植物外来种入侵及其对生态系统的影响

对植物外来种的入侵及生态系统的影响进行综述与分析,植物入侵多种因子的影响,可分为外因和内因两类,植物外来种对生态系统的影响主要体现在生产力,土壤营养,水分,干扰体制,群落的结构和动态等方面,在管理外来种时,需对外来种的特性和影响因子进行系统的观察研究,采用机械法,化学方法和生物控制法等综合办法控制植物的入侵,引进植物引来种时,要对引进种的行为特性进行了调查研究,注意其安全性。     

广东省农业生态系统外来入侵植物的种类调查与危害评估

为了掌握广东省农业生态系统中外来入侵植物的种类和分布状况,本文通过定点调查和线路调查的方法对广东省21市农业生态系统中205个样点的外来入侵植物进行了分析,共发现外来入侵植物28科90种。其中,菊科植物种类最多,有27种,草本植物有71种,它们分别占入侵植物总数的30.00%和78.89%。处于重度危害的入侵植物有22种;处于中度危害的植物有15种;处于轻度危害的植物有53种。在90种外来入侵植物中,71种来自美洲,占总数的78.89%;其他各洲相对较少。广域分布种最多,为40种,占总数的44.44%;全域分布种则最少,仅有7种,占总数的7.78%。由此可见,广东省农业生态系统入侵植物种类多,分布广,危害严重,需引起有关部门的高度重视。     

Increased Topsoil Mineral Nutrient Concentrations Under exotic invasive plants in Belgium

Exotic invasive plants can alter ecosystem processes. For the first time in Europe, we have analysed the impacts of exotic invasive plants on topsoil chemical properties. At eight sites invaded by five exotic invasive species (Fallopia japonica, Heracleum mantegazzianum, Solidago gigantea, Prunus serotina and Rosa rugosa), soil mineral element composition was compared between invaded patches and adjacent, uninvaded vegetation. We found increased concentrations of exchangeable essential nutrients under the canopy of exotic invasive plants, most strikingly so for K and Mn (32% and 34% increase, respectively). This result fits in well with previous reports of enhanced N dynamics in invaded sites, partly due to higher net primary productivity in exotic invasive plants compared to native vegetation. Sonia Vanderhoeven and Nicolas Dassonville - Equally contributing authors.     

Biological soil crusts determine the germination and growth of two exotic plants

In arid and semiarid ecosystems, the potential threats of exotic invasive species are enhanced due to increasing human activities. Biological soil crusts (BSCs), acting as arid ecosystem engineers, may play an important role in preventing the establishment of exotic invasive plants. Our goal was to examine whether BSCs could inhibit the establishment of probable exotic plant species originating from adjacent grasslands located along the southeast edge of the Tengger Desert. In our study, we investigated the effects of three BSC types (cyanobacteria, lichen, and moss crusts) under two disturbance conditions (intact and disturbed) on the establishment of two exotic plant species (Ceratoides latens and Setaria viridis) using indoor experiments. We found both negative and positive effects of BSCs on the establishment of the two exotic plant species. Compared with the disturbed BSCs, the germination percentages of C. latens and S. viridis were reduced by 54% to 87% and 89% to 93%, respectively, in intact BSCs. In contrast, BSCs significantly promoted the height growth and aboveground biomass of the two exotic plant species (p < .05) by enhancing the soil water and nutrient availability for the exotic plants. Our results confirm that BSCs strongly suppress the rapid expansion of exotic plant populations by inhibiting germination of seed with big size or appendages and have a weak inhibitory effect on exotic plant with small and smooth seeds. This may decrease the threat of propagation of exotic species. In the meantime, BSCs promote the growth of a few successful engraftment seedlings, which increased the beta diversity. Our work suggests that better understanding the two opposing effects of BSCs on the establishment of exotic plant species in different growth stages (germination and growth) is important for maintaining the health and stability of revegetated regions.     

A null model of exotic plant diversity tested with exotic and native species-area relationships

At large spatial scales, exotic and native plant diversity exhibit a strong positive relationship. This may occur because exotic and native species respond similarly to processes that influence diversity over large geographical areas. To test this hypothesis, we compared exotic and native species–area relationships within six North American ecoregions. We predicted and found that within ecoregions the ratio of exotic to native species richness remains constant with increasing area. Furthermore, we predicted that areas with more native species than predicted by the species–area relationship would have proportionally more exotics as well. We did find that these exotic and native deviations were highly correlated, but areas that were good (or bad) for native plants were even better (or worse) for exotics. Similar processes appear to influence exotic and native plant diversity but the degree of this influence may differ with site quality.     

