Genetic diversity of the endangered Chinese endemic herb Primulina tabacum (Gesneriaceae) revealed by amplified fragment length polymorphism (AFLP).

Primulina tabacum Hance, is a critically endangered perennial endemic to limestone area in South China. Genetic variability within and among four extant populations of this species was assessed using AFLP markers. We expected a low genetic diversity level of this narrowly distributed species, but our results revealed that a high level of genetic diversity remains, both at population level (55.5% of markers polymorphic, H (E) = 0.220, I (S) = 0.321), and at species level (P = 85.6% of markers polymorphic, H (E) = 0.339, I (S) = 0.495), probably resulting from its refugial history and/or breeding system. High levels of genetic differentiation among populations was apparent based on Nei's genetic diversity analysis (G (st)=0.350). The restricted gene flow between populations is a potential reason for the high genetic differentiation. The population genetic diversity of P. tabacum revealed here has clear implications for conservation and management. To maintain present levels of genetic diversity, in situ conservation of all populations is necessary.

[Correlation analysis on the damage of Mikania micrantha to plant communities in Neilingdind Island of Guandong Province, China].

The analysis showed that 58 species of trees, short-trees and shrubs in Neilingding Island of Guangdong Province were damaged by M. micrantha, of which, woody trees accounted for 67%. Short-trees and sunny shrubs were damaged most seriously, followed by the communities with low canopy density consisted of only 2 dominant species, and those with high canopy density consisted of 5 or 6 dominant species. The coverage of M. micrantha mainly related to the vertical structure of plant communities. The taller the community height and the more the synusia, the lesser was the coverage of M. micrantha. The damaging ratio mainly related to species diversity and community density. The higher the species diversity and community density, the lower the damaging ratio was. The damaging degree mainly related to the coverage of other liana. The more the coverage of other liana, the higher was the damaging degree of M. micrantha.

[Interspecies covariation analysis of dominant tree species in secondary succession of forest communities in Heishiding Natural Reserve, Guangdong Province].

Based on a 2 x 2 contingency table, the Pearson product-moment correlation coefficient and Spearman rank correlation coefficient were used to analyses the interspecies covariation of dominant tree species in different communities of secondary succession series in Heishiding Natural Reserve, Guangdong Province. In early succession stage, 14 pairs of tree species showed a significant interspecies covariation, and 9 pairs of species showed a negative coraviation, indicating that the species pairs needed the same habitats, while five pairs of species showed a positive covariation, which indicated that the species pairs needed different habitats. In the stage of needle broad-leaved mixed forest, only 5 pairs of species showed a significant interspecies covariation, and they were all positive covariation, which indicated the main species needed the same habitats and the interspecies competition were going. In the stage of evergreen broadleaved forest dominated by heliophytes, 4 pairs of species showed a significant interspecies covariation, which was the least one in secondary succession series. Three pairs of them showed a positive covariation. It was the result of interspecies competition that the species pairs needed the same habitats. In the stage of evergreen broadleaved forest dominated by mesophytes, 20 pairs of species showed a significant interspecies covariation, which was the most one in secondary succession series. Nineteen pairs of them showed a positive covariation. It showed positive covariation between species in upper tree layer and in middle or lower tree layer, but dominant species in upper tree layer had no significant interspecies covariation.

[Fractal characteristics of particle size distributions of mangroves soils in Yingluo Bay].

Based on fractal theory, the fractal characteristics of particle-size distributions of mangrove soils in Yingluo Bay (21 degrees 28'N, 109 degrees 43'E) were studied. The results show that the fractal dimensions of the soils ranged from 2.6837 to 2.8834, and decreased in the order of sand loam < light loam < medium loam < heavy loam < light clay. The fractal dimensions of the soils on exterior beach were lower than those on middle and inner beaches. There was a significant positive linear relationship between fractal dimension and soil salinity and organic matter content. The major factors that influenced the fractal dimensions of the soils were community type, soil texture, beach position, soil salinity, and soil organic matter content.

[Dynamics of biomass and net primary productivity in succession of south subtropical forests in southwest Guangdong].

Coniferous forest (Pinus massoniana community), pine-borad leaved mixed forest (Pinus massoniana + Castanopsis kawakamii + Schima superba + Liquidambar formosana) and evergreen broad-leaved forest (Ixonanthes chinensis + Artocarpus styacifolius + Ormosia glaberrima + Cryptocarya concinna) are the three main communities representing 3 major stages in a secondary succession series in Heishiding Nature Reserve, Guangdong Province. Their biomass and net primary productivity (NPP) were studied by using harvest method (for trees and lianas) and clear cut method (for shrub and herb). The biomass and NPP were 246.697 t.hm-2 and 14.715 t.hm-2.yr-1 for the coniferous forest, 287.367 t.hm-2 and 17.179 t.hm-2.yr-1 for the pine-broad leaved mixed forest, and 357.976 t.hm-2 and 18.730 t.hm-2 yr-1 for the evergreen broad-leaved forest, respectively. These results indicated that these three stages were very close in the succession process, and that coniferous forest and mixed forest were more mature, while broad-leaved forest was relatively young. Therefore, under the conditions of no or only minor disturbance, their biomass and NPP showed an increasing trend with the succession of the forest communities in Heishiding.

[Accumulation and cycle of heavy metal in Sonneratia apetala and S. caseolaris Mangrove Community at Futian of Shenzhen, China].

The absorption, accumulation, distribution and cycle of Cu, Pb, Zn, Cr and Ni in S. apetala and S. caseolaris Mangrove Community at Futian Mangrove Nature Reserve of Shenzhen were studied. The results showed that the Cu, Pb, Zn, Cr and Ni contents in forest soil were increased from bottom to surface layer, and the storage of the five heavy metals in the surface layer(depth 0-30 cm) was Zn > Pb > Ni > Cr > Cu. The concentration ability was S. caseolaris > S. apetala > K. candel. The existing accumulation of Cu, Pb, Zn, Cr and Ni in the community were respectively 23,019.61 micrograms/m2, 23,429.65 micrograms/m2, 117,870.41 micrograms/m2, 6835.79 micrograms/m2, 12,995.08 micrograms/m2. The annual absorption were 6592.20 micrograms/m2, 2664.77 micrograms/m2, 24,123.56 micrograms/m2, 853.25 micrograms/m2, 1990.86 micrograms/m2, respectively. The annual return were 3179.50 micrograms/m2, 1300.64 micrograms/m2, 8401.31 micrograms/m2, 398.99 micrograms/m2, 646.20 micrograms/m2, respectively. The annual net retention accumulation of Cu, Pb, Zn, Cr and Ni in the community were 3413.07 micrograms/m2, 1364.13 micrograms/m2, 15,722.25 micrograms/m2, 454.25 micrograms/m2, 1344.66 micrograms/m2. The turn over period of Cu, Pb, Zn, Cr and Ni were 8, 19, 15, 18 and 21 years.

[Progress in studies on an exotic vicious weed Mikania micrantha].

Mikania micrantha is a perennial weed of Astraceae native to south and central America. It has invaded Southeast Asia, Pacific region and South China. Because Mikania micrantha grows very fast and is hard to control, it has become one of the world's worst weed. In this paper, the history and status of the study on Mikania micrantha was reviewed. The research on Mikania micrantha was mainly focused on its biology, ecology, harm and control. Although some progress in the research was obtained, there is no dramatic breakthrough in the control of Mikania micrantha so far. There fore, it needs more work to solve the problems resulted from the invading Mikania micrantha.