氮沉降对植物生长的影响研究进展

为了探索全球氮沉降加剧背景下植物生长所受的影响,笔者归纳了森林植物不同生长指标对氮沉降响应的国内外文献数据。在既有研究成果的基础上,详细总结了氮沉降对植物地上部形态(株高、基径)、光合生理(光合色素含量、净光合速率)、可溶性糖含量、地上及地下生物量分配比例、根系形态结构(根长、根直径和根系生物量)以及叶片中氮:磷等指标的影响,并对上述变化做了合理的分析。笔者指出氮沉降加剧在一定程度上对植物的各生长指标都有明显的促进作用,但当氮沉降很严重时,植物的生长就会受到限制。笔者发现目前关于氮沉降对植物生长影响的试验中,很多都是短期模拟试验,而且大多数试验都是有关现象的研究而非原理的探索。笔者认为在今后的研究中应该将模拟时间进一步延长,并对造成响应变化的机理进行探索,以期更好的为进一步研究氮沉降增加对森林植物生长状况的影响提供参考依据。     

基坑开挖及降水对坑外地表沉降的影响

考虑降水、支护结构变形以及基坑隆起3个因素引起的基坑周围土体的沉降,根据降水引起土体沉降的机理,运用修正的分层总和法单独计算出由降水引起的周围土体沉降。通过研究基坑开挖引起坑外土体沉降的规律,推导出由基坑开挖引起的坑外土体沉降理论公式。把降水引起的沉降及基坑开挖引起的沉降进行叠加,加入修正系数,最终以简化的理论公式合理地计算出基坑周围土体沉降。具体工程验证表明,推导的理论解析解与实测数据十分接近,能有效预估基坑周围土体沉降,为施工方案编制提供可靠的理论依据,最大限度减少基坑施工对周围环境的影响。     

硫对不同类型春小麦湿面筋和沉降值及氨基酸的效应

以6个不同品质类型春小麦为材料,在不同氮水平下,研究施硫对湿面筋、沉降值及氨基酸的调节效应。结果表明,高氮条件下（施尿素128 kg/hm2）,施硫可提高湿面筋含量和沉降值,对高蛋白品种作用更明显。低氮（施尿素60 kg/hm2）条件下施硫,除辽10的湿面筋和沉降值均降低外,其它品种表现湿面筋含量降低而沉降值提高。高蛋白     

氮沉降对北方森林土壤微生物的影响研究进展

大气氮沉降导致土壤有效氮含量增加,将改变作为陆地生态系统重要组成部分的土壤微生物群落结构,尤其在高纬度氮限制地区,土壤微生物对这种变化更为敏感。北方森林地处高纬度地区,氮沉降将改变其土壤微生物的结构、功能和动态。为全面了解近年来氮沉降对北方森林土壤微生物的影响,笔者综述了氮沉降对北方森林土壤微生物量、群落结构和生物多样性、功能和酶活性等方面的影响。结果表明:(1)氮沉降减少了土壤微生物量;(2)氮沉降改变土壤中真菌与细菌,革兰氏阴性细菌(G-)与革兰氏阳性细菌(G+)之间的比值,而这种改变大多数是趋向于减小;(3)氮沉降加剧,将导致土壤微生物群落中贫营养微生物处于劣势地位,富营养微生物处于优势地位,间接地影响了微生物群落结构和生物多样性;(4)氮沉降抑制了微生物呼吸,但对于土壤酶的影响尚无统一规律;(5)氮沉降改变了微生物底物利用模式,导致土壤微生物对复杂有机物质的分解能力下降;(6)氮沉降导致固氮基因等功能基因相对丰度下降。     

交变应力对杨树光肩星天牛产卵量及孵化率的影响

把成对的天牛放在特制的强声波发生装置产生频率和强度可调的交变应力场,研究不同频率和强度的交变应力作用后光肩星天牛产卵量及卵孵化率的变化.实验结果表明,在声波强度为110 dB、频率8000 Hz作用下直接影响天牛产卵量及卵孵化率,6对光肩星天牛在10 d实验中,平均每天每对产卵量为3.7±2.00个.而对照组平均每天每对产卵量为 10.8±1.48个.经T-检验处理组与对照组之间差异显著.在声波强度为110 dB、频率8000 Hz作用下的天牛卵最终孵化率为31%,而对照最终孵化率98%.根据上述结果提出并讨论了应用交变应力防治光肩星天牛的新方法.     

