Soil organic carbon stocks in Laos: spatial variations and controlling factors

Surface soils, which contain the largest pool of terrestrial organic carbon (C), may be able to sequester atmospheric C and thus mitigate climate change. However, this remains controversial, largely due to insufficient data and knowledge gaps in respect of organic C contents and stocks in soils and the main factors of their control. Up to now and despite numerous evaluations of soil organic carbon (SOC) stocks worldwide, the sloping lands of southeast Asia, one of the most biogeochemically active regions of the world, remain uninvestigated. Our main objective was to quantify SOC stocks and to evaluate the impact of various environmental factors. We, therefore, selected Laos with 230 566 km² of mostly forested steep slopes, and where cultivation is still mainly traditional, i.e. a system of shifting cultivation without fertilization or mechanical tillage. Analytical data from 3471 soil profiles demonstrated that the top 1 m of soil depth holds an estimated 4.64 billion tons of SOC, 65% of which is in the first 0.3 m. SOC stocks to 0.3 m exhibit a high coefficient of variation (CV=62%) with values from 1.8 to 771 Mg C ha^?1 and a mean at 129 Mg C ha^?1. Furthermore, these stocks are significantly (at P<0.05 level) affected by land use as shown by principal components analysis and t‐tests with the largest amount being found under forest, less under shifting cultivation and the smallest under continuous cultivation. Moreover, SOC stocks correlated regionally to total annual rainfalls and latitude, and locally at the hill‐slope level to the distance to the stream network and the slope angle. It is hypothesized that this correlation is through actions on mineral weathering, soil clay content, soil fertility and SOC redistributions in landscapes. These relationships between SOC stocks and environmental factors may be of further use in (1) predicting the impact of global changes on future SOC stocks; and (2) identifying optimal strategies for land use planning so as to minimize soil C emissions to the atmosphere while maximizing carbon sequestration in soils.     

夜郎湖水库水体不同形态汞的时空分布

于2006年7月(夏季)、2007年1月(冬季)和3月(春季)采集了贵州省夜郎湖水库水样,研究了不同形态汞(总汞、溶解态汞、颗粒态汞)的时空分布特征及其影响因素.结果表明,夏季水体总汞、溶解态汞、颗粒态汞平均含量分别为4.48±2.59、2.37±1.40、2.11±1.86 ng·L-1,均显著高于冬季和春季(P＜0.001),而冬春2季不同形态汞含量无明显差异.水质参数悬浮颗粒物(SPM)和硝酸盐(NO-3)与不同形态汞之间均存在显著的正相关关系,表明这些参数对于不同形态汞的季节分布起着重要作用.夏季农业耕作活动相对活跃,表层土壤的扰动增加,雨水冲刷农田土壤,带进大量的外源颗粒物,致使夜郎湖水体夏季总汞水平较高.空间分布表明,夜郎湖水库夏季总汞平均浓度从水库入库河流至大坝方向、出库河流呈现总体下降的分布趋势,但水体各采样剖面没有明显的分布规律.     

破囊壶菌脂肪酶基因的克隆、双温控自诱导表达及酶学性质研究

【目的】克隆破囊壶菌Aurantiochytrium sp.PKU#SW7的脂肪酶基因,实现其在大肠杆菌细胞中异源高效表达,并进行初步酶学性质研究。【方法】基于转录组数据注释,获得脂肪酶基因lip,构建重组基因工程菌Rosetta(DE3)/p ET30-lip,利用双温控自诱导方法高效表达蛋白,表达产物(LIP)经Ni-Agarose His亲和层析柱纯化后进行酶学性质研究。【结果】从Aurantiochytrium sp.PKU#SW7中克隆得到一个大小为873 bp的脂肪酶基因(Gen Bank登录号为KT305964),该酶对p-NPB最适反应温度和pH分别为40°C和8.0。以不同浓度的金属离子Ca~(2+)和Co~(2+)溶液分别保温处理酶液30 min可使酶活提高1.3倍左右;甲醇对脂肪酶的抑制作用不明显。在最适反应条件下对p-NPP与p-NPB的酶活力分别为70.0±3.1 U/mg和102.5±2.6 U/mg。【结论】Aurantiochytrium sp.PKU#SW7脂肪酶具有良好的特性,符合生物柴油生物催化剂基本要求。     

Small mammal (rodents and lagomorphs) European biogeography from the Late Oligocene to the mid Pliocene

