不同类型耕地紫色土中3,5,6-三氯-2-吡啶醇迁移试验与模拟

3,5,6-三氯-2-吡啶醇(TCP)的化学结构稳定、水溶性高、运移能力强,对水体具有潜在的污染风险。在有机质含量低、大孔隙度高、导水性好的紫色土地区,风险更加显著。为研究TCP在紫色中的迁移规律,该研究依据紫色土的典型耕作类型,在中国科学院盐亭国家紫色土农业生态试验站采集3组土样(小麦-玉米轮作的坡地、水稻-油菜轮作的水旱农田和萝卜-白菜套种的菜地),通过批量平衡法研究紫色土对TCP的吸附特征,并采用稳定流场饱和均质土柱的易混合置换试验研究TCP的动态迁移过程,最后对其迁移动态进行模拟。结果表明:紫色土对TCP的吸附特征呈线性,在坡地、水旱农田和菜地中的吸附系数分别为1.94、1.22和1.02 L/kg,且黏土含量和矿物组成是主要影响因子;TCP的出流平衡浓度分别为初始浓度的77%(坡地)、84%(水旱农田)和92%(菜地),相应的平衡时刻分别为2.88PV、4PV和6.5PV,表明TCP对环境的污染风险较高;用非平衡两点对流弥散模型模拟TCP在3种耕作条件下迁移,表明TCP以瞬时吸附为主,其水动力弥散系数和分形系数在坡地、水旱农田和菜地中依次减小,但一阶动力学常数依次增大。研究结果为探索TCP在紫色土壤中的迁移机制和预测防止TCP对环境的污染提供了参考依据。     

Management practices have a major impact on nitrifier and denitrifier communities in a semiarid grassland ecosystem

Purpose

Nitrification and denitrification, two of the key nitrogen (N) transformation processes in the soil, are carried out by a diverse range of microorganisms and catalyzed by a series of enzymes. Different management practices, such as continuous grazing, mowing, and periodic fencing off from grazing, dramatically influenced grassland ecosystems. This study aimed to examine the effects of management practices on the abundance and community structure of nitrifier and denitrifier communities in grassland ecosystems.

Materials and methods

Soil samples were collected from a semiarid grassland ecosystem in Xilingol region, Inner Mongolia, where long-term management practices including free-grazing, different periods of enclosure from grazing, and different frequencies of mowing were conducted. Real-time quantitative polymerase chain reaction (Q-PCR), denaturing gradient gel electrophoresis (DGGE), sequencing, and phylogenetic analysis were applied to estimate the abundance and composition of amoA, nirS, nirK, and nosZ genes.

Results and discussion

The ammonia-oxidizing archaea (AOA) amoA copies were in the range 5.99?×?10⁸ to 8.60?×?10⁸, while those of ammonia-oxidizing bacteria (AOB) varied from 3.02?×?10⁷ to 4.61?×?10⁷. The abundance of AOA was substantially higher in the light grazing treatment (LG) than in the mowing treatments. The quantity and intensity of DGGE bands of AOA varied with pasture management. In stark contrast, AOB population abundance and community structure remained largely unchanged in all the soils irrespective of the management practices. All these results suggested that ammonia oxidizers were dominated by AOA. The higher gene abundance and greater intensity of DGGE bands of nirS and nosZ under the enclosure treatments would suggest greater stimulated denitrification. The ratio of nosZ/(nirS?+?nirK) was higher in mowing treatments than in the free-grazing and enclosure treatments, possibly leading to more complete denitrification. Correlation analysis indicated that soil moisture and inorganic nitrogen content were the two main soil environmental variables that influence the community structure of nitrifiers and denitrifiers.

Conclusions

In this semiarid neutral to alkaline grassland ecosystem under low temperature conditions, AOA mainly affiliated with Nitrososphaera dominated nitrification. These results clearly demonstrate that grassland management practices can have a major impact on nitrifier and denitrifier communities in this semiarid grassland ecosystem, under low temperature conditions.

