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1.
    
Buffelgrass (Pennisetum ciliare (L.) Link), a C4 perennial bunchgrass native to Africa and parts of Asia, has invaded broadly across the southwestern United States and northern Mexico. Buffelgrass establishment may occur earlier than the natives it displaces which may preempt resource acquisition by native species and contribute to its invasion success. In a greenhouse, buffelgrass aboveground growth was tested against Arizona cottontop (Digitaria californica (Benth.) Henr.), a native C4 perennial bunchgrass, in pairwise combinations in a randomized complete block factorial design with 10 replications, three neighbor identities (self, other, and no neighbor), and three competition treatments (21‐day younger neighbor, 21‐day older neighbor, and same‐aged neighbor). When compared with control plants, there was no significant effect on aboveground biomass for older Arizona cottontop plants competing with younger buffelgrass plants (p > 0.05). However, when Arizona cottontop plants were of the same age or younger than buffelgrass plants, buffelgrass caused 95 and 88% reductions, respectively, in aboveground biomass (p < 0.05 in both cases). Intraspecific competition between same‐aged Arizona cottontop plants resulted in only 55% decline in aboveground biomass production (p < 0.05), thus interspecific competition with buffelgrass was more intense than intraspecific competition for Arizona cottontop when plants had similar emergence times. These results suggest that establishing native plants immediately following a disturbance event could be a practical technique for restoring or retaining diversity on sites with high potential for invasion by buffelgrass.  相似文献   

2.
    
The grasslands of the northern Great Plains (NGP) region of North America are considered endangered ecosystems and priority conservation areas yet have great ecological and economic importance. Grasslands in the NGP are no longer self‐regulating adaptive systems. The challenges to these grasslands are widespread and serious (e.g. climate change, invasive species, fragmentation, altered disturbance regimes, and anthropogenic chemical loads). Because the challenges facing the region are dynamic, complex, and persistent, a paradigm shift in how we approach restoration and management of the grasslands in the NGP is imperative. The goal of this article is to highlight four key points for land managers and restoration practitioners to consider when planning management or restoration actions. First, we discuss the appropriateness of using historical fidelity as a restoration or management target because of changing climate, widespread pervasiveness of invasive species, the high level of fragmentation, and altered disturbance regimes. Second, we highlight ecosystem resilience and long‐term population persistence as alternative targets. Third, because the NGP is so heavily impacted with anthropogenic chemical loading, we discuss the risks of ecological traps and extinction debt. Finally, we highlight the importance of using adaptive management and having patience during restoration and management. Consideration of these four points will help management and restoration of grasslands move toward a more successful and sustainable future. Although we specifically focus on the NGP of North America, these same issues and considerations apply to grasslands and many other ecosystems globally.  相似文献   

3.
    
Protein-precipitating polyphenolics (PPPs) serve as a plant defense against herbivory, increasing with stress. We studied how varying intensities of simulated and Melanoplus differentialis herbivory affected (1) PPP concentration; (2) protein bound by PPP (PB); and (3) N concentration of panicled tick-clover (Desmodium paniculatum; PTC) and sericea lespedeza (Lespedeza cuneata; SL) leaf regrowth. Leaves of PTC that were submitted to simulated herbivory had lesser (p?≤?.05 for all significant differences) PPP concentration than the control for most treatments. For PTC, PPP concentration decreased with increasing herbivory intensity for both herbivory types. For SL, PPP was similar between herbivory types for Harvest 1 but not for 2, decreasing as herbivory intensity increased for both herbivory types. Simulated herbivory resulted in lower PB concentrations for PTC and SL compared to the grasshopper herbivory. Nitrogen concentration was similar for PTC and SL between herbivory types but variable among degree of herbivory. Herbivory type affects PPP.  相似文献   

4.
铁扫帚中总多糖提取工艺的研究   总被引：1，自引：0，他引：1  
研究了铁扫帚中总多糖提取的最佳工艺,并对其进行了薄层层析,结果表明:A3B2C1条件下,总多糖提取率最高。薄层层析得两个组分,其Rf值分别为:0.65和0.55  相似文献   

5.
    
