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在田间持水量WFPS为70％、温度为20℃的条件下，通过室内静态培养方法研究铵态氮源与不同碳源结合，对华北平原典型小麦-玉米轮作体系土壤N2O、CO2释放的影响。其中，碳源种类分别为葡萄糖、果胶、淀粉、纤维素、木质素和秸秆。结果表明添加葡萄糖和果胶有效促进了土壤N2O的释放，并在第1d达到最大值，分别为4039．85μgN2O-N·kg^-1·d^-1和2533．44μgN2O-N·kg^-1·d^-1；添加纤维素和只施秸秆处理降低了N2O释放。施入碳源增加了CO2释放，顺序为纤维索〉淀粉〉葡萄糖〉果胶〉秸秆〉木质素。培养结束后土壤中铵态氮几乎消耗完全，除添加葡萄糖处理外，其他施碳土壤的硝态氮含量均有所增加。在培养前3d，土壤NH4^＋和NO3^-总含量与N2O释放量显著相关。

将NaCl和Na2SO4两种盐按4：1配制，并作为复盐，基质中复盐含量分别为0、2．5、5、10g·kg^-1研究了7种野生宿根花卉植物的耐盐性。结果表明：7种植物均不能在含盐量为10g·kg^-1的土壤基质中出苗，但在含盐量为2．5g·kg^-1基质中均能出苗、生长。在盐含量为2．5g·kg^-1基质中出苗率最高的是紫花地丁，比对照高出46．35％；在盐含量为5g·kg^-1基质中只有马蔺、蒲公英、多变小冠花等3种植物出苗，且出苗时间明显推迟，出苗率明显降低。7种野生宿根花卉植物在盐胁迫下脯氨酸含量成倍增加，但对可溶性糖含量影响不大。5g·kg^-1盐处理，使出苗的3种植物丙二醛含量明显增加，说明对3种植物造成严重伤害。

通过分析离体叶片保水力大小、荧光参数随胁迫程度加深的变化及荧光参数与水分参数的相关性，探讨了毛白杨、华山松等华北地区主要造林树种离体枝叶叶绿素荧光参数随不同干旱胁迫程度的变化，主要结论如下：（1）针叶树种保水力普遍较阔叶树种强，各树种保水机制具有较大差异；（2）失水时间对荧光参数的变化具有显著影响，失水过程中，5种针叶树种荧光参数Fv／Fm、Fm／Fo与失水率均呈明显的线性关系，不同的是，参数Fv／Fm的变化曲线呈“凸”状，Fm／Fo的变化曲线呈倒“S”状；（3）不同胁迫程度时，树种荧光参数与水分参数的相关性具有明显差异，程度愈深，相关性愈显著；（4）荧光参数能对树种抗旱性给予定性的描述，但作为定量度量指标则表现出一定的局限性。

Climate change is one of the most important factors that affect vegetation distribution in North China. Among all climatic factors, drought is considered to have the most significant effect on the environment. Based on previous studies, the climate drought index can be used to assess the evolutionary trend of the ecological environment under various arid climatic conditions. It is necessary for us to further explore the relationship between vegetation coverage（index） and climate drought conditions. Therefore, in this study, based on MODIS-NDVI products and meteorological observation data, the Palmer Drought Severity Index（PDSI） and vegetation coverage in North China were first calculated. Then, the interannual variations of PDSI and vegetation coverage during 2001–2013 were analyzed using a Theil-Sen slope estimator. Finally, an ecoregion perspective of the correlation between them was discussed. The experimental results demonstrated that the PDSI index and vegetation coverage value varied over different ecoregions. During the period 2001–2013, vegetation coverage increased in the southern and northern mountains of North China, while it showed a decreasing trend in the Beijing-Tianjin-Tangshan City Circle area and suburban agricultural zone located in Hebei Province and Henan Province）. Over 13 years, the climate of the northeastern part of North China became more humid, while in the southern part of North China, it tended to be dry. According to the correlation analysis results, 73.37% of North China showed a positive correlation between the vegetation coverage and climate drought index. A negative correlation was observed mainly in urban and suburban areas of Beijing, Tianjin, Hebei Province, and Henan Province. In most parts of North China, drought conditions in summer and autumn had a strong influence on vegetation coverage.

