湖泊磷酸酶与微生物活性对内源磷负荷的贡献及其与富营养化的关系

磷酸酶可通过增加磷的生物可利用性促进富营养化过程,在太湖、龙阳湖与莲花湖探讨了这种机制。磷酸酶活性与磷营养水平以及叶绿素a浓度相关。反胶团酶学方法的实验结果表明,溶解态磷酸酶稳定性的不同可能源于酶分子大小、结构与活性基团的差异。太湖微囊藻水华发生处间隙水溶解态磷酸酶在胶团中的活性高且稳定,溶解反应性磷浓度较低,沉积物不同形态磷的含量与好气性细菌数量均低,且呼吸强度明显较高,无机磷与有机磷细菌以及其它微生物均在表层富集,却极少见诸于沉积物。因此,来自酶促水解或其它途径的大量内源磷可能在厌氧状态下经上覆水随细

Assessment effects of cage culture on nitrogen and phosphorus dynamics in relation to fallowing in a shallow lake in China

Nitrogen and phosphorus dynamics in relation to fallowing in a fish cage farm was investigated in a shallow lake in China. Four sampling sites were set: beneath the cages, at the cage sides, and 50 and 100 m east of the cage farm. Total nitrogen (TN) and total phosphorus (TP) in lake water and sediment were analyzed during a 2-year rearing cycle. The cage culture had a fish yield of 16.3-39.2 tonnes in the study period. Based on the mass balance equation, 1533-3084 kg TN and 339-697 kg TP were contributed to the lake environment. Nitrogen and phosphorous concentrations showed greater increase in the first culture period than in the second rearing cycle. No obvious changes were found at the sampling sites 50 and 100 m east of the cages during the study periods. Main impacts were found close to the cages (beneath the cages and at the cage side); the sampling points at the cage side showed relatively high TN and TP sedimentation. After 3 months of fallowing, water TN and TP decreased significantly but the sediment TN and TP contents remained high. Therefore, recovery seems to happen during fallowing but attention should be paid to whether the culture continues to operate in the future.

Cloning and characterization of interferon stimulated genes Viperin and ISG15, and their promoters from snakehead Channa argus

By suppression subtractive hybridization, rapid amplification of cDNA ends and gene walking methods, interferon stimulated genes (ISGs), Viperin and ISG15, and their promoters have been cloned and characterized from snakehead Channa argus. The Viperin cDNA was found to be 1474 nt and contain an open reading frame (ORF) of 1059 nt that translates into a putative peptide of 352 amino acid (aa). The putative peptide of Viperin shows high identity to that in teleosts and mammals except for the N-terminal 70 aa. The ISG15 cDNA was found to be 758 nt and contain an ORF of 468 nt that translates into a putative peptide of 155 aa. The putative peptide of ISG15 is composed of two tandem repeats of ubiquitin-like (UBL) domains, and a canonical conjugation motif (LRGG) at C-terminal. Viperin and ISG15 promoter regions were characterized by the presence of interferon stimulating response elements (ISRE) and gamma-IFN activation sites (GAS). ISRE is a feature of IFN-induced gene promoter and partially overlaps interferon regulatory factor (IRF) 1 and IRF2 recognition sites. GAS is responsible for the gamma-IFN mediated transcription. One conserved site for NF-kappa B was found in the promoter region of Viperin. This is the first report of conservative binding motif for NF-kappa B in accordance with the consensus sequence (GGGRN-NYYCC) among teleost ISG promoters. Moreover, there were also TATA, CAAT and Sp1 transcription factor sites in Viperin and ISG15 promoters. In 5' untranslated region (UTR), snakehead ISG15 gene contains a single intron, which differs from Viperin gene. The transcripts of Vipeirn and ISG15 mRNA were mainly expressed in head kidney, posterior kidney, spleen and gill. The expression levels in liver were found to increase obviously in response to induction by IFN-inducer poly I : C.

Influence of spacer layer thickness on the current-voltage characteristics of pseudomorphic AlAs/In0.53Ga0.47As/InAs resonant tunnelling diodes

This paper investigates the dependence of current-voltage characteristics of AlAs/In0.53Ga0.47As/InAs resonant tunnelling diodes (RTDs) on spacer layer thickness. It finds that the peak and the valley current density J in the negative differential resistance (NDR) region depends strongly on the thickness of the spacer layer. The measured peak to valley current ratio of RTDs studied here is shown to improve while the current density through RTDs decreases with increasing spacer layer thickness below a critical value.