Cover and richness of a 5‐year revegetation effort were studied with ,respect to small‐scale disturbance and nutrient manipulations. The site, originally a relict tallgrass prairie mined for gravel, was replanted to native grasses using a seed mixture of tall‐, mixed‐, and short‐grass species. Following one wet and three relatively dry years, a community emerged, dominated by species common in saline soils not found along the Colorado Front Range. A single species, Alkali sacaton (Sporobolus airoides), composed nearly 50% of relative vegetation cover in control plots exhibiting a negative relationship between cover and richness. Seeded species composed approximately 92% of vegetation cover. The remaining 8% was composed of weeds from nearby areas, seed bank survivors, or mix contaminants. Three years of soil nutrient amendments, which lowered plant‐available nitrogen and phosphorus, significantly increased relative cover of seeded species to 97.5%. Fertilizer additions of phosphate enhanced abundance of introduced annual grasses (Bromus spp.) but did not significantly alter cover in control plots. Unmanipulated 4‐m2 plots contained an average of 4.7 planted species and 3.9 nonplanted species during the 5‐year period, whereas plots that received grass herbicide averaged 5.4 nonplanted species. Species richness ranged from an average 6.9 species in low‐nutrient, undisturbed plots to 10.9 species in the relatively high‐nutrient, disturbed plots. The use of stockpiled soils, applied sparingly, in conjunction with a native seed mix containing species uncommon to the preexisting community generated a species‐depauperate, novel plant community that appears resistant to invasion by ruderal species.  相似文献   

6.
    
Aims In this study, we examined the effects of Solidago altissima (hereafter Solidago) and two species in the genus Verbesina, Verbesina virginica and Verbesina occidentalis (hereafter Verbesina), on the structure of an old-field plant community and establishment by an invasive plant species, Lespedeza cuneata (hereafter Lespedeza).Methods We removed Solidago, Verbesina and both Solidago and Verbesina from 4-m 2 plots in an intact old-field community during two growing seasons. We then quantified the effects of these removals on richness, evenness, diversity and composition of the subdominant plant community. We also measured the total aboveground biomass and the aboveground biomass of the subdominant community. To assess how these removals affected establishment by Lespedeza, we planted 20 seeds in each plot and tracked seedling emergence and survival for one growing season.Important findings Subdominant community evenness and Shannon diversity were higher in plots from which Solidago and Verbesina were removed relative to control plots. However, there were no effects of dominant species removal on species richness or composition of the subdominant community. Total aboveground biomass was not affected by dominant species removal, suggesting that the community of subdominant species exhibited compensation. In fact, subdominant community biomass was greater when Solidago, but not Verbesina, was removed. Light availability was also greater in plots where Solidago was removed relative to control plots throughout the growing season. In addition, removal of dominant species, in particular Solidago, indirectly reduced the emergence, but not survival, of Lespedeza seedlings by directly promoting subdominant community biomass. Taken together, our results suggest that dominant old-field plant species affect subdominant community structure and indirectly promote establishment by Lespedeza .  相似文献   

7.
    
Understanding the degree to which species assemblages naturally vary over time will be critically important when assessing whether direct management effects or contingency is responsible for species gain or loss. In this study, we tested three predictions related to short‐term variation in prairie moth communities: (1) communities would only exhibit significant temporal variation in newly restored sites (1–3 years old); (2) prairie size and age would positively influence community reassembly, with larger, older restorations sampling a greater proportion of the regional species pool; and (3) older restorations (7–10 years old) would have yet to converge on the community composition of prairie remnants. Moths were sampled from 13 Tallgrass prairie restorations and remnants in central Iowa in 2004–2005. Repeated measures analysis of variance revealed significant effects of sampling year on moth species richness and abundance as well as on the richness of two functional groups, but difference among prairie types was only observed in 2005. Rarefaction analysis revealed that older restorations and prairie remnants supported higher species richness compared to recently planted sites, and nonmetric, multidimensional scaling ordination indicated that restorations older than 7 years were clearly converging on the species composition of remnants. These results suggest that moth communities in restorations and remnants are highly variable in time but that as restorations age, they appear to reaccumulate moth species found in prairie remnants. The long‐term persistence of a particular species assemblage within a given site, however, might be a difficult endpoint to attain in central Iowa prairies because of significant annual variation in species occurrence.  相似文献   

