Release and activity of allelochemicals from allelopathic rice seedlings

3-Isopropyl-5-acetoxycyclohexene-2-one-1 (1), momilactone B (2), and 5,7,4'-trihydroxy-3',5'-dimethoxyflavone (3) were isolated and identified from an allelopathic rice accession PI312777. These three compounds at low concentrations could inhibit the growth of weeds Echinochloa crusgalli and Cyperus difformis associated with rice, especially mixtures of the compounds had stronger inhibitory activity than did individual compounds. Studies with hydroponic culture, continuous root exudates trapping system (CRETS), and direct resin adsorption methods showed that a total of 7.6 n moles 1, 2, and 3 were exuded from living roots of each seedling into the environment at 10 days after seedlings were transplanted. Furthermore, 1, 2, and 3 were found in the soil growing PI312777 seedlings at day 15 after seedlings emergence and reached a total of 39.5 microg/g soil at day 30. The results indicated that PI 312777 seedlings could release sufficient quantities of 1, 2, and 3 into the environment to act as allelochemicals inhibiting the growth of associated weeds. Investigations on the distribution of 1, 2, and 3 in PI 312777 plant, and its root exudates showed that the levels of 1, 2, and 3 were significantly higher in the shoots and root exudates than in the roots, and only trace 1 was observed in the roots. The results suggest that the roots of rice seedlings are not major site of synthesis or accumulation 1, 2, and 3, but a pathway for their release into the environment. The levels of 1, 2, and 3 in the root exudates were over 2-folds higher under direct resin adsorption than under hydroponic culture and CRETS, and hence, it is the preferred method to collect and identify active allelochemicals in rice exudates in future studies on rice allelopathy.     

青藏高原农田生态系统碳平衡

为探讨青藏高原农田生态系统碳平衡规律及其影响因子 ,并揭示其对全球含碳温室气体源、汇变化的贡献与响应 ,1 998～ 1 999连续 2年在拉萨农业生态站农田用静态箱法和生物量取样法开展土壤—植被界面CO2 吸收与排放的试验研究。农作物生长季 ,以冬小麦为例 ,生长前期 (从播种到拔节 )土壤碳排放量高于植被碳固定 ,生长后期 (灌浆到成熟 )则是植被碳固定高于土壤碳排放量 ,从全年来看 ,土壤碳排放量略高于植被碳固定     

Quantification of the group B soyasaponins by high-performance liquid chromatography

High-performance liquid chromatographic methods were developed for the isolation and quantitative determination of the group B soyasaponins, including 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP)-conjugated soyasaponins alphag, betag, and betaa, and their non-DDMP counterparts, soyasaponins V, I, and II, respectively, with formononetin used as the internal standard. The limits of quantification for soy products were 0.11-4.86 micromol/g. The within-day and between-days assay coefficients of variation were <9.8 and < 14.3%, respectively. The group B soyasaponin concentrations in 46 soybean varieties ranged from 2.50 to 5.85 micromol/g. Soy ingredients (soybean flour, toasted soy hypocotyls, soy protein isolates, textured vegetable protein, soy protein concentrates, and Novasoy) and soy foods (commercial soy milk, tofu, and tempeh) contained the group B soyasaponins from 0.20 to 114.02 micromol/g. There was no apparent correlation between isoflavone and soyasaponin concentrations in the soy products examined.     

植物低聚糖提取和生物活性鉴定

应用酶解法从小麦细胞壁中提取出低聚糖。经过活性鉴定,具有诱导大豆和小麦抗毒素产生,特别是从小麦代谢、细胞、植株等水平上改善该作物体内防御功能等生物作用。水解酶的种类、纯度、酶活值与所降解低聚糖的活性程度密切相关;高纯度、高酶活单位的水解酶提取的低聚糖,具有较强的生物功能。对来源不同的低聚糖进行了活性差异的比较,同时还讨论了其它因素——诸如小麦细胞的生理状态,低聚糖保存条件等对低聚糖活性的影响。     

以土壤水为中心的农区——非农区水均衡模型

针对干旱地区平原绿洲水土资源利用的特点,建立了以土壤水为中心的农区－ 非农区水均衡模型,该模型在已知地表水引用的情况下,可以对农区,非农区以及农区与非农区之间的水分迁移转化进行分析。本文给出了叶尔羌河平原绿洲１９９３～１９９６ 年农区,非农区的潜水蒸发量,农区向非农区地下水迁移量等的分析结果     

摆线转子泵转子结构参数的确定

介绍了在摆线转子泵的设计中。如何较准确地选择内、外转子的各种参数，以及选择这些参数的步骤和判定方法，并对外转子齿根圆和齿面的过渡圆弧与齿面相切之点所应处的正确位置进行了分析研究，为避免设计过程中因过渡圆弧半径r0选择的随意性而导致r0过大出现干涉，或r0过小而降低圆弧的过渡效果，给出了正确选择该参数值的求解公式。     

蛇腹鳞表面的超微结构及减阻机理

用原子力显微镜观测了竹叶青蛇、短尾蝮蛇和赤链华游蛇腹鳞表面的超微结构,分析了腹鳞表面的减阻机理。结果表明:3种蛇腹鳞表面的超微结构均为微凸体、微孔和凹坑周期排列的规律结构;蛇的栖息环境不同,超微结构的排间距、微凸体长度以及微孔的直径、数量不同。从陆栖到水栖,微凸体长度逐渐减小,微孔数量逐渐增加。微凸体减少了腹鳞和地面间的实际接触面积,从而减小了滑动时的粘着力;腹鳞表面的疏水性,减少了接触面间水的粘附力。     

RRR-RRR Ⅱ级杆组的等效系统动力学建模

将等效的思想与有限元的方法结合起来，用等效元素法建立了RRR Ⅱ级杆组的动力学等效模型，给出了其动力学微分方程，将建模的关键归结为二阶张量Tia和三阶张量Tibc的建立以及等效质量阵的组装。对给定的RRR—RRR六杆机构进行了建模和求解，给出了其动力响应曲线。实例表明，此方法与传统方法比较，无论从微分方程的列写，还是由计算机进行的解算，都显示出强大优势，解题效率高。     

考虑冷却流场的缸套失圆耦合分析

以ANSYS为平台,在整体冷却水系统数值计算结果的基础上,应用流固共轭耦合传热的数值方法,计算了冷却水流动对缸体与冷却水耦合模型的温度和气缸体热变形分布的影响,给出了整体冷却水系统的流场、压力场.对冷却水流动影响下的耦合模型的温度场、缸体的热变形及缸套的失圆问题进行了研究分析.     

机械化保护性耕作的技术体系与应用效果

农业保护性耕作技术是当今国际上先进的农业生产技术.实施以残茬覆盖和免耕、少耕为主要内容的机械化保护性耕作,可以减少地表径流,避免土壤流失,降低土壤风蚀,增加土壤有机质含量,改善耕地肥力及理化性状,是实现保土、保水、保肥和保持生态环境的重要措施,是旱作农业实现可持续发展的重要途径.