Different belowground responses to elevated ozone and soil water deficit in three European oak species (Quercus ilex, Q. pubescens and Q. robur).

Effects on roots due to ozone and/or soil water deficit often occur through diminished belowground allocation of carbon. Responses of root biomass, morphology, anatomy and ectomycorrhizal communities were investigated in seedlings of three oak species: Quercus ilex L., Q. pubescens Willd. and Q. robur L., exposed to combined effects of elevated ozone (ambient air and 1.4 × ambient air) and water deficit (100% and 10% irrigation relative to field capacity) for one growing season at a free-air ozone exposure facility. Effects on root biomass were observed as general reduction in coarse root biomass by -26.8% and in fine root biomass by -13.1% due to water deficit. Effect on coarse root biomass was the most prominent in Q. robur (-36.3%). Root morphological changes manifested as changes in proportions of fine root (<2 mm) diameter classes due to ozone and water deficit in Q. pubescens and due to water deficit in Q. robur. In addition, reduced fine root diameter (-8.49%) in Q. robur was observed under water deficit. Changes in root anatomy were observed as increased vessel density (+18.5%) due to ozone in all three species, as reduced vessel tangential diameter (-46.7%) in Q. ilex due to interaction of ozone and water, and as generally increased bark to secondary xylem ratio (+47.0%) due to interaction of ozone and water. Water deficit influenced occurrence of distinct growth ring boundaries in roots of Q. ilex and Q. robur. It shifted the ectomycorrhizal community towards dominance of stress-resistant species, with reduced relative abundance of Tomentella sp. 2 and increased relative abundances of Sphaerosporella brunnea and Thelephora sp. Our results provide evidence that expression of stress effects varies between root traits; therefore the combined analysis of root traits is necessary to obtain a complete picture of belowground responses.

Composition and emission of VOC from biogas produced by illegally managed waste landfills in Giugliano (Campania, Italy) and potential impact on the local population.

The composition in Volatile Organic Compounds (VOC) of the biogas produced by seven landfills of Giugliano (Naples, Campania, Italy) was determined and VOC emission rates assessed to verify if these compounds represent a potential threat to the population living nearby. VOC composition in the biogas could not be predicted, as heterogeneous waste was dumped from the late 1980s to the early 2000s and then underwent biological degradation. No data are available on the amount and composition of VOC in the biogas before the landfills closure as no operational biogas collection system was present. In this study, VOC composition was determined by gas chromatography-mass spectrometry (GC-MS), after collecting samples from collection pipes and from soil fractures in cover soil or capping. Individual VOC were quantified and data compared with those collected at two landfills in Latium, when they were still in operation. Relevant differences were observed, mainly due to waste aging, but no specific VOC revealing toxic waste dumping was found, although the concurrent presence of certain compounds suggested that dumping of industrial wastes might have occurred. The average VOC emission was assessed and a dispersion model was run to find out if the emitted plume could affect the health of population. The results suggested that fugitive emissions did not represent a serious danger, since the concentrations simulated at the neighboring cities were below the threshold limits for acute and chronic diseases. However, VOC plume could cause annoyance at night when the steady state conditions of the atmosphere enhance pollutants accumulation in the lower layers. In addition, some of the emitted VOC, such as alkylbenzenes and monoterpenes, can contribute to tropospheric ozone formation.

Testing a ratio of photosynthesis to O3 uptake as an index for assessing O3-induced foliar visible injury in poplar trees.

