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Aim: To determine and compare the taxonomic identity and diversity of root nodule and rhizospheric microbial symbionts associated with Acacia pycnantha Benth. in its native (Australian) and invasive (South African) ranges, and to establish whether these associations are general or host specific. Location: The native range of A. pycnantha in Australia and invasive ranges in South Africa and Western Australia. Methods: Bacteria were isolated from root nodules collected from 18 populations of A. pycnantha. Repetitive element polymerase chain reaction (REP-PCR) fingerprinting was used to assess overall bacterial diversity and clustering. Molecular phylogenies for a subset of isolates representing major REP-PCR clades were reconstructed using maximum parsimony and Bayesian phylogenetic analyses of the nuclear 16S—23S rRNA intergenic spacer (IGS), 16S rRNA, and the symbiotic nodA genes. Results: Twelve clusters were identified from the REP-PCR analysis; 11 included isolates from both the native range in Australia and invasive range in South Africa, while one cluster comprised only Australian isolates. Six rhizobial species were found in association with A. pycnantha: Bradyrhizobium japonicum, Rhizobium gallicum, R. lusitanum, R. miluonense, R. multihospitium and R. tropici. We also identified three plant-growth promoting bacteria isolated from root nodules of A. pycnantha: Burkholderia caledonica, B. graminis and B. phytofirmans. Phylogenetic analysis of the IGS gene retrieved clades containing symbionts from both Australia and South Africa while others comprised only South African taxa, suggesting the introduction of bacterial lineages from Australia to South Africa. Our phylogeographic analysis of the nodA gene confirmed that A. pycnantha was co-introduced with its symbionts to South Africa. Main conclusions: Acacia pycnantha is a promiscuous legume, associated with at least six different rhizobial symbionts, and forms associations with plant-growth promoting rhizosphere bacteria from the genus Burkholderia. In the invasive range of A. pycnantha in South Africa, nodules contained some symbionts of South African origin while other symbionts appear to have been cointroduced from Australia. Acacia pycnantha is associated with a wider suite of symbionts in its invasive than native range.

Aim: Our study aimed to identify and explore the main factors that influence tree recruitment of multiple species at a regional scale across peninsular Spain, an understanding of which is essential for predicting future forest species composition in the face of ongoing environmental change. The study focused on the dynamics of the key transition phase from saplings to adult trees. Location: The forests of peninsular Spain. Methods: We used the extensive network of plots sampled in two consecutive Spanish national forest inventories (> 30,000 plots) to identify the factors that determine regeneration patterns of the 10 most abundant forest species of Spain at relatively large temporal (c. 10 years) and spatial scales (across Spain): five coniferous species of Pinus (pines) and five broadleaved species of the genera Fagus and Quercus. We fitted separate generalized linear models for the pine species and the broadleaved species to assess the response of sapling abundance and ingrowth rate to the spatial variability of climate (temperature, water availability and recent warming), forest structure (tree density, understorey and overstorey canopy cover, and basal area change) and disturbances (previous forest logging, wildfires and grazing). Results: Mean sapling abundance was four times higher for broadleaved species than for pines, while mean annual ingrowth was twice as high. Sapling abundance and ingrowth rate were mainly determined by stand structure, both in pines and broadleaved trees. The direct effects of disturbances and climate were comparatively smaller, and there was no detectable effect of recent warming. Main conclusions: The higher values of ingrowth rate of broadleaved species can be explained by their ability to maintain a higher sapling bank due to their greater shade tolerance. This differential response of pines and broadleaved species to canopy closure suggests a probable increase in broadleaved species at the expense of pines. This transition could occur earlier in stands with faster canopy closure dynamics. Spatially explicit, mixed-species demographic models incorporating both the ingrowth and the tree mortality components are needed for predicting the composition of future forests.

Aim: Various coral reef organisms display distinct gradients in taxonomic turnover throughout the tropical Pacific Ocean. Marine macrophytes are one of the most dominant and ecologically important benthic components of tropical reefs, yet little is known about the ecological biogeography of the macrophyte assemblages throughout this biodiverse region. This study assessed: (1) the geographical clustering of macrophyte assemblages in the tropical Pacific; (2) the environmental/geographical factors that best explain the observed patterns in taxon richness and taxon composition; and (3) the validity of large-scale biogeographical hypotheses with respect to the distribution of macrophyte assemblages. Location: Coral reefs of 39 US Pacific islands. Methods: Surveys of reef macrophytes for all 39 Pacific islands were conducted from 2004 to 2007. Rank-order data of quadrats were transformed to proportional abundance data in order to compute site averages for each of the 84 macrophyte categories. Further data analysis employed taxon accumulation curves, generalized additive models, and multivariate techniques. Results: Pacific macrophyte assemblages displayed consistently higher within-archipelago similarities than between-archipelago similarities, which is reflected in pronounced differences in functional group composition between archipelagos. The maximum land elevation, maximum seasonal sea surface temperature, reef extent, and longitude of the investigated islands were the predictor variables that best described the similarities in macrophyte assemblage structure among islands. Maximum land elevation and reef extent, however, were the two predictor variables that best explained macrophyte richness per island. Main conclusions: Macrophyte assemblages of the Pacific Islands cluster in geographical groups, indicative of the importance of evolutionary factors related to dispersal and speciation. Whereas macrophyte assemblage structure is governed by both local (habitat diversity and availability) and regional (geographical and environmental descriptors related to oceanic isolation and latitude) variables, the macrophyte richness of these islands is defined primarily by local habitat diversity and availability. Biogeographical patterns of marine macrophyte assemblages in the tropical Pacific deviate from those of other well-studied marine organisms.