Effects of Sb, N, and period on the electronic properties of GaAs/GaInNAsSb superlattices

We have calculated the bond distributions and atom positions of GaAs/GalnNAsSb superlattices using Keating's semiempirical valence force field (VFF) model and Monte Carlo simulation. The electronic structures of the superlattices are calculated using folded spectrum method (FSM) combined with an empirical pseudopotential (EP) proposed by Williamson et al.. The effects of N and Sb on superlattice energy levels are discussed. We find that the deterioration of the optical properties induced by N can be explained by the localization of the conduction-band states around the N atom. The electron and hole effective masses of the superlattices are calculated and compared with the effective masses of the bulk GaAs and GaInAs.

HCl/HF/CrO3溶液对 InGaAs/InGaAsP的选择性湿法刻蚀--应用于楔形结构的制备

利用动态掩膜湿法腐蚀技术,研究了HCl/HF/CrO3溶液对与InP衬底晶格匹配的InxGa1-xAs1-yPy(y=0,0.2,0.4,0.6)材料的腐蚀特性.对于HCl(36wt%)/HF(40wt%)/CrO3(10wt%)的体积比为x∶0.5∶1的溶液,随着x由0增加到1.25,相应的腐蚀液对In0.53Ga0.47As/In0.72Ga0 28As06P0.4的选择性由42.4降到1.4;通过调节腐蚀液的选择性,在In072Ga0.28As06P0.4外延层上制备出了倾角从1.35°到35.9°的各种楔形结构;当x为0.025和1.25时,相应的In0.72Ga0.28As0.6P0.4腐蚀表面的均方根粗糙度分别为1.1nm和1.6nm.还研究了溶液的组分与InxGa1-xAs1-yPy(y=0,0.2,0.4)的腐蚀速率间的关系,并对腐蚀机理进行了分析.

N,Sb和单分子层数对GaAs/GaInNAsSb超晶格性能的影响

用Keating的价力场(valence force field)模型和蒙特卡罗方法计算了GaAs/GaInNAsSb超晶格中键的分布、原子的精确位置以及应变.用折叠谱法(folded spectrum method)结合Williamson经验赝势法计算了GaAs/GaInNAsSb超晶格应变条件下的电子结构.讨论了N和Sb原子以及超晶格单分子层数对电子结构的影响.发现导带底电子态在N原子周围的局域化减小了光跃迁矩阵元,从而影响了该超晶格的发光性能.计算并讨论了超晶格的电子和空穴的有效质量.

