Wide adoption of a few homogeneous lines of germplasm would reduce the genetic diversity of crops, and decrease their resistance and/or tolerance to biotic and abiotic stresses, and therefore reduce the stability of crop production. Based on analysis of pedigrees of varieties from 20 major maize producing provinces in China between 1982-1997, we studied economic impacts of genetic uniformity on maize production. The results indicate that there is a significant negative correlation between genetic uniformity and maize yield. One percent increase of genetic uniformity will cause 13% average yield decline. At the same time, the research also showed that genetic uniformity and variety uniformity are two independent variables. To enrich genetic diversity of the varieties, the government should make policies to increase breeder's incentives to develop new improved varieties using diverse materials.

Metasequoia glyptostroboides, a “living fossil” plant endemic to China, has been cultivated for more than fifty years. In order to evaluate to what extent the cultivated populations have conserved the genetic variation of the wild ones, we estimated the allozymic variation and genetic diversity in eight cultivated populations using isoelectric focusing in thin-layer polyacrylamide slab gels. Twenty-three loci of nine enzyme systems were detected and used for estimating population genetic diversity. Obvious difference in allele frequency was observed in eight of 23 loci, and rare alleles were detected in two populations. Genetic variability of cultivated M. glyptostroboides was low (PPL = 33.15%, A = 1.375, H_e = 0.161), and the genetic diversity was lower in cultivated populations than in relict ones, indicating that genetic diversity of cultivated populations could not completely cover that of relict M. glyptostroboides. Based on the allozymic variation data, a UPGMA dendrogram was constructed, comprising nine individuals of Metasequoia glyptostroboides var.caespitosa from Qianjiang of Hubei Province and nine individuals from each of three M. glyptostroboides populations, i.e., Qianjiang, Wuhan and Shanghai. Moreover, the genetic relationships among the population of M. glyptostroboides var. caespitosa and eight populations of M. glyptostroboides were analyzed. These analysis suggested that Metasequoia glyptostroboides var. should not be treated as a variety of M. glyptostroboides.

The genetic diversity of Paeonia delavayi, a species endemic to Southwest China, was analyzed using inter-simple sequence repeat markers (ISSR). A total of 116 bands were amplified from 16 natural populations and one ex situ conserved population by 10 informative and reliable primers of 100 pre-screened primers. Of them, 92 ISSR loci were polymorphic. A relatively high level of intraspecific genetic diversity was revealed: PPB = 44.61%,H = 0.1657 and I = 0.2448 at population level; PPB = 79.31%, H = 0.2947 and I = 0.4355 at species level. The G_ST = 0.4349 indicated a high degree of genetic differentiation occurred among P. delavayi populations. The results of genetic diversity study, combined with field survey and previous investigations, suggest that P. delavayi is not endangered.

Euryodendron excelsum, Apterosperma oblata, and Camellia changii are three species of the family Theaceae endemic to China. Genetic diversity of the three endangered species was studied using random amplified polymorphic DNA (RAPD). A total of 206－305 bands were generated by 20-24 random primers. Percentages of polymorphic loci(PPL) of the three species were 51.80％, 80.26％ and 38.83％, respectively, and coefficients of gene differentiation (G_ST) were 0.3566, 0.1713, and 0.1242, respectively. The results indicate that Apterosperma oblata, with wider natural distribution, has higher genetic diversity than the other two species with restricted natural distributions. Genetic variation mainly existed within populations; however, population genetic differentiation was obviously higher in Euryodendron excelsumthan in the other two species, which possibly resulted from habitat fragmentation. Based on the different genetic structure, we put forward some conservation strategies, including in situ preservation, establishing a conservation centre for endangered species of the family Theaceae in Guangdong, and developing fast propagation techniques.

Adiantum reniforme var. sinense is an economically important plant species endemic to China. It is only found in a few regions of the Chongqing Municipal Region. For decades, its distribution has been shrinking as a result of over-exploitation, which has caused endangerment of this species. To assist in efforts to effectively conserve this species, we investigated the genetic variation of six natural populations using isoelectric focusing in thin-layer polyacrylamide slab gels. Fourteen loci of five enzyme systems were detected, of which seven were polymorphic. The mean number of effective alleles per locus (A_e) = 1.778, the percentage of polymorphic loci (P) = 0.441, the mean expected heterozygosity (H_e)= 0.199， and the mean observed heterozygosity (H_o)= 0.235. The results revealed that low levels of genetic diversity existed within the natural populations of A. reniforme var. sinense in comparison with other species of ferns. Only 1.49% of the genetic variation occurred among populations whereas 98.51% existed within populations, suggesting a very low genetic divergence among the populations. The equilibrium state of the populations was measured using Hardy-Weinberg equilibrium and the Fixation Index (F). The results showed that a mixed mating system was possibly the main heterogamy of this species, and its endangerment was caused by overexploitation and habitat loss.

