An aboveground–belowground assessment of ecosystem properties associated with exotic annual brome invasion

Exotic annual brome invasion has been well studied in western North American rangelands, particularly for Bromus tectorum L. invasion in sagebrush (Artemisia tridentata) grasslands. We examined both aboveground and belowground properties in native sagebrush grassland and adjacent areas dominated by exotic annual bromes (B. tectorum L. and Bromus japonicus Thunb.) to better understand the fundamental ecological differences between native and invaded areas. Field sites were located in north central Wyoming, USA, and plots were established in areas that had been historically subject to wildfire and either (1) recolonized by native sagebrush grassland vegetation or (2) invaded by exotic annual bromes. We employed measures of vegetation community structure as well as soil physical, chemical, and microbiological properties. Plots with greater than 20 % exotic annual brome cover had significantly less cover of all native vegetation functional groups resulting in lower richness and evenness than native plots. Invaded plots also had low diversity plant communities that were continuous and uniform across space. Soils beneath invaded plant communities had higher infiltration rates, higher levels of total nitrogen, and a lower C/N ratio than the native soils. Invaded soils also had 90–96 % lower abundance of all soil microbial groups measured by phospholipid fatty acid. We conclude that areas dominated by exotic annual bromes display different aboveground and belowground properties compared to the native community, and these changes possibly include spatial and temporal shifts in soil resources and organic matter processing.     

Exotic invasive knotweeds (Fallopia spp.) negatively affect native plant and invertebrate assemblages in European riparian habitats

Invasive plants are, simply by occupying a large amount of space in invaded habitats, expected to impose a significant impact on the native vegetation and their associated food webs. However, little is known about the impact of invasive plants both on native vegetation and on different invertebrate feeding guilds at the habitat level. Yet, studies addressing multiple trophic levels, e.g. plant species, herbivores, predators and detrivores, are likely to yield additional insight into how and under which conditions invasive weeds alter ecosystem structures and processes. We set out to assess whether plant species richness and invertebrate assemblages in European riparian habitats invaded by exotic knotweeds (Fallopia spp.) differed from those found in native grassland- or bush-dominated riparian habitats, which are both potentially threatened by knotweed invasion. Our findings suggest that riparian habitats invaded by knotweeds support lower numbers of plant species and lower overall abundance and morphospecies richness of invertebrates, compared to native grassland-dominated and bush-dominated habitats. Total invertebrate abundance and morphospecies richness in Fallopia-invaded riparian habitats were correlated with native plant species richness, suggesting that there is a link between the replacement of native plant species by exotic Fallopia species and the reduction in overall invertebrate abundance and morphospecies richness. Moreover, biomass of invertebrates sampled in grassland and bush-dominated habitats was almost twice as high as that in Fallopia-invaded habitats. Large-scale invasion by exotic Fallopia species is therefore likely to seriously affect biodiversity and reduce the quality of riparian ecosystems for amphibians, reptiles, birds and mammals whose diets are largely composed of arthropods.     

Diversity declines in Microstegium vimineum (Japanese stiltgrass) patches

The spread of invasive plant species and their impacts on plant communities have received international attention as global trade and global environmental change enhance the colonization and establishment of introduced species and threaten the integrity of native ecosystems. Because introduced species vary in their impact, studying the relationship between invasion and native communities is necessary to guide allocation of finite management resources. By studying adjacent pairs of invaded and uninvaded plots across an eastern United States forested landscape, we demonstrate Microstegium vimineum was associated with local declines in species richness and cover of native species. Negative impacts of M. vimineum on species richness did not emerge until August when M. vimineum cover and height were greatest, highlighting the value of following study subjects through the growing season. In contrast, native species cover was already lower in invaded plots early in the growing season. M. vimineum invasion was not the only important driver of species richness and community composition within the study region; abiotic environmental gradients, such as soil nitrate concentration and pH, across the six study sites were also important in affecting species richness and cover, but lessened in explanatory power through the growing season. We conclude that M. vimineum has effects on community structure that may have long-term consequences for biodiversity. Studies which track sites through time and consider multiple scales are required as invaders impact multiple biotic and abiotic factors operating at different spatial and temporal scales.     

