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This study was organised to quantify the effect of upgrading the filter efficiency in balance ventilation systems on indoor exposure to traffic-related air pollution, in 4 primary school classrooms. The standard air filters (EU F7) were compared with more efficient EU F9, and with F7+active carbon filters. Particulate matter (PM), ultrafine particles (UFP), black carbon (BC), PM2.5, organic/elemental carbon in PM2.5 (EC/OC), and NO2 were quantified, air tightness and air supply rates were assessed and pupils’ indoor comfort was surveyed. Analysis of indoor air as function of outdoor air and filter type indicated a significant but small reduction of indoor levels when upgrading the filter, except for PM10, TSP and UFP. The indoor comfort survey indicated a small but significant and positive effect as well.

Parasitic angiosperms are represented in the majority of ecosystems worldwide and are considered keystone species in many ecosystems worldwide. Parasitic plants affect population dynamics, community structure and plant diversity through (1) direct ‘parasite effects’ on the host community and (2) indirect ‘litter effects’ through the redistribution of nutrients in the ecosystem. (1) Hemiparasitic infection directly reduces host and total aboveground biomass production. If a host preference exists for dominant graminoids, hemiparasitic infection can alter the competitive balance in favour of forbs. This reduced competition may in turn increase species richness and accelerate the restoration of species-rich grasslands. (2) Most parasites shed their leaves or die of early in the season and produce high quality litter that mineralizes faster. This can enhance nutrient cycling and could indirectly reduce species richness when higher nutrient availability favours competitive species. Here we focus on the indirect effect of litter of two hemiparasitic plants (Rhinanthus angustifolius and Pedicularis sylvatica) on the composition of their host communities. In a tracer experiment we determined which co-occurring species profit most of the addition of hemiparasitic litter labelled with nitrogen-15 (15N). We found tenfold differences between species. For Rhinanthus litter, we found a significant positive relation between the N derived from the applied litter (Ndfl) and specific leaf area (SLA). We suggest that plants with a higher SLA have less root biomass (and thus less N storage), but a higher N uptake rate. Because of N stored in root biomass, plants with a lower SLA would take up relatively less N from the soil (and the added litter). Legume species have relatively low Ndfl values, which is due to biological N fixation from the air. On the other hand, saplings and dwarf shrubs have relatively high Ndfl values.

Chapitre 5.2; International audience

Growing awareness of air pollution effects on forests has, from the early 1980s on, led to intensive forest damage research and monitoring. This has fostered air pollution control, especially in Europe and North America, and to a smaller extent also in other parts of the world. At several forest sites in these regions, there are first indications of a recovery of forest soil and tree conditions that may be attributed to improved air quality. This caused a decrease in the attention paid by politicians and the public to air pollution effects on forests. But air pollution continues to affect the structure and functioning of forest ecosystems not only in Europe and North America but even more so in parts of Russia, Asia, Latin America, and Africa. At the political level, however, attention to climate change is focussed on questions of CO2 emission and carbon sequestration. But ecological interactions between air pollution including CO2 and O3 concentrations, extreme temperatures, drought, fire, insects, pathogens, and fire, as well as the impact of ecosystem management practices, are still poorly understood. Future research should focus on the interacting impacts on forest trees and ecosystems. The integrative effects of air pollution and climatic change, in particular elevated O3, altered nutrient, temperature, water availability, and elevated CO2, will be key issues for impact research. An important improvement in our understanding might be obtained by the combination of long-term multidisciplinary experiments with ecosystem-level monitoring, and the integration of the results with ecosystem modelling within a multiple-constraint framework.

Semi-natural ecosystems such as forests are exposed to higher inputs of atmospheric pollutants originating from anthropogenic sources. This increased deposition has caused changes in biogeochemical processes, which may have adverse effects on forest structure and functioning. Therefore, an accurate quantification of total atmospheric deposition is required. One widely known technique is the throughfall method, in which the amount and quality of water above and beneath the canopy are compared. Total atmospheric deposition is then quantified by a so-called canopy budget model (Draaijers and Erisman, 1995), which estimates ion-exchange reactions between the canopy and throughfall water. Although this model is applied worldwide, it has rarely been validated (Staelens et al., 2008), and dry deposition and canopy exchange of nitrogen (N) generally cannot be quantified accurately from throughfall measurements. Therefore, this study focused on the assessment of aboveground N uptake from wet deposition, which can be quantified directly by the application of 15N labelled sources. A better understanding of the direct aboveground N uptake by different tree species under varying N pollution levels may lead to an improved canopy budget model.