Species richness of herbivores on exotic host plants increases with time since introduction of the host

Aim Species richness of insect herbivores feeding on exotic plants increases with abundance as well as range size of the host in the area of introduction. The formation of these herbivore assemblages requires a certain amount of time, and the richness of insect faunas should also increase with the length of time an exotic plant has been present in the introduced range. Location Central Europe. Methods We analysed the variation in species richness of leaf‐chewing Lepidoptera larvae and sap‐sucking Auchenorrhyncha (Hemiptera) associated with 103 exotic woody plant species in Germany in relation to time since introduction, range size, growth form (trees versus shrubs), biogeographical origin (distance from Central Europe) and taxonomic isolation of the host plant (presence or absence of a native congener in the introduced area). Results Using simple correlation analyses we found for Lepidoptera and Auchenorrhyncha that species richness increased with time since introduction of the host plant. For the Lepidoptera the increase of species richness with time since introduction remained significant even after removing the effects of all other independent variables. Main conclusions Our results provide some evidence that assemblages of insects on exotic plants do not reach saturation within a time scale of few hundred years. This contrasts with previous findings for crop plants.     

A novel photographic approach for monitoring the structural heterogeneity and diversity of grassland ecosystems

Aims Studies that investigate the space-filling heterogeneity of biological structures in plant communities remain scarce. The main objective of this study was to evaluate the relationship between newly developed photographic measures of structural heterogeneity in digital images and plant species composition in the context of a long-term grassland experiment.Methods We tested a close-range photographic protocol using measures of structural heterogeneity in gray-tone images, namely mean information gain (MIG) and spatial anisotropy, to assess differences in the compositional (species richness) and functional characteristics (plant height and flowering) of 78 managed grassland communities. We also implemented a random placement model of community assembly to explore the links between our measures of structural complexity and the geometric pattern of plant communities.Important findings MIG and spatial anisotropy correlated with the growth and species richness of grassland communities. Simulations showed that structural heterogeneity in gray-tone digital images is a function of the size distribution and orientation pattern of plant modules. This easy, fast and non-destructive methodological approach could eventually serve to monitor the diversity and integrity of various ecosystems at different resolutions across space and time.     

外来植物凋落物分解对底栖动物多样性及其摄食功能群的影响

在亚热带地区一条2级溪流中比较了本地植物(红锥和薏米)和外来植物(托里桉和马缨丹)凋落物的分解速率及底栖动物定殖及其摄食功能群的组成。结果显示,本地植物凋落物的分解速率为:0.020 d-1(红锥)和0.056 d-1(薏米),外来树叶的分解速率则为:0.038 d-1(托里桉)和0.041 d-1(马缨丹),它们均属于快速分解组。定殖在外来和本地树叶凋落物上的大型底栖动物种类分别为21种和24种。在外来和本地树叶上定殖的底栖动物平均密度差异不显著(P0.05)。从大型底栖动物摄食功能群的比例来看,定殖在本地凋落物上的集食者的比例最高(73.5%),其次是撕食者(10.9%)和捕食者(8.7%),刮食者(6.8%)的比例最低,在外来凋落物上,摄食功能群的比例分别为集食者(67.6%)、撕食者(13.9%)、刮食者(12.1%)和捕食者(6.1%),两者相比,底栖动物的摄食功能群均以集食者和撕食者为主,在组成比例上并无显著差异。结果表明2种外来植物凋落物分解对底栖动物多样性及其摄食功能群的影响不明显。     

外来植物入侵对陆地生态系统地下碳循环及碳库的影响

生物入侵是当今全球性重大环境问题之一, 是全球变化的主要研究内容.评价外来植物入侵对于生态系统影响的研究多集中在地上部分,对于生态系统地下部分影响的研究相对较少.陆地生态系统地下部分对于生态系统过程的重要性之一体现在它处于生态系统碳分配过程的核心环节.入侵种通过影响群落凋落物的输入数量、质量以及输入时间,影响到对于土壤的碳输入,而入侵种与土著种根系的差异以及入侵种对微生物群落的影响是造成土壤呼吸强度发生变化的主要因素,前者土壤呼吸强度一般比后者高.多数研究表明外来植物入侵对生态系统地下碳循环和碳库产生影响,但由于入侵植物种类较多以及研究地点环境条件的不同,关于外来植物入侵对于土壤碳库和土壤有机碳矿化影响的研究结论并不统一.最后,提出了今后该研究领域应加强的一些建议和方向.     

