The Tertiary relic species, Metasequoia glyptostroboides , is naturally distributed in a narrowly restricted area bordering Hubei, Hunan Provinces and Chongqing City in central China. The genetic background of its overall genetic diversity and population structure is prerequisite for formulating an efficient conservation program and effective practice in management of remnant populations. The spatial structure of gene frequencies of M. glyptostroboides remnant populations in its original habitat was investigated using AFLP markers followed by spatial autocorrelation analysis. A total of 39 individuals were sampled from remnant populations and subjected to spatial autocorrelation analysis in two approaches of equal gene frequency correlograms with five classes and equal distance interval correlograms with ten classes, respectively. Of 46 polymorphic bands generated by six selective primer-pairs, 27 polymorphic bands with frequencies ranging from 25% to 75% were then used to calculate Moran's I spatial autocorrelation coefficient. The result revealed a lack of spatial structure of genetic variation existing in the remnant population of M. glyptostroboides , indicating that genetic variations of the most polymorphic loci were randomly distributed, strongly supported by insignificant Moran's I coefficients. However, lump, depression or double cline structures of the genetic variation were found in a few AFLP markers with significant Moran's I in several distance classes. The distance interval 4 - 8 km is probably a sufficient barrier to gene flow, as evidenced by Moran's I coefficients showing negative correlations within this distance class. In addition, remnant individuals were not absent in distance classes from 12 to 28 km, suggesting that the habitat of the remnant populations had been disturbed since humans moved in and subsequent agricultural activities occurred. Apparently, habitat fragmentation resulted in an island distribution and genetic drift had occurred even before M. glyptostroboides was rediscovered in 1941. Based on the results of the present study combined with the lower genetic diversity previously detected in the remnant populations, possible mechanisms causing the endangerment of M. glyptostroboides are discussed and a conservation strategy for M. glyptostroboides remnant populations is proposed. The results provide valuable information for formulating future in situ and ex situ conservation programs of this relic species.

Ginkgo biloba , now unique in the Ginkgopsida, is referred as a “living fossil” plant. As a wild species, Ginkgo biloba is endemic to China. ISSR analysis was conducted on the possible natural populations (Tianmushan, Wuchuan, and Dahongshan) and the cultivated populations (Taixing and New York) in order to investigate the genetic diversity and the genetic structure of the populations. Out of 100 ISSR primers, 13 generated highly reproducible and stable DNA fragments. Using these primers, 88 discernible DNA fragments were produced. Of these, 62 (PPB = 70.5%) were polymorphic loci, which indicated that high levels of genetic variation existed in the possible natural populations. The result of POPGENE analysis indicated that the level of genetic variation of Ginkgo biloba ( H_e = 0.2408; H_o = 0.3599) was higher than other endangered or relict gymnosperms. The Wuchuan population possessed the highest level of genetic diversity(PPB = 56.82%, H_e= 0.2089, H_o = 0.3087),while the cultivated populations, Taixing(PPB = 34.09%, H_e= 0.1269, H_o= 0.1858) and New York(PPB= 23.86%, H_e = 0.0884, H_o= 0.1312), exhibited lower levels of genetic diversity than the possible natural populations (Tianmushan, Wuchuan and Dahongshan). Nei's genetic diversity analysis and analysis of molecular variance (AMOVA) showed that there was a certain level of genetic differentiation (G_st = 0.1476, Ф_st=14.26%) among the three possible natural populations. Some differentiation may be caused by human selective pressures and barriers to gene flow. The dendrograms of genetic relationships among populations and among individuals were constructed based on Nei's genetic distance. The Wuchuan and Tianmushan populations clustered in a clade. Close relationship was revealed between the New York and Dahongshan populations, which means that they are likely the offspring of the same natural population. The combined results of the analysis of population genetic structure and community investigation suggest that Wuchuan may be a natural population. Based on ecological and genetic information available for Ginkgo biloba , two management strategies are proposed. The first would consist of an in situ conservation plan that defines conservation areas free from significant disruption for the genetically most diverse population and the optimal habitat (namely Wuchuan). The second would be to cross-transplant adult plants or seedlings mutually among populations in order to enhance the gene flow. By this means, the genetic diversity resources of the species can be preserved to the greatest extent.