8.
Derner  J.D.  Briske  D.D. 《Plant and Soil》2001,237(1):117-127
An experiment was conducted to compare below-ground soil organic carbon and total nitrogen accumulation between caespitose and rhizomatous perennial grasses in long-term (<25 yrs) grazed and ungrazed sites in semi-arid and mesic communities in the North American Great Plains. Development of greater nutrient pools beneath than between clones occurred at minimal clone basal areas (<60 cm2) for both caespitose species. Caespitose grasses accumulated substantially greater pools of carbon (20–200 fold) and nitrogen (50–500 fold) in soils to a depth of 10 cm beneath clones than rhizomatous grasses accumulated in rhizomes in both communities. Carbon and nitrogen pools in soils beneath caespitose clones exceeded combined (soil + rhizome) pools for rhizomatous grasses for a majority of the clone basal areas (>90 cm2) in the mesic community. In contrast, both pool sizes were smaller beneath the caespitose grass at all clone basal areas than the combined pools for the rhizomatous grass in the semi-arid community. The occurrence of larger soil nutrient pools beneath the rhizomatous species in the semi-arid community was largely a consequence of niche separation for microsites characterized by soils with higher nutrient concentrations, rather than plant-induced increases in nutrient concentrations. Although nutrient islands do not occur beneath rhizomatous grasses, their distribution in the semi-arid community was restricted to microsites characterized by soils with higher SOC and N concentrations. A greater efficiency of nutrient accumulation per unit rhizome mass and the maintenance of rhizome nutrient pools of similar magnitude to those of the rhizomatous grass in the mesic community may also contribute to the distribution of rhizomatous grasses in semi-arid communities. The existence of nutrient islands beneath a wide range of clone sizes in both mesic and semi-arid communities provides circumstantial evidence to suggest that nutrient islands beneath caespitose grasses may contribute to clone fitness in this growth form.  相似文献   

9.
    
Ecological restoration can reverse biodiversity loss worldwide, yet restoration goals and outcomes vary widely, which limits this potential. Divergent restoration outcomes may stem from variation in conditions at the outset of restoration, but empirical evidence is lacking and typically confounded with site differences. Additionally, precipitation is usually cited as the source of this variation, although a wide range of conditions can vary annually. We tested for effects of planting year on seedling establishment by installing identical restorations in three different years. Within those years, we manipulated rainfall with rain‐out shelters to disentangle the effects of precipitation from other annually variable conditions. Additionally, we tested whether increasing seed mix richness buffers against adverse planting conditions. For the first growing season after planting, we followed emergence and survival of sown prairie species and nonsown weed species to determine how planting year conditions influence an establishing plant community, if at all. We found that seedling establishment differed across planting years and precipitation treatments, and that varying emergence patterns by species led to differences in the composition of the first‐year community. We also found significant variation in sown species establishment across years when precipitation was held constant, illustrating the previously overlooked role of nonprecipitation drivers on planting year effects. Higher seed mix richness did not consistently improve establishment of sown species under different planting conditions. This research provides important experimental evidence for effects of interannual variation in planting conditions on first‐year establishment. Future work will examine how these initial changes affect longer‐term assembly dynamics.  相似文献   

