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半个世纪来江苏省丹阳县儿童生长的长期趋势   总被引:1,自引:1,他引:0  
本文对江苏省丹阳县儿童1936、1956及1985年的生长发育资料进行了对比分析。观察到,半个世纪来,该县7—14岁男女儿童身高分别增长了9.3、11.4厘米,体重平均增长了3.9、4.0公斤,坐高平均增长了4.2、5.0厘米,表现出明显的生长长期加速趋势。1956—1985年阶段的身高每10年增长值显著大于1936—1956年阶段(P<0.01),而体重每10年增长值在两个阶段间无明显差异(P>0.05)。以1985年实测体重均数与估计体重均数比较,女童明显地表现出体重增长相对不足,体型向细长型发展。本文还将丹阳县儿童生长长期趋势与南京市、上海市及日本国同时期、同年龄儿童的生长长期趋势进行了比较。  相似文献
2.
目的 分析长安区农村学生身体形态发育的10年动态变化和规律,为学校卫生管理部门制定相应政策提供科学的依据。方法 采取分层、整群随机抽样方法,选取长安区农村学生1990年与1999年身高、体重两项指标进行统计分析。结果 10年间长安区农村学生身体形态发育有明显改善,7—18岁男、女学生身高10年平均增长2.23cm、1.93cm,体重平均增长1.74kg、1.21kg,其增长幅度均低于全国农村学生水平。1999年最大年增长值和最大年增长率均低于1990年,身高、体重发育高峰年龄女生分别提前0.77岁、0.32岁,男生推后0.52岁、0.60岁,结论 本地区农村学生身体形态发育仍处于生长长期趋势中,但增长速度已经减慢,学生生长发育的潜力有待充分发挥。  相似文献
3.
Rapidly accumulating evidence indicates that light reduces the human pineal's inhibitory effect on the gonads. Artificially extended daily photoperiods, by allowing increased production of gonadal steroids, have probably accentuated the secular growth trend and may be causing males, especially adolescents and young adults, to have an overready hormonal response to situations which elicit aggressive behavior.The author thanks George M. Vaughan, Harry J. Lynch, Mark D. Altschule, Edmund M. Dewan, Solomon H. Katz, George Adelman, John Ott, and Melvin J. Konner for much needed encouragement and edification. Thanks also to Heide Duda and Wesley Taoka (Countway Library, reference desk, Harvard Medical School) for gracious help on so many occasions.  相似文献
4.
目的鉴定基因spd—ABC、spd-1672、sp-1673和长间隔序列spd—J在肺炎链球菌(Streptococcus pneumoniae,S.pn)毒力中的作用。方法采用长臂同源聚合酶链反应(LFH—PCR)的方法分别构建这4个序列的红霉素抗性基因(erm)替代缺失突变体,通过PCR和测序鉴定是否构建成功;通过绘制生长曲线观察基因对细菌生长繁殖的影响,通过小鼠毒力实验观察基因对细菌致病性的影响。结果所构建缺陷菌目的基因由eFm基因完全替代;spd—ABC、spd-1673和长间隔序列spd—J3个片段缺陷菌的生长趋势与野生菌没有明显差异,生长大约5hA值均可达到峰值,而spd-1672缺陷菌出现明显的延迟现象,生长8h后其4值才达到最高值;野生菌与缺失spd—ABC、spd-1673和长间隔序列spd—J的缺陷菌感染小鼠各组半数死亡时间分别为19、22、24和24h,差异无统计学意义,而spd-1672缺陷菌感染小鼠的半数死亡时间在75h左右,显著长于野生菌感染小鼠组(P〈0.05)。结论在构建的4个单个基因缺失突变体中,spd-1672缺陷后.S.pn生长明显延迟,毒力显著下降,提示spd-1672是s-Pn的一个新的毒力因子。  相似文献
5.