Aquatic insect subsidies influence microbial composition and processing of detritus in near-shore subarctic heathland

Insects are major conduits of resources moving from aquatic to terrestrial systems. While the ecological impacts of insect subsidies are well documented, the underlying mechanisms by which these resources change recipient ecosystems remain poorly understood. Most subsidy inputs enter terrestrial systems as detritus; thus, soil microbes will likely influence the processing of insect subsidies, with implications for plant community composition and net primary productivity (NPP). In a subarctic ecosystem near Lake Mývatn, Iceland where midge (Diptera: Chironomidae) deposition to land is high, we investigated how insect subsidies affected litter processing and microbial communities. We also evaluated how those belowground effects related to changes in inorganic nitrogen, plant composition and NPP. We simulated subsidies by adding midge carcasses to 1-m² heathland plots, where we measured effects on decomposition rates and the plant community. We then studied how fertilization treatments (control, KNO₃ and midge-carcass addition) affected graminoid biomass and inorganic nitrogen in greenhouse experiments. Lastly, we conducted a soil-incubation study with a phospholipid fatty acid analysis (PLFA) to examine how midge addition to heathland soils affected microbial respiration, biomass and composition. We found that midge addition to heathland soils increased litter decomposition and graminoid plant cover by 2.6× and 2×, respectively. Greenhouse experiments revealed similar patterns, with midge carcasses increasing graminoid biomass by at least 2× and NH₄⁺ concentrations by 7×. Our soil-incubation study found that midge carcasses elevated microbial respiration by 64%, microbial biomass by 43% and shifted microbial functional composition. Our findings indicate that insect subsidies can stimulate soil microbial communities and litter decomposition in subarctic heathlands, leading to increased NPP and changes in plant community composition.     

外来种湿地松凋落物对土壤微生物群落结构和功能的影响

外来种湿地松是我国亚热带地区大面积造林树种,研究其凋落物影响下土壤微生物群落结构和功能的变化,对于全面科学的评价湿地松的生态影响具有重要的理论与实践意义。通过凋落物袋 小盆模拟试验研究,分两个时期(分解5个月和18个月)比较了外来种湿地松与本地种马尾松的凋落物对土壤微生物群落结构(磷脂脂肪酸)和功能(碳代谢)的影响,结果表明：(1)外来种湿地松凋落物的C:N高于本地种马尾松;(2)两个时期,湿地松凋落物处理土壤细菌和放线菌的磷脂脂肪酸含量均低于马尾松,18个月时湿地松凋落物处理土壤真菌含量和群落真菌/细菌显著高于马尾松处理;(3)湿地松凋落物影响下土壤微生物群落功能多样性显著低于马尾松;(4)土壤微生物群落的结构显著影响微生物的活性和功能多样性：土壤微生物群落碳源代谢的强度、多样性及丰富度与细菌磷脂脂肪酸含量呈极显著正相关,细菌特征脂肪酸14:0、15:0、a15:0、i16:0、16:1ω7c、a17:0和cy19:0的含量显著影响土壤微生物群落碳代谢功能。上述结果表明：与本地种马尾松相比,引进种湿地松的凋落物显著改变了土壤微生物群落结构,降低了微生物群落的功能。     