Effects of 30-year-old Aleppo pine plantations on runoff,soil erosion,and plant diversity in a semi-arid landscape in south eastern Spain

Forest management policies in Mediterranean areas have traditionally encouraged land cover changes, with the establishment of tree cover (Aleppo pine) in natural or degraded ecosystems for soil conservation purposes: to reduce soil erosion and to increase the vegetation structure. In order to evaluate the usefulness of these management policies on reduced erosion in semi-arid landscapes, we compared 5 vegetation cover types (bare soil, dry grassland, shrublands, afforested dry grasslands and afforested thorn shrublands), monitored in 15 hydrological plots (8 × 2 m), in the Ventós catchment (Alicante, SE Spain), over 4 years (1996 to 1999). Each cover type represented a different dominant patch of the vegetation mosaic on the north-facing slopes of this catchment. The results showed that runoff coefficients of vegetated plots were less than 1% of the precipitation volume; whereas runoff in denuded areas was nearly 4%. Soil losses in vegetation plots averaged 0.04 Mg ha^− 1 year^− 1 and increased 40-fold in open-land plots. The evaluation of these forest management policies, in contrast with the natural vegetation communities, suggests that: (1) thorn shrublands and dry grassland communities with vegetation cover could control runoff and sediment yield as effectively as Aleppo pine afforestation in these communities, and (2) afforestation with a pine stratum improved the stand's vertical structure resulting in pluri-stratified communities, but reduced the species richness and plant diversity in the understorey of the plantations.     

Effects of the invader Solidago canadensis on soil properties

A perennial goldenrod weed, Solidago canadensis, is rapidly spreading in China and now poses a serious threat to native ecosystem structure and function. Little is known about the effects of S. canadensis invasion on rhizosphere physico-chemical properties and microbial communities. The objective of this study was to compare the soil physico-chemical properties and microbial communities of invaded (two ecotone sites and one monoculture site) and native plant rhizospheres in field areas of Zhejiang Province, Eastern China. Compared with those in the native site, soil total nitrogen, total phosphorus, NO₃-N, available phosphorus content, and aggregate stability consistently decreased with S. canadensis invasion, while soil organic carbon, NH₄-N content, pH, and bulk density in the invaded sites significantly increased. Soil microbial biomass (expressed by carbon, nitrogen, or phosphorus content), activity (basal respiration and substrate induced respiration), and functional diversity (calculated from the average well color development (AWCD) of 31 carbon sources in a BIOLOG Ecoplate) significantly increased with S. canadensis invasion. Microbial utilization of carbohydrate groups significantly increased in the invaded sites, while the utilization of carboxylic acids and amines/amides groups significantly decreased. Principal components analysis (PCA) of the AWCD data indicated that the heavily invaded site (monoculture) was clearly separated from the native site. Redundancy analysis (RDA) indicated that soil organic carbon, NH₄-N, NO₃-N, and pH significantly impacted the dynamics of microbial parameters across the invaded sites. These results suggested that several soil chemical properties (e.g., organic carbon, NH₄-N, and pH) and microbial parameters (e.g., microbial biomass, basal respiration, substrate induced respiration, and functional diversity) might be used as indicators of S. canadensis invasion density.     

Is invasion of deforested Amazonia by the earthworm Pontoscolex corethrurus driven by soil texture and chemical properties?

Pontoscolex corethurus (Müller, 1857) is the most common invasive earthworm in disturbed lands in the tropics. Conditions required for its successful colonization of new plots are still not understood since some areas can be invaded while others, sometimes in the vicinity, are not. We kept newly hatched P. corethrurus in a wide range of Amazonian soils where population densities had been previously evaluated. We identified soil conditions that best sustain survival, soil ingestion and growth of P. corethrurus in controlled laboratory conditions and checked if presence/absence in the field was consistent with laboratory observations. While pH and Ca influenced survival; Mg and C content were the greatest determinants for growth and C:P, Mg and clay contents determined soil ingestion rates. Soil ingestion and growth rate were correlated. There were no differences in earthworm soil ingestion rates between invaded and non-invaded soils. However, growth rate and survival were higher in soils from invaded sites than in soils from non invaded sites, indicating that soil quality may play a role in the invasion process. We identified two cases where P. corethrurus did not occur: (1) unfavourable soil texture and chemical properties, but also some areas with and (2) favourable soil texture and chemical properties but no invasion. Other parameters, like vegetation cover (grass or trees), soil structure and compaction, soil hydrologic processes or biotic resistance of native earthworm communities could potentially also be key elements for understanding why P. corethrurus populations occur in some sites and not in others.     

