Dispersal and seed limitation affect diversity and productivity of montane grasslands

So far, seed limitation as a local process, and dispersal limitation as a regional process have been largely neglected in biodiversity-ecosystem functioning research. However, these processes can influence both local plant species diversity and ecosystem processes, such as biomass production. We added seeds of 60 species from the regional species pool to grassland communities at 20 montane grassland sites in Germany. In these sites, plant species diversity ranged from 10 to 34 species m(-2) and, before manipulation, diversity was not related to aboveground biomass, which ranged from 108 to 687 g m(-2). One year after seed addition, local plant species richness had increased on average by six species m(-2) (29%) compared with control plots, and this increase was highest in grasslands with intermediate productivity. The increased diversity after adding seeds was associated with an average increase of aboveground biomass of 36 g m(-2) (14.8%) compared with control plots. Thus, our results demonstrate that a positive relationship between changes in species richness and productivity, as previously reported from experimental plant communities, also holds for natural grassland ecosystems. Our results show that local plant communities are dispersal limited and a hump-shaped model appears to be the limiting outline of the natural diversity-productivity relationship. Hence, the effects of dispersal on local diversity can substantially affect the functioning of natural ecosystems.

Initializing a National Grid Infrastructure: Lessons Learned from the Swiss National Grid Association Seed Project

In addition to multi-national Grid infrastructures, several countries operate their own national Grid infrastructures to support science and industry within national borders. These infrastructures have the benefit of better satisfying the needs of local, regional and national user communities. Although Switzerland has strong research groups in several fields of distributed computing, only recently a national Grid effort was kick-started to integrate a truly heterogeneous set of resource providers, middleware pools, and users. In the following. article we discuss our efforts to start Grid activities at a national scale to combine several scientific communities and geographical domains. We make a strong case for the need of standards that have to be built on top of existing software systems in order to provide support for a heterogeneous Grid infrastruc

Seed availability in hay meadows: Land-use intensification promotes seed rain but not the persistent seed bank

Intensification of land use in semi-natural hay meadows has resulted in a decrease in species diversity. This is often thought to be caused by the reduced establishment of plant species due to high competition for light under conditions of increased productivity. Sowing experiments in grasslands have found reliable evidence that diversity can also be constrained by seed availability, implying that processes influencing the production and persistence of seeds may be important for the functioning of ecosystems. So far, the effects of land-use intensification on the seed rain and the persistence of seeds in the soil have been unclear. We selected six pairs of extensively managed (Festuco-Brometea) and intensively managed (Arrhenatheretalia) grassland with traditional late cutting regimes across Switzerland and covering an annual productivity gradient in the range 176–1211 gm−2. In each grassland community, we estimated seed rain and seed bank using eight pooled seed-trap or topsoil samples of 89 cm2 in each of six plots representing an area of c. 150 m2. The seed traps were established in spring 2010 and collected simultaneously with soil cores after an exposure of c. three months. We applied the emergence method in a cold frame over eight months to estimate density of viable seeds. With community productivity reflecting land-use intensification, the density and species richness in the seed rain increased, while mean seed size diminished and the proportions of persistent seeds and of species with persistent seeds in the topsoil declined. Stronger limitation of seeds in extensively managed semi-natural grasslands can explain the fact that such grasslands are not always richer in species than more intensively managed ones.

Gastropod Seed Dispersal: An Invasive Slug Destroys Far More Seeds in Its Gut than Native Gastropods

Seed dispersal is one of the most important mechanisms shaping biodiversity, and animals are one of the key dispersal vectors. Animal seed dispersal can directly or indirectly be altered by invasive organisms through the establishment of new or the disruption of existing seed dispersal interactions. So far it is known for a few gastropod species that they ingest and defecate viable plant seeds and consequently act as seed dispersers, referred to as gastropodochory. In a multi-species experiment, consisting of five different plant species and four different gastropod species, we tested with a fully crossed design whether gastropodochory is a general mechanism across native gastropod species, and whether it is altered by the invasive alien slug species Arion lusitanicus. Specifically, we hypothesized that a) native gastropod species consume the seeds from all tested plant species in equal numbers (have no preference), b) the voracious invasive alien slug A. lusitanicus – similarly to its herbivore behaviour – consumes a higher amount of seeds than native gastropods, and that c) seed viability is equal among different gastropod species after gut passage. As expected all tested gastropod species consumed all tested plant species. Against our expectation there was a difference in the amount of consumed seeds, with the largest and native mollusk Helix pomatia consuming most seeds, followed by the invasive slug and the other gastropods. Seed damage and germination rates did not differ after gut passage through different native species, but seed damage was significantly higher after gut passage through the invasive slug A. lusitanicus, and their germination rates were significantly reduced.