     

Logistic模型模拟乙醇发酵产物动力学

乙醇发酵产物动力学的研究有助于更好的认识发酵过程,为其工业放大及生产操作条件的优化提供理论基础。基于Logistic方程的菌体生长动力学模型可较好的描述细胞生长期及细胞自身抑制作用,但由于该模型方程中的比例参数与积分常数没有明显的生物学意义,使其应用受到了限制。该文从生物学与化学工程学结合角度对Logistic模型方程重新参数化,将发酵产物乙醇生成动力学与酵母生长动力学方程类比,给出了乙醇浓度的显式函数模型,模型中不再出现酵母菌浓度变量,大大简化了模型,并且赋予参数其物理意义;在研究了以葡萄糖和玉米淀粉为原料乙醇质量浓度、总糖质量浓度在不同底物质量浓度和料液比条件下随发酵时间的变化规律的基础上运用该模型拟合了以葡萄糖和玉米淀粉为原料进行乙醇发酵的试验数据,结果表明:模型值与试验数据具有较好一致性,拟合度均大于0.97,可见该重新参数化的Logistic模型可以描述发酵生产乙醇过程中产物乙醇的动力学行为,具有预测工业上实际发酵过程中乙醇浓度的潜力。     

基于可拓评价方法的土地开发整理项目立项决策研究

项目立项决策是实施土地开发整理项目管理的重要内容，项目评价结果是立项决策的依据。该文在全国建立统一的项目评价指标体系的基础上，按区域和项目类型制定指标评分标准。并从初评合格的项目中抽取6个不同区域、不同类型的土地开发整理项目，运用可拓评价方法对其进行立项决策评价。     

农业旱灾脆弱性评价及生态减灾研究——以湖南省衡阳市为例

农业旱情是农业旱灾脆弱性和干旱风险性共同作用的结果。随着全球变暖,蒸发力增大,干旱的风险性变大,因此降低农业旱灾脆弱性是防旱抗旱的重要措施。灾害脆弱性可以看成是生态安全性的另一面,故加强生态安全建设可以降低农业旱灾脆弱性。衡阳市是湖南省重要的农业生产基地之一,也是农业旱情较重地区之一,而其农业旱情与农业旱灾脆弱性密切相关。这种脆弱性是生态环境因素和社会因素在一定的时空条件下偶合的产物。详细地分析了气候因素、植被和土壤等环境因素和水利设施、经济发展水平等社会因素在农业旱灾脆弱性形成中的作用。依据长时间序列的气象资料和经济统计数据,运用数学模型和有关优化分析方法,对衡阳市农业旱灾脆弱性进行定量评估。提出了降低农业旱灾脆弱性的生态措施。     

干旱缺水地区森林植被蒸散耗水研究

 系统总结近年来在宁夏固原六盘山、北京延庆等干旱缺水地区进行的森林植被蒸散耗水研究结果。乔、灌、草作为土壤水分限制型生态系统的坡面植被,蒸散都是水分平衡的最大分项,其中植被蒸腾又是蒸散的最大分项。植被蒸散量一般表现为高大乔木林>亚乔木林>灌木林>自然草地,但人工草地>自然草地。可依坡面产水功能将不同植被分类,自然草地和灌丛为水源生产型,亚乔木林为水源平衡型,高大乔木林和人工草地为水源消耗型。植株密度不是坡面植被蒸散大小的决定性因子,其作用更多的是调控蒸腾量及其占蒸散比例。虽然降低植株密度一般会减小蒸散,但并不是相同比例地线性下降,不同植被类型反应也不一样,表现出降低密度减少蒸散的作用从乔木、亚乔木到灌木而变弱的趋势,降低密度减少蒸散的作用是有限的。对降低密度减少蒸散的作用大小,作为调控措施的有效性,有效的密度调控范围等,还需严格的对比实验和理论研究。估计和评价植被蒸散耗水时,用叶面积指数或叶生长量指标可能比密度更符合生物学逻辑。从在干旱缺水地区建立节水、稳定、高效、多功能的坡面植被的角度而言,草地和灌丛的蒸散低于乔木林,建立稀树草原或稀树灌丛式的植被可能更利于流域产水和植被稳定。从小流域管理的角度而言,还需考虑在土壤水分承载力空间差异的基础上,探讨能兼顾产水功能、水土保持、水源涵养、植被稳定的植被空间优化配置的理论和技术。     