通过对青花菜显性细胞核雄性不育系(DGMS)、改良的萝卜细胞质雄性不育系(Ogura CMS)和由其与相同父本配制的F1杂交种植株的主要农艺性状的生长趋势和花球相关性状的研究,明确两类雄性不育系的应用价值,为青花菜两类雄性不育系的选育和利用及新品种的选育提供理论依据。本研究以结球甘蓝中的显性细胞核雄性不育材料DGMS 79-399-3和改良的细胞质雄性不育材料Ogura CMSR3629为原始不育源,利用优良的青花菜自交系8554和93219为转育父本,通过回交和杂交的方法获得的青花菜高代(n≥9代)两类雄性不育系和由不育系与相同父本配制的F1为试材,采取定期观测整个生长期内植株主要农艺性状和绘制生长曲线相结合的方法,系统地研究了植株的主要农艺性状的生长趋势和花球相关性状。结果表明,相同遗传背景下,保持系、DGMS、Ogura CMS及由不育系与相同父本配制的F1在株幅、株高、外叶长和外叶数方面的生长趋势基本一致,其中株幅、株高、外叶长,总体上表现出前期增长速度较快,之后变慢,最后趋于平缓或略呈下降的趋势;外叶数均表现出先增加后减少的趋势;侧枝数目因年份和遗传背景不同而异。由相同保持系获得的两类不育系的显球时间、采收时间基本相同,由其配制的F1显球和采收时间相同,花球产量因遗传背景的不同而异,花球外观品质性状表现一致。由DGMS和改良的Ogura CMS两类不育源转育的青花菜雄性不育系表现优良,该两类雄性不育源在青花菜杂交育种中具有重要的应用价值。  相似文献
6.
Upper treeline ecotones are important life form boundaries and particularly sensitive to a warming climate. Changes in growth conditions at these ecotones have wide‐ranging implications for the provision of ecosystem services in densely populated mountain regions like the European Alps. We quantify climate effects on short‐ and long‐term tree growth responses, focusing on among‐tree variability and potential feedback effects. Although among‐tree variability is thought to be substantial, it has not been considered systematically yet in studies on growth–climate relationships. We compiled tree‐ring data including almost 600 trees of major treeline species (Larix decidua, Picea abies, Pinus cembra, and Pinus mugo) from three climate regions of the Swiss Alps. We further acquired tree size distribution data using unmanned aerial vehicles. To account for among‐tree variability, we employed information‐theoretic model selections based on linear mixed‐effects models (LMMs) with flexible choice of monthly temperature effects on growth. We isolated long‐term trends in ring‐width indices (RWI) in interaction with elevation. The LMMs revealed substantial amounts of previously unquantified among‐tree variability, indicating different strategies of single trees regarding when and to what extent to invest assimilates into growth. Furthermore, the LMMs indicated strongly positive temperature effects on growth during short summer periods across all species, and significant contributions of fall (L. decidua) and current year's spring (L. decidua, P. abies). In the longer term, all species showed consistently positive RWI trends at highest elevations, but different patterns with decreasing elevation. L. decidua exhibited even negative RWI trends compared to the highest treeline sites, whereas P. abies, P. cembra, and P. mugo showed steeper or flatter trends with decreasing elevation. This does not only reflect effects of ameliorated climate conditions on tree growth over time, but also reveals first signs of long‐suspected negative and positive feedback of climate change on stand dynamics at treeline.  相似文献
7.
Tree‐rings offer one of the few possibilities to empirically quantify and reconstruct forest growth dynamics over years to millennia. Contemporaneously with the growing scientific community employing tree‐ring parameters, recent research has suggested that commonly applied sampling designs (i.e. how and which trees are selected for dendrochronological sampling) may introduce considerable biases in quantifications of forest responses to environmental change. To date, a systematic assessment of the consequences of sampling design on dendroecological and‐climatological conclusions has not yet been performed. Here, we investigate potential biases by sampling a large population of trees and replicating diverse sampling designs. This is achieved by retroactively subsetting the population and specifically testing for biases emerging for climate reconstruction, growth response to climate variability, long‐term growth trends, and quantification of forest productivity. We find that commonly applied sampling designs can impart systematic biases of varying magnitude to any type of tree‐ring‐based investigations, independent of the total number of samples considered. Quantifications of forest growth and productivity are particularly susceptible to biases, whereas growth responses to short‐term climate variability are less affected by the choice of sampling design. The world's most frequently applied sampling design, focusing on dominant trees only, can bias absolute growth rates by up to 459% and trends in excess of 200%. Our findings challenge paradigms, where a subset of samples is typically considered to be representative for the entire population. The only two sampling strategies meeting the requirements for all types of investigations are the (i) sampling of all individuals within a fixed area; and (ii) fully randomized selection of trees. This result advertises the consistent implementation of a widely applicable sampling design to simultaneously reduce uncertainties in tree‐ring‐based quantifications of forest growth and increase the comparability of datasets beyond individual studies, investigators, laboratories, and geographical boundaries.  相似文献
8.