Compacted loess is widely used as fills of road embankments in loess regions of northern China.Generally, densely-compacted loess can satisfy the requirements of embankment strength and postconstruction deformation. However, uneven subsidence, pavement cracks and other related damages can affect the integrity of loess subgrade after several years of operation,and even cause some hazards, especially in North China, where the strong freeze-thaw erosion occurs. In this study, cyclic freeze-thaw tests for both densely and loosely compacted loess samples were performed to determine the variation in engineering properties such as volume, void ratio, collapsible settlement,microstructure, and the related mechanisms were addressed. The experimental results showed that an obvious water migration and redistribution occurred within the samples during freeze-thaw cycles. Ice lenses and fissures could be identified in the upper frozen layers of the samples. After freeze-thaw cycles,the dry densities of the upper layers of samples changed significantly due to strong freeze-thaw erosion. The dry densities decreased for the dense sample and increased for the loose sample. It can be found that dense samples become loose, while loose samples became dense with the increasing number of freeze-thaw cycles. Their related void ratios changed reversely. Both void ratios tended to fall into a certain range, which verified the concept of a residual void ratio proposed by Viklander. The loosening process of densely compacted samples involves the formation of large pores, volume increase and density reduction as well as the related changes in mechanical properties because freeze-thaw cycles may be important contribution to problems of loess road embankments.Adverse effects of freeze-thaw cycles, therefore,should be taken into account in selecting loess parameters for the stability evaluation of road embankment in seasonally frozen ground regions.

This paper revealed the climatic change characteristics of fog and haze of different levels over North China and Huang-Huai area （NCHH）. It was found that the haze-prone period has changed from winter into a whole year, and the haze days （HD） in winter have increased significantly. The foggy days （FD） are half of HD. There are little difference on the number of days and trends of fog at various levels. The HD and FD show no obvious positive correlation until the 1980s. Fog has larger spatial scale, showing more in the south than in the north. Haze occurs mainly around large cities with a discrete distribution. In the background of weakened East Asian Winter Monsoon （EAWM） and sufficient particulate matter, the negative correlation be- tween haze and wind speed is weakened, but the positive correlation between haze and moisture conditions （precipitation and humidity） is significantly strengthened. In recent years, small wind and variability appear frequently. Meanwhile, as the stable source and strong moisture absorption of the aerosol particles, the moisture condition becomes one key control factor in the haze, especially wet haze with less visibility. In contrast, the FD presents a stable positive correlation with precipitation and relative humidity, but has no obvious negative correlation with wind speed.

From the 1960 s to 1970 s, North China has been hit by a series of large earthquakes. During the past half century,geophysicists have carried out numerous surveys of the crustal and upper mantle structure, and associated studies in North China.They have made significant progress on several key issues in the geosciences, such as the crustal and upper mantle structure and the seismogenic environment of strong earthquakes. Deep seismic profiling results indicate a complex tectonic setting in the strong earthquake areas of North China, where a listric normal fault and a low-angle detachment in the upper crust coexist with a high-angle deep fault passing through the lower crust to the Moho beneath the hypocenter. Seismic tomography images reveal that most of the large earthquakes occurred in the transition between the high-and low-velocity zones, and the Tangshan earthquake area is characterized by a low-velocity anomaly in the middle-lower crust. Comprehensive analysis of geophysical data identified that the deep seismogenic environment in the North China extensional tectonic region is generally characterized by a low-velocity anomalous belt beneath the hypocenter, inconsistency of the deep and shallow structures in the crust, a steep crustalal-scale fault,relative lower velocities in the uppermost mantle, and local Moho uplift, etc. This indicates that the lithospheric structure of North China has strong heterogeneities. Geologically, the North China region had been a stable craton named the North China Craton or in brief the NCC, containing crustal rocks as old as ～3.8 Ga. The present-day strong seismic activity and the lower velocity of the lower crust in the NCC are much different from typical stable cratons around the world. These findings provide significant evidence for the destruction of the NCC. Although deep seismic profiling and seismic tomography have greatly enhanced knowledge about the deep-seated structure and seismogenic environment, some fundamental issues still remain and require further work.