Invasive Acacia longifolia induce changes in the microbial catabolic diversity of sand dunes

Acacia longifolia is one of the main plant species invading Portuguese dune ecosystems. Areas invaded by this exotic tree have reduced plant diversity and altered soil microbial processes and nutrient pools, but the impacts on microbial functional diversity in the soil have been little explored. Soil samples were collected in areas invaded by A. longifolia for more than 20 years, in areas invaded after 1995 and in non-invaded areas. Respiration responses to 20 different substrates were analysed, in order to assess the catabolic response profile (CRP) as a measure of microbial functional diversity. Five substrate groups were tested: amino acids, carbohydrates, carboxylic acids, plant litters, and plant polymers. CRP clearly discriminated between the three different areas. Respiratory responses to the individual substrates α-ketoglutaric acid, oxalic acid, starch, citric acid, and xylose and to the groups of amino acids and plant polymers were similar in both invaded areas and different in the non-invaded. The responses to tartaric acid, gallic acid, fumaric acid, Cistus litter, and Acacia litter were the same in long- and non-invaded areas, but different from recently invaded areas. The duration of invasion, carbon (C) content, nitrogen (N) content, C/N ratio, pH, and litter quantity explained 39.6% of the variance of catabolic responses. It is concluded that invasion by A. longifolia has substantial effects on the catabolic diversity of the soil microbial communities. These effects may have wider implications for nutrient cycling and ecosystem-level processes and for the invasibility of the system.     

Historical influences on the vegetation and soils of the Martha’s Vineyard, Massachusetts coastal sandplain: Implications for conservation and restoration

Both disturbance history and previous land use influence present-day vegetation and soils. These influences can have important implications for conservation of plant communities if former disturbance and land use change species abundances, increase colonization of nonnative plant species or if they alter soil characteristics in ways that make them less suitable for species of conservation interest. We compared the plant species composition, the proportion of native and nonnative plant species, and soil biogeochemical characteristics across seven dominant land use and vegetation cover types on the outwash sandplain of Martha’s Vineyard that differed in previous soil tillage, dominant overstory vegetation and history of recent prescribed fire. The outwash sandplain supports many native plant species adapted to dry, low nutrient conditions and maintenance of native species is a management concern. There was broad overlap in the plant species composition among pine (Pinus resinosa, P. strobus) plantations on untilled soils, pine plantations on formerly tilled soils, scrub oak (Quercus ilicifolia) shrublands, tree oak (Q. velutina, Q. alba) woodlands, burned tree oak woodlands, and sandplain grasslands. All of these land cover categories contained few nonnative species. In contrast, agricultural grasslands had high richness and cover of nonnative plants. Soil characteristics were also similar among all of the woodland, shrubland and grassland land cover categories, but soils in agricultural grasslands had higher pH, extractable Ca²⁺ and Mg²⁺ in mineral soils and higher rates of net nitrification. The similarity of soils and significant overlap in vegetation across pine plantations, scrub oak shrublands, oak woodlands and sandplain grasslands suggests that the history of land use, current vegetation and soil characteristics do not pose a major barrier to management strategies that would involve conversion among any of these vegetation types. The current presence of high cover of nonnative species and nutrient-enriched soils in agricultural grasslands, however, may pose a barrier to expansion of sandplain grasslands or shrublands on these former agricultural lands if native species are not able to outcompete nonnative species in these anthropogenically-enriched sites.     

Original vegetation type affects soil nematode communities

The effect of land use changes on the composition of nematode communities has been well documented, however, the applicability of such studies limited to areas with relatively uniform soil and environmental conditions. To determine whether the historical difference in vegetation types affects soil nematode communities during the land use change processes, we carried out a study along two transects where contrasting natural vegetation types (grass versus shrub) were replaced by tea monocultures. Soil nematode communities were compared between two transects at three chronosequence stages: natural vegetations, 3–7 years old tea plantations. Nematode abundance, generic richness, diversity, and proportions of bacterivores and fungivores were higher at each stage of GT transect (from grassland to tea plantation) than at the equivalent stage of ST transect (from shrubland to tea plantation), whereas lower values of maturity index and nematode channel ratio occurred at each stage of GT transect relative to ST transect. MDS ordination analyses, SIMPER analyses and β_w indices indicated that the difference in nematode community structure was greatest between the two 3-year-old tea plantations, although the greatest difference in environmental conditions was observed between two original vegetation habitats. This suggested that the original vegetation types may affect the following nematode community development; however, the effects can decrease over time. Different trophic groups responded to land use in different ways along the vegetational development. This supports the viewpoint that the addition of a common resource can evoke disparate responses from individual food-web components.     

