A multi-scale approach to identify invasion drivers and invaders’ future dynamics

Climate, land use and disturbances are well known drivers of invasion. However, their relative influence may change across spatial scales, where climate is expected to be the main filter at broad scales; land use is expected to have more influence at intermediate scales, and disturbance, at fine ones. Understanding the underlying processes that drive invasion patterns at different spatial scales is thus crucial to be able to anticipate the future spread of invaders. Here, we quantified the relative importance of climate, land use, and disturbance on the distribution of the invasive trees Ailanthus altissima and Robinia pseudoacacia, across three nested spatial scales, namely global, country (Spain) and riverbank (three riparian riverbanks). To do so, for each species and scale, we built ensemble species distribution models. We also identified their range filling and inferred the most suitable areas in Spain for them to spread. In general, our study confirms that climate acts as an initial coarse filter of species distribution, whilst both climate and land use were important at the country scale; at the riverbank scale human-mediated disturbances gained importance. However, R. pseudoacacia and A. altissima showed differences in their degree of range filling, where A. altissima has a higher potential for range expansion in the near future. Overall, the integration of different scales into invasion studies shows a great potential to enrich our understanding of species-habitat relationships, and to help anticipate their future dynamics.     

Unresolved native range taxonomy complicates inferences in invasion ecology: <Emphasis Type="Italic">Acacia dealbata</Emphasis> Link as an example

Elaborate and expensive endeavours are underway worldwide to understand and manage biological invasions. However, the success of such efforts can be jeopardised due to taxonomic uncertainty. We highlight how unresolved native range taxonomy can complicate inferences in invasion ecology using the invasive tree Acacia dealbata in South Africa as an example. Acacia dealbata is thought to comprise two subspecies based on morphological characteristics and environmental requirements within its native range in Australia: ssp. dealbata and spp. subalpina. Biological control is the most promising option for managing invasive A. dealbata populations in South Africa, but it remains unknown which genetic/taxonomic entities are present in the country. Resolving this question is crucial for selecting appropriate biological control agents and for identifying areas with the highest invasion risk. We used species distribution models (SDMs) and phylogeographic approaches to address this issue. The ability of subspecies-specific and overall species SDMs to predict occurrences in South Africa was also explored. Furthermore, as non-overlapping bioclimatic niches between the two taxonomic entities may translate into evolutionary distinctiveness, we also tested genetic distances between the entities using DNA sequencing data and network analysis. Both approaches were unable to differentiate the two putative subspecies of A. dealbata. However, the SDM approach revealed a potential niche shift in the non-native range, and DNA sequencing results suggested repeated introductions of different native provenances into South Africa. Our findings provide important information for ongoing biological control attempts and highlight the importance of resolving taxonomic uncertainties in invasion ecology.     

Present and future distribution of three aquatic plants taxa across the world: decrease in native and increase in invasive ranges

Inland aquatic ecosystems are vulnerable to both climate change and biological invasion at broad spatial scales. The aim of this study was to establish the current and future potential distribution of three invasive plant taxa, Egeria densa, Myriophyllum aquaticum and Ludwigia spp., in their native and exotic ranges. We used species distribution models (SDMs), with nine different algorithms and three global circulation models, and we restricted the suitability maps to cells containing aquatic ecosystems. The current bioclimatic range of the taxa was predicted to represent 6.6–12.3% of their suitable habitats at global scale, with a lot of variations between continents. In Europe and North America, their invasive ranges are predicted to increase up to two fold by 2070 with the highest gas emission scenario. Suitable new areas will mainly be located to the north of their current range. In other continents where they are exotic and in their native range (South America), the surface areas of suitable locations are predicted to decrease with climate change, especially for Ludwigia spp. in South America (down to ?55% by 2070 with RCP 8.5 scenario). This study allows to identify areas vulnerable to ongoing invasions by aquatic plant species and thus could help the prioritisation of monitoring and management, as well as contribute to the public awareness regarding biological invasions.     