Spartina alterniflora，originating in North America, has been introduced to China and has now invaded many inter-tidal zones of gulfs and estuaries in China. With its spread, Scirpus mariqueter,a native grass species, has experienced a concurrent decrease in area. Based on field investigation at Chongming Dongtan Wetland and potted plant competition experiments at Fudan University, we compared growth characteristics and relative competitive ability between the two species. The results indicated that in terms of height, coverage, above-ground biomass, below-ground biomass, and mean seed number per spike, values for Spartina alterniflora were all significantly higher than those of Scirpus mariqueter.However, the density and number of flowering tillers per square meter for Spartina alterniflora were significantly lower than those of Scirpus mariqueter.In terms of seed output per square meter and seed germination rate, there were no significant differences between the mature populations of the two species. Both interspecific and intraspecific competition between Spartina alterniflora and Scirpus mariqueter remarkably reduced the number of ramets, the proportion of fruiting ramets, the above-ground biomass and the number of corms (only Scirpus mariqueter has corms). The interspecific relative competitive ability (measured as relative neighbour effect index, RNE) of Spartina alterniflora was significantly greater than that of Scirpus mariqueter. The obvious growing advantage of Spartina alterniflora compared with Scirpus mariqueter might explain its greater interspecific competitive ability, which might explain its successful invasiveness into the native Scirpus mariqueter community in the Yangtze River estuary.

Epiphytes play important roles in biodiversity sustainability, water and nutrient cycling in forests. Based on data from 80 host trees, we analyzed the composition and distribution of epiphyte species in the montane moist evergreen broad-leaved forest at Xujiaba region, in Ailao Mountain of Yunnan. The results showed that the epiphytes were abundant in this montane forest. In total, 69 epiphyte species belonging to 49 genera and 33 families were identified. Of these, 46.4% and 53.6% were vascular and bryophyte epiphytic species, respectively. The Shannon-Wiener index and Simpson index were 2.93 and 0.91 for vascular epiphytic species, and 3.31 and 0.95 for bryophyte epiphyte species, respectively. Among the epiphytic fern species, Lepisorus scolopendrium, Vittaria flexuosoides, and Polypodiodes amoena var. pilosa were abundant. Aeschynanthus buxifolius, Briggsia longifolia and Agapetes mannii were the dominant epiphytic seed plant species. Most trees investigated were covered with rich bryophyte epiphyte species. The common species were Bazzania praerupta, B. ovistipula, Chandonanthus hirtellus, Homaliodendron flabellatum, Symphyodon perrottetii, Dicranodontium denudatum, Meteoriella soluta and Kindbergia praelonga. The bryophyte epiphyte species mainly distributed on the trunks, while vascular epiphyte species were in the tree crowns. A significant positive correlation was found between trunk size and epiphyte association. Major epiphytes, especially larger epiphytic species, occurred on medium and large stems. There was no significant positive relationship between epiphyte species and hosts, although a small number of epiphyte species only occurred on some specific trees.

Wuyishan National Nature Reserve is a key area for biodiversity in SE China. We investigated the species composition and species diversity of the evergreen broad-leaved forests, a widely distributed vegetation type in the reserve. Our study was conducted on two 2400-m2 plots, the permanent plots of the China State Forestry Administration. A total of 311 vascular plant species, belonging to 138 genera and 67 families, were recorded. Among them, there were 160 tree species, 89 shrubs, 25 lianas, and 37 herbs. Based on importance value, Castanopsis carlesii, C. eyrei, Adinandra millettii, Dendropanax dentiger, C. fabri, Engelhardtia fenzelii, C. fargesii, and Cyclobalanopsis glauca are the top eight dominant species. Based on relative basal area (RBA), Castanopsis, Cyclobalanopsis and Adinandra are the dominant genera in the tree layer, with RBA values of 52.0%, 6.4%, and 4.5%, respectively. Fagaceae and Theaceae are the dominant families, with the RBA value being 60.1% and 12.2%, respectively. The Shannon-Wiener index (H′) of the tree layer is about 3.0. The indicies of H′and Pielou evenness index (E) both increased with sampling area, and stabilized at 1500 m2 and 1000 m2, respectively. The species-area curve indicated that specie richness stabilized when sampling area was above 4500 m2. The trees with DBH less than 10 cm accounted for 76.3% of the total trees. The forest community is dominated by evergreen tree species although deciduous species are frequent.