大气沉降对水稻各器官铅镉汞砷积累的影响

为了解大气沉降对水稻中重金属积累的可能影响,选择非污染和污染2种土壤,分别在工业区和农村等2种大气环境下开展露天种植与大棚种植对水稻各器官重金属积累的影响试验。结果表明,水稻中积累的重金属主要来自土壤,其各器官中铅、镉、汞和砷的积累量在污染土壤中明显高于非污染土壤;但试验区大气环境与种植条件对水稻茎叶和谷壳中重金属含量也有较大的影响,工业区生长的水稻茎叶和谷壳中重金属含量高于农村,露天种植的水稻茎叶和谷壳重金属含量高于大棚种植。工业区与农村之间、露天种植与大棚种植之间水稻根系和糙米中重金属含量差异不明显,说明大气污染对糙米中重金属的积累无显著的作用。     

中国小麦品质鉴定指标的研究：沉降值的优势及影响因素探讨

本文以我国１５个省市１５１份小科样品为研究对象,分别测定其粗蛋白含量,面筋值,沉降值并进行粉质实验,拉伸实验和烘焙实验。通过对实验数据分析和比较,并引用了国内外近期文献资料,以及从沉降值沉降过程机理阐述了沉解值指标在我国小麦面偻品质鉴定中的优势和作用,指出反映我国小麦面粉品质的综合指标是沉降值。     

杉木幼苗光合及叶绿素荧光特征对氮沉降的短期响应

为了探究模拟氮沉降条件下杉木幼苗光合及叶绿素荧光特征变化规律,从光合生理的角度探讨不同季节杉木幼苗对氮沉降的短期响应。选取杉木幼苗为实验对象,模拟氮沉降实验,设置4个处理水平对照(N0)、低氮(N30:30 kg/(hm²·a)、中氮(N60:60 kg/(hm²·a)、高氮(N90:90 kg/(hm²·a)。结果表明：添加氮以后,杉木幼苗的净光合速率(Pn),初始荧光产量(F₀)、最大荧光产量(F_m)、最大PSII光能转换效率(F_v/F_m)、PSII潜在活性(F_v/F₀)显著降低,水分利用率(Wue)显著增高(P<0.05)。随着氮沉降水平的增加,气孔导度(Gs)与蒸腾速率(Tr)呈现先升高后下降趋势,水分利用率呈现先下降后升高趋势。在中氮和高氮处理下,F_v/F_m、F_v/F₀值显著降低(P<...     

北方森林细根对氮沉降和二氧化碳浓度升高的响应

北方森林是全球第二大生物群区,约占全球森林面积的30%,尽管其细根生物量仅占森林生态系统很小的一部分,但其周转率更快,更易分解,因此,其对土壤碳循环和大气CO_2通量贡献很大。笔者综述了氮沉降和CO_2浓度升高的背景数据,总结了细根对二者变化的响应,主要从细根的形态特征、解剖结构和生理功能方面入手,探讨了其对氮沉降和CO_2浓度升高的响应。结论如下:(1)大气氮沉降量一直处于上升状态,与人类活动密切相关的有机氮量所占比例逐渐加大,而无机氮中NH_4~-N和NO_3~-N的变化趋势表现不同;(2)大气CO_2浓度一直呈上升趋势,细根形态特征、解剖结构和生理功能对其表现出明显的响应;(3)树种、年龄、土壤类型等都会改变细根形态、解剖结构和生理功能对氮沉降和CO_2浓度升高的响应结果,但改变的程度不同。研究结果可为北方森林乃至温带森林生态系统功能对氮沉降和CO_2浓度升高的响应提供参考依据和数据支持。     

北方森林细根对大气N沉降增加和温度升高的响应

为了在全球大气N沉降增加和温度升高的背景下,细根生产和细根生理生态的潜在变化将如何影响森林土壤中的养分供应和陆地C循环。本研究基于34篇国内外已发表的北方森林N沉降、温度升高及其交互作用的170组细根数据,通过meta分析的方法,研究了细根对升温、增N以及二者交互作用的响应。结果表明:（1）增N显著抑制了北方森林细根生物量,明显增加了细根C、N含量,而P则显著减少,细根的呼吸速率显著增加,细根形态变得细长;（2）增温显著增加了土壤C素的有效性,细根的生物量、组织密度、N吸收速率、组织N浓度和呼吸显著增加,但是细根的C和N含量、比根长、直径和呼吸速率却随着温度的增加明显减少;（3）在升温增N的交互作用下,除组织N浓度受到抑制以外,细根生物量、呼吸速率、C、N含量均显著增加。研究表明:升温增N显著影响了北方森林细根的生物量、周转率、养分含量和形态特征,可为改进和完善C收支模型提供参考依据和数据支持。     

Deformation of Soft Ground with Consideration of the Concomitant Damage

On the basis of continuum damage mechanics theory, the effective stress theory of damaged porous media was presented and its modified self contained seepage differential equation was deduced. The traditional Drucker Prager yield criterion subsequently was modified, and a coupled seepage and damage finite element computer program compiled that was combined with the modified Biot consolidation equation. A simple roadbed foundation model then was analyzed and calculated using the computer program we compiled, and the typical node settlement, pore pressure, and damage variables were discussed and compared with those from the analytic solution. The results show that the damage finite element program we compiled is reasonable and effective.     

