Contrasted spatial and long-term trends in precipitation chemistry and deposition fluxes at rural stations in France

The long-distance effect of atmospheric pollution on ecosystems has led to the conclusion of international agreements to regulate atmospheric emissions and monitor their impact. This study investigated variations in atmospheric deposition chemistry in France using data gathered from three different monitoring networks (37 stations) over the period from 1995 to 2007. Despite some methodological differences (e.g. type of collector, frequency of sampling and analysis), converging results were found in spatial variations, seasonal patterns and temporal trends. With regard to spatial variations, the mean annual pH in particular ranged from 4.9 in the north-east to 5.8 in the south-east. This gradient was related to the concentration of NO3- and non-sea-salt SO42- (maximum volume-weighted mean of 38 and 31 µeq l-1 respectively) and of acid-neutralising compounds such as non-sea-salt Ca2+ and NH4+ In terms of seasonal variations, winter and autumn pH were linked to lower acidity neutralisation than during the warm season. The temporal trends in atmospheric deposition varied depending on the chemical species and site location. The most significant and widespread trend was the decrease in non-sea-salt SO42- concentrations (significant at 65% of the stations). At the same time, many stations showed an increasing trend in annual pH (+0.3 on average for 16 stations). These two trends are probably due to the reduction in SO2 emissions that has been imposed in Europe since the 1980s. Temporal trends in inorganic N concentrations were rather moderate and not consistent with the trends reported in emission estimates. Despite the reduction in NOx emissions, NO3- concentrations in atmospheric deposition remained mostly unchanged or even increased at three stations (+0.43 meq l-1 yr-1 on average). In contrast NH4+ concentrations in atmospheric deposition decreased at several stations located in western and northern areas, while the estimates of NH3 emissions remained fairly stable. The decrease in non-sea-salt SO42- and NH4+ concentrations was mainly due to a decrease in summer values and can in part be related to a dilution process since the precipitation amount showed an increasing trend during the summer. Furthermore, increasing trends in NO3- concentrations in the spring and, to a lesser extent, in NH4+ concentrations suggested that other atmospheric physicochemical processes should also be taken into account

Composition chimique des dépôts atmosphériques à l’horizon 2020-2040

Les dépôts atmosphériques peuvent causer des dommages importants aux milieux naturels. Des mesures à long terme issues de la surveillance des dépôts atmosphériques en France ont été exploitées pour construire un modèle statistique prévisionnel afin d'estimer les changements de la composition chimique des dépôts atmosphériques à l'horizon 2020-2040. À partir de simulations d'évolutions possibles du climat et des émissions de polluants atmosphériques, les dépôts de sulfate non marin et les dépôts d'ammonium sont susceptibles de diminuer, mais ceux de nitrate pourraient augmenter de façons diverses selon les régions. Le changement des variations saisonnières de pluviométrie pourrait augmenter les flux de dépôts

MASTREE+: Time-series of plant reproductive effort from six continents.

Significant gaps remain in understanding the response of plant reproduction to environmental change. This is partly because measuring reproduction in long-lived plants requires direct observation over many years and such datasets have rarely been made publicly available. Here we introduce MASTREE+, a data set that collates reproductive time-series data from across the globe and makes these data freely available to the community. MASTREE+ includes 73,828 georeferenced observations of annual reproduction (e.g. seed and fruit counts) in perennial plant populations worldwide. These observations consist of 5971 population-level time-series from 974 species in 66 countries. The mean and median time-series length is 12.4 and 10 years respectively, and the data set includes 1122 series that extend over at least two decades (≥20 years of observations). For a subset of well-studied species, MASTREE+ includes extensive replication of time-series across geographical and climatic gradients. Here we describe the open-access data set, available as a.csv file, and we introduce an associated web-based app for data exploration. MASTREE+ will provide the basis for improved understanding of the response of long-lived plant reproduction to environmental change. Additionally, MASTREE+ will enable investigation of the ecology and evolution of reproductive strategies in perennial plants, and the role of plant reproduction as a driver of ecosystem dynamics

Scots pine responses to number and density of inoculation points with Leptographium wingfieldii Morelet, a bark beetle-associated fungus