The effects of invasive North American beavers on riparian plant communities in Cape Horn, Chile: Do exotic beavers engineer differently in sub-Antarctic ecosystems?

North American beavers (Castor canadensis) were introduced into southern South America in 1946. Since that time, their populations have greatly expanded. In their native range, beavers shape riparian ecosystems by selectively feeding on particular plant species, increasing herbaceous richness and creating a distinct plant community. To test their effects as exotic engineers on sub-Antarctic vegetation, we quantified beaver impacts on tree canopy cover and seedling abundance and composition, as well as their impacts on herbaceous species richness, abundance and composition on Navarino Island, Cape Horn County, Chile (55°S). Beavers significantly reduced forest canopy up to 30 m away from streams, essentially eliminating riparian forests. The tree seedling bank was greatly reduced and seedling species composition was changed by suppressing Nothofagus betuloides and Nothofagus pumilio, but allowing Nothofagus antarctica. Herbaceous richness and abundance almost doubled in meadows. However, unlike beaver effects on North American herbaceous plant communities, much of this richness was due to invasion by exotic plants, and beaver modifications of the meadow vegetation assemblage did not result in a significantly different community, compared to forests. Overall, 42% of plant species were shared between both habitat types. Our results indicate that, as predicted from North American studies, beaver-engineering increased local herbaceous richness. Unlike in their native range, though, they did not create a unique plant community in sub-Antarctic landscapes. Plus, the elimination of Nothofagus forests and their seedling bank and the creation of invasion pathways for exotic plants together threaten one of the world’s most pristine temperate forest ecosystems.     

Co-introduction of exotic rhizobia to the rhizosphere of the invasive legume Acacia saligna,an intercontinental study

Invasive woody legumes have profound impacts in the nitrogen content and cycling of invaded ecosystems due to the ability to enter into symbiosis with nitrogen-fixing bacteria. In spite of the relevance of this symbiosis, the identity and origin of the symbionts involved in invasion are not well understood. We conducted a study to assess the diversity of symbiotic root-nodulating bacteria associated with the invasive Acacia saligna, in newly colonized areas in Portugal and Australia. BOX-PCR was used to discriminate the isolated bacteria and 16S rRNA and nifD genes were sequenced to identify the different isolates and their geographic origin. Bradyrhizobium and Mesorhizobium nodulated A. saligna in Australia while only Bradyrhizobium spp. were found in Portugal. The dominant strains nodulating A. saligna were related to Bradyrhizobium liaoningense and Bradyrhizobium canariense. Co-occurring Acacia longifolia and A. saligna in Australia harbor different rhizobial communities. As an example, we found Mesorhizobium sp. and Phyllobacterium trifolii in A. saligna and A. longifolia respectively, being this the first report for this association. The analysis of the phylogeographic marker nifD clustered most of the sequences obtained in this study with sequences of Australian origin, indicating that exotic bradyrhizobia might have been co-introduced with A. saligna in Portugal. This result highlights the risks of introducing exotic inoculants that might facilitate the invasion of new areas and alter native soil bacterial communities, hindering the recovery of ecosystems.     