As one of the regions with intensive agriculture and rapid economic development in China, North China also has a high nitrogen (N) deposition. This study characterized the spatial pattern of N deposition in North China, combining the tropospheric columns from satellite measurements and the simulated profiles from an atmospheric chemistry transport model. The total N deposition fluxes ranged from 16.3 to 106.5 kg N ha −1 yr −1 , with an average of 54.5 ± 17.2 kg N ha −1 yr −1 . The high values were concentrated in urban and farmland areas, while low values were found in forests and grasslands with less human activities. Of the total N deposition, 36% was deposited via precipitation, 12% was deposited through dry particulate deposition, and the remaining 52% was comprised of dry gaseous deposition. For the seasonal variation of dry deposition, gaseous HNO 3 and particulate NO 3 − were higher in winter and autumn, but lower in spring and summer. In contrast, gaseous NH 3 and particulate NH 4 + were higher in spring and summer, but lower in winter and autumn. This is possibly caused by the seasonal differences in emission intensity between NO x and NH 3 emission sources. The gaseous NO 2 deposition did not show strong seasonal variation. The wet deposition was mainly affected by precipitation, with high values in summer and low values in winter. This research provides an objective spatial perspective and insight into the total N deposition in North China.

There has been a significant debate about the nature and causes of the Pleistocene evolution of the Nihewan Basin, North China. We studied the eastern Nihewan Basin sedimentary facies at two main sites, Hutouliang and Donggou. A combination of field observations and measurements of sediment grain-size distribution was used to reconstruct the sequence of sedimentary environments since the middle Pleistocene, and optically-stimulated luminescence measurements were used to date the sediments. Our results indicate that a shallow lake occupied the basin center along the Sanggan River, probably lasting until -440 kyr ago before disappearing completely -340 kyr ago. It was succeeded by a phase of fluvial-dominated sediment accumulation which ended -30 kyr ago. We suggest that the formation of the gorge resulted from the relative uplift of the Niuxin Mountain along the Liulengshan fault -140 kyr ago. However, since -30 kyr ago the fault may have become inactive and the river downcutting near Shixia was no longer offset by the relative uplift, which caused a shift from deposition to denudation in the Nihewan Basin from then on. The disappearance of the paleolake -340 kyr ago may have been the culmination of the ongoing process of basin infilling.

Background： Venom allergy is significantly underestimated in China. Venom-specific IgE may not provide accurate clinical reactions. Our conducted retrospective analysis observes alternative diagnostic considerations in assessing confirmation and severity of honeybee veuom allergy, Methods： Retrospective review of honeybee venom allergy versus nonallergy patients presenled v,ith positive honeybee venom （iI） sIgE results. According to clinically observed reactions caused by a honeybee sting, patients were divided into three groups. Patient residence and exposure types were analyzed. The slgE/T-IgE among allergy and control groups was compared, Results： Gender ratio male：female was 32：22： median age was 39 years （31. 50）. 48% （26/54） of patients live in urban areas. 52% （28/54） in rural areas. Based on bee sting reactions, patients were divided into common localized reactions （32/54）. large localized reactions （7/54）, and systemic reactions （15/54）, In the systemic reaction group, patients presented as Type Ⅱ （6/15）, Type Ⅲ （6/15）. There is significant difference （P 〈 0,001 ） between the three groups in regards to exposure types. In the systemic reaction group. 8.7% （13/15） of patients are beekeepers. A significant difference （P 〈 0.001 ） was observed between allergic and control groups based on slgE/T-lgE results. As well as significant difference observed between the systemic reaction group to the other two reaction groups in regards to slgE/T-IgE results. Six systemic reaction patients presented with large localized reactions before onset of system symptoms 1 month to 1year of being stung. Conclusions： Occupational exposure is the most common cause in honeybee venom allergy induced systemic reactions. The use of sIgE/T-IgE results is a useful diagnostic parameter in determining honeybee venom allergy,