Abstract:The fragility of ecosystem is a wide-confining term and is regarded as inherent property of an ecosystem. It could display only when exposed to disturbance which causes the degradation of ecosystem however it is impacted by natural or nonnatural factors. The concepts of fragility and stability, the fragility in relation to species invasion and extriction, to diversity and stability of ecosystem, to primary productivity, to niche differentiation as well as to microclimatic change of ecosystem are discussed. The application of theory of fragility to the vegetation recovery is suggested.

Abstract:Phytosociological parameters, soil and temperature conditions, importance values of species, life form, leaf size and grass biomass in vegetation of Pirghar Hills, South Waziristan Agency, Pakistan, were investigated during summer 1995. The air and soil temperatures were higher on south facing slopes which decreased with increase in altitude.The vegetation, life form and leaf size of south and north slopes differed at similaraltitudes. Leptophyllous species increased with the rise in altitude. The fresh herbage production was 500 g m-2 at 2000 m on north slope which gradually decreased to 170 g m-2 at the hill top. A similar trend was observed for the south slope which had higher productivity than comparable north slope. The original woody species are present on the hills as isolated individuals due to degradation. There is need for restoration of the habitat.

Abstract:Botanical surveys were conducted during June 1995 and January 1996 toinvestigate the invasion and establishment of native plant species in plantations. Ten plotswith the areas varying from 200 to 400 m² were surveyed in three types of plantations,Lophostemon confertus, Acacia confusa, and Schima superba forests. A total of 184 wildgrowing and mostly pioneer species, belonging to 70 families and 139 genera. were found in these plantations. Approximately 42% were tree taxa, representing 20% of the total tree flora in Hong Kong. The most common native species in plantations were bird-dispersed and were also common in natural secondary forests. The Shannon's indices of the surveyed plantations varied from 0 to 2.66, and appeared to increase with age of the plantations. Plantations play an important role in accelerating restoration of forest cover in degraded areas and the development of biodiversity. The ecological function of plantations can be improved by using a combination of fast growing exotic species and bird dispersed native species so as to accelerate succession.

Abstract:The community structure including species composition, horizontal structure and vertical structure, and the organization structure of Pinus massoniana community on Nan' ao Island were investigated in 1996. The results showed that the community was composed of 28-32 species in 3 plots, and could be divided into 2 tree layers, a brushwood layer and a herb layer. The average individual density of tree layer in 3 plots of the community was 1.7- 3.2 individuals m^-2, and the Shannon-Weiner index of diversity was 1 .715 - 3.269. The ecological dominance of the community was 0.223 - 0.102, and the evenness index being 0.439 - 0.818. Pinus massoniana community is a pioneer community on disturbed island which can be developed into coniferous-broadleaf mixed forest.

Abstract:This paper deals with nutrient characteristics of litterfall in forest of Dinghushansituated at 23°08'N, 112 ° 35'E. The dynamics, variation among seasons and species, and composition of litter nutrient were investigated during 1991. It was shown that 1itter nitrogen content slightly changed seasonally with variation coefficient below l5% for most species. Seasonal variation of P, K and Na contents in litterfall was greater than that of N. No significant correlation between elements was found in litterfall. The analysis of variance indicated that litter nutrient except for phosphorus differed significantly among species, and the litter nutrient except for magnesium did not differ significantly among seasons. The annual nutrient return through litterfall amounted to 37.1 1 kg hm^-2 N, 15.03 kg hm^-2 P, 27.01 kg hm^-2 K, 37.1 1 kg hm^-2 Ca, and 12.19 kg hm^-2 Mg. The amount of nutrients in litter of Castanopsis chinensis ranked first, following by Schima superb a. The nutrient peak in littelfall occurred in August when typhoon brought down lots of branches and feares. Another peak was detected in April. Lowest litter nutrient appeared in December.

Abstract:The Rhizobium sp. strains 8638L, 8638M and 86385 were isolated from root nodules of Albizia falcataria which were Gram-negative rods with a subpolar flagellum, the cell sizes being 0.53 ×1 .17, 0.66 ×1.95 and 0.66 × 2.03 up, respectively. The growth of the three strains colonies in yeast-mannitol (YM) liquid medium had long doubling time (7.79, 10.16 and 8.7 h, respectively). They grew slowly on YM agar, and could produce alkali, but could not grow on medium with 5% NaCl and at 39 ℃. Physiological and biochedrical characteristics of the three rhizobial strains were examined. The nodulation and nitrogenase activity in seedlings of A. falcataria inoculated with the strains isolated from nodules of the same tree species were tested, which provided satisfactory results. The strains were shown to have nitrogen fixing ability under self-growing condition.