外来植物紫茎泽兰入侵对菌根菌群落的影响

为了研究紫茎泽兰(Ageratina adenophora)入侵对土壤菌根真菌(mycorrhizal fungi, MF)群落的影响,采用嵌套PCR 技术分析了外来植物紫茎泽兰入侵生境内土著植物群落、土著植物与紫茎泽兰混生群落、紫茎泽兰单优群落中, 侵染紫茎泽兰及土著植物的MF 群落结构, 及紫茎泽兰与土著植物根围土壤中MF 群落结构。结果表明, 紫茎泽兰不同入侵进程MF 群落结构存在差异, 其中, 从土著植物群落的植物根内检测到内养球囊霉(Glomus intraradices)型克隆; 从土著植物与紫茎泽兰混生群落的紫茎泽兰根内也检测到内养球囊霉型克隆, 而在土著植物根内检测到1 个球囊霉属(Glomus sp 2)型克隆; 从紫茎泽兰单优群落的紫茎泽兰根内未检测到MF, 但从其根围土壤中检测到2 个球囊霉属(Glomus sp 1 和Glomus sp 2)型克隆。在土著植物与紫茎泽兰混生群落中, 从紫茎泽兰根围土壤中检测到4 个克隆型, 分别为毛舌菌阔孢(Trichoglossum hirsutum)、皂味口磨(Tricholoma saponaceum)、亚盖趋本菌(Xylobolus subpileatus)和翘鳞肉齿菌(Sarcodon imbricatus), 从土著植物根围土壤中也检测到4 个克隆型, 分别为小皮伞(Camarophyllopsis hymenocephala)、肉色香蘑(Lepista irina)、皂味口磨及亚侧耳(Panellus serotinus)型克隆; 在土著植物群落中, 从根围土壤只检测到皂味口磨型克隆。紫茎泽兰入侵改变了土著MF 群落结构, 其中在土著植物占据的土壤中以外生菌根真菌为主, 而外来植物紫茎泽兰则更多地积累了丛枝菌根真菌。文中讨论了紫茎泽兰改变入侵地土壤菌根菌群落及其可能对紫茎泽兰入侵的反馈。     

Exotic annuals reduce soil heterogeneity in coastal sage scrub soil chemical and biological characteristics

Exotic plant invasions alter ecosystem structure and function above- and below-ground through plant–soil feedbacks. The resistance of ecosystems to invasion can be measured by the degree of change in microbial communities and soil chemical pools and fluxes, whereas their resilience can be measured by the ability to recover following restoration. Coastal sage scrub (CSS) is one of the most highly invaded ecosystems in the US but the response of CSS soils to exotic plant invasion is little known. We examined resistance and resilience of CSS soil chemical and biological characteristics following invasion of exotic annual grasses and forbs and restoration of the native plant community. We hypothesized that invasion of exotic plant species would change biological and chemical characteristics of CSS soils by altering soil nutrient inputs. Additionally, we expected that if exotic plants were controlled and native plants were restored, native soil characteristics would recover. We sampled two locations with invaded, restored and native CSS for plant community composition, soil chemistry and microbial communities, and phospholipid fatty acid (PLFA) profiles. Communities invaded by exotic annuals were resistant to some measured parameters but not others. Extractable nitrogen pools decreased, nitrogen cycling rates increased, and microbial biomass and fungal:bacterial ratios were altered in invaded soils, and these effects were mediated by the phenological stage of the dominant plant species. The largest impact of invasion on soils was an overall reduction of spatial heterogeneity in soil nutrients, nutrient cycling and microbial communities. Restored plots tended to recover in most biotic and chemical parameters including increased resource heterogeneity compared to invaded plots, suggesting that CSS soils are resilient but not resistant to invasion.     

The relative efficiency of four representative cropland conversions in reducing water erosion: evidence from long‐term plots in the Loess hilly area,China

Large areas of traditional slope cropland were recently converted to other land‐use types in the semiarid Loess Plateau of China. In this study, we selected four representative conversion options of slope croplands, i.e., pastureland rotated with cropland (cultivated with Medicago sativa L. and rotated with Triticum aestivum L.), shrubland and woodland (afforested with Hippophae rhamnoides L. and Pinus tabulaeformis), and grassland (native herbage Stipa breviflora) to study the effect of land‐use conversion by comparing with traditional cropland. Compared with slope cropland, the relative effects of different conversion options on surface runoff and soil erosion were assessed over a 14‐year measurement period. Observations showed that distinct features and consequences of vegetation succession were found among the conversion options. Plots of shrubland had the highest vegetation coverage with dense undergrowth; natural herbaceous and subshrub species gradually spread into plots of grassland resulting in higher vegetation cover. Neither bushes nor herbs colonized the plots of Pinus tabulaeformis, which resulted in a higher percentage of bare soil. Significant differences in runoff generation, sediment yield and conservation efficiencies among the selected conversion options were detected through an analyses of variance (ANOVA). Compared with cropland, total runoff and sediment decreased by 65 per cent and 95 per cent in shrubland, 41 per cent and 92·5 per cent in grassland, 18 per cent and 77 per cent in woodland, and 12 per cent and 58 per cent in pastureland, respectively. The ranking of soil and water conservation efficiencies was shrubland > grassland > woodland > pastureland > cropland. Based on the effectiveness of soil and water conservation, shrubland and grassland are highly recommended as promising options for cropland conversion projects. However, pastureland and woodland are not suggested as potential options for slope‐cropland conversion because of low soil and water conservation in the long term. Copyright © 2006 John Wiley & Sons, Ltd.     

