Diversity of AMF associated with Ammophila arenaria ssp. arundinacea in Portuguese sand dunes

Abstract Dune vegetation is essential for the formation and preservation of sand dunes and the protection of the coast line. Coastal sand dunes are harsh environments where arbuscular mycorrhizal fungi (AMF) play an important role in promoting plant establishment and growth. We present a study of the diversity of AMF associated with A. arenaria ssp. arundinacea in two locations of the Portuguese coast under a Mediterranean climate. These two locations were selected to compare a well-preserved dune system from a protected area with a degraded dune system from a public beach. AMF diversity was assessed mainly by cloning and sequencing of a fragment of the ribosomal SSU using the primer NS31 and AM1. Most of the 89 AMF clones obtained from the rhizosphere and roots of A. arenaria belonged to the genus Glomus, the largest clade within the Glomeromycota. Higher AMF diversity was found in the least disturbed site, in which spores of Scutellospora persica, Glomus constrictum and Glomus globiferum were found in the rhizosphere of A. arenaria

Negative plant-soil feedback and species coexistence

Different mechanisms, including equilibrium and non-equilibrium processes, have been taken into account as possible theoretical explanations of species coexistence. Despite the ample evidence on the existence of negative plant-soil feedback in both agriculture and natural vegetation, the role of these processes in the organization and dynamics of plant communities has so far been neglected. In this study, simulations by an individual-based competition model show how the intensity of negative feedback on individual plant performance can produce faster successional dynamics and allow species coexistence in two- and multi-species systems. The results show that even low levels of negative plant-soil feedback can enable species coexistence and often produce cyclic population dynamics. Moreover, the model highlights how negative feedback can generate positive reciprocal interspecific interactions at the population level, despite the fact that only competitive interactions is present between individual plants. In fact, competitive effects occur on a short-term scale, but positive reciprocal species interactions emerge only if negative feedback affects all species and if longer periods of simulation, more than the species life span, are considered. An important outcome of the model is the evidence that the effects at population level are timescale-dependent, thus showing the limitation of short-term species removal experiments used in traditional competition studies

Evidence of population differentiation in the dune grass Ammophila arenaria and its associated root-feeding nematodes

The interactions between herbivores and their host plants determine, to a great extent, the formation, structure and sustainability of terrestrial communities. The selection pressures that herbivores exert on plants and vice versa might vary geographically, leading eventually to population differentiation and local adaptation. In order to test whether there was reciprocal population differentiation among plants and belowground herbivores, we performed a cross-inoculation experiment using combinations of species and populations of root-feeders belonging to the genus Pratylenchus and the dune grass Ammophila arenaria from different geographic origins. Plant and herbivore responses in terms of growth and multiplication, respectively, were assessed at the end of the experiment. The 16 plant-herbivore combinations tested showed a high variation in the outcome of the interaction and revealed population differentiation in the responses of both, the host plant and the root-herbivores. The outcome in plant and herbivore performance was strongly case-dependent and for the sympatric combinations tested, support for local adaptation was not found. Nonetheless, the variation in plant-herbivore responses to experimental conditions highlights the plasticity of the interaction and may be pointing at spatial structuring in belowground plant-herbivore interactions

Changes in landscape and vegetation of coastal dunes in northwest Europe: a review

In coastal dunes, landscape changes are a rule, rather than an exception. This paper gives an overview of changes in landscape and vegetation with a focus on the past century. The history of dunes is characterised by phases of sand drift, alternated with geomorphological stability. The historical development of dune woodland during these stable phases has been documented for sites all over Europe. Vegetation reconstructions of historical open dune habitats however is very difficult due to limited preservation of fossil remains. People have drastically altered coastal dune landscapes through centuries of exploitation and more recently development of the coast. Historical land use has generally pushed vegetation back into a semi-natural state. During roughly the past century a tendency of increasing fixation and succession is observed on coastal dunes throughout northwest Europe. Six causes of change are discussed. 1) Changes in land use, mainly abandonment of agricultural practices, have led to the development of late successional stages such as scrub and woodland. 2) Crashing rabbit populations due to myxomatosis in the 1950s caused vigorous grass growth and probably stimulated scrub development. 3) A general tendency of landscape fixation is observed due to both natural and anthropogenic factors. 4) Eutrophication, mainly due to atmospheric nitrogen deposition is clearly linked to grass encroachment on acidic but also on some calcareous dunes. 5) The impact of climate change on vegetation is still unclear but probably lengthening of growing season and maybe enhanced CO2 concentrations have led to an acceleration of succession. 6) A general anthropogenisation of the landscape occurs with rapid spread of non-native species as an important consequence. The reconstruction of a natural reference landscape is considered largely unattainable because of irreversible changes and the long tradition of human impact, in many cases since the development of the dunes. Two contradictory elements need reconciliation. First, the general acceleration of succession and scrub and woodland development in particular is partly caused by a decreased anthropogenic interference in the landscape and deserves more appreciation. Second, most biodiversity values are largely linked to open, early succession dune habitats and are threatened by the same tendency. Apart from internal nature management, in which grazing plays an important part, re-mobilisation of stable, senescent dunes is an important challenge for dune management