Sizing up your enemy: individual predation vulnerability predicts migratory probability

Partial migration, in which a fraction of a population migrate and the rest remain resident, occurs in an extensive range of species and can have powerful ecological consequences. The question of what drives differences in individual migratory tendency is a contentious one. It has been shown that the timing of partial migration is based upon a trade-off between seasonal fluctuations in predation risk and growth potential. Phenotypic variation in either individual predation risk or growth potential should thus mediate the strength of the trade-off and ultimately predict patterns of partial migration at the individual level (i.e. which individuals migrate and which remain resident). We provide cross-population empirical support for the importance of one component of this model—individual predation risk—in predicting partial migration in wild populations of bream Abramis brama, a freshwater fish. Smaller, high-risk individuals migrate with a higher probability than larger, low-risk individuals, and we suggest that predation risk maintains size-dependent partial migration in this system.

Reprint of "Seed availability in hay meadows: Land-use intensification promotes seed rain but not the persistent seed bank''

Intensification of land use in semi-natural hay meadows has resulted in a decrease in species diversity. This is often thought to be caused by the reduced establishment of plant species due to high competition for light under conditions of increased productivity. Sowing experiments in grasslands have found reliable evidence that diversity can also be constrained by seed availability, implying that processes influencing the production and persistence of seeds may be important for the functioning of ecosystems. So far, the effects of land-use intensification on the seed rain and the persistence of seeds in the soil have been unclear. We selected six pairs of extensively managed (Festuco-Brometea) and intensively managed (Arrhenatheretalia) grassland with traditional late cutting regimes across Switzerland and covering an annual productivity gradient in the range 176-1211 gm(-2). In each grassland community, we estimated seed rain and seed bank using eight pooled seed-trap or topsoil samples of 89 cm(2) in each of six plots representing an area of c. 150 m(2). The seed traps were established in spring 2010 and collected simultaneously with soil cores after an exposure of c. three months. We applied the emergence method in a cold frame over eight months to estimate density of viable seeds. With community productivity reflecting land-use intensification, the density and species richness in the seed rain increased, while mean seed size diminished and the proportions of persistent seeds and of species with persistent seeds in the topsoil declined. Stronger limitation of seeds in extensively managed semi-natural grasslands can explain the fact that such grasslands are not always richer in species than more intensively managed ones. (C) 2013 Elsevier B.V. All rights reserved.

AtPTR1, a plasma membrane peptide transporter expressed during seed germination and in vascular tissue of Arabidopsis

For the efficient translocation of organic nitrogen, small peptides of two to three amino acids are posited as an important alternative to amino acids. A new transporter mediating the uptake of di- and tripeptides was isolated from Arabidopsis thaliana by heterologous complementation of a peptide transport-deficient Saccharomyces cerevisiae mutant. AtPTR1 mediated growth of S. cerevisiae cells on different di- and tripeptides and caused sensitivity to the phytotoxin phaseolotoxin. The spectrum of substrates recognized by AtPTR1 was determined in Xenopus laevis oocytes injected with AtPTR1 cRNA under voltage clamp conditions. AtPTR1 not only recognized a broad spectrum of di- and tripeptides, but also substrates lacking a peptide bond. However, amino acids, omega-amino fatty acids or peptides with more than three amino acid residues did not interact with AtPTR1. At pH 5.5 AtPTR1 had an apparent lower affinity (K-0.5 = 416 mum) for Ala-Asp compared with Ala-Ala (K-0.5 = 54 mum) and Ala-Lys (K-0.5 = 112 mum). Transient expression of AtPTR1/GFP fusion proteins in tobacco protoplasts showed that AtPTR1 is localized at the plasma membrane. In addition, transgenic plants expressing the beta-glucuronidase (uidA) gene under control of the AtPTR1 promoter demonstrated expression in the vascular tissue throughout the plant, indicative of a role in long-distance transport of di- and tripeptides.

Peptide and amino acid transporters are differentially regulated during seed development and germination in faba bean

Two peptide transporter (PTR) homologs have been isolated from developing seeds of faba bear, (Vicia faba). VfPTR1 was shown to be a functional peptide transporter through complementation of a yeast mutant. Expression patterns of VfPTR1 and VfPTR2 as well as of the amino acid permease VfAAP1 (Miranda et al., 2001) were compared throughout seed development and germination. In developing seeds, the highest levels of VfPTR1 transcripts were reached during midcotyledon development, whereas VfAAP1 transcripts were most abundant during early cotyledon development, before the appearance of storage protein gene transcripts, and were detectable until late cotyledon development. During early germination, VfPTR1 mRNA appeared first in cotyledons and later, during seedling growth, also in axes and roots. Expression of VfPTR2 and VfAAP1 was delayed compared with VfPTR1, and was restricted to the nascent organs of the seedlings. Localization of VfPTR1 transcripts showed that this FTR is temporally and spatially regulated during cotyledon development. In germinating seeds, VfPTR1 mRNA was localized in root hairs and root epidermal cells, suggesting a role in nutrient uptake from the soil. In seedling roots, VfPTR1 was repressed by a dipeptide and by an amino acid, whereas nitrate was without influence.