Nitrogen:sulphur ratio alters competition between Trifolium repens and Lolium perenne under cutting: Production and competitive abilities

Grasslands species, like others crops, no longer benefit from high atmospheric sulphur deposition. This may cause sulphur limitation and in turn may induce a shift in plant communities by altering species performance and competitive abilities. To test this hypothesis, a greenhouse pot experiment was designed to investigate the interacting effects of sulphur (S) and nitrogen (N) availability on production, morphology and competitive abilities of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.). Plants were grown in monocultures and mixtures during 4 months. They were supplied with combinations of three levels of S and three levels of N and subjected to three defoliation events. Both S and N gradients altered plants performance and modulated competitive interactions. In L. perenne, above- and below-ground dry matter production, leaf and tiller number and contribution to mixture DM production were little affected by S, but highly by N. For T. repens, these traits were significantly increased by S, but only slightly by N. At establishment, T. repens was subjected to a significant interspecific competition at low N–low S and high N–high S. But at regrowth (cuts 2 and 3), T. repens was much more affected by intra- than interspecific competition. L. perenne was only sensitive to competition (intraspecific) when N supply was combined with no or moderate S supply. We conclude that N:S ratio of soil appears to drive species production, morphology and competitive abilities, which in turn affect leguminous–gramineous species ratio and grassland plant community structure. Since the growth of T. repens was significantly reduced in low S treatments, our results suggest that the drastic fall in atmospheric sulphur deposition could restrict leguminous species in high N soil conditions.     

Transmission of a pestivirus infection in a population of Pyrenean chamois

Outbreaks of a previously unrecorded disease have recently affected Pyrenean chamois (Rupicapra pyrenaica pyrenaica) populations across the mountain range. A pestivirus was hypothesized to be the cause of this emerging disease and this type of virus can cross the species barrier and be transmitted to or from wildlife. Using an epidemiological survey conducted from 1995 to 2004 at Orlu, France, we characterized the virus and analyzed its transmission. A phylogenetic analysis of viral sequences and virus neutralization tests showed that the virus belonged to the newly described border disease virus-4 group. The increase of seroprevalence with age indicated that infection can occur at any age and resulted in lifelong immunity. Overall, 70.3% of 323 samples were positive for anti-p80 antibodies and 10.2% of 167 samples showed viremia, as demonstrated by either positive ELISA antigen test or RT-PCR. Infection has thus been widespread in this population since 1995, whereas no mass mortality or clinical signs have been observed. Incidence and seroprevalence varied seasonally and according to number of individuals aged less than 2 years old in the population, so viral transmission was dependent on host population age structure. We propose that the virus is now endemic in this population and is likely detrimental for reproduction and juveniles. Further investigation is needed to estimate the impact of pestivirus on host population dynamics and the risk of cross-transmission to farm animals.     

LTSER platforms as a place-based transdisciplinary research infrastructure: learning landscape approach through evaluation

Landscape Ecology - Place-based transdisciplinary research involves multiple academic disciplines and non-academic actors. Long-Term Socio-Ecological Research (LTSER) platform is one concept with ~...