Abstract:Plant population dynamics of a human-impacted masson pine (Pinus massoniana) plantation was studied in Dinghushan Biosphere Reserve in Guangdong for 5 years from 1990. Twenty paired plots with total area of 4 000 m² were investigated in plots of harvesting under-story, ground cover, and litter as the local peasants did for fuel annually once or twice, and in undisturbed plots as control. The results indicated that understory coverage and the shrub coverage in undisturbed plots increased annually, but those in disturbed plots remained little changed．However,the coverage of herbs was slightly increased before 1 992，and then decreased markedly in undisturbed plots，while that in disturbed plots was on the contrary． The coverage of main shrub and herb species was also measured． Species number of un derstory plants decreased annually from 41 to 30 in un disturbed plots． but that in disturbed plots remained more or less stable， only 2 species lost．The result showed that appropriate disturbance in understory of masson pine plantation could maintain species abundance，an d exhibited positive efect on natural regeneration of pine tree，but negative impact on pine growth． The possible succession of open masson pine forest toward pine-broadleaved mixed forest is discussed.

Abstract:According to the data collected for litter fall from Cunninghamia lanceolata-broadleaved mixed forest and C. lanceolata forest in Wuyishan National Nature Reserve in Fujian, a model of wave-type time series for analyzing the dynamics of litter fall was used to simulate the monthly change in litter fall in the two forests. Result showed that the model could satisfy the actual data. It is suggested that this method can be applied to the study of litter fall dynamics.

Abstract:The seeds of Castanopsis forgesii from evergreen broadleaved forest in Tiantong National Forest Park in Zhejiang Province were collected and embedded in the forest and in gaps to investigate seed germination and the growth of the seedlings. Germination rates of the seeds under forest and in gaps were 33.3±2.l％ and 31.7±7.1％, respectively, showing no obvious difference in the two habitats. Mean heights of one-year-old seedlings were 5.88±1.09 cm and 6.56±1.2 cm, respectively, showing that the difference was obvious．Biomass allocation of the seedlings in the gaps tended to be more in the roots，while those under forest was more in leaves.

Abstract:Fractal characteristics of soil aggregate structure under Cunninghamia lanceolata and Phyllostachys edulis mixed plantations in Fujian were studied by using fractal theory. Six plots with different Cunninghamia lanceolata and Phyllostachys edulis densities in mixed plantations, and two plots of pure stands of the two species were chosen. All the plants in plots were 19-year-old. Regression models for fractal dimension (D) of aggregated structure and water stable aggregate (>0.25 mm) content, and for D and destroyed structure percentage，were established．The effect of fractal dimension of aggregates on soil properties were evaluated by elasticity and limit analyses． The results showed that the higher the content of water stable aggregates(>0．25 mm or>5．0 mm)in soil，the smaller the fractal dimension of aggregates，and thus the beaer structure and stability the soil． The regression relationships of all the model were remarkable． Fractal dimension variation of aggregate structure had a great effect on soil properties， which will provide a scientific basis for the culture of such mixed forest.

Abstract:The distribution pattern of the species of Viscum L. and their host plants in China were studied. Based on the results of the biogeographical analyses of the host flora, with the distribution pattern of its extant species and data from karyotypical studies on the genus taking into consideration, the possible centre of origin of Viscum is speculated, and the migration route is suggested.

Abstract:The karyotypes of four species of Dunaliella were analyzed using Giemsa staining method. The organisms were cultured in Ben-Amotz medium with 1.5 mol/L NaCl at 25℃ in a 12/12 h light-dark cycle for three days to induce synchronous growth of the algae. The karyotypes were observed after a series of treatments including pretreatment with 0.05% colchicine for 12-16 h, hypoosmotic shock, fixation, and dropping from 60 cm high to glass slide for breaking the surface coat of Dunaliella cells. All species observed are haploid with short and bacilliform chromosomes． The chromosome numbers of Dunaliella species are n=13 in D．salina，n=20 in D．primolecta， n=l0 D．bardawil，and n=l6 D．parva．All the chromosomes are wim median centromere, and the primary constrictions were obvious.