Shade tolerance of <Emphasis Type="Italic">Ailanthus altissima</Emphasis> revisited: novel insights from southern Switzerland

The tree of heaven (Ailanthus altissima (Mill.) Swingle) is considered to be an early-successional, gap-obligate pioneer species with vigorous height growth, low shade tolerance, early fecundity and large seed production. It is a highly invasive species in many temperate and Mediterranean ecosystems outside its natural range, especially after disturbance. Due to its low shade tolerance, the potential of A. altissima to colonise undisturbed forests is thought to be low. In this study we analysed the potential of juvenile A. altissima to grow and survive in sweet chestnut (Castanea sativa Mill.) forests in southern Switzerland. We used hemispherical photography to assess the light conditions of 204 individuals of A. altissima (31 % generative, 69 % vegetative) aged between 1 and 7 years (median: 3 years) in six sites. Generative (seed-borne) and vegetative (clonal ramet) offspring of A. altissima are able to grow in light conditions well below the requirements of shade-intolerant tree species such as European larch (Larix decidua Mill.) and Scots pine (Pinus sylvestris L.). The relatively low light conditions found to be sufficient for the growth and survival of generative regeneration of A. altissima suggest a higher shade tolerance for this species than previously stated, at least for early regeneration. Consequently, the colonisation frontier of A. altissima should be intensively monitored in both forest openings but also in closed canopy forests in the vicinity of seed-bearing A. altissima.     

<Emphasis Type="Italic">Tamarix</Emphasis> (Tamaricaceae) hybrids: the dominant invasive genotype in southern Africa

Hybridization is regarded as a rapid mechanism for increasing genetic variation that can potentially enhance invasiveness. Tamarix hybrids appear to be the dominant genotypes in their invasions. Exotic Tamarix are declared invasive in South Africa and the exotic T. chinensis and T. ramosissima are known to hybridize between themselves, and with the indigenous T. usneoides. However, until now, it was not known which species or hybrid is the most prevalent in the invasion. With a biocontrol programme being considered as a way of suppressing the alien Tamarix populations, it is important to document the population genetic dynamics of all species in the region. This investigation sought to identify Tamarix species in southern Africa and their hybrids, describe their population structure, and reveal the geographic origin of the invasive species. To achieve this, nuclear Internal Transcribed Spacer (ITS) sequence data and the multilocus Amplified Fragment Length Polymorphisms (AFLPs) markers were used. Phylogenetic analysis and population genetic structure confirmed the presence of three species in South Africa (T. chinensis, T. ramosissima and T. usneoides) with their hybrids. The indigenous T. usneoides is clearly genetically distant from the alien species T. chinensis and T. ramosissima. Interestingly, the Tamarix infestation in South Africa is dominated (64.7 %) by hybrids between T. chinensis and T. ramosissima. The exotic species match their counterparts from their places of origin in Eurasia, as well as those forming part of the invasion in the US.     

Invasive <Emphasis Type="Italic">Tamarix</Emphasis> (Tamaricaceae) in South Africa: current research and the potential for biological control

Most species of Tamarix originate in Eurasia and at least five species have become invasive around the world, including South Africa. However, T. usneoides is indigenous to southern Africa, where the potential for biological control of the invasive species is being investigated. Recent research on the invasive species is reviewed here with particular reference to these South African biocontrol efforts. The successful biological control programme against invasive Tamarix in the USA, using several species of “Tamarisk beetle”, is being used as a guide for the South African research. The South African programme is complicated by firstly, the presence of the indigenous T. usneoides which raises the precision of host-specificity required, and secondly, the introduced and indigenous Tamarix have a high intrinsic value for phytoremediation of mine tailings dams in South Africa. The phylogenetic proximity of these Tamarix species to each other has contributed to this challenge, which has nevertheless been successfully addressed by molecular techniques used to separate the species. In addition, classical morphological techniques have been used to separate the Tamarisk beetles, so that now they can generally be matched to Tamarix tree species. Overall, it is concluded that given the broad knowledge now available on the ecology and identity of both the trees and their biocontrol agents, the prospects for successful biological control of Tamarix in South Africa are good.     