During 2002 and 2003, the habitat characteristics of wild Chinese alligator were studied in the National Nature Reserve for Chinese Alligator in the south of Anhui Province by collecting samples from among the 22 locations where wild Chinese alligator used to occur or occur currently. Eight ecological factors potentially related to alligator occurrence, i.e., shelter condition of bank, situation of islands, stability of water, pH value of water area, snail abundance, texture of soil, density of bamboo, and vegetation type, were measured according to data collected from each location. The habitat characteristics of wild Chinese alligator have been analyzed and studied with the methods of resource selection functions (RSF) and principal component analysis. The results showed that association of the above 8 factors to the survival of the wild Chinese alligator followed the following descending order: shelter condition of bank, pH value of water area, snail abundance, density of bamboo, stability of water, texture of soil, situation of islands and vegetation type, with the shelter condition of bank as the major factor (OR=13.628) and situation of islands and vegetation type as the least associated.

Brown eared pheasant (Crossoptilon mantchuricum) is a globally threatened species endemic to China. From 1998 to 2000, we studied the habitat factors influencing the wintering population density and flock size of the brown eared pheasant at two study sites in Luyashan Nature Reserve, Shanxi Province. The result showed that coniferous forests are suitable wintering habitat for brown eared pheasant, significant by χ2 test. Of the two sites studied, Chedaogou has larger area of coniferous forest, and better habitat connectivity for brown eared pheasant. In contrast, at Meidong, there are fewer feeding sites and shelters, resulting from more farmland and bare land. The results of one-way ANOVA analysis of microhabitat structure, combined with wintering habitat selection factors, indicate that canopy density and height of trees are the main factors influencing habitat selection by brown eared pheasants. In Chedaogou, tall trees and dense forests provide richer food, better roost sites and shelters, and thus attract more brown eared pheasants. The results suggest that habitat connection, microhabitat structure and human disturbance are the key factors influencing local population density and flock size of the brown eared pheasant.

Based on the data from four oceanographic censuses in the East China Sea （23°30′－33°00′ N, 118°30′－128°00′ E）during 1997－2000, and by means of qualitative and quantitative parameters, we analyzed the species composition, species number, and species diversity of pteropods and their relationships with environmental factors. A total of 21 pteropods species were observed in the East China Sea, of which Creseis acicula， Limacina trochiformis，Agadina syimpsoni， Desmopterus papilio，C. virgula var. comica， Cavolinia longirostris，Creseis virgula，C. clava，Hyalocyliz striata and Paraclione longicaudata were common species; Limacina inflata and Pneumoderma atlanticum were subordinate species; and the remaining 9 species were rare. According to seasonal alteration rates (R), obvious alternations of pteropods species occurred from spring to summer and from autumn to winter. The species number of pteropods peaked in autumn (20 species), followed by summer (15 species) and winter (14 species), and was lowest in spring (5 species). Results of regression analysis showed that the distribution of species number was affected only by water temperature in spring and winter, whereas it was dependent on water temperature, 10-m salinity and bottom salinity in summer and autumn. In winter and spring, because of low temperature and a nearshore weak warm current, species number was relatively low, and species diversity (H′) was greater in the south or in nearshore areas than in the north or nearshore. From summer to autumn, though this trend still remained, the difference between nearshore and offshore areas was significantly reduced. This is because the Taiwan Warm Current brought more species to the nearshore region and the north part of the East China Sea.

Microsorium membranaceum var. carinatum, a newly published variety, can be distinguished easily from the original variety M. membranaceum var. membranaceum by the stipe morphology. The cross section of stipes is triangular in the former， but semicircular in the latter. Here phylogenetic relationship of the two varieties was investigated based on the sequence analysis of chloroplast rbcL，rps4，trnL-trnF， and rps4-trnS intergenic spacers. Furthermore, the published relevant sequences from other ferns were also analyzed for the comparison of genetic distance. As a result, no sequence difference in the studied four cpDNA regions was found between M. membranaceum var. carinatum and M. membranaceum var. membranaceum, but some difference in the corresponding DNA fragments is present among other fern varieties. Hence, the status of Microsorium membranaceum var. carinatum as a distinct variety is not supported by the DNA analysis.