山东四种草本植物的核型研究

本文对山东４种草本植物进行了染色体研究。结果表明：阿尔泰狗哇花（Ｈｅｔｅｒｏｐａｐｐｕｓａｌ ｔａｉｃｕｓ（Ｗｉｌｄ）Ｎａｖｏｐｏｋｒ）的染色体数目为２ｎ＝３６,核型公式为Ｋ（２ｎ）＝３６＝３６ｍ,核型“１Ａ”型;求米草（Ｏｐｌｉｓｍｅｎｕｓｕｎｄｕｌａｔｉｆｏｌｉｕｓ（Ａｒｄｕｉｎｏ）ＲｏｅｍｅｔＳｃｈｕｌｔ）的染色体数目为２ｎ＝１２,核型公式为Ｋ（２ｎ）＝１２＝８ｍ＋４ｓｍ,核型“２Ａ”型;红秋葵（Ｈｉｂｉｓｃｕｓｃｏｃｉｎｅｕｓ（Ｍｅｄｉｃ）Ｗａｌｔ）的染色体数目为２ｎ＝３８,核型公式为Ｋ（２ｎ）＝３８＝１４ｍ＋２２ｓｍ＋２ｓｔ,核型“２Ｂ”型;蟋蟀草（Ｅｌｅｕｓｉｎｅｉｎｄｉｃａ（Ｌ）Ｇａｅｒｔｎ）的染色体数目为２ｎ＝１８,核型公式为ｋ（２ｎ）＝１８＝１６ｍ＋２ｓｍ,核型“２Ａ”型。     

Relationships among the seed rain,seed bank and vegetation of a Hawaiian forest

Abstract. Hawaiian ecosystems are prone to invasion by alien plant species. I compared the seed rain, seed bank, and vegetation of a native Hawaiian forest to examine the potential role that seed ecology plays in allowing alien species to invade native forest. Absolute cover of seed plants in the forest was 126 %, annual seed rain was 5 713 seeds m^-2 yr^-1, and the mean density of seedlings emerging from the seed bank averaged across four seasons was 1 020/m². The endemic tree Metrosideros polymorpha was the most abundant species in the vegetation, seed rain and winter seed bank. Overall, native seed plants comprised 95 % of the relative cover in the vegetation and 99 % of the seeds in the seed rain, but alien species comprised 67 % of the seeds in the seed bank. Alien species tended to form persistent seed banks while native species formed transient or pseudo-persistent seed banks. Dominance of the seed bank by alien species with persistent seed banks suggests that aliens are favorably placed to increase in abundance in the vegetation if the forest is disturbed.     

Flood drift and propagule bank of aquatic macrophytes in a riverine wetland

Abstract. Drift of aquatic macrophyte propagules was investigated in a wetland along the River Rhône, during the first flood after the growing season (i.e. in the winter of 1995–1996). Input and output drift were studied at the beginning, around the top, and at the end of the river overflow in the upper reach of a cut-off channel. The soil propagule bank was sampled along the study area before and after the flood. The amount and composition of viable propagule drift and bank were determined, analysed and compared. Drift densities and richness were on average higher at the outlet of the channel than at the inlet (respectively: 23.2 vs 13.1 viable propagules/100 m³ of water and 8.7 vs 2.6 taxa per sample). Immigrating taxa were mostly in the form of helophyte seeds, whereas numerous resident hydrophyte species left the disturbed area rather as vegetative propagules. Temporal variability in propagule bank structure was weak, and mean bank densities did not change before and after the flood (respectively: 33 047 ± 10 510 vs 35 653 ± 15 070 viable propagules/m² of ground, including Chara). However, the density of Elodea canadensis significantly increased after the flood while that of Eleocharis acicularis decreased. This contrast suggests that flood responses vary among species. Despite a broad overlap in the taxa (18 out of 25 were common both to drift and bank collections), no significant relationship occurred in composition or structural changes between flood drift and propagule bank. Flood acted as a means of distribution of existing propagules and also as a provider of new vegetative dispersal units.     