Potential Distribution of Fossil Xenarthrans in South America during the Late Pleistocene: co-Occurrence and Provincialism

Species distribution models (SDMs) are helpful for understanding actual and potential biogeographical traits of organisms. These models have recently started to be applied in the study of fossil xenarthrans. SDMs were generated for 15 South American late Pleistocene xenarthrans: eight Cingulata (Glyptodon clavipes, Doedicurus clavicaudatus, Panochthus tuberculatus, Neosclerocalyptus paskoensis, Pampatherium typum, Pampatherium humboldtii, Holmesina paulacoutoi, and Holmesina occidentalis) and seven Folivora (Glossotherium robustum, Lestodon armatus, Mylodon darwinii, Catonyx cuvieri, Catonyx (=Scelidodon) chilensis, Megatherium americanum, and Eremotherium laurillardi). Models were evaluated for three periods: the last interglacial (LIG), the last glacial maximum (LGM), and the Holocene climatic optimum (HCO). Co-occurrence records were studied based on the overlap of the potential distributions and compared with the available biome reconstructions of South America during the LGM to analyze species distribution patterns, ecological requirements, and possible interactions. Our results suggest the existence of provincialization within xenarthran megamammals grouped in at least three bioregions. Northern and southwestern taxa overlap in the Río de la Plata region where also some endemic taxa are found. We observed overlapping potential distributions but separated and continuous realized distributions between closely related xenarthrans suggesting competitive exclusion. A generalized reduction in potential habitats at the end of the Pleistocene was not obvious as some taxa show stable potential areas during HCO when comparing with LGM. Nonetheless, fragmentation of the most suitable areas due to climate variation and the impact of reduction in available land due to sea level changes cannot be ruled out as involved in the extinction.     

Identification and genetic diversity of two invasive <Emphasis Type="Italic">Pissodes</Emphasis> spp. Germar (Coleoptera: Curculionidae) in their introduced range in the southern hemisphere

During the first half of the twentieth century, two accidental cases of introduction of Pissodes weevils were recorded from the southern hemisphere. The weevils in South Africa were identified as the deodar weevil (Pissodes nemorensis) and those in South America as the small banded pine weevil (Pissodes castaneus). Wide distribution of the two species in their invasive range, general difficulty in identifying some Pissodes spp., and the varying feeding and breeding behaviours of the species in South Africa has necessitated better evidence of species identity and genetic diversity of both species and population structure of the species in South Africa. Barcoding and the Jerry-to-Pat region of the COI gene were investigated. Morphometric data of the South African species was analysed. Our results confirmed the introduction of only one Pissodes species of North American origin to South Africa. However, this species is not P. nemorensis, but an unrecognized species of the P. strobi complex or a hybrid between P. strobi and P. nemorensis. Only P. castaneus, of European origin, was identified from South America. We identified ten mitochondrial DNA haplotypes from South Africa with evidence of moderate genetic structure among geographic populations. Terminal leader and bole-feeding weevils did not differ at the COI locus. A single haplotype was identified from populations of P. castaneus in South America. Results of the present study will have implications on quarantine, research and management of these insect species.     

