Abstract:Canopy meteorological factors, including solar radiation (R_s), precipitation (P), wind speed (W), relative humidity (RH), maximum temperature (T_max) and minimum temperature (T_min), and soil moisture content (SMC) within 4 m soil depth were daily monitored from Oct. 1, 1999 to Sep. 30, 2000 in an eucalypt plantation in Leizhou peninsula, Guangdong, China. Canonical correlation analysis (CCA) was employed to assess impacts of canopy meteorological factors on SMC. SMC differed significantly at different layers within 4 m soil depth, which was influenced mainly by precipitation in rainy seasons. SMC in rainy seasons increased with time due to the abundant precipitation. The coefficient of variance of SMC in rainy seasons was higher than that in dry seasons. SMC at 50 cm soil depth fluctuated obviously, which had a significant correlation with some meteorological factors such as solar radiation, precipitation, wind speed, vapour pressure deficit, and maximum temperature. Meteorological factors that affected soil moisture at deep layers (150, 250, and 350 cm) had almost similar pattern but differed from that at layer of 50 cm. The values of canonical correlation coefficients in rainy seasons were significant. Among the three canonical correlation coefficients and variables, the value of the first canonical correlation and its variance in covariates explained by canonical variables was the highest, which indicated that the canopy meteorological factors affecting soil moisture content were mainly by the first canonical variables.

Abstract:Nutrient accumulation and distribution in 33-year-old Fokienia hodginsii and Cunninghamia lanceolata plantation communities were determined during 1999 to 2000 in Sanming, Fujian, China. The results showed that the biomass in tree layer of F. hodginsii and the C. lanceolata communities were 228.8 t hm^-2 and 235.1 t hm^-2, respectively, and total accumulation of nutrient elements (N, P, K, Ca, and Mg) being 1283 kg hm^-2 and 1060 kg hm^-2, respectively. The accumulation of nutrient elements in tree layer or in the whole community for both plantations were in the order of K>N>Ca>Mg>P. The total accumulation of the 5 nutrient elements in different parts of trees was in the order of stem wood>branch>root>stem bark>leaf>dead branch for F. hodginsii plantation, and stem wood>root>stem bark>leaf>branch>dead branch for C. lanceolata plantation. The nutrient utilization efficiency of F. hodginsii was lower than that of C. lanceolata. Although over 94% of the nutrient elements in both ecosystems were stored in the soil, available nutrient elements in the soil which could be easily utilized by the plants were rather low, particularly, the reserve of available P in the soil was lower than that in the plants. The amount of annual retention of all the 5 elements in tree layer of the F. hodginsii and the C. lanceolata communities were 30.75 kg hm^-2 and 16.53 kg hm^-2, respectively.

Abstract:Castanopsis kawakamii is a rare species recorded as second grade of protected plant in China. A natural community of C. kawakamii forest with an area of 700 hm^2 at Shanmin in Fujian Province is considered to be the largest and unique C. kawakamii forest in China. According to data obtained from field investigation, the intraspecific and interspecific competitions of C. kawakamii in six communities were analyzed quantitatively by using Hegyi's competition index model for individual tree. Intraspecific competition intensity in this species reduced with the increase of diameter class of the trees. The competition intensity among each pair of species was in the order Pinus massoniana-Castanopsis kawakamii>C. kawakamii-C. kawakamii>Schima superba-C. kawakamii>Elaeocarpus decipiens-C. kawakamii>Litsea mollifolia-C. kawakamii>Symplocos stellaris-C. kawakamii. A remarkable regression model of the relationship between competition intensity and diameter class of objective tree individuals is established. The model can be applied to predict the competition intensity in forest of C. kawakamii.

Abstract:Eucalyptus grandis×Eucalyptus urophylla seedlings were used as materials to study the effects of boron on membrane lipid peroxidation and endogenous protective systems in leaves under low temperature. The results showed that relative conductivity rate, O₂^-. production rate, malondialdehyde (MDA) content and polyphenol oxidase (PPO) activity in leaves were increased at 5℃ with boron-deficiency (≤10 μmol/L). On the contrary, the contents of ascorbate (ASA) and soluble protein, the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were decreased. However, addition of 15 μmol/L boron in the culture medium could alleviate chilling injury and enhance the tolerance to low temperture in the seedlings.

Abstract:Artificial pure forests of Pinus rigida var. serotina, P. elliottii, Eucalyptus robusta, Schirna superba, Liquidambar formosana, and mixed forests of L. formosana/P. massoniana or P. elliottii, which were planted in 1991 in seriously disturbed lower hilly land in Taihe county, Jiangxi Province, were investigated after 10 years. Changes of species diversity in the restored vegetation were measured. Before afforestation there were only 7 species such as Setaria viridis, Arundinella hirta, Rosa laevigata and Smilax china. In 1993 and 2001, the number of species increased to 21 and 58, respectively. In condition of the same density of plantation, the species diversity in the vegetation of the plantations was high in pure conifer forest, followed by conifer broadleaved mixed forest and broadleaved pure forest. The effects of afforestation species, stand structure (pure or mixed) and especially stand density on species diversity were obivious. However, conifer forest was poor in water holding, the soil under which had lower content of organic matters. Conifer broadleaved mixed forest is best for maintenance and restoration of species diversity and for improvement of soil and ecological environment.