10.
土壤养分含量降低是我国草原退化的主要原因之一,养分添加是退化草原恢复的有效措施,但过量养分添加会导致物种多样性降低。为了探讨适宜的养分添加量以及养分添加促进退化草原恢复的机制,本研究选择内蒙古典型草原的退化群落,通过氮(N)磷(P)养分共同添加梯度试验,研究了退化典型草原在群落、功能群和物种3个组织水平上对养分添加的响应。结果表明: 在群落水平,养分添加显著促进了退化典型草原生物量,但没有降低物种多样性;群落生物量随养分添加水平表现为饱和曲线响应,在12.0 g N·m-2、3.8 g P·m-2水平趋于饱和;物种多样性在低养分添加水平(N<9.6 g·m-2、P<3.0 g·m-2)较对照显著增加,在其余养分添加水平未发生显著变化。在功能群水平,随着养分添加量的增加,多年生根茎禾草在群落中优势度增加,生物量和密度均显著提高;一年生植物生物量和密度在高养分水平添加下显著增加,多年生丛生禾草和杂类草无显著变化。在物种水平,6个物种对养分添加响应不同,羊草通过增加种群密度和个体大小显著增加了种群生物量;大针茅、冰草和糙隐子草种群生物量没有显著变化;星毛委陵菜和黄囊苔草分别因为降低个体大小和种群密度减少了种群生物量。养分添加作为草原恢复的措施,可以显著增加退化草原生物量和物种多样性,降低植物群落中退化指示种,增加多年生根茎禾草。  相似文献   

11.
    
This study investigated the relationship among plant diversity, production, stability, and susceptibility to invasion in restored northern tall grass prairies (United States). The experiment consisted of 50 species mixtures fertilized with N or P, at high or low levels. Results from the past 5 years were as follows: (1) aboveground biomass increased and year‐to‐year variability declined with increases in plant species and functional form richness, mostly as a result of substantial increases in minimum biomass (maximum biomass was unaffected). (2) Aboveground biomass and biomass stability increased when the species in the mixture had: (a) high relative growth rates, root density, root surface area per unit of root biomass, uptake rates of N or P per unit of root surface area, and N use efficiency and (b) low root to shoot ratio. (3) Invasion of nonseeded species declined with increases in plant species and functional form richness. (4) The results from this experiment did not provide a single specific criterion for selecting an optimal species mixture. However, if the objectives of the restoration were simply to achieve an aboveground biomass variability that is less than that of growing‐season precipitation, then the seed mixtures need to have a minimum of nine species and three functional forms.  相似文献   

12.
    
Abstract Exotic plant invasions are a significant problem in urban bushland in Sydney, Australia. In low‐nutrient Hawkesbury Sandstone communities, invasive plants are often associated with urban run‐off and subsequent increases in soil nutrients, particularly phosphorus. Fire is an important aspect of community dynamics in Sydney vegetation, and is sometimes used in bush regeneration projects as a tool for weed control. This study addressed the question: ‘Are there differences in post‐fire resprouting and germination of native and exotic species in nutrient‐enriched communities, compared with communities not disturbed by nutrient enrichment?’ We found that in non‐enriched areas, few exotic species emerged, and those that did were unable to achieve the rapid growth that was seen in exotic plants in the nutrient‐enriched areas. Therefore, fire did not promote the invasion of exotic plants into areas that were not nutrient‐enriched. In nutrient‐enriched areas after fire, the diversity of native species was lower than in the non‐enriched areas. Some native species were able to survive and compete with the exotic species in terms of abundance, per cent cover and plant height. However, these successful species were a different suite of natives to those commonly found in the non‐enriched areas. We suggest that although fire can be a useful tool for short‐term removal of exotic plant biomass from nutrient‐enriched areas, it does not promote establishment of native species that were not already present.  相似文献   