Abstract:A study was conducted to determine the effects of UV-B on seedling growth and chloroplast ultrastructure of Psychotria rubra, Schefflera octophylla, Archidendron clypearia, Pterospermum heterophyllum, Sapium discolor and Albizia lebbeck. The seeds of these species were collected from Nature Reserves in Guangdong, and the seedlings were grown in growth cabinets programmed for a 28/20℃ light/dark temperature regime and a 12 h photoperiod. The 15-day-old seedlings were exposed to visible light (23μmol m^-2s^-1) supplemented with 7.2 kJ m^-2d^-1 or 14.4 kJ m^-2d^-1， or without UV-B radiation (contro1) for 30 and 60 days． Results demonstrated that UV-B radiation inhibited the growth of main roots and stems，decreased the number of lateral roots and leaf number as well as leaf area．UV—B radiation damaged membrane of leaf cells，particularly the structure of chloroplast membrane．Affected symptoms varied with plant species．Under UV-B radiation，the plasma membrane in Schefflera octophylla was contracted and corrugated， and separated from cell wal1． Chloroplast in S．octophylla and Pterospermum heterophyllum was dilated and even broken， the thylakoid dilated and adhered．In A rchidendron clypearia the mitochondria appeared to be cavitate．Starch grains in chloroplast in A．clypearia and Pterospermum heterophylla were increased， and the black particles in chloroplast in Schefflera octophyUa and Sapium discolor were also increased， and appeared on mitochondrial membrane of S．octophylla.

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Abstract:By using modified logistic model, the growth rate for basal area of dominant populations was studied in semi-natural mixed forest in Fujian Province. Among populations in communities Cunninghamia lanceolata I Alniphyllum fortunei I Castanopsis carlesii ( I ), Cunninghamia lanceolata I Castanopsis fissa I C. carlesii ( II ), Castanopsis carlesii I Cunninghamia lanceolata (Ⅲ), and Cunninghamia lanceolata / Alniphyllum fortunei / Castanopsis carlesii / C. fissa (IV), community IV had best growth rate for Cunninghamia lanceolata，showing that the more dominan t broad-leaved tree species dominated in mixed forest the better the C．1anceolata grew．In com un ity with dominant broad—leaved species not more than three，maximum growth rate for C．1anceolata appeared at 4-6 cm dbh，while that more than three，at 8-10 cm dbh．The growth rate for C． 1anceolata in the four com unities was in order in IV>II>I>Ⅲ.

Abstract:The effects of illumination, temperature and soil miosture content on germination and longevity of Hopea hainanensis seeds were studied. The results indicated that the best temperature for seed germination was 15-20℃. The seeds treated under full dark and under light (2 800 lx for 14 h and dark for 10 h) showed no obvious difference in germination rate. Optimum soil moisture content for seed germination was 30%-50%. Seeds spread in the room at ambient temperature in May in South Yunnan for 14 days had only 20％ germination rate， and the germination ability was completely lost at the l8th day.

Abstract:Mikania micrantha is considered to be one of the most serious tropical and subtropical weeds which is now widely distributed in Guangdong Province and mainly in Pearl Delta. Of the 51 counties and cities investigated in Guangdong, 24 were found to have its distribution. The habitat of this weed has a wide range: among natural vegetation, in cultivated land, orchards, nurseries, vegetable plots, forest plantations, roadside, plant hedge, refuse dump, and under sun or shade, in dryland or moist soil．The climatic condition，harmful effect，and the control of the weed are analysed and discussed．

Abstract:Great concern is focused on fruit softening since it occurs soon after harvest. It is generally accepted that fruit softening is due to the hydrolysis of cell wall components mediated by enzymes such as polygalacturonase, pectinesterase, cellulase, etc. Advances in studies of these enzymes and their role during fruit ripening and softening are summarized. Antisense RNA transgenic fruits showed that the fruits softened normally when gene expression in each of these enzymes was inhibited, which indicated that other factors may attribute to fruit softening． Several evidences indicated that turgor chan ge caused by amylase and invertase and the solution of pectin play role in fruit softening.

Abstract:A review is described of the accumulation of small molecule osmotic substance, such as proline, betain, polyol, polyamine, fructan, and macromolecule protein synthesis, such as late embryogenesis abundant protein, osmotin, water channel protein, K⁺ channel protein, ATPase and their related gene expression, which are closely correlated with salt tolerance in plants.