Long-term impact of exotic ants on the native ants of Madeira

Abstract.  1. The earliest exotic records for two notorious invasive ants, the big-headed ant ( Pheidole megacephala ) and the Argentine ant ( Linepithema humile ), both come from the Atlantic islands of Madeira, where the two species underwent population explosions in the 1850s and 1890s respectively. Researchers have long assumed that these invaders spread across all of Madeira and exterminated most or all native ants, despite no research actually documenting such impact.
2. Re-examination of first-hand nineteenth century accounts suggest that P. megacephala and L. humile may never have spread beyond coastal lowland areas, representing < 10% of Madeira's land area. In 2002, native ants dominated most of Madeira; P. megacephala and L. humile were restricted to ≈ 0.3% and ≈ 6% of Madeira's land area respectively.
3. Of the 10 native ant species known from Madeira, only one ( Temnothorax wollastoni ) was not present in 1999–2002 surveys. Although exotic ants may have exterminated T. wollastoni , it seems likely that this species still survives.
4. Thus, even after 150 or more years of residence, P. megacephala and L. humile have come to occupy only a small part of Madeira, and appear to have had little impact.
5. Most of Madeira may be too cool for P. megacephala and perhaps too moist for L. humile to dominate. Also, Madeira's vast natural areas may generally lack weedy vegetation that can support high densities of plant-feeding Hemiptera critical for the ecological dominance of invasive ants. Finally, a dominant native ant, Lasius grandis , inhabiting ≈ 84% of Madeira, may actively exclude P. megacephala and L. humile .     

植物氮形态利用策略及对外来植物入侵性的影响

氮是影响外来植物入侵性的重要因素之一, 但相关研究多关注土壤氮水平的效应, 较少考虑氮形态的作用。为从土壤氮形态利用的角度阐释外来植物的入侵机制, 本文在植物氮形态利用策略分析的基础上, 综述了外来植物氮形态利用的偏好性及其对入侵性的影响。植物的氮形态利用策略有偏好性和可塑性两种, 这可能与植物对土壤氮形态特性的长期适应有关; 植物不仅可以对土壤氮形态做出响应, 而且还能改造土壤氮形态, 并对改变后的土壤氮形态做出反馈响应。很多外来植物入侵硝态氮占优势的干扰生境, 偏好硝态氮的外来植物与本地植物竞争硝态氮; 而偏好铵态氮的外来植物通过抑制土壤硝化作用, 营造铵态氮环境, 促进自身生长, 同时抑制偏好硝态氮的本地植物生长。然而, 植物氮形态利用策略不是一成不变的, 而是受多种生物和非生物因素共同作用影响的复杂过程, 今后应加强多因素交互作用对外来入侵植物氮形态利用策略的影响及机制研究, 更好地揭示氮形态利用策略, 尤其是氮形态利用的可塑性与外来植物入侵性的关系。     

Ecological impacts of invasive alien plants: a meta-analysis of their effects on species, communities and ecosystems

Biological invasions cause ecological and economic impacts across the globe. However, it is unclear whether there are strong patterns in terms of their major effects, how the vulnerability of different ecosystems varies and which ecosystem services are at greatest risk. We present a global meta-analysis of 199 articles reporting 1041 field studies that in total describe the impacts of 135 alien plant taxa on resident species, communities and ecosystems. Across studies, alien plants had a significant effect in 11 of 24 different types of impact assessed. The magnitude and direction of the impact varied both within and between different types of impact. On average, abundance and diversity of the resident species decreased in invaded sites, whereas primary production and several ecosystem processes were enhanced. While alien N-fixing species had greater impacts on N-cycling variables, they did not consistently affect other impact types. The magnitude of the impacts was not significantly different between island and mainland ecosystems. Overall, alien species impacts are heterogeneous and not unidirectional even within particular impact types. Our analysis also reveals that by the time changes in nutrient cycling are detected, major impacts on plant species and communities are likely to have already occurred.     

Impacts of invasive plants on resident animals across ecosystems,taxa, and feeding types: a global assessment

As drivers of global change, biological invasions have fundamental ecological consequences. However, it remains unclear how invasive plant effects on resident animals vary across ecosystems, animal classes, and functional groups. We performed a comprehensive meta‐analysis covering 198 field and laboratory studies reporting a total of 3624 observations of invasive plant effects on animals. Invasive plants had reducing (56%) or neutral (44%) effects on animal abundance, diversity, fitness, and ecosystem function across different ecosystems, animal classes, and feeding types while we could not find any increasing effect. Most importantly, we found that invasive plants reduced overall animal abundance, diversity and fitness. However, this significant overall effect was contingent on ecosystems, taxa, and feeding types of animals. Decreasing effects of invasive plants were most evident in riparian ecosystems, possibly because frequent disturbance facilitates more intense plant invasions compared to other ecosystem types. In accordance with their immediate reliance on plants for food, invasive plant effects were strongest on herbivores. Regarding taxonomic groups, birds and insects were most strongly affected. In insects, this may be explained by their high frequency of herbivory, while birds demonstrate that invasive plant effects can also cascade up to secondary consumers. Since data on impacts of invasive plants are rather limited for many animal groups in most ecosystems, we argue for overcoming gaps in knowledge and for a more differentiated discussion on effects of invasive plant on native fauna.     