Aim To analyse the fossil species assemblages of rodents and lagomorphs from the European Neogene in order to assess what factors control small mammal biogeography at a deep‐time evolutionary time‐scale. Location Western Europe: 626 fossil‐bearing localities located within 31 regions and distributed among 18 successive biochronological units ranging from c. 27 Ma (million years ago; Late Oligocene) to c. 3 Ma (mid Pliocene). Methods Taxonomically homogenized pooled regional assemblages are compared using the Raup and Crick index of faunal similarity; then, the inferred similarity matrices are visualized as neighbour‐joining trees and by projecting the statistically significant interregional similarities and dissimilarities onto palaeogeographical maps. The inferred biogeographical patterns are analysed and discussed in the light of known palaeogeographical and palaeoclimatic events. Results Successive time intervals with distinct biogeographical contexts are identified. Prior to c. 18 Ma (Late Oligocene and Early Miocene), a relative faunal homogeneity (high interregional connectivity) is observed all over Europe, a time when major geographical barriers and a weak climatic gradient are known. Then, from the beginning of the Middle Miocene onwards, the biogeography is marked by a significant decrease in interregional faunal affinities which matches a drastic global climatic degradation and leads, in the Late Miocene (c. 11 Ma), to a marked latitudinal pattern of small mammal distribution. In spite of a short rehomogenization around the Miocene/Pliocene boundary (6–4 Ma), the biogeography of small mammals in the mid Pliocene (c. 3 Ma) finally closely reflects the extant situation. Main conclusions The resulting biogeographical evolutionary scheme indicates that the extant endemic situation has deep historical roots corresponding to global tectonic and climatic events acting as primary drivers of long‐term changes. The correlation of biogeographical events with climatic changes emphasizes the prevalent role of the climate over geography in generating heterogeneous biogeographical patterns at the continental scale.     

黄兔尾鼠防治中经济阈值的探讨

本文以新疆荒漠草原的主要害鼠——黄兔尾鼠Lagurus luteus为例,应用经济阈值,对该鼠的防治指标作了探讨。为确定草场鼠害的防治指标提供一种可行的测算方法。     

生物防治稻田与普通稻田水体中浮游植物的生态特征研究

通过对大沙镇生物防治稻田及普能稻田水体中浮游植物的调查研究,共检出藻类112种,其中生物防治稻田中82种,普通稻田中89种,稻田水体中的浮游植物以硅藻、裸藻和绿藻占优势,在普通稻田中,硅藻种类数超过生物防治稻田,其优势度最高的5种藻类中除双对栅藻外,其余4种均为硅藻;而在生物防治稻田中,裸藻种类数高于普通稻田,且其优势度最高的5种藻类中有两种为裸藻,通过比较发现,生物防治稻田不体中浮游生物的密度明显高于普通稻田,对水体浮游植物多样性及均匀度的分析表明,稻田水体中的浮游植物自秧苗插上至干田期间,多样性指数略有上升（上要是由于种类数的增加引起的）,而均匀度呈下降趋势。     

半干旱区人工林草地土壤旱化与土壤水分植被承载力

近年来在黄土高原地区多年生林草地。出现了以土壤旱化为主要特征的土壤退化现象。退化土壤反过来影响植物的生长和发育,最终将导致植物群落衰败和生态系统的退化,从而影响到林草植被的长期稳定,经济效益和生态效益的持续稳定发挥,这已成为当前林草植被建设的重大问题之一。分析了土壤旱化现象与土壤干层的关系,探讨了土壤干层的划分标准。认为防止土壤旱化的主要措施就是控制林草地密度和生产力,而控制林草地密度和生产力的理论依据就是土地植被承载力。在黄土高原大部分地区植物吸收和利用的土壤水分主要依靠当地的天然降水。土壤水分是限制植物生长的决定因子,该类地区土地植被承载力实质上为土壤水分的植被承载力。作者定义土壤水分植被承载力为土壤水分承载植物的最大负荷。它是指在较长时期内,在现有的条件下,当植物根系可吸收和利用土层范围内土壤水分消耗量等于或小于土壤水分补给量时,所能维持特定植物群落健康生长的最大密度。探讨了土壤水分植被承载力的确定方法和影响因素,认为凡是影响林草地土壤水分的补给和消耗,植物群落生长发育和植物水分利用效率的因素,包括地理位置、地形、气候、植被类型及其发育阶段,抚育管理措施都影响土壤水分植被承载力数值。开展土壤水分植被承载力研究对于林草地合理经营与管理具有重要意义。     

植物转基因沉默及控制

植物基因工程的目的就是获取外源基因能够按照设计要求正常表达和稳定遗传的转基因植物。近几年来,广泛报道了转基因植物中存在转基因沉默现象。主要阐述了两种转基因沉默的机理即转录水平的基因沉默和转录后水平的基因沉默,各种机理都涉及DNA DNA,DNA RNA,RNA RNA的相互作用。同时,还讨论一些控制转基因沉默现象的策略,特别是MAR在转基因植物中具有增强基因表达和减少株间差异的作用。     

植物组织培养中的内生细菌污染问题

植物组织中普遍存在内生菌,当植物组织进行离体培养时,这些内生菌就会产生污染。对内生菌污染概念进行了界定,对内生菌污染的种类、普遍性、症状与危害性作了阐述,综合了有关防治方法,并讨论了抗生素使用的效果、稳定性和应注意的问题。