The polycyclic aromatic hydrocarbons (PAHs) located on the epidermal tissues showed distinctive toxic effects to root, while the retention and distribution of PAHs on mangrove seedlings poorly understood. Our results confirmed that the partition coefficients (Kf) of the PAHs retained on the epidermal tissue of mangrove roots, such as Kandelia obovata, Avicennia marina and Aegiceras corniculatum, were much higher than the Poaceae plants roots, for example wheat and maize (Wild et al., 2005). Moreover, to the parent and alkyl PAHs, a well negative correlation was observed between the surface polarity of these three species of mangrove root and the Kf values (p < 0.05). To the N/O/S containing PAHs, these relationships were not obviously due to existing of the π-π, n-π interactions and hydrogen bonding between the N/O/S-containing PAHs and epidermal tissues. The PAHs retained on these three species of mangrove root epidermal tissues formed larger clusters than that of on Poaceae plants, such as wheat and maize (Wild et al., 2005) due to the limitation of the suberization of the root exodermis and endodermis. After exposure of 30 d, rhizo- and endophytic bacteria degraded parts of the N/O/S-containing PAHs to medium-lifetime fluorescence substances. To our knowledge, this is the first time to assess the retention of PAHs on the epidermal tissue of mangrove root, which will improve our understanding of the root uptake PAHs process.

A large increase of grasses Calamagrostis epigejos, Bromus inermis and Brachypodium pinnatum has often been observed in many regions enriched by higher nitrogen (N) wet deposition inputs. Competitive relationships between these grasses under enhanced N loads have not yet been studied. Therefore an outdoor experiment was established which involved monocultures of Calamagrostis, Bromus and Brachypodium and their 1:1 mixtures in containers under two N treatments, i.e., unfertilized and fertilized (+50 kg N ha⁻¹). In monocultures, the total aboveground biomass of Calamagrostis, Bromus and Brachypodium were 1.1, 3.6 and 2.5 times higher respectively due to enhanced N fertilization. Relative crowding and aggressivity coefficients indicate that Calamagrostis and Bromus dominate when mixed with Brachypodium at both levels of N availability. When mixed with Bromus, Calamagrostis is the poorer competitor at lower N loads, however, it can be dominating in N fertilized treatments.

Nitrous oxide (N₂O) emissions from Phragmites australis (reed) – dominated zones in Baiyangdian Lake, the largest shallow lake of Northern China, were investigated under different hydrological conditions with mesocosm experiments during the growing season of reeds. The daily and monthly N₂O emissions were positively correlated with air temperature and the variation of aboveground biomass of reeds (p < 0.05), respectively. The N₂O emissions from reeds were about 45.8–52.8% of that from the sediments. In terms of the effect of hydrological conditions, N₂O emissions from the aquatic-terrestrial ecotone were 9.4–26.1% higher than the submerged zone, inferring that the variation of water level would increase N₂O emissions. The annual N₂O emission from Baiyangdian Lake was estimated to be about 114.2 t. This study suggested that N₂O emissions from shallow lakes might be accelerated by the climate change as it has increased air temperature and changed precipitation, causing the variation of water level.

The effect of atmospheric nitrogen deposition on the species richness of acid grasslands was investigated by combining data from a large Danish monitoring program with a large European data set, where a significant non-linear negative effect of nitrogen deposition had been demonstrated (Stevens et al., 2010). The nitrogen deposition range in Denmark is relatively small and when only considering the Danish data a non-significant decrease in the species richness with nitrogen deposition was observed. However, when both data sets were combined, then the conclusion of the European survey was further corroborated by the results of the Danish monitoring. Furthermore, by combining the two data sets a more comprehensive picture of the threats to the biodiversity of acid grasslands emerge; i.e., species richness in remnant patches of acid grassland in intensively cultivated agricultural landscapes is under influence not only from nitrogen deposition, but also from current and historical land use.

In this pilot-scale constructed wetland (CW) study for treating groundwater contaminated with benzene, MTBE, and ammonia-N, the performance of two types of CWs (a wetland with gravel matrix and a plant root mat) was investigated. Hypothesized stimulative effects of filter material additives (charcoal, iron(III)) on pollutant removal were also tested. Increased contaminant loss was found during summer; the best treatment performance was achieved by the plant root mat. Concentration decrease in the planted gravel filter/plant root mat, respectively, amounted to 81/99% for benzene, 17/82% for MTBE, and 54/41% for ammonia-N at calculated inflow loads of 525/603 mg/m²/d, 97/112 mg/m²/d, and 1167/1342 mg/m²/d for benzene, MTBE, and ammonia-N. Filter additives did not improve contaminant depletion, although sorption processes were observed and elevated iron(II) formation indicated iron reduction. Bacterial and stable isotope analysis provided evidence for microbial benzene degradation in the CW, emphasizing the promising potential of this treatment technique.