Isoetes is a genus of primitive vascular plants classified in the subdivision Lycopsida and occupies a very important position in the evolutionary history of the pteridophytes. In recent years, Isoetes has declined rapidly in population quantity (number) and has even disappeared from many locations in Mainland China. The genus is now considered to be rare and threatened or endangered in China and is listed among first category protected plants. The progressive decline in populations of Isoetes in Mainland China has been attributed to on-going anthropogenic changes; however, no data have been adduced to support this assumption. In this study, all present locations of Isoetes populations and locations where the genus had been previously recorded but is now extinct were investigated in Mainland China. The habitat characteristics, including elevation, water pH value and the conditions of substrate were measured at each site. Associated plants growing together with Isoetes were collected from each population. The result indicated that the geographic distribution of Isoetes in Mainland China is discontinuous and that every population of Isoetes is insulated from other populations. The three species of Isoetes in Mainland China occur at different elevations. The current populations showed no obvious differences in water pH and other characteristics. But habitats where Isoetes plants had been extirpated currently have higher water and substrate pH values compared to the period when the sites supported Isoetes populations. These sites also had higher readings than the current locations of remaining Isoetes populations. This study indicates that populations of Isoetes growing in marshy areas close to farmland are faced with intense competition from other hydrophyte species whose proliferation is encouraged by the use of fertilizers in adjacent farmland. The populations of Isoetes growing in the freshwater intertidal zone avoid competition with other hydrophytes because of the periodic fluctuation of water level and thus grow comparatively well. The results indicate that the geographic distribution and occurrence of Isoetes plants in Mainland China is closely correlated with elevation, water pH, competition with other species, and water depth.

From the background of sustainable development of forestry, biodiversity in forest should be maintained and protected when managing an ecosystem. However, as a result of the complex meaning of biodiversity, ordinary indices used in ecology and forestry are not commonly used by forest managers because of their high requirements of data and precision in order to convey so much information on biodiversity in a single index. On the basis of recent research on virgin forests around the world, Franklin advocates that diversity of forest stand structure could be used as an indirect indicator of forest biodiversity, and this has been accepted by many forest experts. As a result, some new ideas on how to manage forest ecosystems through structure control or restructuring have been put forward. In order to manage forest ecosystem through stand structure control, the significance of forest structure must be clarified and some new indices must be created for use in forest survey and in proper forest measurements. In this study, a set of structural diversity indices for broadleaved Korean pine forest were put forward and tested in different types of stands, including virgin forest, forest after selection cutting, and forest regenerated after clear cutting. Based on the measurement of stratified coverage in addition to plotless sampling, the vertical structure index (VSI ) and horizontal heterogeneity index ( HHI ) were generated, along with descriptions of other structural elements such as downed logs, standing poles and canopy gaps. The basic meaning of VSI is the volume of space occupied by branches and leaves, which was calculated by coverage in each layer and its weight. The basic meaning of HHI is the difference of coverage in all layers between locations in the stands, which was calculated as a community dissimilarity index. The bigger the two indices, the more habitat types for living organisms exist in the forest. At the same time, other ancillary indices, such as species composition, amount of coarse woody debris and gaps were surveyed through plotless sampling methods and transects with plots. Comparison between different stands of virgin forest indicates that these indices were precise enough to describe the spatial structure of the stands and were in agreement with analyses resulting from common forestry survey methods. Used in secondary forest stands, they could also provide more information than common single biodiversity indices. Before using data from plotless sampling, the similarity coefficients between plot sampling and plotless sampling were calculated. The precision of the two methods proved to be identical. Used in stands with different disturbance histories, these indices illustrated remarkable differences in the structures of the stands, indicating that the indices are suitable for forest survey and for guiding choice of management measures in forest ecosystem management. Disadvantages and methods for improvement of the indices are discussed and research priorities are proposed.

