Response to climate change of different tree species and NDVI variation since 1923 in the middle arid region of Ningxia, China

The normalized difference vegetation index (NDVI) is used extensively to describe vegetation cover and ecological environment change. The purpose of this study was to contrast the response of different tree species growing in the same habitat to climate change and retrieve past NDVI using tree-ring width data from tree cores collected from the transitional zone of Pinus tabulaeformis and Picea crassifolia in the Luoshan Mountains in the middle arid region of Ningxia. Correlation analysis indicated that radial growth of P. tabulaeformis is more sensitive to precipitation and temperature change than that of P. crassifolia. Natural factors such as water availability and heat at this elevation are more suited to the growth of P. crassifolia, and are more advantageous to its renewal and succession. P. crassifolia is probably the better of the two species for protecting the forest ecosystem and conserving water in the Luoshan desertification area. Ring width of P. crassifolia correlates significantly with average NDVI for April–May (r =0.641, p <0.01), and both of them are influenced positively by precipitation in April–May. The reconstructed NDVI for 1923–2007 shows the relatively low vegetation cover occurred in the 1920s–1930s, the 1960s–1970s, and the early 21st century. The reconstructed NDVI better reflected the drought climate in the study area.     

晋城矿区粘土矿物特征及沉积-成岩响应

在X射线衍射和扫描电镜观测的基础上,结合区域沉积演化分析,探讨了晋城矿区粘土类型、组合特征、微观结构与沉积-成岩作用的关系。结果表明,晋城矿区粘土矿物以高岭石为主,其次为伊利石和伊利石/蒙脱石混层,还有少量的绿泥石和蒙脱石;山西组粘土矿物颗粒排列定向性优于太原组,多呈带状或平叠状产出,而太原组多为蜂巢状、花朵状或凝絮状;由于太原期频繁的海侵海退致使煤层顶底板处于pH值较高的碱性环境,使成岩过程中高岭石向伊利石转化,造成太原组粘土矿物的伊利石含量明显高于山西组,而高岭石含量相对较低。     

毛蚶受精和早期卵裂过程核行为的荧光显微镜观察

利用Hoechst33258染色、荧光显微镜观察方法,对毛蚶受精和早期卵裂过程中核行为的细胞学变化进行了详细观察.结果表明,毛蚶成熟未受精卵呈卵圆形,卵径为52.909±2.092μm,核相处于第一次成熟分裂中期.在水温为26±1℃条件下进行受精,在受精后15~18、20~25 min,受精卵先后排出第一、第二极体,完成第一次和第二次成熟分裂;受精后30 min左右,雌、雄性原核形成;受精后35 min,雌、雄性原核各自形成染色体组,在卵子中央发生联合,染色体共同排列在纺锤体的赤道板上,形成第一次有丝分裂的中期分裂相;受精后40 min左右,受精卵进行第一次卵裂,形成2个大小不等的卵裂球;受精后55~60 min,受精卵完成第二次卵裂,形成1大3小4个卵裂球.另外,在研究中还发现了极少量的多精受精、多极分离等异常细胞学现象,对其成因及机制进行了分析和探讨.     

腾格里沙漠南缘近315年5～6月PDSI指数变化

利用昌灵山早材宽度年表重建腾格里沙漠南缘在过去315 a的5～6月份PDSI指数变化,重建方程的方差解释量达42.0%。腾格里沙漠南缘5～6月的PDSI指数重建序列平均值为-0.32。腾格里沙漠南缘5～6月的PDSI指数重建序列对西北地区干旱极端历史事件有良好的响应。空间分析显示腾格里沙漠南缘5～6月的PDSI指数重建序列与亚洲季风尾闾区PDSI指数的变化比较一致,同时还与西北地区的多条PDSI指数重建序列有着良好的相关性。腾格里沙漠南缘5～6月的PDSI指数重建序列具有25 a(95%)、12 a(95%)、3.4 a(99%)、2.8 a(99%)、2.6 a(99%)、2.3 a(95%)的周期变化。     

树轮最大密度记录的吉尔吉斯斯坦天山山区公元1650年以来的7-8月温度变化

利用吉尔吉斯斯坦天山山区3个采样点的雪岭云杉树轮最大密度数据建立区域树轮最大密度年表（RC）。气候响应分析发现,区域树轮最大密度年表与7-8月平均温度显著相关。在此基础上,利用区域树轮最大密度年表重建了吉尔吉斯斯坦天山山区自1650年以来的7-8月温度变化,重建方程的方差解释量高达45．3％（Radj^2=44．7％,N=95,F=77．029）。重建结果显示,在过去的346a中吉尔吉斯斯坦天山山区7-8月平均温度的异常高温年份为40a,异常低温年份为46a,且存在11个低温时段（16501654,1662-1678,1693-1703,1779-1794,1801-1805,1811-1819,1834-1854,1882-1910,1917-1923,1952-1975和1986-1992年）和11个高温时段（1655-1661,1679-1692,1704-1778,1795-1800,1806-1810,1820-1833,1855-1881,1911-1916,1924-1951,1976-1985和1994-至今）。突变和周期分析揭示该地区的温度变化受到了火山、太阳活动和海陆气交互作用的共同影响。此外,在过去的346a来气候以暖干／冷湿为主,近20a来出现了明显暖湿化趋势。     