Abstract:Based on a long term survey of plant population dynamics, we investigated 26 gaps to study the factors that affect sapling species composition and biodiversity in gaps at different succession stages in Dinghushan Biosphere Reserve. Gap formation, gap size and age, topography and location, adult tree around gaps, saplings of tree species growing in the gaps were investigated. The formation of gaps resulted from landslide, storm, pest damage, etc. Sapling composition, sapling density and diversity in gaps were different due to different causes of gap formation. Species growing in the gaps were quite different because of their differences in shade tolerance and in succession stages. Differentiation of regeneration niche was caused by variation of gap size, age and topographic factor, which resulted in the appearance of sapling guild in the gaps.

Abstract:The pollens of rice (Oryza sativa), maize (Zea mays) and Pennisetum alopecuroides were stored under low temperature (4℃) how humidity (RH 45%) , low temperature (4℃) high humidity (RH 90%), high temperature (35℃) how humidity (RH 45%) and high temperature (35℃) /high humidity (RH 90%) to determine the changes in proteinase activity, contents of proteins and free amino acids in the pollens. The results showed that the degradation of protein and the increase of the content of free amino acids were slow under low temperature and high humidity, but it was rapid under high temperature. Among the pollens of the three species, proteinase activity in rice pollen was high, and the degradation of protein contents and the increase of free amino acids were rapid. However, proteinase activity in pollen of Pennisetum alopecuroides was low, and the changes in protein content and free amino acids were slow. These changes in maize were intermediate between the above two species.

Abstract:The roots of 13-day-old rice seedlings were pretreated with 50 μmol/L chlorpromazine or 500 μmol/L lanthanum chloride (LaCl₃) at 25℃ for 15 h to determine the changes in relative water content (RWC), malondialdehyde (MDA) content, relative permeability of cell membrane, and proline (Pro) accumulation in the seedlings under cold stress at 6-7℃ and light intensity at 200 μmol m^-2s^-1. The experiments showed that the RWC decreased, relative permeability of cell membrane and MDA content increased, meanwhile, the proline was accumulated under cold stress. Such trends were enhanced significantly in the seedlings pretreated with chlorpromazine or LaCl3 under cold stress.

Abstract:The leaves of Carica papaya seedlings cultured in pots were sprayed on both surfaces with free radical scavengers, i.e. vitamins C (10 mmol/L), E (6 mmol/L) and sodium benzoate (5 mmol/L), respectively one day before water stress treatment. Soil in pots was dried naturally to 12%-14% of moisture content, whereas for control at 60%-65%. The results showed that the pretreatment with free radical scavengers could effectively decrease the increment level of plasma membrane permeability, POD activity, MDA and H₂O₂ contents, retard the decrease of chlorophyll and soluble protein contents and the SOD activity in papaya under water stress. Among the free radical scavengers, the protective effect of vitamin C was best.

Abstract:Pollen morphology of 11 Bauhinia species endemic to China has been studied by light and scanning electron microscopy. A considerable variation in pollen morphology was observed among the investigated species, particularly in exine oranmentation and characters of the apertures. Pollen grains are tricolporate, but some of them are both tricolporate and syncolpate as in B. damiaoshanensis and B. quinanensis. All pollen grains are semitectate. Ornamentation are rugulose, rugulose-perforate, verrucose, foveolate-perforate, perforate-reticulate and reticulate. Based on exine ornamentation, two subtypes, Aurea subtype and Paucinervata subtype, are established under Integrifolia type of Larsent's classification.

Abstract:Development of aposporous embryo sac, embryo and pseudogamy were studied in tetraploid Paspalum distichum. In most cases, shortly after the megasporocyte developed into a tetrad, it began to deteriorate, meanwhile several nucellar cells became active and enlarged, Normally, 1-3 nucellar cells developed into mature aposporous embryo sacs characterized by 1 egg cell and 2 polar nuclei. The egg cell could spontaneously develop into proembryo prior to anthesis, whereas polar nuclei were involved in pseudogamy to develop endosperm after heading and pollination. When several aposporous sacs occurred in an ovule, only the sac near the micropyle developed endosperm while the other sacs did not. The frequency of twin-embryo seedlings geminated from mature seeds was low. Few sexual 8-nucleus embryo sacs as well as both sexual and aposporous sacs in the same ovule were found. It is suggested that the tetraploid P. distichum is considered to be a facultative apomict reproduced by apospory.

Abstract:Chromosome number and karyotype of Cycas debaoensis Y. C. Zhong et C. J. Chen from China isreported for the first time, which has karyotype formula of K(2n)=2x=22=6m+4sm+12T, belonging to Stebbins'3B type. Total length of chromosomes is 93.49μm, and ratio of asymmetric karyotype (As.K%) being 85.53%. The result reveals that the karyotype of this species is basically similar to that of C. micholitzii Dyer and C.multipinnata C. J. Chen et S. Y. Yang.