The spatial patterns of birds are closely related to the structure of habitats where they live and variations of habitat structure in different seasons may affect avian spatial use. Brown eared pheasant, Crossoptilon mantchuricum, is a world threatened species of pheasant that is native to China. From 1997 to 1998, the spatial pattern and its variations in this species in winter and breeding seasons, as well as its relation to habitat structure, were studied in Wulushan Nature Reserve of Shanxi Province, China. According to Poisson tests and χ2 tests, the spatial pattern of brown eared pheasant had a clustered distribution both in winter and in the breeding season, but most obviously in the wintering period. The comparisons of habitat availability with habitat utilization among the five types of habitat in winter and breeding seasons revealed remarkable differences in habitat selection. Brown eared pheasants avoided deciduous forests in winter. In the breeding season, they preferred to select deciduous forests and shrubs, while the utilization of coniferous forests and coniferous-deciduous mixed forests decreased in the study area. The results of discriminant analysis on habitat samples and control samples indicated that the amount of grasses, height of grasses, and diameter and height of trees were the main factors affecting habitat selection of brown eared pheasant in winter and breeding seasons. The results also indicated that the population spatial patterns of brown eared pheasant varied with seasonal changes of habitat structure and resource distribution. In winter, due to snow cover and cold temperatures, grasses were withered and the coverage in deciduous forests was very poor, which limited the activities of brown eared pheasants. In such harsh conditions, brown eared pheasants prefered to inhabit coniferous forests and coniferous-deciduous mixed forests, and they often aggregated in large flocks and fed together in habitats with good cover. In the breeding season, as the coverage in deciduous forests improved and the richness of grasses in the forests and shrubs increased, flocks of brown eared pheasant dissolved and most individuals lived in pairs. The tendency for clustered distributions of brown eared pheasant was generally decreased during this time. However, brown eared pheasant showed strict selection of habitats, which led to most breeding pairs concentrating in certain specific ranges with higher quality of habitats to defend territories and build nests. Thus the population of brown eared pheasant still lived in a clustered pattern on a large scale.

The nodulation and nitrogen-fixing resources of legumes from 54 counties (or towns) of Guangdong Province were investigated, and the corresponding rhizobia were isolated and collected. The investigation on nodulation and rhizobial collection for leguminous crops was representative of Guangdong because a widespread area was investigated within the province (from 110°54′ to 117°11′E and from 21°04′to 24°52′N). However, the investigation for wild leguminous plants was not complete due to their scattered distribution in the field and the restricted time. In total, 484 nodule samples were collected, belonging to 78 species and 37 genera, of which those of Crotalaria micans , Phyllodium elegans and Podorcarpium leptopus have not been previously reported. All of the nodule samples were collected from the natural nodulation legumes without inoculation with rhizobia, and two-thirds of the nodulated legumes originated from or are distributed in China, such as Albizia turgida , Archidendron (Pithecellobium) clypearia, Erythrophleum fordii, Ormosia glaberrima, Desmodium reticulatum, Phyllodium elegans , Podorcarpium leptopus , Millettia dielsiana, Mucuna birdwoodiana, and Kummerowia striata . The species Mimosa sepiaria, Crotalaria pallida, Sesbania cannabina, Acacia confuse, Acacia auriculiformis (all perennial legumes), Glycine max, Arachis hypogaea, Vigna rabiata, Vigna unguiculata subsp. sesquipedalis, and Vigna unguiculata subsp. cylindrica (all annual leguminous crops) were widely distributed in Guangdong Province. Their nodules were round, ellipse or coralloid in shape and pink or yellow in color, with sizes ranging from 1 to 10 mm in length. The nitrogenase activity of 24 species was determined using acetylene reduction method, and it ranged from 1 to 10 μmol C₂H₄·g^-1 fresh nodule·h^-1 . High nitrogenase activities were found among leguminous crops in the nodule sample of Glycine soja (21.29 ～ 46.76 μmol C₂H₄·g^-1 fresh nodule·h^-1) and among wild legumes in Codariocalyx gyroides (38.93 μmol C₂H₄·g^-1 fresh nodule·h^-1) of wild legumes. Among the 410 rhizobial strains isolated from the nodule samples, 58.4% colonies appeared within seven days and 41.6% after the 8th day. Of the 312 strains reinoculated to their corresponding host legumes, the nodulation rate was 96.3% for the leguminous crops and 86.9% for the wild legumes. Our investigation showed that all the 20 species of leguminous crops which had been recorded in the Flora of Guangzhou were nodulation and nitrogen-fixing.