水土保持林土壤改良效应及其效益评价

土壤侵蚀是土地退化的一种重要表现形式，是当今世界重大环境问题之一。水土保持林正是针对这一环境问题而采取的一项生态林业工程措施，对于防止土壤侵蚀，控制水土流失具有极其重要的作用。论文以大量的文献为基础，对土壤侵蚀的定义、成因、规律和研究进展，以及水土保持林的功能进行了分析研究，发现有关土壤侵蚀规律和水土保持林水文效应方面的研究较多，可是关于土壤侵蚀内在机制和水土保持林土壤改良效应方面的研究较少。而事实上，水土保持林防止土壤侵蚀和改善区域水文状况的作用，与其改良土壤的作用有着密切的关系。水土保持林对生态环境的改善，正是以改良土壤的作用为前提的基础的。通常认为，森林改良土壤就是改善土壤的理化性状，提高土壤的肥力水平。论文通过对国内外有关文献的分析和朝阳地区的区域性考察，首次提出水土保持林作为保持水土、防止土壤侵蚀的特有林种，它的土壤改良效应不仅体现在土壤肥力水平的提高，更重要地表现为土壤抗蚀性能和抗冲性能的增强。这恰恰体现了水土保持林保持水土、防止土壤侵蚀的功能所在。因此对水土保持林土壤改良效应内容的拓展，有利于进一步认识土壤改良效应与水土保持林功能之间的关系，为高效、多功能水土保持林体系的建设提供了理论依据。水土保持林土壤改良效应是通过林冠截留、枯枝落叶层的作用以及根系的活动来实现的。论文通过对不同类型水土保持林林冠层的厚度和面积、枯枝落叶层的现存量和分解状况、以及根系分布特点的分析，阐明针阔叶混交林与针叶纯林相比，其水土保持性能更有利于土壤改良。随着林龄的增长，林分的水土保持性能增强，土壤改良效果更好。论文还着重对水土保持林土壤改良效应进行了研究，明确指出水土保持林土壤改效应包括土壤肥力提高、土壤抗蚀性能增强和土壤抗冲性能增强三个方面的内容。并根据其各自的性质和特点，分别选择土壤酶活性、土壤有机质含量、有机－无机复合体和微团聚体等作为土壤肥力的评价指标：水稳性团聚体含量及其平均重量直径、团聚度、分散率等作为土壤抗蚀性能的指标：土壤硬度、渗透系数等作为土壤抗冲性能的指标。用这些指标对不同类型水土保持林土壤肥力、土壤抗蚀性能和抗冲性能进行评价，得出的结论是一致的，即：针阔叶混交林土壤肥力、土壤抗蚀性能和抗冲性能均高于针叶纯林：同一树种林龄越大的林分，土壤肥力越高，土壤抗蚀、抗冲性能越强。例如，以土壤中脲酶、磷酸酶和蔗糖酶活性对土壤肥力进行评价时得出：与纯林相比，混交林土壤中脲酶活性提高了6.4 ～ 142.36%，磷酸酶活性提高了20.55 ～ 99.04%，蔗糖酶活性提高了4.23 ～ 198.96%。以水稳性团聚体含量对土壤抗蚀性能进行评价时，混交林土壤中水稳性团粒含量比纯林增加了1.71 ～ 38.53%，48年生和28年生油松林比15年生油松林增加了89.94 ～ 149.27%，等等。因此论文指出，与针叶纯林相比，针阔叶混交林改良土壤的效果更好。林龄越大的林分，土壤改良效果越佳。森林效益评价是目前林业研究的热点，也是难点。论文在掌握足够文献的基础上，对水土保持林综合效益评价做了较为系统、全面的分析和论述，提出了一套比较完整的效益评价方法和步骤。水土保持林土壤改良效益是其综合效益的一个非常重要的方面，也是水土保持林最直接、最基本的一项效益。论文在水土保持林土壤改良效应研究的基础上，明确提出了效益评价的方法和思路，这在目前还是不多见的。在所取和参与专家意见的基础上，筛选出了水土保持林土壤改良效益的评价指标，建立了由指标维、时间维和地类维构成的三维效益评价指标体系，确定了由总目标层、准则层和指标层构成的指标维的结构图，指出总目标层为水土保持林土壤改良效益评价综合指标：准则层包括土壤肥力、土壤抗蚀性能和土壤抗冲性能；指标层有土壤酶活性、土壤有机质含量、水稳性团粒平均重理直径、分散率、团聚度、土壤硬度、土壤渗透系数和pH值等。进而用层次分析法确定了指标体系中各项指标的权重，用于的评价计算。论文按照效益结构图中的层次，分步求算得到了水土保持林土壤改良效益评价综合指数。并尝试用消除立地因子影响的方法，对效益评价综合指数进行了校正。文中还分别以林地枯落物生物量(x_1)、林分平均胸径（地径）生长量(x_2)、林分平均树高生长量(x_3)以及平均胸径（地径）平方和树高乘积(x_4)为自变量，以效益评价综合指数为因变量进行模拟运算，得到了水土保持林土壤改良效益的评价模型，模拟结果较好的模型有：y = 0.7 + 0.2208x_1 - 0.0053x_1~2 R~2 = 0.5396 y = 0.5815x_2~(0.4885) R~2 = 0.4827 y = 0.8529 + 0.1869x_3 - 0.004x_3~2 R~2 = 0.3391 y = 2.7695x_4~(0.1533) R~2 = 0.4410生产实践中，可根据实际情况选择适当的模型加以应用。论文根据计算得到的效益评价综合指数的相对值，将朝阳地区水土保持林土壤改良效益划分为四个等级，即相对值>3为好；2.5 ～ 3为较好；2 ～ 2.5为中等；<2为较差。最后，还通过实例说明了效益评估模型和评价标准在当地生产实践中的应用。