International audience | Evidence from an international survey in the Atlantic biogeographic region of Europe indicates that chronic nitrogen deposition is reducing plant species richness in acid grasslands. Across the deposition gradient in this region (2–44 kg N ha−1 yr−1) species richness showed a curvilinear response, with greatest reductions in species richness when deposition increased from low levels. This has important implications for conservation policies, suggesting that to protect the most sensitive grasslands resources should be focussed where deposition is currently low. Soil pH is also an important driver of species richness indicating that the acidifying effect of nitrogen deposition may be contributing to species richness reductions. The results of this survey suggest that the impacts of nitrogen deposition can be observed over a large geographical range. Atmospheric nitrogen deposition is reducing biodiversity in grasslands across Europe.

The replenishment and persistence of marine species is contingent on dispersing larvae locating suitable habitat and surviving to a reproductive stage. Pelagic larvae rely on environmental cues to make behavioural decisions with chemical information being important for habitat selection at settlement. We explored the sensory world of crustaceans and fishes focusing on the impact anthropogenic alterations (ocean acidification, red soil, pesticide) have on conspecific chemical signals used by larvae for habitat selection. Crustacean (Stenopus hispidus) and fish (Chromis viridis) larvae recognized their conspecifics via chemical signals under control conditions. In the presence of acidified water, red soil or pesticide, the ability of larvae to chemically recognize conspecific cues was altered. Our study highlights that recruitment potential on coral reefs may decrease due to anthropogenic stressors. If so, populations of fishes and crustaceans will continue their rapid decline; larval recruitment will not replace and sustain the adult populations on degraded reefs.

Depuis plus de 10 ans, les charges critiques ont été à la base des négociations internationales pour la réduction de la pollution atmosphérique. Les calculs de charges critiques d'acidité reposent sur l'estimation d'un flux de cations issu de l'altération des minéraux du sol et de la roche et sur un drainage acceptable de protons et d'aluminium. Les charges critiques d'acidité ont été calculées puis cartographiées au 1/1 000 000 pour les écosystèmes forestiers français. La carte obtenue résulte de la combinaison de données pédologiques, géochimiques, climatiques et de données minéralogiques extrapolées à partir d'un nombre limité de sites de référence (issus entre autres du réseau RENECOFOR). Pour la France, les charges critiques d'acidité sont faibles (moins de 1,0 keq/ha/an) pour moins de 15 pour cent des forêts françaises de production, soit 17 000 km2. Les surfaces où les charges critiques sont dépassées se situent principalement dans le nord-est de la France : Vosges, Ardennes, et dans une moindre mesure dans le sud-ouest de l'Ile-de-France et le long des bordures du Massif central, en Bretagne et en Normandie

To investigate the consequences of acidification and metal accumulation on the biology of aquatic bryophytes, the acid-tolerant liverwort Scapania undulata (L.) Dum. and the acid-sensitive moss Rhynchostegium riparioides (Hedw.) Cardot were transplanted from one stream to two other streams of differing acidity (pH 5.20 and 6.38). The bryophytes were collected in a circumneutral (pH 6.57) stream in the Vosges Mountains. Metal accumulation was semiquantitatively measured in shoots by energy dispersive TEM X-ray spectroscopy (EDXS). After 1 month, the two species remained green without alteration signs. Although no marked ultrastructural damage was observed in either species, some cells seemed to be necrotic, with flattened chloroplasts, in R. riparioides. Lipid droplet accumulation was observed in some leaf cells of S.undulata when transplanted to the most acidic stream. Metal was mostly localised in the cell wall, and was only sometimes detected in small vacuoles. Under acidic conditions, R. riparioides showed the highest relative amount of Al and the lowest amount of Fe, whereas the acid-tolerant bryophyte species S. undulata contained more Fe and less Al. The capability to limit the uptake of metals into the cytoplasm varies according to the bryophyte species. This could be an explanation of the tolerance of S. undulata to acidification. | International audience