Recent studies have suggested that tropical forests may not be resilient against climate change in the long term, primarily owing to predicted reductions in rainfall and forest productivity, increased tree mortality, and declining forest biomass carbon sinks. These changes will be caused by drought‐induced water stress and ecosystem disturbances. Several recent studies have reported that climate change has increased tree mortality in temperate and boreal forests, or both mortality and recruitment rates in tropical forests. However, no study has yet examined these changes in the subtropical forests that account for the majority of China's forested land. In this study, we describe how the monsoon evergreen broad‐leaved forest has responded to global warming and drought stress using 32 years of data from forest observation plots. Due to an imbalance in mortality and recruitment, and changes in diameter growth rates between larger and smaller trees and among different functional groups, the average DBH of trees and forest biomass have decreased. Sap flow measurements also showed that larger trees were more stressed than smaller trees by the warming and drying environment. As a result, the monsoon evergreen broad‐leaved forest community is undergoing a transition from a forest dominated by a cohort of fewer and larger individuals to a forest dominated by a cohort of more and smaller individuals, with a different species composition, suggesting that subtropical forests are threatened by their lack of resilience against long‐term climate change.  相似文献
9.
Tree‐ring analysis is often used to assess long‐term trends in tree growth. A variety of growth‐trend detection methods (GDMs) exist to disentangle age/size trends in growth from long‐term growth changes. However, these detrending methods strongly differ in approach, with possible implications for their output. Here, we critically evaluate the consistency, sensitivity, reliability and accuracy of four most widely used GDMs: conservative detrending (CD) applies mathematical functions to correct for decreasing ring widths with age; basal area correction (BAC) transforms diameter into basal area growth; regional curve standardization (RCS) detrends individual tree‐ring series using average age/size trends; and size class isolation (SCI) calculates growth trends within separate size classes. First, we evaluated whether these GDMs produce consistent results applied to an empirical tree‐ring data set of Melia azedarach, a tropical tree species from Thailand. Three GDMs yielded similar results – a growth decline over time – but the widely used CD method did not detect any change. Second, we assessed the sensitivity (probability of correct growth‐trend detection), reliability (100% minus probability of detecting false trends) and accuracy (whether the strength of imposed trends is correctly detected) of these GDMs, by applying them to simulated growth trajectories with different imposed trends: no trend, strong trends (−6% and +6% change per decade) and weak trends (−2%, +2%). All methods except CD, showed high sensitivity, reliability and accuracy to detect strong imposed trends. However, these were considerably lower in the weak or no‐trend scenarios. BAC showed good sensitivity and accuracy, but low reliability, indicating uncertainty of trend detection using this method. Our study reveals that the choice of GDM influences results of growth‐trend studies. We recommend applying multiple methods when analysing trends and encourage performing sensitivity and reliability analysis. Finally, we recommend SCI and RCS, as these methods showed highest reliability to detect long‐term growth trends.  相似文献
10.
The important role of tropical forests in the global carbon cycle makes it imperative to assess changes in their carbon dynamics for accurate projections of future climate–vegetation feedbacks. Forest monitoring studies conducted over the past decades have found evidence for both increasing and decreasing growth rates of tropical forest trees. The limited duration of these studies restrained analyses to decadal scales, and it is still unclear whether growth changes occurred over longer time scales, as would be expected if CO2‐fertilization stimulated tree growth. Furthermore, studies have so far dealt with changes in biomass gain at forest‐stand level, but insights into species‐specific growth changes – that ultimately determine community‐level responses – are lacking. Here, we analyse species‐specific growth changes on a centennial scale, using growth data from tree‐ring analysis for 13 tree species (~1300 trees), from three sites distributed across the tropics. We used an established (regional curve standardization) and a new (size‐class isolation) growth‐trend detection method and explicitly assessed the influence of biases on the trend detection. In addition, we assessed whether aggregated trends were present within and across study sites. We found evidence for decreasing growth rates over time for 8–10 species, whereas increases were noted for two species and one showed no trend. Additionally, we found evidence for weak aggregated growth decreases at the site in Thailand and when analysing all sites simultaneously. The observed growth reductions suggest deteriorating growth conditions, perhaps due to warming. However, other causes cannot be excluded, such as recovery from large‐scale disturbances or changing forest dynamics. Our findings contrast growth patterns that would be expected if elevated CO2 would stimulate tree growth. These results suggest that commonly assumed growth increases of tropical forests may not occur, which could lead to erroneous predictions of carbon dynamics of tropical forest under climate change.  相似文献
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