Biomass burning as fuel in the traditional grass-roofed rural households of Western Province of Kenya in open fire places, in poorly ventilated conditions, lead to accumulation of soot under the roofs. This study characterized and quantified the polycyclic aromatic hydrocarbons (PAHs) in accumulated soot in these households and determined the variation in PAHs concentrations with fuel biomass type. Soot samples collected from the households were extracted, cleaned and analysed by gas chromatography. The PAHs were identified using retention times, verified by gas chromatographic mass spectral analysis and quantified from peak area responses using the internal standard method. The PAHs levels significantly varied (P≤0.05) with biomass type in the order: dung≥indigenous trees≥exotic trees≥shrubs and crop residues. Use of dung and wood from indigenous trees as fuel should be discouraged since they are higher emitters (P≤0.05) of carcinogenic PAHs.

Few studies have investigated effects of increased background ozone in the absence of episodic peaks, despite a predicted increase throughout the northern hemisphere over the coming decades. In this study Leontodon hispidus was grown with Anthoxanthum odoratum or Dactylis glomerata and exposed in the UK to one of eight background ozone concentrations for 20 weeks in solardomes. Seasonal mean ozone concentrations ranged from 21.4 to 102.5 ppb. Ozone-induced senescence of L. hispidus was enhanced when grown with the more open canopy of A. odoratum compared to the denser growing D. glomerata. There was increased cover with increasing ozone exposure for both A. odoratum and D. glomerata, which resulted in an increase in the grass:Leontodon cover ratio in both community types. Carry-over effects of the ozone exposure were observed, including delayed winter die-back of L. hispidus and acceleration in the progression from flowers to seed-heads in the year following ozone exposure.

Effects of high atmospheric nitrogen-deposition partly depend on availability of phosphate. Lime-poor, but iron-rich dune grasslands are supposedly protected from grass-encroachment, due to P-fixation in iron phosphate. However, in iron-rich Dutch hinterdunes, dunes have low, but dry former beach plains high grass-encroachment. To test whether these zones differ in nutrient availability, and whether this changed with duration of grass-encroachment, we measured net N-mineralization, microbial characteristics and different fractions of P and Fe from pioneer and shortgrass to tallgrass stages approximately 10, 20 and >25 years old. N-mineralization did not differ between zones, but increased in older tallgrass stages in the organic layer. P-availability was significantly lower in the low grass-encroachment zone, with SOM values below 3% and mineral Fe above 40% allowing for P-fixation in iron phosphates. In the high grass-encroachment zone, however, P-availability increased, because SOM increased and Fe became incorporated in organic matter complexes, with more reversible P-sorption. Iron-rich dune grasslands may be protected from high N-deposition and grass-encroachment only when SOM is low, because only then P-fixation in iron phosphates occurs.

The deposition of high levels of reactive nitrogen (N) and sulphur (S), or the legacy of that deposition, remain among the world's most important environmental problems. Although regional impacts of acid deposition in aquatic ecosystems have been well documented, quantitative evidence of wide-scale impacts on terrestrial ecosystems is not common. In this study we analysed surface and subsoil chemistry of 68 acid grassland sites across the UK along a gradient of acid deposition, and statistically related the concentrations of exchangeable soil metals (1 M KCl extraction) to a range of potential drivers. The deposition of N, S or acid deposition was the primary correlate for 8 of 13 exchangeable metals measured in the topsoil and 5 of 14 exchangeable metals in the subsoil. In particular, exchangeable aluminium and lead both show increased levels above a soil pH threshold of about 4.5, strongly related to the deposition flux of acid compounds. S and N deposition contribute to regional-scale soil acidification and metal mobilisation.

Loss of nitrogen from the soil-plant system has raised environmental concern. This study assessed the fluxes of nitrous oxide (N2O) in the subsurface flow constructed wetlands (CWs). To better understand the mechanism of N2O emission, spatial distribution of ammonia-oxidizing bacteria (AOB) in four kinds of wetlands soil were compared. N2O emission data showed large temporal and spatial variation ranging from -5.5 to 32.7 mg N2O m-2 d-1. The highest N2O emission occurred in the cell planted with Phragmites australis and Zizania latifolia. Whereas, the lower emission rate were obtained in the cell planted with P. australis and Typha latifolia. These revealed that Z. latifolia stimulated the N2O emission. Transportation of more organic matter and oxygen for AOB growth may be the reason. The study of AOB also supported this result, indicating that the root structure of Z. latifolia was favored by AOB for N2O formation. Zizania latifolia has a large contribution to global warming.