The effects of different densities and total distribution of inoculation points with Leptographium wingfieldii, a fungus associated with the bark beetle Tomicus piniperda, were investigated in Scots pine (Pinus sylvestris). During April 1993, 40 8-year-old Scots pine trees were inoculated into the trunk and until the cambium, at breast height. Inoculation points were distributed over a circular belt of 20, 40, 70 and 100 cm width, at two densities (200 and 400 m -2). Three months after inoculation, the average length of the induced reaction zone was recorded on the external side of the phloem. The fraction of sapwood section that appeared blue-stained, desiccated or soaked with resin was also measured. The length of the visible, induced reaction zone in the phloem was affected neither by inoculation density nor by width of the inoculation belt. Similarly, the fraction area of damaged sapwood was small and constant at 200 m-2. It increased significantly only at the highest density (400 m-2) as a function of belt width, reaching 70 % at 100-cm width. It is concluded that: i) the average length of the induced reaction zone in the phloem is insensitive to inoculation density, and ii) the importance of damage in the sapwood is increasing only at inoculation densities above 400 m-2 over a sufficiently large area. This result is discussed in relation to the physiological meaning of the different symptoms, and in relation to the concept of threshold of attack density to explain why pine trees are affected only when the density of bark beetle attacks overrides this limit. (© Inra/Elsevier, Paris.)Réponses du pin sylvestre à la densité et au nombre de points d'inoculation réalisés avec Leptographium wingfieldii Morelet, un champignon associé aux scolytes. Les effets de la densité d'inoculation avec Leptographium wingfieldii (un champignon associé au scolyte Tomicus piniperda) et de l'augmentation du nombre de points d'inoculation, ont été étudiés sur le pin sylvestre (Pinus sylvestris). En avril 93, quarante pins sylvestres âgés de 8 ans ont été inoculés dans le tronc à 1,30 m. Les inoculations étaient réparties sur des ceintures de 20, 40, 7Q ou 100 cm de largeur, avec deux densités (200 et 400 m-2). Trois mois après inoculation, la longueur des zones de réaction induites a été mesurée sur le côté externe du liber. Les fractions de section d'aubier bleui, desséché, ou imprégné de résine ont également été mesurées. La longueur de la zone de réaction visible dans le liber n'a été affectée ni par la densité d'inoculation, ni par la largeur des ceintures d'inoculations. De la même manière, la fraction d'aubier affectée est restée faible et constante à 200 inoculations m-2. En revanche, elle a augmenté de manière très importante en fonction de la largeur de ceinture d'inoculation pour la densité d'inoculation de 400 m-2; 70 % de surface d'aubier étant affecté pour une ceinture de 100 cm de largeur. Deux conclusions sont déduites de ces résultats : i) la longueur de la zone de réaction induite dans le liber ne dépend pas de la densité d'inoculation, et ii) l'importance des dégâts dans l'aubier augmente uniquement pour des densités d'inoculations au dessus de 400 m-2 et des ceintures d'inoculations suffisamment larges. Ce résultat est discuté en fonction de la signification physiologique des différents symptômes, et en fonction du concept de seuil critique de densité d'attaque, pour tenter d'expliquer pourquoi la survie des pins est affectée uniquement quand la densité d'attaques de scolytes dépasse cette limite. (© Inra/Elsevier, Paris.

La réduction des émissions polluantes se répercute-t-elle pleinement dans les retombées atmosphériques de soufre et d'azote en France ?

National audienc

La réduction des émissions polluantes se répercute-t-elle pleinement dans les retombées atmosphériques de soufre et d'azote en France ? Rendez-vous techniques de l’ONF. N° Spécial, n°4, « RENECOFOR 25 ans de suivi des écosystèmes forestiers, bilans et perspectives », 72-76, p. 189.

National audienc

Assessing the roles of temperature, carbon inputs and airborne pollen as drivers of fructification in European temperate deciduous forests

International audienceWe aimed at identifying which drivers control the spatio-temporal variability of fruit production in three major European temperate deciduous tree species: Quercus robur, Quercus petraea, and Fagus sylvatica. • We analysed the relations of fruit production with airborne pollen, carbon and water resources and meteorological data in 48 French forests over 14 years (1994-2007). • In oak, acorn production was mainly related to temperature conditions during the pollen emission period, supporting the pollen synchrony hypothesis. In beech, a temperature signal over the two previous years eclipsed the airborne pollen load. • Fruit production in Quercus and Fagus was related to climate drivers, carbon inputs and airborne pollen through strongly non-linear, genus-specific relations. • Quercus and Fagus also differed as regards the secondary growth vs. fructification trade-off. While negative relationships were observed between secondary growth and fruit production in beech, more productive years benefited to both secondary growth and reproductive effort in oak

Fungal community composition predicts forest carbon storage at a continental scale

Forest soils harbor hyper-diverse microbial communities which fundamentally regulate carbon and nutrient cycling across the globe. Directly testing hypotheses on how microbiome diversity is linked to forest carbon storage has been difficult, due to a lack of paired data on microbiome diversity and in situ observations of forest carbon accumulation and storage. Here, we investigated the relationship between soil microbiomes and forest carbon across 238 forest inventory plots spanning 15 European countries. We show that the composition and diversity of fungal, but not bacterial, species is tightly coupled to both forest biotic conditions and a seven-fold variation in tree growth rates and biomass carbon stocks when controlling for the effects of dominant tree type, climate, and other environmental factors. This linkage is particularly strong for symbiotic endophytic and ectomycorrhizal fungi known to directly facilitate tree growth. Since tree growth rates in this system are closely and positively correlated with belowground soil carbon stocks, we conclude that fungal composition is a strong predictor of overall forest carbon storage across the European continent