Abstract:Asymmetric somatic hybrids having wheat appearance were obtained from protoplast fusion of Triticum aestivum L cv. Jinan 177 (as acceptor) and UV irradiated A gropyron elongatum (as donor) using PEG (polyethylene glycol) method. The karyotype analysis was made in root tip of F₅ of different lines (Ⅱ-2,8-1,Ⅱ-Ⅰ-8) from a somatic hybrid, and was compared with the parent wheat cultivar Jinan 177. The results indicated that the hybrids were basically stable in chromosome morphology and number. However, some differences in chromosome morphology were observed between the hybrids and the parent, as well as among the three hybrids, suggesting that small chromosome fragments from Agropyron elongatum were integrated into the chromosomes of the acceptor (wheat).

Abstract:Three types of Dioscorea zingiberensis C. H. Wright, the diploid and the triploid from Qina, Yunnan Province, and the tetraploid from Chengkou, Chongqing, were compared by means of examining the morphology, chromosome numbers and isozymes. The results showed that the three types have obvious differences in leaf morphology and chromosome numbers: the diploid, 2n=2x=20； the triploid, 2n=3x=30； the tetraploid, 2n=4x=40. Zymograms of esterase isozyme and superoxide dismutase showed an obvious relation among the three types, but the polyploid ones had less bands and showed lighter-colored compared to the diploid one.

Abstract:Most serious threat to herbarium sheets is insect pest, the protection and control of which constitute one of the main works in herbarium management. Based on the experience for over 70 years of the management in the Herbarium of South China Institute of Botany and the improved technique for prevention of insect damage in recent years, some methods for herbarium pest control are proposed, such as using insect repellants, decontamination by deep freezing, fumigation with pesticides, and others.

Abstract:In specific rank, Blastus longiflorus Hand.-Mazz. has priority over B. apricus Hand.-Mazz. Therefore, a new combination, B. longiflorus var. apricus (Hand.-Mazz.) Y. L. Zheng et N. H. Xia, is made.

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Abstract:The development of embellum in guineagrass (Panicum maximum Jacq.) was observed under light microscope with traditional paraffin sectioning methods. At megaspore mother cell stage, one or more nucellar epidermal cells in micropylar end differentiated into embellum. As the ovule grew, the embellum developed more greatly and appeared to be enlarged and elongated. Mature embellums showed obvious polarity, the nucleus of which was near the micropylar pole of the cell. A big vacuolus almost occupied the whole chalazal pole. No starch grain accumulation was seen in embellum during its development in the present study, but its cell wall and cytoplasm were stained more densely than that of the common nucellar cells, suggesting that the embellum was full of soluble polysaccharide.

Abstract:The theoretical and technical updates of several research programs of vicarism historical biogeography (here as a counterpart of dispersalism historical biogeography), especially the cladistic biogeography and panbiogeography are briefly reviewed. The routinely use of molecular techniques in a broad field of historical biogeographical studies, and the rapid recognition of the theoretical and technical aspects of the phylogeography, have been the most remarkable characteristics in historical biogeography in the last decade. A prospect for the science is also briefly depicted.

Abstract:In vitro fertilization technique using male and female gametes completely isolated from their paternal and maternal structures has been developed for ten years. Using electric fusion, zygote, embryo and fertile plants of maize can now be produced in vitro from individual fusions of pairs of sperm and egg cells. The culture conditions allow control of the parameters of fertilization and early steps of zygote development. Although this technique was successfully performed only in maize it helped us to understand a lot of information about fertilization mechanism of higher plants. Following successful isolating male and female gametes and culturing artificial zygote, in vitro fertilization as a research platform can be extended to more purposes in the research of sexual reproduction in higher plants. We knew the phenomenon of sperm dimorphism in many plants and also confirmed the preferential fertilization of both sperm cells in Plumbago zeylanica since 1985. We, however, know nothing for molecular mechanism of gamete recognition in higher plants. Now the special genes of male and female gametes, and zygote can be screened out using isolated gametes, which changes the research method from cell structure to molecular level. Zygote activation is a very interesting topic in plant developmental biology. But it is difficult to probe the mechanism of zygote activation because egg cell and zygote are imbedded deeply in ovules. Using microculture of zygote from both in vivo and in vitro created, the zygote can be observed on schedule and manipulated using modern biological techniques. The first confirmed zygote activation was free calcium change at the beginning of development after fusion of both male and female gametes of maize. Fertile plants can be easily developed from few zygotes under in vitro condition by means of embryogenesis, which is greatly interested in transgenic study in higher plants. in vitro fertilization and zygote culture also have great potential in overcoming incompatibilities of interspecies barriers in creating new hybrid plants. The fusion of isolated gametes from different plants can create a artificial hybrid zygote which can not be obtained from normally sexual crossing. This review describes the significant advances in in vitro fertilization in the research of sexual plant reproduction of angiosperms and discusses its use in plant improvement in higher plants.