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411.
为实现混合底物的高效定向转化,以产絮菌根癌农杆菌(Agrobactrium tumefaciens)F2为研究对象,考察不同单一碳源及不同初始浓度对菌体生长、絮凝效能及絮凝剂产量的变化规律,采用BP算法构建絮凝效能及产量预测神经网络.产絮菌F2利用葡萄糖时的絮凝效能和产量分别为88.98%和2.20 g·L-1,过低的初始浓度将影响产量,不低于7.5 g·L-1为佳.以D-(+)-葡萄糖、D-半乳糖和D-甘露糖3种单糖为混合碳源,构建网络结构为3-5-2的产絮效能及絮凝剂产量预测模型,对两个输出层的预测误差范围均在4%以内,预测葡萄糖、半乳糖、甘露糖浓度的最优解为6.59 g·L-1、1.32 g·L-1、3.57 g·L-1,经验证混合碳源发酵产絮可使絮凝效能和产量比单一葡萄糖发酵时分别提高6.87%和26.82%,本文为产絮菌F2利用含糖有机质废液发酵产絮凝剂提供数据参考. 相似文献
412.
生态足迹方法的理论解析 总被引:67,自引:0,他引:67
论文系统地解析了生态足迹概念,在简要介绍生态足迹账户框架建立的假设条件,计算方法的基础上,系统总结了生态足迹最近的国际研究进展。同时,重点介绍了生态足迹计算中容易引起误解和疏忽的两个问题:化石能源用地的处理,均衡因子和产量因子的计算。在此基础上,从生态足迹计算过程中化石能源的处理和“利息”的处理两个角度评价了生态足迹方法的局限性。同时从贸易的处理缺乏可持续性基础,忽视国家和区域尺度上空间地理情况的差异,忽视人类社会对自然资产“利息”流的积累和储存,忽视自然资产存量的状况四个角度,分析了生态足迹在不同尺度上应用中存在的问题,最后通过将生态足迹分析还原到IPAT等式,并从热力学和生态经济学的角度解释了现有生态足迹分析政策建议少并且雷同、及其政策建议缺乏可操作性的实质价值的原因。 相似文献
413.
绿肥可以解决有机肥源不足的困难,减少化肥用量,节省成本和能源消耗,改善土壤环境,提高土壤肥力和地力;提高作物产量和产品质量;促进畜牧业的发展。本文根据广东的实际,指出广东的现代化农业需要大种绿肥,也可以大种绿肥。要使广东的绿肥生产得到恢复和发展,必须抓好如下的措施:从战略高度来认识绿肥的重要性;加强领导,把它提到重要的议事日程上来;广泛开展试验示范,并加强宣传发动;增加经济投入,省、市、县各级要设立绿肥种子繁育和经营风险金。 相似文献
414.
单产提升潜力衰减模型法在河南粮食单产中长期预测中的应用研究 总被引:1,自引:0,他引:1
粮食单产水平的提高是河南粮食增产的主要原因,准确预测粮食单产水平,对科学判断河南粮食生产能力、制定粮食生产战略意义重大。论文针对目前直接以单产为变量建立的预测模型未能反映出单产增长的有限性和增速的减缓性之不足,研究提出了一种基于单产提升潜力衰减过程的单产预测方法。该方法利用河南耕地的平均单产潜力和历年实际单产数据,计算得到河南历年单产可提升潜力值;依据单产提升潜力理论上呈逐渐衰减之变化特点,可采用指数衰减函数建立单产提升潜力回归模型,以达到间接预测单产之目的。结果表明:1)单产提升潜力对数值与时间t之间具有高度负线性相关关系,适宜建立指数回归模型;2)回归模型Vq-Vt=e-0.009 5t+9.464 7拟合优度R2=0.973 1,在0.01置信水平上回归显著;3)预测模型反映出了单产提升潜力的有限性和衰减性,即单产潜力对单产水平的限制性,模型理论诠释清晰;4)利用河南1978—2000年的单产数据作为样本建立预测模型,用样本以外2001—2015年的实际单产作为观测值,对预测单产进行模型预测检验,结果表明该模型预测单产绝对误差均值为129.15 kg/hm2,仅为现有方法的0.17~0.82倍,且误差平稳,适宜于单产中长期预测;5)预测得河南2020、2025、2030年的平均单产分别为6 375、6 765、7 155 kg/hm2,年均增幅为85.20~74.55 kg/hm2,增速呈逐渐减缓趋势。 相似文献
415.
416.