Abstract:Pollination ecologyofa liana spedes， Bauhinia championii(Benth．) Benth， was investigated in Hong Kong in August 1997．It turned out that the flowefs of this species were pollinated／visited by several species of wasps， bees and butterflies． The peaks of stigma reeeptivity roughly Concurred with the peaks of insect activities．

Abstract:The Hengduan Mountains Region is a part of the Qinghai-Xizang Plateau and islocated in the east of Xizang, west of Sichuan and northwest of Yunnan provinces insouthwest China with a total area of c. 0.5 million square kilometers. During the revision of Taraxacum for Florae Reipublicae Popularis Sinicae, the author examined the specimens that deposited in the major herbaria of China. Eighteen species of Taraxacum was reported in this region.

Abstract:Based on the study of Illigera B1. specimens from China, I. grandiflora W. W. Sm. et J. F. Jeff. var. microcarpa C. Y. Wu ex Y. R. Li and I. grandiflora W. W. Sm. et J. F. Jeff. var. pubescens Y. R. Li are regarded as two new synonyms of I. grandiflora W. W. Sin. et J. F. Jeff., while I. rhodantha Hance var. Dunniana (Levi.) Kubitzki is regarded as a nwe synonym of I. rhodantha Hance. I. brevistaminata Y. R. Li is a new record to Guangdong and Guangxi, and I. grandiflora W. W. Sm. et J. F. Jeff. is a new record to Sichuan.

Abstract:Diurnal changes of SOD, POD and PEPCase activities, pigment contents and chlorophyll fluorescence parameters were compared between C₃ plant peanut (Arachis hypogaea) and C₄ plant maize (Zea mays) under natural condition and photooxidation condition. Plant leaves were collected at g:00(a.m.), 12:00(noon) and 15t00(p.m.) in the field during a day, respectively, and then treated by 500 umol/L methyl viologen (MV) under 1500 umol m^-2s^-1 light intensity for 30 min. In the midday (12: 00), Fv/Fm in untreated peanut leaves decreased by 16% indicating that the photoinhibition occured, while that in untreated maize leaves showed no change. After MV-photooxidation treatment, the maximal decrease in chlorophyll and carotenoid were found in both peanut and maize leaves at 12:00. The antioxidative ability was related to SOD activity but seemed not to be related to PEPCase activity. Under MV-photooxidation, Fv/Fm, q_p and PSII were found to have a maximal decrease in maize leaves and a minimal decrease in-peanut leaves at 12: 00. MV-induced q_N and KD (coefficient of heat dissipation) were increased in peanut leaves but decreased in maize leaves during a day. It is proposed that a different mechanism in response to photooxidation may exist between C₃ plant and C₄plant.

Abstract:Jasmonic acid and its derivative such as methyl jasmonate (Me-Ja) belong to ubiquitous cyclopentanane compounds that are claimed to represent a new type of regulator for plant groWth and development. Its physiological activities were similar to those of abscisic acid (ABA). A biological role of Me-Ja was suggested to substitute ABA in the developmental regulation of seeds under desiccation. So we wish to test the idea that it might be involved in seed germination. After peanut seeds germinating in the Me-Ja solution (0.01 -5 mmol/L or 0.001 - 100 umol/L) for 7 days in the dark (28 ±1℃), the germination percentage could hardly be decreased, but the growth of hypocotyl and radicle were much slower in high Me-Ja concentration than that in water. The activities of amylase and endopeptidase in cotyledons were inhibited partially by high concentration of Me-Ja, and promoted by low concentration. But the lipase activity was strongly inhibited in all Me-Ja treatments. The degradation of starch and salt soluble protein were inhibited partially by high Me-Ja concentration, while arachin and lipid degradation were inhibited partially at all Me-Ja concentrations. Our previous experiment showed that the inhibition of peanut seed germination by ABA was mainly via the depression of endopeptidase activity, while in present study, the decrease of germination by Me-Ja was probably due to the inhibition of lipase activity and lipid degradation. It is suggested that there is an essential difference between ABA and Me-Ja in inhibiting the gerdrination of peanut seeds.

