared the S_tY genomes with a relatively low level of differentiation, but species from different regions, e.g. between eastern and western Asia, shared substantially differentiated S_tY genomes. Species from Central Asia contained intermediately differentiated S_tY genomes compared with those from western and eastern Asia. The discovery of geographical differentiation of the S_tY genomes in tetraploid Elymus species has significance for study of evolutionary processes and mechanisms of homoploid speciation in Elymus. In addition to other wellrecognized factors responsible for the isolation between parental species and their hybrid derivatives during the hybridizationdifferentiation process (such as temporal, spatial, genic, and ecological isolation), the authors believe that meiotic irregularity caused by genomic differentiation between species also provides an important mechanism for homoploid speciation.

The genetic diversity of 128 individuals from six Psilopeganum sinense populations from the Three-Gorges Reservoir area was analyzed using RAPD. Thirteen primers produced a total of 85 scorable markers, of which 57 (67.06%) were polymorphic. The percentage of polymorphic loci of the six populations was 25.97% (FD), 29.73% (WX), 24.32% (WS), 43.21% (BD), 30.26% (XS), and 39.19% (ZG)， respectively. As analyzed by POPGENE 1.31 and NTSYS 2.10, the genetic diversity of Psilopeganum sinense was high, with an average Nei's gene diversity of 0.2082 and an average Shannon's Information Index of 0.3196. In contrast, the genetic diversity within each population was low, with an average Nei's gene diversity of 0.1094 and an average Shannon's Information Index 0.1641. In addition, G_st was 0.5391 and N_m was 0.4275，indicating more differentiation and less gene exchange between populations than within populations. The UPGMA cluster analysis showed that the six populations were genetically clustered into two groups, of which one was the Fengdu population and the other consisted of the remaining five populations distributed geographically with the Badong population as the center. A positive correlation (r=0.93094，p=0.9861) existed between geographical distance and genetic distance. Finally we discussed the cause of the endangerment status Psilopeganum sinense and proposed some management strategies for effectively protecting this species.

Abies fabri is the dominant species of sub-alpine coniferous forest on the east slope of Mt. Gongga, distributing up to the alpine treeline. Nineteen tree plots dominated by A. fabri were sampled along the altitudinal gradient, covering the vertical range of the species in Hailuo Valley. Altitudinal patterns of community structure and species diversity were analyzed. Major results include：(1) The 19 plots were classified into 5 community types by TWINSPAN, including mixed A. fabri + Picea brachytyla +Tsuga dumosacommunity, A. fabri +deciduous tree-mixed shrub community, A. fabri +broadleaf trees- Bashania fangiana community, A. fabri-shrubs-lichen community, and A. fabri-Rhododendron spp.-lichen community. The spatial differentiation between the community types were mainly controlled by elevation and micro-topographic features, e.g. slope and position. (2) Species richness and the Shannon-Wiener index of the canopy and shrub layers decreased with increasing elevation, whereas no trend was detected in the herb layer. (3) The β diversity indices of each layer decreased with increasing elevation. The difference in species composition decreased above an elevation of 3300 m. (4) Maximum tree height, mean tree height, maximum DBH, and mean DBH of A. fabri forests decreased with increase of elevation. Environmental limitations near timberline to the height and girth growth of A. fabri individuals became clear above 3550 m a.s.l., whereas stem densities of all species or A. fabri with DBH>5 cm increased as elevation rose. (5) The average timber volume of A. fabri was 846.4 m3/hm2, and declined with increase of elevation.

Coastal Vatica hainanensis forest in Hainan is a special type of tropical rainforest. To analyze this community, we used methods of sampling area analysis, including both quantitative mathematical modeling and qualitative comparison. Eight mathematical models (species-area curves) were used to calculate the minimum sampling area and relevant coefficients. Importance values were derived to confirm the modeling consequences. Species diversity was also analyzed by various kinds of diversity indices. Results showed that the minimum sampling area of coastal Vatica hainanensis forest in Shimei Bay was 800 m2. This value of minimum sampling area was the lowest in global tropical rainforest types. Coastal Vatica hainanensis forest in Shimei Bay was a strongly mono-dominant forest with low species diversity. Thirdly, the pattern of tree layers in Shimei Bay, measured by the Gleason index, differed greatly from that of mountain rainforest on Hainan Island. The study revealed that Shimei Bay, Hainan Island hosts a natural rainforest climax community which has low species diversity and salient monodominant community characteristics.

