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排序方式: 共有530条查询结果,搜索用时 593 毫秒
161.
Abstract: Introducing rare plants to new sites for conservation to offset effects of habitat destruction requires detailed knowledge of habitat requirements, plant demography, and management needs. We conducted a factorial experiment replicated at three coastal prairie sites to test the effects of clipping frequency and litter accumulation on seed germination, seedling survival, reproduction, and seedling recruitment of introduced populations of the endangered, tall-stature, annual forb, Holocarpha macradenia (DC.) E. Greene. Clipping favored H. macradenia , primarily by enhancing seed germination and flower production. Litter accumulation had no effect on seed germination, even after 5 years of treatments. Seedling recruitment was highly site specific with large numbers of recruits recorded at only one of three sites. Although recruitment of seedlings was higher in clipped plots for 2–3 years, by 4–5 years after introduction very few seedlings survived to reproduction in any treatment. We attribute this result to a combination of poor habitat quality, small population size, and lack of a seed bank. We were unsuccessful in introducing this relatively well-studied species of concern to apparently suitable habitat at multiple sites in multiple years, which suggests that translocating rare plant populations to mitigate for habitat destruction is an expensive and highly uncertain endeavor. 相似文献
162.
Nitrous oxide (N2O) fluxes from soils were measured using the closed chamber method during the snow-free seasons (middle April to early November),for three years,in a total of 11 upland crop fields in central Hokkaido,Japan.The annual mean N2O fluxes ranged from 2.95 to 164.17 μgN/(m2·h),with the lowest observed in a grassland and the highest in an onion field.The instantaneous N2O fluxes showed a large temporal variation with peak emissions generally occurring following fertilization and heavy rainfall eve... 相似文献
163.
池火灾热辐射计算及模拟 总被引:2,自引:0,他引:2
在油罐火灾中,着火罐所释放的热辐射对附近的人员以及设备造成一定的危害,分别采用经验公式以及FDS模拟来计算热辐射强度,并对计算结果进行比较及分析,结果表明两种方法可互相补充完善。 相似文献
164.
A/O池-沉淀池-消毒工艺在处理医院废水中是可行的。原污水经过厌氧、好氧两个生物处理过程,可以同时去除水中大部分的COD、BOD5、悬浮物、氨氮、磷。通过实际的运行操作表明:该工艺具有效率高、能够脱氮除磷、处理效果好、投资低、占地面积小、运行费用低、管理操作方便等优点。 相似文献
165.
Alois Honek Zdenka Martinkova Pavel Saska Stanislava Koprdova 《Agriculture, ecosystems & environment》2009,134(1-2):126-135
Dandelion Taraxacum agg. (formerly Taraxacum officinale G.H. Weber ex Wiggers) is a common weed species associated with pastures, grasslands and no-tillage cropping systems throughout its native range in Europe, and more recently introduced into North America, Australasia and elsewhere. Following wind-dispersal from the parent plant, its seeds are subject to predation from a host of invertebrate predators. Similarly, seedling predation may also significantly limit dandelion recruitment. Although such post-dispersal mortality is central to our understanding of dandelion population dynamics and therefore weed control, the precise spatio-temporal role played by different putative seed and seedling predators is poorly understood. Here we studied how seed viability, and seed and seedling predation influenced dandelion recruitment at two contrasting sites in central Europe. The abundance in the field and seed and seedling consumption in the laboratory were determined for the main groups of predators—ground beetles (Coleoptera: Carabiade), terrestrial isopods (Isopoda: Oniscidea) and molluscs (Gastopoda: Pulmonata). At particular sites, seed viability and seedling predation were negatively correlated while the percentage of seeds that succumbed to seed predation was similar. Combined factors accounted for the death of 98% and 87% of exposed seeds. Ground beetles (particularly Amara spp.) and terrestrial isopods (Armadillidium vulgare) were efficient and dominant seed predators, while slugs (Arion lusitanicus) and isopods were important predators of seedlings. While there was no seasonal trend in the intensity of seed predation it decreased towards autumn in parallel with the feeding activity of the declining population of A. lusitanicus. The mortality factors thus varied in their importance, largely between sites and less with the course of the season. Although seed inviability, seed and seedling predation did not stop the recruitment of dandelion seedlings they are crucial factors limiting dandelion populations. Methods of increasing the efficiency of predation of seed as a means of managing weeds are worthy of further study, particularly in areas where dandelion is an invasive species. 相似文献
166.
167.
为了探索不同水稻种植区水稻品种对酸雨胁迫的响应规律,采用室内实验方法研究pH值为2.0、2.5、3.0、3.5、4.0、5.0的模拟酸雨对隆安优8、天协1、协优57水稻品种种子发芽率、发芽势、发芽指数、活力指数和异状发芽率5个指标的影响.结果表明:酸雨持续胁迫7d后,上述3个品种的发芽势(率)、发芽(活力)指数随胁迫强度增加(pH值为5.0~3.0)呈先增后减的变化,pH值为2.5时种子仅有异状发芽,pH值为2.0时均不发芽;3者的发芽势(率)、发芽(活力)指数等均与胁迫时间(1~7d)呈显著负相关(异状发芽率呈正相关).综合分析认为,酸雨对3个水稻品种的伤害阈限为pH值2.5~3.5;一定胁强(pH值为2.5)下,3类种子上述5项萌发指标与CK呈显著差异的胁时不同:隆安优8、协优57(4d,2d,2d,2d,4d)大于或等天协1(3d,2d,2d,2d,3d),表明3者对酸雨的抗性存在一定差异,即隆安优8、协优57大于天协1. 相似文献
168.
孙有仙 《安全.健康和环境》2007,7(5):37-39
分析了事故后果模拟分析方法在安全评价应用中存在的问题,方法中有关参数要根据现场实际情况计算、测量选取,否则计算结果就会失真. 相似文献
169.
170.