Abstract:Mango(Mangifera indica L. cv. Zihua) inflorescences were treated with salicylic acid at 0, 50, 100, 150, 200 and 250 mg L-1. The results indicated that the disease index of mango fruitS caused by Colletotrichum gloesporioides was decreased significantly when the inflorescences were treated with salicylic acid loo mg L-1. salicylic acid had no inhibitory effect on the spore germination and the colony growth. It may be concluded that salicylic acid could induce mango fruits to have the effect resistant to Colletotrichum gloesporioides.

Abstract:The plant growth retardant triadimefon was used in culture by shoot apex of Brassica campestris ssp. chinensis var. utills. Triadimefon at low concentration (1- 5 umol/L) increased the propagation coefficient of shoot and leaf number, decreased shoot vitrification, and improved the growth of seedlings. It was also found that the rooting ratio was increased with increasing concentration of triadimefon in the medium. It is suggested that triadimefon may be used as a good plant growth regulator in rapid multiplication of Brassica campestris ssp. chinensis var. utilis.

Abstract:Excised cotyledons of mature cucumber seeds were cultured on wet filter paper without exogenous hormones and nutrients (26 ±1℃, 2.92 W m-2, 14h day length). During 0 to 4 days after excision, the size and fresh weight of cotyledons increased rapidly, and the dry weight remained almost constant. After the 4th day of culture, the fresh weight and the area of cotyledons continued to increase, although more slowly than before, while the dry weight decreased quickly (Fig. 1). Respiration intensity and chlorophyll content of the cotyledons increased quickly before the 4th day, and reached the peak simultaneously at day 4, and then declined obviously (Fig. 2). The contents of mineral elements in detached cotyledons appeared to change within 0 to the 6th day (Table 1). With the exception of putrescine content decreasing slightly in the 2nd day of culture, all of the contents of spermine. spermidine and cadaverine in cotyiedons increased steadily. butthe increment was different. Thus, polyamine synthesis in cucumber cotyledons was not generally impaired after excision (Table 2). The contents of GA3 and ABA in cotyledons were to some extent increased, and the contents of IAA and ZT increased markedly, indicating that the detached cotyledons were capable of synthesizing the hormones during this period (Table 2). The contents of DNA, RNA and acid-soluble protein increased obviously within the first 2 days, while DNA content declined quickly, and the acid-soluble protein content fluctuated, meanwhile, RNA content remained almost unchanged. In the first 4 day, the content of alkali-soluble protein decreased continuously (Fig. 3), indicating that the detached cotyledons kept metabolic activity of nucleic acids and proteins.

Abstract:Fourteen DNA samples, of which 2 cultivated and 12 wild rices, were amplified for random amplified polymorphic DNA (RAPD) analysis with 18 random primers, and 147 polymorphic bands were obtained. The genetic similarity coefficient was calculated by UPGMA cluster analysis. Results showed that (1) Oryza rufipogon had close relation to cultivated rice, and Jiangyong wild rice was more closely related to Japonica, (2) The polymorphism of O. latifolia with CCDD genome was singular to that of O. australiensis wi...

Abstract:The influences of different explants from organs of Azadirachta indica, culture media and subculture times on callus growth and azadirachtin content in cultures were studied. The results showed that all of the calli induced from root, leaf, stem and bark had the capability of synthesizing azadirachtin, among which callus growth rate and azadirachtin from leaf explants were the highest. BS medium with low anunonium salt had good result for callus growth, while MS medium with high ammonium salt was beneficial...

Abstract:β-croyclodextrin promoted the formation of adventitious roots in cuttings of mung beau. 10^-3- 10^-2 mol/L β-cyclodextrin stimulated the formation of adventitious root primordia and increased the adventitious root number and the length of total adventitious roots. 10^-4- 10^-2 mol/L β-cyclodextrin enhanced the fresh weights, dry weights and content of soluble protein of adventitious roots, and decreased the average length per adventitious root and activity of IAA oxidase in hypocotyl cuttings. 10^-3 mol/L β-roycl...