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利用漂浮水生植物和陆生植物对去除超富营养化湖水的总氮总磷能力及抑藻效果进行研究(10月~11月),在45d的培养周期中,水龙、水禾、凤眼莲、竹叶菜对总氮的平均去除速率用平均生物量法计算分别是31.91、32.91、21.65、38.27mg.kg-1.d-1,去除率分别是80%,77%,87%,86%;对磷平均去除速率用平均生物量法计算,分别是6.45、2.58、4.01、3.97mg.kg-1.d-1,去除率分别是85%,51%,94%,77%;研究了这些植物的生长速率、抑藻效果、干物质含量,初步探讨了乡土物种在水质净化中的应用。  相似文献
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The ecological and economic advantages of preventing introduction of species likely to become invasive have increased interest in implementing effective screening tools. We compared the accuracy of the Australian Weed Risk Assessment (WRA) system with that across the six geographies in which it has been tested (New Zealand, Hawaii, Hawaii and Pacific Islands, Czech Republic, Bonin Islands and Florida). Inclusion in four of the tests of a secondary screening tool, developed to reduce the number of species requiring further evaluation, decreased the number of species with that outcome by over 60% on average. Averaging across all tests demonstrated that the WRA system accurately identified major invaders 90%, and non-invaders 70%, of the time. Examined differently, a species of unknown invasive potential is on average likely to be correctly accepted or rejected over 80% of the time for all of these geographies when minor invaders are categorized as invasive. Whereas increasing consistency in definitions and implementation would facilitate understanding of the general application of the WRA system, we believe that this tool functions similarly across islands and continents in tropical and temperate climates and has been sufficiently tested to be adopted as an initial screen for plant species proposed for introduction to a new geography.  相似文献
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Numerous studies show that an increase in the availability of limiting resources can increase invasion by non-native plants into natural communities. One possible explanation is that the ability of natives to compete with non-natives tends to decrease when resource availability is increased. We tested this hypothesis in a competition experiment using two closely matched plant species and two environmental factors related to limiting resources in a coastal grassland system on Bodega Head in northern California. We grew the native grass Bromus carinatus and the non-native grass B. diandrus together and apart at different levels of soil nitrogen crossed with different levels of soil salinity. Both species are abundant in the grassland and previous work suggested that the abundance of B. carinatus is lower and the abundance of B. diandrus is higher on soil that has been enriched with nitrogen. Salinity has been shown to be negatively associated with invasion by B. diandrus into another California grassland, and to vary significantly over short distances in the grassland at Bodega Head, where it could affect water availability, which strongly limits plant growth during the dry season. Contrary to our prediction that low resource availabilities would increase the relative competitive ability of the native, the ability of B. carinatus to compete with B. diandrus was not greater when nitrogen availability was lower or when soil salinity was higher. Instead, high salinity increased the relative competitive ability of the non-native, and low nitrogen had little effect on competition. This suggests that preventing resource enrichment will not suffice to control invasion by non-native plant species in this grassland.  相似文献
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Diversity of an early successional plant community as influenced by ozone   总被引:3,自引:3,他引:0  
An early successional plant community was exposed to various ozone concentrations for two growing seasons (1994–1995) in open-top chambers in Auburn, Alabama, USA. The ozone treatments were: AA, ambient air (open plots); CF, carbon-filtered air ( c . 0·5×ambient air), 1×, non-filtered air, and 2×, twice ambient air. Vegetative canopy cover exhibited a pattern of accumulation in the spring, with maximum canopy cover attained in summer, then senescence of foliage in the autumn 1994. This pattern was not observed in 1995 as a result of a drought during the spring and summer. Varying ozone exposures caused shifts in the competitive interactions between plants, thereby altering community structure. Higher canopy cover, vertical canopy density (layers of foliage), species richness, diversity, and evenness existed in the CF treatments than in the other treatments. In addition, winged sumac ( Rhus copallina L.) became a major component of the CF treatments only during 1995. Surprisingly, blackberry ( Rubus cuneifolius Pursh.), a species considered ozone-sensitive, based on visible injury, dominated canopy cover within the 2× treatments, 41 and 33% of total canopy cover in 1994 and 1995, respectively. From these results it is concluded that plant communities existing in areas where lower ozone concentrations are prevalent might be more complex and diverse than those existing in areas with higher ozone concentrations.  相似文献
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Land managers require landscape-scale information on where exotic plant species have successfully established, to better guide research, control, and restoration efforts. We evaluated the vulnerability of various habitats to invasion by exotic plant species in a 100,000 ha area in the southeast corner of Grand Staircase-Escalante National Monument, Utah. For the 97 0.1-ha plots in 11 vegetation types, exotic species richness (log10) was strongly negatively correlated to the cover of cryptobiotic soil crusts (r = −0.47, P < 0.001), and positively correlated to native species richness (r = 0.22, P < 0.03), native species cover (r = 0.23, P < 0.05), and total nitrogen in the soil (r = 0.40, P < 0.001). Exotic species cover was strongly positively correlated to exotic species richness (r = 0.68, P < 0.001). Only 6 of 97 plots did not contain at least one exotic species. Exotic species richness was particularly high in locally rare, mesic vegetation types and nitrogen rich soils. Dry, upland plots (n = 51) had less than half of the exotic species richness and cover compared to plots (n = 45) in washes and lowland depressions that collect water intermittently. Plots dominated by trees had significantly greater native and exotic species richness compared to plots dominated by shrubs. For the 97 plots combined, 33% of the variance in exotic species richness could be explained by a positive relationship with total plant cover, and negative relationships with the cover of cryptobiotic crusts and bare ground. There are several reasons for concern: (1) Exotic plant species are invading hot spots of native plant diversity and rare/unique habitats. (2) The foliar cover of exotic species was greatest in habitats that had been invaded by several exotic species.(3) Continued disturbance of fragile cryptobiotic crusts by livestock, people, and vehicles may facilitate the further invasion of exotic plant species. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献
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