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81.
Release and activity of allelochemicals from allelopathic rice seedlings 总被引:11,自引:0,他引:11
Kong C Liang W Xu X Hu F Wang P Jiang Y 《Journal of agricultural and food chemistry》2004,52(10):2861-2865
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. 相似文献
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北京典型边缘区25年来土壤有机质的时空变异特征 总被引:7,自引:1,他引:7
采用地统计学和GIS相结合的方法,研究了北京典型边缘区25 a来两个阶段(1981~2000年,2000~2006年)土壤有机质含量(SOM)的时空变异特征.研究结果表明:土地利用类型及土地利用方式的转换对土壤有机质含量产生重要影响.1981~2000年,荒草地向耕地的转换以及因灌溉设施的完善而引起水浇地面积的增加使得整个研究区域土壤有机质含量普遍增加,有机质含量平均值从9.64 g/kg增加到12.35 g/kg,增加了28%;在利益的驱使下,农户改变了土地利用方式,不再向种植粮食作物的土地追加投入,研究区域土壤有机质含量平均值由12.35 g/kg降低到11.46 g/kg(2000~2006年).空间上,1981年土壤有机质含量自北向南逐渐降低;与1981年相比,2000年的土壤有机质含量普遍增加一个级别,增加最多的区域分布在研究区域的中部,这些区域也是土地利用类型变化明显的地方,主要是荒草地向其他农用地的转换;与2000年相比,2006年研究区域内土壤有机质含量增加的只有3个地区,并且大部分增加不显著,增幅不到1g/kg. 相似文献
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Angela Y.Y. Kong Steven J. Fonte Chris van Kessel Johan Six 《Soil & Tillage Research》2009,104(2):256-262
Few studies address nutrient cycling during the transition period (e.g., 1–4 years following conversion) from standard to some form of conservation tillage. This study compares the influence of minimum versus standard tillage on changes in soil nitrogen (N) stabilization, nitrous oxide (N2O) emissions, short-term N cycling, and crop N use efficiency 1 year after tillage conversion in conventional (i.e., synthetic fertilizer-N only), low-input (i.e., alternating annual synthetic fertilizer- and cover crop-N), and organic (i.e., manure- and cover crop-N) irrigated, maize–tomato systems in California. To understand the mechanisms governing N cycling in these systems, we traced 15N-labeled fertilizer/cover crop into the maize grain, whole soil, and three soil fractions: macroaggregates (>250 μm), microaggregates (53–250 μm) and silt-and-clay (<53 μm). We found a cropping system effect on soil Nnew (i.e., N derived from 15N-fertilizer or -15N-cover crop), with 173 kg Nnew ha−1 in the conventional system compared to 71.6 and 69.2 kg Nnew ha−1 in the low-input and organic systems, respectively. In the conventional system, more Nnew was found in the microaggregate and silt-and-clay fractions, whereas, the Nnew of the organic and low-input systems resided mainly in the macroaggregates. Even though no effect of tillage was found on soil aggregation, the minimum tillage systems showed greater soil fraction-Nnew than the standard tillage systems, suggesting greater potential for N stabilization under minimum tillage. Grain-Nnew was also higher in the minimum versus standard tillage systems. Nevertheless, minimum tillage led to the greatest N2O emissions (39.5 g N2O–N ha−1 day−1) from the conventional cropping system, where N turnover was already the fastest among the cropping systems. In contrast, minimum tillage combined with the low-input system (which received the least N ha−1) produced intermediate N2O emissions, soil N stabilization, and crop N use efficiency. Although total soil N did not change after 1 year of conversion from standard to minimum tillage, our use of stable isotopes permitted the early detection of interactive effects between tillage regimes and cropping systems that determine the trade-offs among N stabilization, N2O emissions, and N availability. 相似文献
87.
不同预处理方式对柳枝稷厌氧发酵性能的影响 总被引:1,自引:0,他引:1
以柳枝稷为原料,研究微波,蒸汽加热和NaOH预处理方法对柳枝稷的结晶度和纤维结构的影响,同时考察了预处理后的柳枝稷在中温时的厌氧发酵性能.结果显示:3种处理都可以降低原料的结晶度;微波和NaOH处理可以显著降低柳枝稷的中性洗涤纤维、酸性洗涤纤维、木质素等含量;NaOH处理会降低粗脂肪的含量;蒸汽加热处理和原料的累积产气量(28 486和28 686 mL)及产气率(453.60和456.79mL/g)接近,而NaOH预处理由于C/N较高、阳离子毒害作用和抑制物的作用使得厌氧发酵性能降低.可见预处理可以降低柳枝稷纤维含量,但是对厌氧发酵性能并无明显改善作用. 相似文献
88.
不同硬化地面类型对城市悬铃木物质循环的影响 总被引:7,自引:0,他引:7
研究了城市不同硬化地面类型(水泥地面、水泥砖面和踏实土地面)对悬铃木物质循环、水分循环及营养元素(N,P,K)循环的影响。结果表明:自然降水在城市水泥地面,水泥砖面或坚实的地表上很容易形成较大的地表径流,其中以水泥地面最甚,达48%;各类型地面对雨水的渗透能力有明显差异,对照(花坛土)最强,为876%,踏实土(728%)次之,水泥砖面较差(33%),水泥地面渗透量接近于零。城市土壤营养元素除K外,N,P含量以踏实土最高,分别为00777和00866,其次为水泥砖面(00699和00587)及水泥地面(00562和00631);生产力排序为:踏实土>水泥砖面>水泥地面。树木对土壤养分的吸收量也呈现相似的趋势,表现为:吸收量越大,理论归还量越大,但由于实际归还量较小,则土壤亏损就较多。 相似文献
89.
采用 RAPD 方法对水牛梭形住内孢子虫、待定种及黄牛枯氏住内孢子虫缓殖子基因组 DNA 进行了分析,待定种 PCR 产物的电泳带型与枯氏住肉孢子虫的差异较梭形住内孢子虫大,这与二者表型性状一致的研究结果不吻合.对3种包囊种特异性的 PCR 指纹进行了筛选,回收和纯化了3种包囊种特异性的 DNA 片段,待定种0.7kb 片段经α-~(32)PdATP 标记后用作探针,只与同源 DNA 杂交,不与其它包囊、宿主细胞和艾美耳球虫杂交,用 pGEM-T Easy Vector 对该片段克隆成功,并测出其全长序列,为进一步设计特异引物建立标准 PCR 诊断方法和用作核酸探针奠定了基础。 相似文献
90.
概述了粗山羊草(Ae.tauschii(Coss.)Schmal.)的类别和地理分布以及其在山羊草属(Aegilops)分类中的地位。并从个体、细胞、生化和分子水平上对粗山羊草遗传多样性的研究进展作了系统的综述。这 结果对进一步研究和利用业山羊草以及其它小麦近缘植物具有重要意义。 相似文献