Restoration of high species density in calcareous grassland: the role of seed rain and soil seed bank

Abstract. A small-scale restoration experiment concerning a species-rich calcareous grassland was conducted over a 7-yr period. 20 yr of abandonment (1971-1990) resulted in both a strong reduction of the number of species and an absolute dominance of the shrub Crataegus monogyna and the grass Brachypodium pinnatum - which contributed 98% of the above-ground herb phytomass. The plot (3 m x 6 m) was cleared in September 1990 and thereafter yearly mown in autumn. Small soil seed bank samples were taken immediately after clearing and again in the autumn of 1996. The inner part of the plot showed a reduced soil seed bank compared to the plot underneath the vegetation outside the plot in 1990. Six years later an increased number of seeds in the soil in this inside area could be recorded mainly in the upper soil layer, although the amount was only 40% compared to the outside or control area. Ca. 20% of the species present in the restored vegetation were recorded in seed traps during the main seed dispersal period in 1997. Restoration of high species richness in the plot was a fast process during the first few years: from seven species in 1990 towards 39 three years later. This was significantly faster than the restoration process of the calcareous grassland at the same slope 20 yr earlier. This was probably due to the increased size of the community species pool at the site as a result of appropriate management during the last decades. Relative species number increase was highest at the largest scale during this experiment, viz. at the total plot area. The success of restoration of species-rich, dry grassland vegetation largely depends on the interaction between several conditions, e.g. seed availability, either originating from the seed rain or soil seed bank, favourable germination conditions and a successful development to a mature, seed producing individual. Germination and establishment strongly depend on suitable vegetation structure as a result of sustainable management.     

Classification of peatland vegetation in Atlantic Canada

Abstract. The peatlands of Atlantic Canada are classified in four plant alliances, consisting of 10 plant associations. The four plant alliances comprise the dry bog communities (Kalmio-Cladonion Wells 1981), wet bog communities (Scirpo-Sphagnion Wells 1981), hummock and ridge communities of slope and string fens (Betulo-Sphagnion Wells all. nov.), and poor, intermediate and rich fen plant communities (Scirpo-Myricion Wells 1981). Distribution maps are presented for relevés in each of the 10 associations. Based on species distributions, floristic regions are defined for peatlands in Atlantic Canada. Nutritional characteristics are also described for each plant association. pH and total soil concentrations of calcium, nitrogen and iron proved reliable in separating bog from fen. A boundary between ombrotrophic peatlands and minerotrophic peatlands is suggested, based on a soil pH of 4.0, total soil concentrations of 3.0 mg g^?1 Ca, 4.0 mg g^?1 Fe, 13.0 mg g^?1 N and a Ca/Mg ratio of 2.5. Comparisons between the syntaxa for peatlands in Atlantic Canada and those in Europe are discussed for higher taxa. The possibility of establishing a new order (Chamaedaphno-Scirpetalia Wells ord. nov.) for peatlands in Atlantic Canada is also discussed.     

On randomization testing in vegetation science: multifactor comparisons of relevé groups

Abstract. Hypothesis testing in phytocoenological applications is likely to be hindered when based on conventional statistical methods. The problem created by unrealistic assumptions can, however, be overcome by randomization. This paper discusses the general idea of randomization testing, describes a method and interprets its application in group comparisons. Two sets of variables are involved, the vegetation set on the basis of which the groups are compared and the environmental factors which delimit the groups under different analytical designs. Although simple partitioning of sum of squares is at the core of the test, the method has versatility of testing uni- or multifactor designs, which is novel in phytocoenological applications. The algorithm has been implemented in programs SYNCSA and MULTIV by V.P. Data from the Campos of southern Brazil are used for illustration.     

Do rivers function as corridors for plant dispersal?