Summary. Surrogate leaves treated with methanolic leaf
surface extracts of Brassica napus L. (cv Express) plants
that received three different sulphur fertilisation treatments
showed even more marked differences by the oviposition
choice of Delia radicum L. than the potted plants. This
confirms that the oviposition preference of D. radicum is
mediated by chemical compounds on the leaf surface and
that the quality of host-plants in terms of their nutrition
status can be perceived by the female insect.The oviposition data were positively correlated with the
content of fractionated surface extracts containing either
CIF (cabbage identification factor; 1,2-dehydro-3-thia-
4,10,10b-triaza-cyclopenta[.a.]fluorine-1-carboxylic acid)
or glucosinolates. Electrophysiological recordings from the
tarsal chemoreceptor sensilla C5 and D3,4 showed that receptor
neurons react to glucosinolate- and CIF-fractions. We
found that the chemosensory activity of specific glucosinolate-
and CIF-receptor neurons corresponded with the
respective behavioural activity in the oviposition choice
assays. The responses of D. radicum to glucosinolates in
the electrophysiological recordings studies corresponded
to the observed oviposition preference on plants or artificial
leaves characterised with an higher amount of glucosinolates
on leave surfaces. The presented data suggested
that CIF and glucosinolates are involved in host-plant
preference of D. radicum and are perceived by tarsal
chemoreceptors. 相似文献
417.
Using Fallout Lead-210 Measurements to Estimate Soil Erosion in Three Small Catchments in Southern Italy 总被引:1,自引:0,他引:1
Paolo Porto Des E. Walling Giovanni Callegari Francesco Catona 《Water, Air, & Soil Pollution: Focus》2006,6(5-6):657-667
Soil erosion and associated off-site environmental impacts have attracted increasing attention in recent decades, and there
is a growing need for reliable information on rates of soil loss. The potential for using 137Cs fallout to quantify rates and patterns of soil redistribution over medium-term timescales (ca. 45 years) has been successfully
demonstrated in a wide range of environments around the world. The similar behaviour of fallout 210Pb in soils offers potential for its use as an alternative to 137Cs, in areas where 137Cs inventories are low or are complicated by additional fallout from the Chernobyl accident. There have, however, to date
been few attempts to validate the use of fallout 210Pb measurements for assessing erosion rates. This paper reports an attempt to explore the use of fallout 210Pb to estimate rates of water-induced soil erosion on uncultivated land. It focuses on three small forest/rangeland catchments
located in Calabria, southern Italy, for which measurements of sediment output are available. Comparison of the estimates
of net soil loss from the catchments derived from 210Pb measurements with the measured sediment output, confirmed the validity of the 210Pb approach. The soil redistribution rates estimated using 210Pb measurements were also consistent with equivalent estimates obtained for the same study catchments using 137Cs measurements. 相似文献
418.
419.
The Pacific Northwest encompasses a range of hydrologic regimes that can be broadly characterized as either coastal (where rain and rain on snow are dominant) or interior (where snowmelt is dominant). Forest harvesting generally increases the fraction of precipitation that is available to become streamflow, increases rates of snowmelt, and modifies the runoff pathways by which water flows to the stream channel. Harvesting may potentially decrease the magnitude of hyporheic exchange flow through increases in fine sediment and clogging of bed materials and through changes in channel morphology, although the ecological consequences of these changes are unclear. In small headwater catchments, forest harvesting generally increases annual runoff and peak flows and reduces the severity of low flows, but exceptions have been observed for each effect. Low flows appear to be more sensitive to transpiration from vegetation in the riparian zone than in the rest of the catchment. Although it appears that harvesting increased only the more frequent, geomorphically benign peak flows in several studies, in others the treatment effect increased with return period. Recovery to pre‐harvest conditions appeared to occur within about 10 to 20 years in some coastal catchments but may take many decades in mountainous, snow dominated catchments. 相似文献
420.
Can China control the side effects of motor vehicle growth? 总被引:2,自引:0,他引:2
Michael P. Walsh 《Natural resources forum》2007,31(1):21-34
Motor vehicle growth in China is the fastest in the world. This is placing great strain on the urban environment and causing a rapid increase in oil imports and motor vehicle carbon dioxide emissions. To deal with the environmental and health effects of air pollution, China has adopted a strong motor vehicle pollution control programme and imposed limits on fuel consumption of new light duty vehicles. The article will review these problems and programmes. Special focus will be given to the need to reduce sulphur levels in both gasoline and diesel fuel. 相似文献