Experimental Study on Influence of Stress Path on the Constitutive Relations for Reshaped Clay

In order to study the influence of stress path on the constitutive relations for reshaped clay,the triaxial compression tests under stress paths with drainage in cases of increased,constant and decreased mean normal stress and undrained conventional triaxial compression test have been carried out,the stress-strain relations under the four stress paths are obtained.Through visualization the three-dimensional surfaces of shear and volume strain in the whole stress field under the four stress paths are given respectively by numerical modeling.In addition,the four families of shear and volume yield loci are plotted respectively.It is found through comparing the deformation results under the four stress paths that there are obvious differences in the stress ranges,the strain peaks,the shapes of strain surfaces and the trends of variation of volume yield loci,however,for the four families the shear yield loci are similar.These results demonstrate that the influence of stress path on the constitutive relations of clay is considerably large and could not be neglected,and it relates to the effective mean normal stress closely.     

Experimental Study Creep Characteristics on Creep and Cyclic of Saturated Soft Clay

Several long term creep and cyclic creep tests of Shanghai soft clay are performed in the laboratory. Test results have been obtained under various combinations of confining stresses, deviation static stress ratios and deviation cyclic stress ratios. The results reveal that the axial creep strain increases with the increase of deviation static stress ratio under a constant confining stress, while it also increases with the increase of confining stress under a constant deviation stress ratio. Such a phenomenon is similar to that from the cyclic creep tests, but the following creep strain increase will be significantly reduced after a period of cyclic loading. The results will benefit the expressway, railroad and underground constructions.     

Settlement Analysis on Building near Retaining Pile of Deep Foundation Pit

The building settlement near a foundation pit project in Yanzhou is calculated by using calculation method related to settlement of the soil near a foundation pit, Comparing and analyzing calculated settlement values with measured settlement ,the reason for the gap between theoretically calculated values and measured settlement values is pointed out, On the foundation of careful research and analysis of the measured building settlement values ,the factors influencing the settlement of building near the foundation pit are summarized. Finally, according to practical measured values and influ- encing factors, how the settlement of building near the foundation pit is influenced was carefully analyzed. A conclusion that has practical role in Engineering is presented,which can serve reasonably for instructing foundation pit retaining design.     

Effect of Considering Anisotropy on the Settlement of Tunnel in Soft Soil

Using different constitutive model to simulate the settlement of the fourth stage of shield excavation respectively,the models used were the anisotropic constitutive model(EVP-SCLAY1 model) and the isotropic models(MC model and MCC model),then the results with the three models and the measured datas were compared.The results show that the simulation result with the anisotropic model is more consistent with the measured results in simulating the settlement rang and surface settlement of shield excavation,and MC model prediction results are the worst.     

山地城市热环境及其聚落特征的关联分析

以重庆主城区为研究对象,利用Landsat 8传感器OLI和TIRS获取的遥感影像为数据源,进行城市聚落特征包括地形特征、土地利用等与地表温度的差异性分析。结果表明：城市的热环境空间分布差异较大,海拔高度对温度的影响强于地形起伏度;（NDVI、NDBI、MNDWI等）和地表温度的相关关系呈分段线性关系;不同土地利用类型的热强度和热变异程度差异明显,建设用地的温度最高且斑块温度间的变异性最强,虽然水体的平均温度最低,但斑块温度间的变异性却较高;从格网分析的结果可以看出,格网内部水体的“冷岛效应”明显、建设用地的“热岛效应”显著,耕地与自然植被面积的增加使得各空间格网温度更趋向于稳定。     

Numerical Analysis on Dynamic Response of Saturated Elasto viscoplastic Soft Clay

In the framework of porous media model developed from mixtures theories, Solid skeleton of soft clay was viewed as elasto viscoplastic material,and an elasto viscoplastic model of saturated soft clay was established. According on the model of saturated so     

Influence of Pile Driving on Soil Resistance in Clay

With the increase of platform size, pipe piles with super large diameter and deep penetration are increasingly used in practice. In order to make accurate prediction of pile drivability, it is essential to evaluate the change of the soil properties under pile driving exactly, and it is the premise to predict the pile bearing capacity after pile driving. In order to learn more about the change of clay properties during pile driving, analysis on the pile driving record of 36 piles in Bohai area is conducted. According to the analysis, the soil resistance in the clay layers decreases as the depth increases, and it is very different from that in the sand layer. The FEM method is used to discuss the mechanism of this decrease. The back analysis is carried out to get more information. The results show that the clay properties are affected by the dynamic effect. The undrained shear strength of clay approximately decreases with the increase of thickness of the layer linearly. At the same time, a prediction is conducted based on results, and the result is closer to the pile driving record than that calculated by method normally used today.