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81.
Northeast China Transect (NECT), one of the fifteen International Biosphere-Geosphere Programme (IGBP) terrestrial transects, has been established for 10 years by Prof. Zhang Xin-Shi, through a core project of the IGBP - the Global Change and Terrestrial Ecosystems (GCTE). This transect is located in the mid-latitude semi-arid region, ranging 42-46°N latitude and 110-132癊 longitude. The primary driving force for global change is precipitation and the secondary one is land use intensity. Research progresses have been performed during the past decade in the following aspects: ecological database development, climate and its variability, ecophysiological response of plants to environments, vegetation and landscape changes, biodiversity patterns and their changes, plant functional types and traits with relation to climatic gradient, productivity and carbon dynamics, pollen-vegetation relationship, trace gas emissions, land use and land cover changes, as well as biogeographical and biogeochemical modelling. In order to achieve the higher level of integrated research, the NECT needs the consistent basic data sets within the same framework, further field experiments and observations, integrated simulations of vegetation structure, process and function from patch, landscape to biome scales, intercomparisons of results and simulations within the transect and to other IGBP transects, multidisciplinary research, national and international co-ordinates, and full scientific plan and implementation strategy.  相似文献   
82.
A group of representative species of the genus Puya was studied to determine if there are allometric relationships between vegetative and floral parts, whether these relationships correlate with their pollination system and if plant size is correlated with elevation and latitude. Fifty-three species representing the morphological variation and distribution of the genus were studied. Total plant height, as well as leaf, inflorescence, petal and sepal length were measured and these data subjected to univariate and multivariate analyses. To test for correlation between plant size and altitudinal and latitudinal distribution, ANOVAs were performed. When the pollination system of a species is known, additional multivariate and univariate analyses were also performed. The results indicate that the characters studied are correlated with a size component, exhibiting positive allometry for sepal and petal length and negative allometry for leaf length. Inflorescence length is an isometric character. There was no significant correlation between plant size and altitudinal or latitudinal distribution. The ANOVAs show that the only character correlated to pollinator type was petal length. Small plants with small flowers are correlated to pollinators such as insects, while medium to large plants with medium to large-sized flowers are correlated with pollinators such as birds and bats. Large plants have small flowers, that are more evident and attract more pollinators.  相似文献   
83.
Evaluation of litterfall production is important for understanding nutrient cycling, forest growth, successional pathways, and interactions with environmental variables in forest ecosystems. Litterfall was intensively studied during the period of 1982–2001 in two subtropical monsoon vegetation gradients in the Dinghushan Biosphere Reserve, Guangdong Province, China. The two gradients include: (1) a successional gradient composed of pine forest (PF), mixed pine and broadleaved forest (MF) and monsoon evergreen broadleaved forest (BF), and (2) an altitudinal gradient composed of Baiyunci ravine rain forest (BRF), Qingyunci ravine rain forest (QRF), BF and mountainous evergreen broadleaved forest (MMF). Mean annual litterfall production was 356, 861 and 849 g m−2 for PF, MF and BF of the successional gradient, and 1016, 1061, 849 and 489 g m−2 for BRF, QRF, BF and MMF of the altitudinal gradient, respectively. As expected, mean annual litterfall of the pioneer forest PF was the lowest, but rapidly increased over the observation period while those in other forests were relatively stable, confirming that forest litterfall production is closely related to successional stages and growth patterns. Leaf proportions of total litterfall in PF, MF, BF, BRF, QRF and MMF were 76.4%, 68.4%, 56.8%, 55.7%, 57.6% and 69.2%, respectively, which were consistent with the results from studies in other evergreen broadleaved forests. Our analysis on litterfall monthly distributions indicated that litterfall production was much higher during the period of April to September compared to other months for all studied forest types. Although there were significant impacts of some climate variables (maximum and effective temperatures) on litterfall production in some of the studied forests, the mechanisms of how climate factors (temperature and rainfall) interactively affect litterfall await further study.  相似文献   
84.