13.
气候变化与人为干扰导致我国退化草地面积持续增加;养分添加是恢复退化草地的有效措施之一。本研究以内蒙古半干旱草甸草原退化草地为对象;通过早春融雪期和夏季生长期的氮（N）磷（P）养分共同添加实验;探究地下芽库及其与地上植被关系对不同时期养分添加的响应。结果表明:夏季养分添加显著增加群落整体地下芽库与地上分株密度;而早春养分添加无显著影响;不同时期养分添加显著降低分生组织制约系数。不同植物功能群对养分添加具有差异化响应;具体表现为养分添加显著降低杂类草地上分株密度;夏季养分添加显著增加丛生禾草地下芽和地上分株密度;其分生组织制约系数在不同时期养分添加下均显著降低;不同时期养分添加显著增加根茎型禾草地下芽和地上分株密度。因此;夏季养分添加将极大增加退化草甸草原植被更新潜力;不同植物功能群对养分添加的响应差异将决定草甸草原植被恢复与演替动态。  相似文献   

14.
    
Genetic variation in populations, both natural and restored, is usually considered crucial for response to short‐term environmental stresses and for long‐term evolutionary change. To have the best chance of successful long‐term survival, restored populations should reflect the extant variation found in remnants, but restored sites may suffer from genetic bottlenecks as a result of founder effects. Kankakee Sands is a large‐scale restoration being conducted by The Nature Conservancy (TNC) in northwestern Indiana. Our goal was to test for loss of genetic variation in restored plant populations by comparing them with TNC’s seed source nursery and with local remnant populations that were the source of nursery seed and of the first few restored sites. Allozyme analysis of Baptisia leucantha, Asclepias incarnata, Coreopsis tripteris, and Zizia aurea showed low levels of allozyme diversity within all species and reductions in polymorphism, alleles per locus, and expected heterozygosity between remnants and restorations for all species except A. incarnata. Almost all lost alleles were rare; restored populations contained almost 90% of alleles at polymorphic loci that occurred in remnants at frequencies greater than 1%. Allele frequencies for most loci did not differ between remnants and restored sites. Most species showed significant allele frequency differentiation among remnant populations and among restored sites. Our results indicate that seed collection techniques used at Kankakee Sands captured the great majority of allozyme variation present in seed source remnant populations.  相似文献   

15.
Land‐use history, recent management, and landscape position influence vegetation at the Rockefeller Experimental Tract (RET), a 40‐year‐old restoration experiment in northeast Kansas. RET is representative of the prairie‐forest ecotone, containing native tallgrass prairie and oak‐hickory forest, but unique in having tracts of replanted prairie, seeded in 1957, that have undergone long‐term restoration treatments: burned, grazed, mowed, or untreated. A land‐use history database for RET was compiled using a geographic information system to integrate historic and contemporary sources of information. Restoration management on the reseeded prairie has had a profound effect on forest development: mowing or burning precluded forest establishment (<3% forest cover), whereas portions of untreated or grazed areas became heavily forested (>97% forest cover). Forest colonization depends upon biotic and edaphic conditions at the time restoration was initiated: for areas replanted to prairie and managed by grazing, forestation was 6% on land in cultivation prior to replanting, 20% on former pastureland, and 98% on land deforested just before replanting. Patterns of forest colonization were also significantly associated with three landscape positions: near existing forest, along water courses, and along ridge tops. Additionally, land‐use history analyses showed that the presence of various prairie and forest species resulted from persistence and not from colonization following restoration. Because of the lasting imprint of historic land use on the landscape, our results indicate that it is essential that restoration studies be evaluated within a site‐specific historical context.  相似文献   

16.
    
The invasion of alien plant species threatens the composition and diversity of native communities. However, the invasiveness of alien plants and the resilience of native communities are dependent on the interactions between biotic and abiotic factors, such as natural enemies and nutrient availability. In our study, we simulated the invasion of nine invasive plant species into native plant communities using two levels of nutrient availability and suppression of natural enemies. We evaluated the effect of biotic and abiotic factors on the response of alien target species and the resistance of native communities to invasion. The results showed that the presence of enemies (enemy release) increased the biomass proportion of alien plants while decreasing that of native communities in the absence of nutrient addition. Furthermore, we also found that the negative effect of enemy suppression on the evenness of the native community and the root-to-shoot ratio of alien target species was greatest under nutrient addition. Therefore, nutrient-poor and natural enemies might promote the invasive success of alien species in native communities, whereas nutrient addition and enemy suppression can better enhance the resistance of native plant communities to invasion.  相似文献   

17.
    