松软土壤上步行轮式气垫车功率优化的研究

通过对步行轮式气垫车在松软土壤上运行状态的分析，首次提出了该种车辆最佳飞高的定义，得到了随土壤条件变化时功率消耗模型，并求出了功率消耗的最优点。为步行轮式气垫车在松软土壤上的功率自适应控制打下一定基础。     

Archaeal communities in the sediments of different mangrove stands at Dongzhaigang,China

Purpose

Knowledge of archaeal communities is essential for understanding of the mechanism of carbon and nitrogen cycle in the mangrove sediment ecosystem. Presently, little is known about archaeal communities in the Dongzhaigang mangrove sediments. This study aimed to characterize the archaeal communities in sediments of different mangrove stands and to find out the correlations between archaeal communities and the environmental factors of sediments.

Materials and methods

Sediment samples were collected from the Dongzhaigang mangrove forest for analysis of soil properties and archaeal communities, by national standard methods and Illumina Miseq archaeal 16S ribosomal RNA (rRNA) gene sequencing, respectively.

Results and discussion

The archaeal community in the Dongzhaigang mangrove forest was constituted by some phyla from “TACK” and “DPANN” supergroups, and dominated by Euryarchaeota. Among sediments of the four mangroves in Dongzhaigang, principal coordinates analysis (PCoA) scatter plot showed a trend of difference in the archaeal community structure in the Bruguiera gymnoihiza and Kandelia candel stands from that in the Laguncularia racemosa and Sonneratia apetala stands. The abundance of the order Methanosarcinales was the highest in the sediments of K. candel mangroves, whereas the order of Methanobacteriales dominated in B. gymnoihiza sediments. The highest richness and diversity values of Archaea occurred in K. candel sediments, while the lowest in B. gymnoihiza. Pearson correlation showed the significant relationships between sediment properties and some dominant genera, with a positive and significant correlation between sediment properties and genus Methanobacterium, coinciding with the maximum values of sediment properties and abundance of Methanobacterium in the sediment of B. gymnoihiza. Such results indicated that the difference of archaeal community structure among mangrove sediments may be caused by the different sediment characteristics. Methanogenic communities in the Dongzhaigang mangrove forest sediments were, at the order level, constituted by Methanobacteriales, Methanomicrobiales, Methanosarcinales, and Methanomassiliicoccales.

Conclusions

The investigation indicated that the Dongzhaigang mangrove sediment ecosystems support diverse archaeal communities and methanogenic communities, and that there was a general trend of difference in the archaeal community structure in the B. gymnoihiza and K. candel mangrove sediments from that in the L. racemosa and S. apetala sediments. Such difference may be caused by the difference in sediment characteristics.

     

利用干酵母细胞微胶囊化丁香油的研究

探讨以干酵母细胞作为囊壁材料制备微胶囊的可行性。以丁香油为囊芯，通过正交试验优化微胶囊制备的工艺条件。结果表明，选择包埋温度70℃、包埋时间9 h和丁香油与干酵母质量配比为1∶1的条件比较适宜，微胶囊中丁香油包埋率可以达到41.26%。通过光学显微镜和电镜观察，丁香油微胶囊呈规则的球形，颗粒直径在2.0～4.0 μm之间，细胞质内能观察到闪亮的油滴存在。在100℃条件下加热20 h，丁香油经微胶囊化后挥发速率下降43.25%；丁香油微胶囊抑菌效果优于同量的丁香油，具有一定的缓释效果。     

单流道叶轮水力设计方法的研究

系统论述了单流道叶轮水力设计的新方法，新方法较原方法简单、可靠和实用，尤其便于编制计算机辅助设计软件。在对现有的优秀单流道叶轮水力模型进行归纳总结的基础上，给出了用速度系数法设计轴面图时的各速度系数值。借鉴双流道叶轮水力设计中平面图的设计方法，提出了新的单流道叶轮平面图水力设计方法。介绍和分析了新的流道截面面积变化规律和平面图流道中线方程，同时还给出了编程方法及其设计实例的实验结果。