Assessing the distribution and conservation status of a long-horned beetle with species distribution models

Data shortfalls on species distribution affect species differently, but it is frequent among insects. Species distribution models (SDMs) are important tools to fill biogeographic deficits and provide support for practical conservation actions, particularly for cryptic or hard to survey species. We employed SDMs to evaluate one such species, the long-horned beetle (Macrodontia cervicornis), listed as ‘vulnerable’ in the IUCN’s Red List of Threatened Species. Given new distributional data for this species, we applied three different SDMs to: (1) provide the first assessment of this species’ distribution and potential dispersal routes; (2) evaluate the effectiveness of the current South American protected areas system for its conservation; and (3) discuss its potential distribution, as well as historical, biogeographical, and taxonomic issues related to it. Our models reached fair True Skilled Statistics values (TSS > 0.5), with the core area for M. cervicornis located in the Amazon forest, although suitable areas were also predicted along the Atlantic forest. Areas in the dry diagonal South American corridor (dry biomes of Cerrado, Caatinga, and Pampas) in South America were not predicted as suitable. The preference of M. cervicornis for humid areas with high temperatures may guarantee a better physiological control for dehydration, considering that large insects are more affected by water loss. In general, approximately 15 % of the distribution of M. cervicornis is in humid protected areas. The disconnected distribution of the long-horned beetle may be an indication of the existence of cryptic species under the same classification. We suggest that similar studies with other insect groups (e.g. butterflies, bees) should be conducted to properly assess their distributions, conservation status, and responses to hot-humid gradients throughout South America.     

Diurnal temperature-related variations in photosynthetic enzyme activities of two C<Subscript>4</Subscript> species of Chenopodiaceae grown in natural environment

The effects of the diurnal variations in ambient temperature on some C₃ and C₄ enzymes in the Salsola dendroides and Suaeda altissima species of Chenopodiaceae family were studied during the intensive vegetation period. Activities of phosphoenolpyruvate carboxylase (PEPC) and cytosolic aspartate aminotransferase (AsAT) were shown to decrease in both species in the afternoon and evening. The activity of the mitochondrial AsAT decreased in S. altissima, remained relatively constant in S. dendroides during the day. The activity of alanine aminotransferase was high in the S. dendroides species in the morning and evening and decreased in the S. altissima species by the evening. Glucose-6-phosphate activated PEPC in both species throughout the day. The study of the redox status-regulated C₃ enzymes showed temperature-related increases in NADP-glyceraldehyde 3-phosphate dehydrogenase activity in both plants, in fructose-2,6-bisphosphatase activity in the S. altissima species, and in NADP-MDH activity in the S. dendroides species in the afternoon.     

Niche dynamics of two cryptic <Emphasis Type="Italic">Prosopis</Emphasis> invading South American drylands

Whether or not species track native climatic conditions during invasions (i.e., climate match hypothesis) is fundamental to understand and prevent potential impacts of invasive species. Recent empirical work suggests that climatic mismatches between native and invasive ranges are pervasive. Whether these differences are due to adaptation to new climatic spaces in the invasive range or due to partial filling of the potential climatic space are still subject to debate. Here, we analyze climatic niche dynamics associated with the invasion of the two most common invasive plants in Brazilian semi-arid areas, Prosopis juliflora and Prosopis pallida. These species have been simultaneously introduced in the region, which creates a unique opportunity to compare their niche dynamics during invasion. Given that P. juliflora have a much wider native range size, we expect these species would present different dispersal potentials, which might translate into different unfilling levels. Using an ordination method with kernel smoother and null models, we contrasted climate spaces occupied by each species in both native and invasive ranges. We further used ecological niche models (ENMs) to compare reciprocal predictions of potentially suitable areas. Against our expectation based on differences in native range sizes, climatic niches of P. juliflora and P. pallida overlapped greatly, both in their native and invasive ranges. Our results support niche conservatism during the invasion process. Climatic mismatches among native and invaded ranges were exclusively attributed to unfilling of native climates in the invasive range. Both species showed similar unfilling levels. Likewise, ENMs predicted regions not yet occupied in the invasive range, revealing a potential for further expansion. We discuss colonization time lag and founder effect as potential mechanisms that may have prevented these species to fully occupy their native niches in the invasive range.     

New records of an invasive bumble bee in northern Chile: expansion of its range or new introduction events?