Soil biota is an important gene library and forms a major part of global biodiversity. Soil biota drive the cycling of soil C and N biogeochemistry and influence trace gases metabolism. Soil microorganisms exercise direct effects on trace gases metabolism. Fungi, methanogens, CH₄-oxidizing bacteria, nitrifiers, and denitrifiers are the key types of communities regulating trace gases metabolism. Fungi often dominate degradation activities in litter due to their large individual body and strong enzyme chemical degradation abilities. “Oxic-anoxic” interfaces are active habitats for microorganisms and easily influence trace gases metabolism. “Organic-inorganic” layers, the rhizosphere of hydrophytes, and soil faunal intestines are the typical interfaces for trace gases metabolism. Soil fauna are pioneers for litter degradation and show indirect effects on trace gases metabolism, and these effects are very important. Arthropods (e.g.termites) and annelid (e.g.earthworms) metabolise CH₄ and N₂O, respectively. Since the soil ecosystem is complicated, it is necessary to develop an integrated technique comprising microbiology, stable isotope and molecular biology for studying soil biodiversity and its effects on trace gases metabolism. Research on soil biodiversity and its relationship to trace gases metabolism urgently needs to be developed in China.

Hybridization is common in nature, and widely used to create new breeds in agriculture. However, it can cause harmful consequences. Outbreeding depression can occur when adaptive gene complexes in one species (or population) are broken down by the immigration of genes that are adapted to some other environment. This causes mal-adaptation of progeny, lowering the future species (population) fitness. Genetic assimilation may dilute the genetic diversity of a small population if it hybridizes with a larger population of a different species. That is, no genetically “pure” progeny will be produced by small populations if their parents have a high probability of hybridizing. Hybrid offspring may be fitter than either parent due to heterosis, and may spread at the expense of the parent strain, and ultimately replace it. Through introgression, species or populations may also gain some adaptive traits such as resistance to disease, adversity, or pesticides, which they have never shown before, thus making them more difficult to control. Implications and suggestions concerning in situ and ex situ conservation of endangered species, ecological restoration and so on are proposed.

Five types of population viability analysis (PVA) models have been developed for estimating extinction risk of endangered species. They are analytic model, deterministic single-population model, stochastic single-population model, metapopulation model and spatially explicit model. The choice of PVA model types for endangered species depends on life history of the species studied and data available on the species. Compared with other tools in conservation practice, PVA is relatively precise and quantitative tool. However, poor quality of data and unclear assumptions on populations of some endangered species could influence precision of predictions of PVA models, therefore, PVA models should be used with cautions. PVA models have been increasingly used in conservation plans and management of endangered species in western countries. It has been used for (1) predicting future population size of endangered species; (2) evaluating extinction risk of endangered species in a given time; (3) assessing conservation options and determining which options will make endangered species persistence longer; (4) exploring effects of assumptions on small population demography,and (5) guiding field data collection for endangered species. Few PVA studies have been conducted on endangered species in China, compared with the disproportionally high number of endangered species in China. There is an urgent need for building PVA models specifically for endemic endangered species and conservation issues in China.