Abstract. We evaluated the importance of dispersal for species frequencies and distribution by comparing dispersal properties of vascular plant species with their frequencies along river banks. We assumed that species with long-floating seeds would be more frequent than species with short-floating seeds. We compiled data on frequencies of vascular plants and their dispersal properties from ten rivers in northern Sweden and compared these with boreal forests and grasslands in the same region. In all rivers, but in none of the reference areas, there was a positive relationship between floating capacity and frequency of species. A comparison of floating capacity between species with and without certain dispersal devices showed that seeds of vegetatively dispersed species had higher floating capacities than other seeds. For other dispersal categories (animal and wind dispersal), floating time did not differ from contrast groups. The results indicate that water dispersal has a certain role in structuring the riparian flora, and provide a basis for explaining species distribution patterns from dispersal characteristics. They also suggest that continuous river corridors are important for maintaining regional biodiversity.     

Establishment of Picea abies seedlings in a central European mountain grassland: an experimental study

Abstract. Secondary meadows in the Kru?né hory mountains, central Europe, are not colonized by woody species, although they have been abandoned for half a century and are surrounded by Picea abies (Norway spruce) forests. The causes of inhibition of establishment of Norway spruce seedlings in the meadows were tested experimentally. The experiment was started in a masting year to ensure sufficient seed input. Four treatments (vegetation cut; vegetation cut and litter removed; all above-ground biomass and topsoil removed; control) were combined in a factorial design. The effect of browsing, mainly by deer, was assessed by fencing half of the experimental plots. Seedling establishment differed among treatments (all pair-wise differences were significant) but was independent of fencing. In contrast, seedling survival was influenced both by the treatment and fencing. At the end of the second year, only the plots with all biomass and organic topsoil removed supported viable populations of spruce seedlings. Dense herb cover and a thick layer of slowly decaying litter are considered the main factors inhibiting the establishment of woody species.     

Estimation of tree replacement patterns in an Appalachian Picea-Abies forest

Abstract. Patterns of tree species replacement in a Picea-Abies forest, determined by several different methods, are compared and the methods are assessed. Methods are grouped as either understory-based or gap-based estimates of replacement. The understory-based methods characterize canopy-understory interactions with spatial statistics, sapling density measurement, sapling frequency measurement, and successor sapling identification beneath live canopy trees. The gap-based methods include sapling density measurement, sapling frequency measurement, and successor sapling identification in tree-fall gaps. Methods except those based on frequency indicate a strong trend of replacement of all canopy species by Abies. Understory-based methods may underestimate canopy recruitment of intolerant trees, while gap-based methods relying on sapling density or frequency may overestimate recruitment of intolerant trees. Estimates based on the selection of successor saplings in the understory or in gaps are reliable. Gap successor estimates consider the process of gap capture and are useful in analyses of forest dynamics.     

Long-term after effects of fertilization on above-ground phytomass and species diversity in calcareous grassland

Abstract. Long-term after effects on species number and productivity in calcareous grassland were analyzed after cessation of fertilization. Three series of permanent plots were monitored yearly from 1971 to 1993. These series differed in duration of fertilization and in fertilizer composition, notably the amount of nitrogen and phosphorus. Yearly above-ground production decreased in all series after fertilization had been stopped, however at different speeds. The grass/forb ratio also decreased, while species number and Shannon index of diversity (H') increased. In the series where fertilizer treatment was stopped in 1967 (1968-series), productivity and grass/forb ratio decreased equally as in the plots where fertilization with a high nitrogen content was stopped in 1979 (80/Npk-series). However, species number in the plots of the 80/Npk-series increased faster than in the 1968-series. This was probably the result of a higher number of species present in the seed rain from the surrounding vegetation in the period after 1980 than from after 1968. In the plots receiving a high amount of phosphorus (80/nPk series), the productivity decreased more slowly than in the high nitrogen plots (80/Npk-series). At approximately the same total production level, the grass/forb ratio remained higher for another five-year period in the 80/nPk-series. Species number and the Shannon index of diversity increased more slowly in the 80/nPk-series than in the 80/Npk-series. Over a given range of productivity, changes in species number and Shannon index correlated better with the grass/forb ratio than with total above-ground phytomass. Therefore, restoration of species-rich grassland should not only be focused on lowering the yearly production, but also on reducing the grass component of the vegetation.