黑河中游不同土地利用方式地面节肢动物对土壤盐渍化的响应

在甘肃河西走廊黑河中游荒漠绿洲过渡区,天然沙质草地被相继转变为农田和防风固沙人工林,但目前尚缺乏不同土地利用/管理方式下地面节肢动物群落对土壤盐渍化响应的系统研究。以天然沙质草地转变的人工梭梭灌木林、人工杨树林、人工樟子松林和农田为研究对象,以天然草地为对照,基于5种研究样地表层土壤盐分及其组成和地面节肢动物群落的观测数据,采用RDA(Redundancy analysis)排序分析等方法,研究了不同土地利用/管理方式下地面节肢动物个体数量和类群丰富度对土壤盐分环境变化的响应机制。主要结果为:(1)土地利用变化与管理措施相互作用驱动了地面节肢动物群落的演变过程,天然草地植被转变为人工林和农田20多年后,显著降低了地面节肢动物群落的数量而对类群丰富度无显著影响。(2)地面节肢动物群落的变化受土壤pH、Na+、Mg2+、Cl-离子的共同影响,其中土壤pH、Na+和Mg2+离子对动物群落变化的贡献率最大,是关键生态因子。(3)动物个体数量随土壤pH的增加而增加,随Mg2+、Cl-离子浓度的增加而下降。研究表明,土地利用变化引起的土壤盐分环境改变是驱动地面节肢动物群落演变的重要因素之一。     

Vegetation development patterns on skislopes in lowland Hokkaido, northern Japan

The Japanese montane zones are usually covered with well-developed forests, and most ski resorts are constructed there. Therefore, the construction of skislopes requires the destruction of forest ecosystems. To detect vegetation development patterns on skislopes, I assessed vegetation on seven skislopes in the lowland of Hokkaido Island, Japan, using 155 2 m×2 m plots. The surrounding vegetation was mostly consisted of broad-leaved forests with a floor of dwarf bamboo, Sasa senanensis. The skislopes were established 5-28 years before the surveys by scraping off the topsoil and subsequent artificial seeding. The data of vegetation analyzed by TWINSPAN resulted in six different grassland types: (A) Miscanthus sinensis-Hypochaeris radicata, (B) introduced herbs with low richness, (C) introduced herbs, (D) Artemisia montana, (E) M. sinensis-Pueraria lobata-A. montana, and (F) Solidago gigantea var. leiophylla. H. radicata and S. gigantea var. leiophylla were alien species. Vegetation dominated by introduced grasses for erosion control, such as Dactylis glomerata and Poa pratensis, should be initial vegetation on the skislopes. Most tree pioneer species established in the vegetation type A, that was most natural vegetation in the skislopes. Type A seemed to proceed from types B and C, and species richness was the highest. Therefore, this type should be preferable for the management and restoration of skislope vegetation. Type D established on newer skislopes, while types E and F established on older skislopes. Results including detrended correspondence analysis suggested that those vegetation types D-F proceeded to distorted succession, i.e. biological invasion changed native successional sere. Based on these results, I recommended that the restriction of alien invasion and careful monitoring on M. sinensis grasslands are required to restore the natural vegetation.     

Soil characteristics and plant exotic species invasions in the Grand Staircase—Escalante National Monument,Utah, USA

The Grand Staircase—Escalante National Monument (GSENM) contains a rich diversity of native plant communities. However, many exotic plant species have become established, potentially threatening native plant diversity. We sought to quantify patterns of native and exotic plant species and cryptobiotic crusts (mats of lichens, algae, and mosses on the soil surface), and to examine soil characteristics that may indicate or predict exotic species establishment and success. We established 97 modified-Whittaker vegetation plots in 11 vegetation types over a 29,000 ha area in the Monument. Canonical correspondence analysis (CCA) and multiple linear regressions were used to quantify relationships between soil characteristics and associated native and exotic plant species richness and cover. CCA showed that exotic species richness was significantly (P<0.05) associated with soil P (r=0.84), percentage bare ground (r=0.71), and elevation (r=0.67). Soil characteristics alone were able to predict 41 and 46% of the variation in exotic species richness and cover, respectively. In general, exotic species invasions tend to occur in fertile soils relatively high in C, N and P. These areas are represented by rare mesic high-elevation habitats that are rich in native plant diversity. This suggests that management should focus on the protection of the rare but important vegetation types with fertile soils.     