The Eurasian bumble bee Bombus terrestris Linnaeus has been used commercially for pollination of a large number of crop species worldwide. This species has become invasive in several countries where it has escaped into natural environments. This species has become naturalized in many zones of Chile and southern Argentina, and may potentially invade other regions and countries in South America. These naturalized populations of B. terrestris have been associated with rapid population declines of the native bee B. dahlbomii Guérin-Méneville. We report new records of the exotic bee B. terrestris in the Region de Arica y Parinacota in the far north of Chile, which includes portions of the Atacama Desert. We used species distribution models (SDMs) and multivariate analyses to evaluate whether these occurrences represent new escapes from managed colonies or natural dispersal of the species from its southern invaded range. These reports of B. terrestris indicate a northward expansion of this bee. In our analyses, these new areas of occurrences have environmental conditions similar to those observed in the species’ southern invaded range, and our SDMs predict that B. terrestris dispersal through the Atacama is possible, although not likely given the occasional flower blooming in that region of Chile. These new occurrences in northern Chile reflect a potential for future invasion into other regions of South America by B. terrestris. Future surveys in the area should be intensified to evaluate if viable populations of this invasive species may become established.     

Lack of human-assisted dispersal means <Emphasis Type="Italic">Pueraria montana</Emphasis><Emphasis Type="Italic">var. lobata</Emphasis> (kudzu vine) could still be eradicated from South Africa

The legume, Pueraria montana var. lobata (kudzu vine) is one of the worst plant invaders globally. Here we present the first study of P. montana in South Africa. We found only seven P. montana populations covering an estimated condensed area of 74 hectares during the height of the growing season. Based on a species distribution model, it appears that large parts of the globe are suitable, including parts of the eastern escarpment of South Africa (where most populations occur). South African populations of P. montana appear to have a similar ecology to populations in the USA: high growth rates, low seed germination, no natural long-distance dispersal, little herbivory and vigorous post-fire resprouting. In contrast to the USA, most South African populations do flower and flowers are capable of producing seed in the absence of pollinators. However, P. montana appears to have never been widely planted in South Africa, and the incursion was for many years restricted to a single introduction site. The comparison between the invasions of P. montana in the USA and South Africa highlights the often overriding importance of human-assisted dispersal and cultivation in creating widespread invasions, and should serve as a warning to people who have proposed to utilize the species in Africa.     

<Emphasis Type="Italic">Anoplodiscus</Emphasis> Sonsino, 1890 (Monogenea: Anoplodiscidae): a new Australian species,and the first African record from South African hosts

Species of Anoplodiscus Sonsino, 1890 were previously only known from host members of Sparidae. A new species, Anoplodiscus hutsonae n. sp. is proposed for museum specimens originally collected from species of Scolopsis Cuvier (Nemipteridae) off Heron Island and Lizard Island, Australia. Additionally, Anoplodiscus tai Ogawa, 1994 is synonymised with Anoplodiscus cirrusspiralis Roubal, Armitage & Rohde, 1983 due to a lack of support for differential characters, and Anoplodiscus richiardii is considered a species inquirenda. Anoplodiscus cirrusspiralis causes visible lesions on the skin and fins of its host, and may also contribute to poor food conversion rates in sparid aquaculture. Anoplodiscus cirrusspiralis has been recorded from cultured sparids in Australia, Japan, South Africa, and South Korea, and was implicated as a disease agent in fish from the former two countries. However, the discovery of A. cirrusspiralis on Chrysoblephus gibbiceps (Valenciennes), Ch. laticeps (Valenciennes) and Cymatoceps nasutus (Castelnau) in South Africa, ?Pagrus major (Temminck & Schlegel) in South Korea, and P. auratus (Forster) in Australia, New Zealand and Japan suggests that this species may have a wide distribution and low host-specificity within the Sparidae. In South Africa, A. cirrusspiralis was first encountered on a morbid C. nasutus and Ch. gibbiceps from two public aquaria in 2009 (Two Oceans Aquarium, Cape Town and uShaka Sea World, Durban, respectively). Additional material was collected from C. laticeps kept at an abalone farm in Hermanus that originated from Struisbaai on the South African south coast. Anoplodiscus cirrusspiralis is redescribed from the South African specimens. This is the first record of a member of Anoplodiscidae Tagliani, 1912 from Africa.     