Exotic species richness and native species endemism increase the impact of exotic species on islands

Aim Exotic species pose one of the most significant threats to biodiversity, especially on islands. The impacts of exotic species vary in severity among islands, yet little is known about what makes some islands more susceptible than others. Here we determine which characteristics of an island influence how severely exotic species affect its native biota. Location We studied 65 islands and archipelagos from around the world, ranging from latitude 65° N to 54° S. Methods We compiled a global database of 10 island characteristics for 65 islands and determined the relative importance of each characteristic in predicting the impact of exotic species using multivariate modelling and hierarchical partitioning. We defined the impact of exotic species as the number of bird, amphibian and mammal (BAM) species listed by the International Union for Conservation of Nature (IUCN) as threatened by exotics, relative to the total number of BAM species on that island. Results We found that the impact of exotic species is more severe on islands with more exotic species and a greater proportion of native species that are endemic. Unexpectedly, the level of anthropogenic disturbance did not influence an island's susceptibility to the impacts of exotic species. Main conclusions By coupling our results with studies on the introduction and establishment of exotic species, we conclude that colonization pressure, or invasion opportunities, influences all stages of the invasion process. However, species endemism, the other important factor determining the impact of exotic species, is not known to contribute to introduction and establishment success on islands. This demonstrates that different factors correlate with the initial stages of the invasion process and the subsequent impacts of those invaders, highlighting the importance of studying the impacts of exotic species directly. Our study helps identify islands that are at risk of impact by exotics and where investment should focus on preventing further invasions.     

Climate change and invasion by intracontinental range-expanding exotic plants: the role of biotic interactions

Background and Aims

In this Botanical Briefing we describe how the interactions between plants and their biotic environment can change during range-expansion within a continent and how this may influence plant invasiveness.

Scope

We address how mechanisms explaining intercontinental plant invasions by exotics (such as release from enemies) may also apply to climate-warming-induced range-expanding exotics within the same continent. We focus on above-ground and below-ground interactions of plants, enemies and symbionts, on plant defences, and on nutrient cycling.

Conclusions

Range-expansion by plants may result in above-ground and below-ground enemy release. This enemy release can be due to the higher dispersal capacity of plants than of natural enemies. Moreover, lower-latitudinal plants can have higher defence levels than plants from temperate regions, making them better defended against herbivory. In a world that contains fewer enemies, exotic plants will experience less selection pressure to maintain high levels of defensive secondary metabolites. Range-expanders potentially affect ecosystem processes, such as nutrient cycling. These features are quite comparable with what is known of intercontinental invasive exotic plants. However, intracontinental range-expanding plants will have ongoing gene-flow between the newly established populations and the populations in the native range. This is a major difference from intercontinental invasive exotic plants, which become more severely disconnected from their source populations.     

Community scale 15N isoscapes: tracing the spatial impact of an exotic N2 -fixing invader

Plant-plant interactions are key processes shaping plant communities, but methods are lacking to accurately capture the spatial dimension of these processes. Isoscapes, i.e. spatially continuous observations of variations in stable isotope ratios, provide innovative methods to trace the spatial dimension of ecological processes at continental to global scales. Herein, we test the usefulness of nitrogen isoscapes (δ(15) N) for quantifying alterations in community functioning following exotic plant invasion. Nitrogen introduced by an exotic N(2) -fixing acacia could be accurately traced through the ecosystem and into the surrounding native vegetation by combining native species foliar δ(15) N with spatial information regarding plant location using geostatistical methods. The area impacted by N-addition was at least 3.5-fold greater than the physical area covered by the invader. Thus, downscaling isoscapes to the community level opens new frontiers in quantifying the spatial dimension of functional changes associated with invasion and in resolving the spatial component of within-community interactions.