Development of microbial community during primary succession in areas degraded by mining activities

Together with plants, soil microbial communities play an essential role in the development of stable ecosystems on degraded lands, such as postmining spoil heaps. Our study addressed concurrent development of the vegetation and soil fungal and bacterial communities in the course of primary succession in a brown coal mine spoil deposit area in the Czech Republic across a chronosequence spanning 54 years. During succession, the plant communities changed from sparse plants over grassland and shrubland into a forest, becoming substantially more diverse with time. Microbial biomass increased until the 21st year of ecosystem development and later decreased. Although there was a close association between fungi and vegetation, with fungi mirroring the differences in plant community assemblages, the development of the bacterial community was different. The early succession community in the barren nonvegetated soil largely differed from that in the older sites, especially in its high abundance of autotrophic and free‐living N₂‐fixing bacteria. Later in succession, bacterial community changes were minor and reflected the chemical parameters of the soil, including pH, which also showed a minor change with time. Our results show that complex forest ecosystems developed over 54 years on the originally barren soil of the temperate zone and indicate an important role of bacteria in the initial stage of soil development. Although the arrival of vegetation affects substantially fungal as well as bacterial communities, it is mainly fungi that respond to the ongoing development of vegetation.     

Soil seed bank compositional change constrains biodiversity in an invaded species-rich woodland

Relationships between plant invasion and the soil seed bank in highly diverse fire adapted mediterranean woodlands are poorly understood, yet critical for that ecosystem’s conservation. Within the biodiversity hotspot of southwest Australia we investigated the composition and diversity of the Banksia woodland soil seed bank in good condition (GC), medium condition (MC) and poor condition invaded by the South African perennial species Ehrharta calycina (PCe) and Pelargonium capitatum (PCp). The investigation assessed three questions: (1) Do soil seed banks of invaded sites have fewer germinants of native species and more germinants of introduced (non-native) species than sites with minimal invasion? (2) Do soil seed banks show shifts in ecological functional types with invasion? (3) Is the soil seed bank of introduced species persistent? Native species germinants, mainly shrubs and perennial herbs, were highest in GC sites and least in poorer condition sites suggesting a reduction in their numbers had occurred over time. Introduced germinants were dominated by perennial and annual grasses, and annual herbs. E. calycina had the greatest seed density (8328 germinants m⁻²). More introduced than native germinants occurred in the litter. Rapid germination of introduced species (30% in week 1) compared to native species (4% in week 1) provides the capacity for their early dominance. A limited native soil seed bank and dominant persistent introduced soil seed bank represent great challenges for the structural and functional conservation and restoration of woodland ecosystems. This study provides key new knowledge, applicable to a wide range of ecosystems, to help formulate conservation protocols to control dominant introduced species and conserve and restore biodiverse-rich woodlands.     

Effect of the exotic invasive plant Solidago gigantea on soil phosphorus status

Invasions by exotic plant species can modify biogeochemical cycles and soil properties. We tested whether invasion by early goldenrod (Solidago gigantea, Asteraceae) modifies soil phosphorus pools at three sites in Belgium. Aboveground phytomass and soil samples (0–10 cm) were collected in early goldenrod patches and in adjacent, uninvaded, grassland vegetation. Soil P fractions varied between the three sites in line with corresponding differences in organic matter, carbonate and clay contents. In addition to site-specific impacts, plots invaded by goldenrods generally had higher concentrations of labile P [i.e. resin-extractable inorganic P (Pi) and bicarbonate-extractable Pi and organic P]. Soil CO₂ release and alkaline and acid phosphomonoesterase activities were also higher in invaded plots, suggesting that the increase in labile Pi was due to enhanced mineralization. Phosphorus uptake by vegetation was 1.7–2.1 times higher in invaded plots, mostly due to the higher annual yield of S. gigantea. Altogether, the results indicate that S. gigantea enhances P turnover rates in invaded ecosystems.