化感作用在入侵植物和本地植物的相互作用中起着重要作用。氮沉降已成为一个全球性问题,但目前尚不清楚氮添加是否调节入侵植物和本地植物的化感作用来影响它们之间的相互作用。本研究通过温室实验,设置入侵植物加拿大一枝黄花(Solidago canadensis)在两种入侵水平下(入侵与未入侵)定植本地植物群落,并同时交叉设置两种化感作用水平处理(添加或不添加活性炭)和两种氮添加水平处理(添加或不添加)。本地植物群落由8种常与加拿大一枝黄花共生的草本植物组成。研究结果表明,加拿大一枝黄花和本地植物群落的化感作用对自身的生长都有显著的积极影响,而相比于未被入侵的本地植物,氮添加对被入侵的本地植物的积极影响更明显。此外,氮添加还改变了本地植物的化感作用。具体表现为,氮添加提高了被入侵时本地植物的化感作用,但降低了未被入侵时本地植物的化感作用。虽然氮添加对加拿大一枝黄花的生长无显著影响,但降低了其化感作用。这些结果表明,氮添加可以通过提高本地植物的化感作用和降低加拿大一枝黄花的化感作用来提高本地植物对加拿大一枝黄花入侵的抵抗能力。本研究结果为管理和控制加拿大一枝黄花的入侵提供了科学依据。  相似文献   

18.
    
Using a multispecies seed sowing experiment, we investigated the roles of seed and microsite limitation in constraining the restoration of native prairie diversity and ecosystem function in an abandoned upland hayfield in northeastern Kansas. Seeds of 32 native and naturalized plant species from the regional pool were sown into undisturbed and experimentally disturbed field plots. After six growing seasons, experimental sowing led to major shifts in species and functional group composition, increases in native species abundance and floristic quality, declines in abundance of non‐native species, and increases in plant diversity. These changes in community structure led to significant changes at the ecosystem level including increases in light capture, peak biomass, primary production, litter biomass, root biomass, and C storage in roots. Our findings reveal the importance of seed limitations in constraining the natural recovery of prairie vegetation, biodiversity, and ecosystem functioning in this grassland and confirm broadcast sowing as a useful tool for the restoration of upland hayfield sites.  相似文献   

19.
Abstract. 1. This study examined the invasion sequence of Drosophila species arriving at decomposing strawberries.
2. It was found that the age of fruit affected the likelihood of Drosophila arrival, flies preferring relatively fresh fruit. However, there were no repeatable trends in invasion sequence of Drosophila species, different species responding in a similar manner to changes in fruit age.
3. Although no systematic trends in invasion sequence were observed, species tended to be temporally separated due to stochastic differences in their arrival at the fruit.
4. It is suggested that stochastic, as well as repeatable, temporal separation of species can have an important influence on subsequent community development.  相似文献   

20.
唐龙  高扬  赵斌  梁宗锁  李博 《生态学报》2008,28(7):3344-3355
生物通过非同化--异化过程影响环境的事实普遍存在,生态学家对此也开展了大量的研究,但缺乏相应理论框架的指导,使得这些工作的潜在价值未能得到充分的体现.学者Clive G.Jones等提出的\"生态系统工程师\"概念,概括了此类生态学现象的一般特征,为认识生物对环境的影响提供了一种新的理论框架.介绍了生态系统工程师概念及相关的理论体系,包括3个术语、2类生态系统工程师、5种生态系统工程概念模型以及工程效应的测定方法.同时,论述了该概念在入侵生态学、保护生物学、恢复生态学等领域的应用前景.最后,讨论了未来的研究方向.可以预料,生态系统工程师概念及相关理论的不断发展将有助于对生态学本质的认识,并为生态系统管理提供新的思路.  相似文献   

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