South African mouse shrews (<Emphasis Type="Italic">Myosorex</Emphasis>) feel the heat: using species distribution models (SDMs) and IUCN Red List criteria to flag extinction risks due to climate change

Five species of mouse or forest shrews (Myosorex) are endemic to South Africa, Lesotho and Swaziland, four of which (Myosorex varius, Myosorex cafer, Myosorex longicaudatus and Myosorex cf. tenuis) are associated with montane or temperate grassland, fynbos and/or forest habitats while a fifth (Myosorex sclateri) is associated with lowland subtropical forests. Due to their small size, specialised habitat, low dispersal capacity, high metabolism and sensitivity to temperature extremes, we predicted that, particularly for montane species, future climate change should have a negative impact on area of occupancy (AOO) and ultimately extinction risks. Species distribution models (SDMs) indicated general declines in AOO of three species by 2050 under the A1b and A2 climate change scenarios (M. cafer, M. varius, M. longicaudatus) while two species (M. sclateri and M. cf. tenuis) remained unchanged (assuming no dispersal) or increased their AOO (assuming dispersal). While temperate species such as M. varius appear to be limited by temperature maxima (preferring cooler temperatures), the subtropical species M. sclateri appears to be limited by temperature minima (preferring warmer temperatures). Evidence for declines in AOO informed the uplisting (to a higher category of threat) of the Red List status of four Myosorex species to either vulnerable or endangered as part of a separate regional International Union for Conservation of Nature (IUCN) Red List assessment.     

Cover thresholds for impacts of an exotic grass on the structure and assembly of a wet prairie community

Potential impacts of an exotic grass, Hemarthria altissima, on restoration of wet prairie community structure (species richness and cover of indicator species) and assembly processes (temporal turnover rates of plant species) on the Kissimmee River floodplain in Central Florida, USA, were evaluated over a 12-year period before and after restoration of hydrologic regimes (2001), and implementation of herbicide treatments (2006–2007) to control its spread. Thresholds for impacts were derived from comparisons of sample sites with variable levels of H. altissima cover. Prior to herbicide treatments, cover of H. altissima exhibited a logistic increase over time, with peak colonization and expansion occurring during major flood events. Mean post-restoration cover of three native wet prairie indicator species (Polygonum punctatum, Panicum hemitomon, and Luziola fluitans) increased to 37.8 ± 3.4 % in plots in which H. altissima cover was <12 %, and did not exceed 15 % in any plots with H. altissima cover >30 %. Prior to and after herbicide treatments, these indicator species largely accounted for observed differences in wet prairie community structure (i.e., cover of wetland forbs and grasses) between heavily infested sites and plots with low or no cover of H. altissima. The cover threshold at which H. altissima began to have these community-level effects was 40–50 %, but lower species richness was found only where H. altissima cover was >80 %. Increasing cover of H. altissima led to a significant decline in temporal turnover rates of plant species (P < 0.001, r² = 0.10), but also was largely due to plots with very high (>75 %) cover of H. altissima. Mean temporal turnover rates of plant species increased significantly (P = 0.03) after herbicide treatments and subsequently were highest during an ensuing flood pulse. However, 2–3 years after herbicide treatments, regrowth of H. altissima reestablished high cover (mean = 59 ± 9.5 %) in over half of the treated plots. The ability of H. altissima to establish dominant cover in restored hydrologic conditions on the Kissimmee River floodplain, and documented regrowth following herbicide treatments, increase the potential for this exotic grass species to be a pervasive threat to successful reestablishment of wet prairie community structure and assembly processes.     