Visible foliar injury by ozone (ozone visible injury) is known as a biomarker to assess potential phytotoxicity of ozone. We investigated ozone visible injury in an ozone-sensitive poplar (Oxford clone) under a 2-year free-air controlled exposure (FACE) experiment and calculated three ozone indices (i.e., accumulative ozone exposure over 40 ppb during daylight hours (AOT40), phytotoxic ozone dose above a flux threshold of 0 nmol m-2 s-1 (POD0), and the cumulative value of the ratio of hourly ozone uptake to net photosynthesis (ΣU/P n ) to assess the critical level (CL) at the time of the first symptom onset of ozone visible injury. We tested the hypothesis that ozone injury depends both on the amount of ozone entering a leaf and on the capacity for biochemical detoxification or repair with photosynthesis as a proxy. The CLs at the time of the first symptom onset of ozone visible injury were 19 ppm h for AOT40, 26 mmol m-2 for POD0, and 1.2 mol mol-1 for ΣU/P n in Oxford clone at the ozone FACE experiment. Our findings were then verified by 4-year observation-based data in central Italy on Oxford clone and white poplar (Populus alba L.). These observation-based data indicated that we found ozone visible injury in Oxford clone even though AOT40 was relatively low (11.7 ppm h). On the other hand, when values of POD0 and ΣU/P n exceeded over the CLs, the occurrence of initial symptoms in Oxford clone was shown. White poplar did not show ozone visible injury. ΣU/P n of white poplar at the field sites reached ~1.0 mol mol-1 (less than the CL = 1.2 mol mol-1, which was obtained from O3 FACE) during May-September, although the values of POD0 were relatively high in white poplar (44-47 mmol m-2 during May-September). The result implies that ozone injury may have occurred in poplars when stomatal ozone flux exceeded the critical range of tolerance due to the assimilate shortage for repair and defense against ozone stress.

How Does the Amount and Composition of PM Deposited on Platanus acerifolia Leaves Change Across Different Cities in Europe?

Particulate matter (PM) deposited on Platanus acerifolia tree leaves has been sampled in the urban areas of 28 European cities, over 20 countries, with the aim of testing leaf deposited particles as indicator of atmospheric PM concentration and composition. Leaves have been collected close to streets characterized by heavy traffic and within urban parks. Leaf surface density, dimensions, and elemental composition of leaf deposited particles have been compared with leaf magnetic content, and discussed in connection with air quality data. The PM quantity and size were mainly dependent on the regional background concentration of particles, while the percentage of iron-based particles emerged as a clear marker of traffic-related pollution in most of the sites. This indicates that Platanus acerifolia is highly suitable to be used in atmospheric PM monitoring studies and that morphological and elemental characteristics of leaf deposited particles, joined with the leaf magnetic content, may successfully allow urban PM source apportionment.

A new-generation 3D ozone FACE (Free Air Controlled Exposure).

To artificially simulate the impacts of ground-level ozone (O3) on vegetation, ozone FACE (Free Air Controlled Exposure) systems are increasingly recommended. We describe here a new-generation, three-dimensional ozone FACE, with O3 diffusion through laser-generated micro-holes, pre-mixing of air and O3, O3 generator with integral oxygen generator, continuous (day/night) exposure and full replication. Based on three O3 levels and assumptions on the pre-industrial O3 levels, we describe principles to calculate relative yield/biomass and estimate impacts even at lower-than-ambient O3 levels. The case study is called FO3X, and is at present the only ozone FACE in Mediterranean climate and one of the very few ozone FACEs investigating more than one stressor at a time. The results presented here will give further impulse to the research on O3 impacts on vegetation all over the world.

Determinants of stomatal sluggishness in ozone-exposed deciduous tree species.

Our knowledge of ozone effects on dynamic stomatal response is still limited, especially in Asian tree species. We thus examined ozone effects on steady-state leaf gas exchange and stomatal dynamics in three common tree species of China (Ailanthus altissima, Fraxinus chinensis and Platanus orientalis). Seedlings were grown and were exposed to three levels of ozone in open-top chambers (42, 69, 100 nmol mol(-1) daylight average, from 09:00 to 18:00). At steady-state, ozone exposure induced an uncoupling of photosynthesis and stomatal conductance, as the former decreased while the latter did not. Dynamic stomatal response was investigated by cutting the leaf petiole after a steady-state stomatal conductance was reached. Ozone exposure increased stomatal sluggishness, i.e., slowed stomatal response after leaf cutting, in the following order of sensitivity, F. chinensis>A. altissima>P. orientalis. A restriction of stomatal ozone flux reduced the ozone-induced sluggishness in P. orientalis. The ozone-induced impairment of stomatal control was better explained by stomatal ozone flux per net photosynthesis rather than by stomatal ozone flux only. This suggests that ozone injury to stomatal control depends both on the amount of ozone entering a leaf and on the capacity for biochemical detoxification or repair. Leaf mass per area and the density of stomata did not affect stomatal sluggishness.