We examined the dynamics and community structure of soil mesomicroarthropods during litter decomposition in tropical rain forests of Xishuangbanna, SW China between May, 2000 and April, 2001.? The experiment was carried out in three plots of tropical seasonal rain forest located within a distance of 15 km. Mixed-species litterbags were constructed and placed in the field for one year. Soil meso-microarthropods were extracted from the litterbags by the Tullgren method each month during litter decomposition. The densities of soil meso-microarthropod groups and individuals were calculated per gram of dry litter (relative density). The data showed that Collembola and Acari were the most abundant groups of arthropods in the tropical seasonal rain forests (above 30%). Diversity indices, numbers of groups and number of individuals of soil meso-microarthropod were all higher in the middle stage of decomposition than in the early and end stages of decomposition. Variation of soil mesomicroarthropod communities, including abundance of some groups, was correlated with litter quantity and quality. Relative density of soil meso-microarthropod reflects the dynamic relationship between litter quality and number of groups and individuals of soil meso-microarthropods during the decomposition process. The differences of diversity and abundance of soil meso-microarthropods among three different plots were higher in the end stage of decomposition than ?in the early stage of decomposition, but litter weight loss did not differ among the three different study site plots.

In 1996 and 1997, a carabid community and its fluctuation were studied by the pitfall method in the salinity transforming area in Quzhou County, Hebei Province, China. The community consists of 19 species belonging to eight genera. Harpalus is the dominant genus and ranks the first in abundance. As a whole, the carabid fauna in this area is simple, having relatively few species and genera. The dominant species are Harpalus simplicidens, H. griseus and H. tridens. Considering the monthly fluctuation of carabid abundance, it reaches a maximum in September, and falls to a minimum in October. The fluctuation of carabids differs among different cropplanting patterns, and is affected to an extent by the changes of the landscape and agricultural activities. Field margins are shelters for carabids where they tend to gather, and these margins play a pivotal role in protecting the carabids. Carabid density in field margins is higher than that in adjacent farmlands, and the monthly fluctuation range there is also narrower.

Abies yuanbaoshanensis (Pinaceae) is an endangered species endemic to Yuanbaoshan Mountain, Guangxi, China. Genetic diversity in 43 individuals of the speices was assessed using the amplified fragment length polymorphisms (AFLP) technique. Four primer combinations generated a total of 261 bands, of which 133 were polymorphic (50.96%). The Nei′s gene diversity of the population was 0.1510, and Shannon′s information index was 0.1735. The results indicate that Abies yuanbaoshanensis has a low level of genetic diversity. This finding provides valuable information for formulating future conservation programs for the species.

A new exotic species of Asteraceae (Compositae) has been appearing in Tianjin City and Hengshui and Langfang of Hebei Province. The result of our investigation shows that it is Flaveria bedentis (Asteraceae), which has never been reported in China before. According to literature references and its ecology, we assign a Chinese name to it, and introduce its original and expanded distributions in the world, as well as the characteristics of its morphology, physiology and ecology. An assessment of its primary invasiveness indicates that F. bidentis is a highly dangerous exotic annual weed with very strong invasiveness, especially to ecosystems of croplands and grasslands. We put forward strategies for preventing and controlling this weed in order to eradicate it as early as possible. We appeal to experts and government departments to make efforts to investigate its route of invasion, to analyze the potential regions it could invade and occupy, and to assess its invasiveness and study strategies to control its diffusion.

Biological invasions, a significant component of global environmental change, can result in serious economic and ecological consequences. Assessing the ecological impacts of invasive plants is one of the most important issues in the study of biological invasion ecology. This paper reviews the ecological consequences of Spartina spp. invasions in the coastal ecosystems of the world, and discusses strategies for controlling their further range expansion. The genus Spartina consists of 14 species, most of which grow in coastal areas. Half of the species of the genus have successfully invaded intertidal ecosystems in coastal areas or estuaries of the world. Because these species often form dense shoot populations under favourable conditions, they can potentially alter the physical conditions of the ecosystems they invade, and have the potential to exclude native plants by competition, which in turn influences benthic fauna, and eventually results in elimination of critical foraging habitat for migratory shorebirds. Unfortunately, arresting and reversing the invasion of Spartina spp. may become infeasible once these species have spread and become established. Therefore, immediate and aggressive actions need to be taken to prevent further degradation and loss of the natural ecological structures and functions of coastal ecosystems, caused by Spartina spp. invasions. The most effective actions are to prevent Spartina spp. from invading new habitats or eradicate populations that have been recently established.

It is well known that plant species diversity is highest in tropical forests. With regard to the mechanisms for the maintenance of tropical plant diversity, different hypotheses have been put forward, but until now, no convincing theory has appeared. Different researchers have obtained different conclusions, from which has arisen heated debate. This review discusses four mechanisms that are frequently invoked to explain the coexistence of the great number of plant species in tropical forests, these being Niche differentiation, Predatory pressure, Life history tradeoffs, and Lottery competition. Niche differentiation is evident from the nonrandom spatial distributions along microenvironmental gradients and plays an important role in sustaining high biodiversity. Pests reduce the survival and growth rate of seedlings near conspecific adults, thereby freeing space for other plant species. Pest pressure remains a promising but not widely proven mechanism for plant coexistence in tropical forests. Life history tradeoffs do occur among tropical forest plants, and thus allow a large number of species to coexist. Suppressed by the canopy, understory plants rarely come into competition with one another, and chance becomes an important determinant of the recruitment of understory plants.