First records of the powdery mildews <Emphasis Type="Italic">Erysiphe platani</Emphasis> and <Emphasis Type="Italic">E. alphitoides</Emphasis> on <Emphasis Type="Italic">Ailanthus altissima</Emphasis> reveal host jumps independent of host phylogeny

The tree-of-heaven Ailanthus altissima (family Simaroubaceae, order Sapindales) is one of the most invasive neophytes in Europe. The tree originated in China and became invasive worldwide in areas with Mediterranean to temperate climates. As known from other invasive plants, only a few pathogens have been reported from A. altissima in Europe, and, to date, powdery mildews on it have been unknown in the European region. Recently, two powdery mildews were found on A. altissima during a survey of neomycetes on non-native plants in Switzerland. Because they did not fit with any of the species known to occur on Simaroubaceae in Asia, they were identified by DNA barcoding using sequences of the ITS region of the n-rDNA, revealing them to be the powdery mildews of plane and oak trees, Erysiphe platani and E. alphitoides. This is the first record of E. platani on a host outside the genus Platanus and its family Platanaceae, as well as its order Proteales. In contrast, E. alphitoides has been reported to occur on several host families and orders. Host jumps over great phylogenetic distances—such as across plant families and orders—appear to be quite common in biogeographically novel associations between Erysiphales species and plants. The consequences of such host jumps for identity and taxonomic placement of species are discussed here. It is further questioned whether both pathogens are usable as biological control agents against the tree-of-heaven.     

Feasibility assessment for the classical biological control of <Emphasis Type="Italic">Tamarix</Emphasis> in Argentina

Saltcedars are woody plants in the genus Tamarix L. (Caryophyllales: Tamaricaceae) and are native to Eurasia and Africa. Several species have become invasive in the Americas, Australia and South Africa. In Argentina there are four species of Tamarix distributed in arid, semi-arid and coastal areas of most provinces. The taxonomic isolation of Tamarix spp. in Argentina, their widespread distribution, negative impact to natural areas and lack of impact from existing natural enemies all indicate that Tamarix is an ideal candidate for classical biological control in Argentina. Biological control of Tamarix spp. has been rapid and highly successful in the USA after the introduction of four Diorhabda spp. (Coleoptera: Chrysomelidae). Biological control of Tamarix spp. in Argentina could be implemented easily, rapidly, and at a low cost by utilizing the information developed in the USA.     

Temporal and spatial impact of <Emphasis Type="Italic">Spartina alterniflora</Emphasis> invasion on methanogens community in Chongming Island,China

Methane production by methanogens in wetland is recognized as a significant contributor to global warming. Spartina alterniflora (S. alterniflora), which is an invasion plant in China’s wetland, was reported to have enormous effects on methane production. But studies on shifts in the methanogen community in response to S. alterniflora invasion at temporal and spatial scales in the initial invasion years are rare. Sediments derived from the invasive species S. alterniflora and the native species Phragmites australis (P. australis) in pairwise sites and an invasion chronosequence patch (4 years) were analyzed to investigate the abundance and community structure of methanogens using quantitative real-time PCR (qPCR) and Denaturing gradient gel electrophoresis (DGGE) cloning of the methyl-coenzyme M reductase A (mcrA) gene. For the pairwise sites, the abundance of methanogens in S. alterniflora soils was lower than that of P. australis soils. For the chronosequence patch, the abundance and diversity of methanogens was highest in the soil subjected to two years invasion, in which we detected some rare groups including Methanocellales and Methanococcales. These results indicated a priming effect at the initial invasion stages of S. alterniflora for microorganisms in the soil, which was also supported by the diverse root exudates. The shifts of methanogen communities after S. alterniflora invasion were due to changes in pH, salinity and sulfate. The results indicate that root exudates from S. alterniflora have a priming effect on methanogens in the initial years after invasion, and the predominate methylotrophic groups (Methanosarcinales) may adapt to the availability of diverse substrates and reflects the potential for high methane production after invasion by S. alterniflora.