采点和去趋势方法对天山西部云杉上树线树轮宽度年表相关性及其气候信号的影响

针对新疆天山西部伊犁、博州三大山体北坡云杉上树线树木年轮资料,采用区域曲线、负指数曲线、样条函数三种不同生长去趋势方法,研制树轮宽度年表,分析不同采点和树轮去趋势方法对树轮宽度年表在不同频域的相关性及气候信号的影响发现：①采点间的距离和是否位于同一气候区是影响云杉上树线树轮宽度年表间相关性的首要因子。三个采点间的树轮宽度变化,在高频变化方面最为相似,低频变化存在着较大差异,表明它们在揭示和重建大范围的高频气候变化方面可能具有较大的应用潜力。②三种不同去趋势方法对天山西部山脉北坡上树线的云杉树轮宽度年表的研制具有一定影响,负指数和样条函数去趋势方法研制的树轮年表较为相似,而区域曲线去趋势方法研制的树轮宽度年表中则可保留较多的轮宽低频变化信息。③降水是天山西部云杉上树线的树轮宽度生长的主要限制因子,且树轮宽度生长对降水的响应具有显著的滞后性。④在天山西部的云杉上树线采点,使用区域曲线去趋势方法有利于在树轮宽度年表中保留较多的与水分有关的气候信息。     

Asymmetric variability between maximum and minimum temperatures in Northeastern Tibetan Plateau: Evidence from tree rings

Ecological systems in the headwaters of the Yellow River, characterized by hash natural environmental conditions, are very vulnerable to climatic change. In the most recent decades, this area greatly attracted the public's attention for its more and more deteriorating environmental conditions. Based on tree-ring samples from the Xiqing Mountain and A'nyêmagên Mountains at the headwaters of the Yellow River in the Northeastern Tibetan Plateau, we reconstructed the minimum temperatures in the winter half year over the last 425 years and the maximum temperatures in the summer half year over the past 700 years in this region. The variation of minimum temperature in the winter half year during the time span of 1578―1940 was a relatively stable trend, which was followed by an abrupt warming trend since 1941. However, there is no significant warming trend for the maximum temperature in the summer half year over the 20th century. The asymmetric variation patterns between the minimum and maximum temperatures were observed in this study over the past 425 years. During the past 425 years, there are similar variation patterns between the minimum and maximum temperatures; however, the minimum temperatures vary about 25 years earlier compared to the maximum temperatures. If such a trend of variation patterns between the minimum and maximum temperatures over the past 425 years continues in the future 30 years, the maximum temperature in this region will increase significantly.     

Tree-ring-based reconstruction of the April to September mean temperature since 1826 AD for north-central Shaanxi Province, China

Long-time series of high-resolution temperature record from Chinese Loess Plateau is rare. An April-September mean temperature reconstruction (1826-2004) has been developed for the north-central Shaanxi Province, China, based on tree-ring width analysis. The reconstruction captures 39.3% (p<0.001) of the variance in the instrumental data over the calibration period from 1951 to 2002. The reconstruction shows a high temperature period of 1928-1933, which coincides with the timing of the extreme drought event in 1920s in the entire northern China. The two low temperature periods in reconstruction are 1883-1888 and 1938-1942. With the global warming, the April-September mean temperature in study area has also increased since the 1970s, but has not exceeded the temperature in 1928-1933. Besides the statistical analysis, the reconstruction is also verified by the local dryness/wetness index and other dendroclimatological results.     

动力排水固结前后软土微观结构分析

通过液氮冷冻干燥制样技术制备饱和软土试样,借助扫描电子显微镜技术,得到经室内动力排水固结前后土样的微观结构图像,用编制的计算机程序分析其微观结构参数变化。通过比较试样的孔隙个数、总面积、总周长、面积分级、平均孔径、形状系数、圆度和各向异性率、分形维数,研究了在动力排水固结作用下土体微观结构在垂直向和水平向发生的变化。     

胶东地区与金矿成矿有关的花岗岩体中的流体包裹体研究

与胶东金矿有密切关系的玲珑片麻状花岗岩、栾家河二长花岗岩、郭家岭花岗闪长岩、上庄二长花岗岩4种类型花岗岩中矿物包裹体的发育程度、类型、大小及其特点, 以及包裹体的显微测温结果, 反映出玲珑岩体是经历了高级区域变质作用形成的重熔型花岗岩, 郭家岭岩体是由高温、高粘度岩浆结晶成岩的。栾家河岩体是由一种富CO₂的高温、高粘度的岩浆中结晶演化而来, 岩体的侵入深度也较浅。上庄岩体形成温度压力较低。