Body shape variation is integrally related to many aspects of fish ecology, including locomotion and foraging, and can indicate the functional diversity of fish assemblages. Few studies have thoroughly characterized body shape in a diverse marine fish clade, or investigated both temporal and spatial patterns of variation in body shape disparity. Here, I use digital photographs to measure geometric body shape in 66 species of north‐east Pacific rockfish (Sebastes spp.), including a correction for error introduced by arching of specimens. Different components of interspecific shape variation show associations with fish size, depth habitat, trophic niche and phylogenetic relationships. Overall, the accumulation of body shape disparity appears to have been near‐constant over time, and shows little variation across the latitudinal range of rockfish.  相似文献   
85.
K-ras基因突变检测可用于大肠癌的早期筛查与诊断,并有利于筛选出抗表皮生长因子受体靶向药物治疗有效的大肠癌患者,以实现肿瘤的个体化治疗.采用以倾斜式热辐射原理建立的微流控温度梯度毛细管电泳(temperature gradient capillary electrophoresis,TGCE)基因突变检测系统,实现了对98例石蜡包埋大肠癌组织中K-ras基因突变的高灵敏度筛查,突变阳性检出率为47.96%,显著高于PCR产物直接测序的23.47%.克隆测序显示该方法至少能检测到2.08%的K-ras基因突变体.K-ras基因突变与临床病理学参数的关系分析显示,直肠癌中K-ras基因突变率明显高于结肠癌(P < 0.05),而与年龄、性别、组织学类型和肿瘤分期等无显著相关性.该检测方法为肿瘤早期诊断和指导临床用药提供了一种灵敏度高、检测速度快、便于大规模筛查的有效手段.  相似文献   
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88.
In the present study, we investigated the effect of hillslope gradient on vegetation recovery on abandoned land of shifting cultivation In Hainan Island, south China, by measuring community composition and structure of 25-year-old secondary forest fallows along a hillslope gradient (up-, middle-, and down-slope position). A total of 49 733 free-standing woody plant stems higher than 10 cm and belonging to 170 species, 112 genera, and 57 families was found in the three l-hm2 investigation plots. Stem density was highest in the down-slope stand and lowest in the up-slope stand. Species richness and the Shannon-Wiener Index were both highest in the middle-slope stand, and lower In the down-slope and up-slope stands. The recovery forest fallows on different hiUslope positions were all dominated by a few species. The five most abundant species accounted for 70.1%, 58.8%, and 72.9% of total stem densities in stands in the up-, middle-, and down-slope positions, respectively. The five species with the greatest basal areas accounted for 74.5%, 84.3%, and 74.7% of total stem basal area for the up-, middle-, and down-slope positions, respectively. The number of low-density species (stem abundance less than five) Increased from the up-slope position downward. Of the nine local common species among three different functional groups, the short-lived pioneer species dominated the up-slope position, but long-lived pioneer species dominated the middle- and down-slope positions. The climax species of primary tropical lowland rain forest was found in the downslope position. Both the mean diameter at breast height (DBH) and mean height of the trees Increased with decreasing hillslope gradient. The stem density and basal area in different size classes were significantly different in stands In different slope positions. Our results indicated that the rate of secondary succession varies, even over small spatial scales caused by the hlllslope gradient, in early vegetation recovery.  相似文献   
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90.
Forests of the future need to cope with adverse climatic conditions, in particular drought, to ensure forest stability and productivity. Given the usually long rotation period of forests, forest managers need to select appropriate, i.e. productive and climate-change resilient tree species and/or provenances, to lower tree-mortality risks and sustain current wood production rates at the end of the 21st century. A frequent means of assessing which provenances of a given species are adapted to anticipated climate conditions is common garden experiments, where trees from different provenances are planted under similar climate conditions. However, in this context soil conditions also play an important role, since they govern how climate translates into plant-available water and hence plant’s ability to cope with extreme drought events. Here, we examine the effects of soil conditions on pedunculate oak (Quercus robur L.), by studying 10 different Dutch oak provenances that were planted in three provenance trials on different soil types in 1988 in the Netherlands. Using dendroecological methods, we quantified provenance-specific productivity and assessed provenance- and site-specific growth patterns. Our results indicated clear differences in productivity among provenances as well as soil-type specific growth patterns. Consequently, our study highlights the importance of incorporating soil characteristics when evaluating the growth performance of provenances within common garden experiments.  相似文献   
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