Soil fungal networks maintain local dominance of ectomycorrhizal trees

The mechanisms regulating community composition and local dominance of trees in species-rich forests are poorly resolved, but the importance of interactions with soil microbes is increasingly acknowledged. Here, we show that tree seedlings that interact via root-associated fungal hyphae with soils beneath neighbouring adult trees grow faster and have greater survival than seedlings that are isolated from external fungal mycelia, but these effects are observed for species possessing ectomycorrhizas (ECM) and not arbuscular mycorrhizal (AM) fungi. Moreover, survival of naturally-regenerating AM seedlings over ten years is negatively related to the density of surrounding conspecific plants, while survival of ECM tree seedlings displays positive density dependence over this interval, and AM seedling roots contain greater abundance of pathogenic fungi than roots of ECM seedlings. Our findings show that neighbourhood interactions mediated by beneficial and pathogenic soil fungi regulate plant demography and community structure in hyperdiverse forests.

Inbreeding and competition, but not abiotic stresses, increase fluctuating asymmetry of Mimulus guttatus flowers

Genetic and environmental disturbances are expected to increase developmental instability, which may result in higher fluctuating asymmetry (FA), i.e. small random deviations from symmetry. Plant leaves often do not show this pattern, possibly due to high phenotypic plasticity of leaf shape and low adaptive significance of leaf symmetry. In contrast, symmetry in many animal traits but also in flower shape is considered to be under selection, and FA in such traits may better reflect developmental instability. Using geometric morphometrics, I analysed the symmetry of flowers of inbred and outbred Mimulus guttatus (Phrymaceae) plants grown under five stress treatments with and without grass competition. Flower FA was not increased by abiotic stress, but by inbreeding and competition. As inbreeding and competition affected different principal components of flower FA, different mechanisms may be involved in their effects on FA. FA decreased with individual biomass particularly in selfed offspring, which suggests that inbreeding increased FA particularly when growth was limited by environmental or genetic constraints. Increased flower FA of inbred offspring may explain increased flower handling time and reduced pollinator preference for inbred plants in other M. guttatus studies, and could thus have important consequences for plant demography and plant–pollinator interactions.

Population demography, genetic variation and reproductive biology of two rare and endangered Neoregelia species (Bromeliaceae)

Although plant demography, genetics and reproduction are inter-related processes, few studies on rare tropical plants have attempted to integrate them. We used an integrated approach to study two endangered Neoregelia spp. from the Brazilian Atlantic Forest. The floral phenotypes of N. ibitipocensis and N. oligantha are similar, and both species are visited and pollinated only by bumblebees. Flowers of N. ibitipocensis secrete copious nectar, which bees can access only by forcing the corolla to open, whereas flowers of N. oligantha are nectarless. Neoregelia ibitipocensis is self-incompatible and pollen-limited, whereas N. oligantha is self-compatible and sets fruits spontaneously. Population growth rates indicate an increasing population size for both species, although to a lesser extent for N. oligantha. Genetic diversity as a whole was moderate; Bayesian analysis indicated a spatially structured cluster for N. ibitipocensis populations, and genetic diversity was scattered across the distribution of N. oligantha. Despite these differences, vegetative reproduction via clonal growth was the main component of population structuring in both species. Limited seed production in N. ibitipocensis and the risk of genetic drift in N. oligantha seem to be the main threats to their persistence.