Chemical composition of vegetation along urbanisation gradients in two European cities.

Accumulation of particulate matter (PM) and metals on leaves of three deciduous woody species was studied along urbanisation gradients in Stavanger and Warsaw. Differences between rural and urban sites explained most of the observed variation in leaf chemistry, followed by differences between regions. Highest leaf accumulation of elements was found in Warsaw, but also composition of elements differed between the cities. Overall, species showed similar patterns of element accumulation, but differed in accumulation of specific elements. These differences could in part be explained by differences in epicuticular waxes and PM accumulation. Expected source of elements and their chemical characteristics did not explain the observed accumulation patterns. A better differentiation between elements taken up from soil and air would be required for his. Species specific accumulation of elements has to be taken into consideration using leaf samples for biomonitoring.

Particulate Matter deposition on Quercus ilex leaves in an industrial city of central Italy.

A number of studies have focused on urban trees to understand their mitigation capacity of air pollution. In this study particulate matter (PM) deposition on Quercus ilex leaves was quantitatively analyzed in four districts of the City of Terni (Italy) for three periods of the year. Fine (between 0.2 and 2.5 µm) and Large (between 2.5 and 10 µm) PM fractions were analyzed. Mean PM deposition value on Quercus ilex leaves was 20.6 µg cm(-2). Variations in PM deposition correlated with distance to main roads and downwind position relatively to industrial area. Epicuticular waxes were measured and related to accumulated PM. For Fine PM deposited in waxes we observed a higher value (40% of total Fine PM) than Large PM (4% of total Large PM). Results from this study allow to increase our understanding about air pollution interactions with urban vegetation and could be hopefully taken into account when guidelines for local urban green management are realized.

Accumulation of particulate matter and trace elements on vegetation as affected by pollution level, rainfall and the passage of time.

Particulate matter is harmful to human health. To reduce its concentration in air, plants could be used as biological filters, accumulating particulate matter on their foliage. In a study carried out at three sites with differing pollution levels and exposure to precipitation, the capacity of evergreen species (Taxus baccata L., Hedera helix L. and Pinus sylvestris L.) to accumulate particulate matter and trace elements from ambient air in urban areas was investigated. The effects of rainfall and the passage of time on particulate matter deposition on foliage were also determined. The results showed that foliage accumulated an increasing quantity of particulate matter in successive months, but the actual amount of particulate matter and trace elements accumulated differed considerably between sites and plant species. The greatest accumulation of air pollutants occurred on the foliage of plants protected from the rain at a site exposed to traffic related pollution and the smallest accumulation at a rural site. Among the species analysed, the deposited mass of particulate matter and trace elements was the greatest on P. sylvestris. In all species, precipitation removed a considerable proportion of particles accumulated on foliage. Most of the removed particulate matter was large size fraction, but little belong to the smallest size fraction. These results showed that both, the dynamics of deposition and leaf washing by rain during the season need to be considered when evaluating the total effect of vegetation in pollutant remediation.

Plant species differences in particulate matter accumulation on leaf surfaces.

Particulate matter (PM) accumulation on leaves of 22 trees and 25 shrubs was examined in test fields in Norway and Poland. Leaf PM in different particle size fractions (PM(10), PM(2.5), PM(0.2)) differed among the species, by 10- to 15-folds at both test sites. Pinus mugo and Pinus sylvestris, Taxus media and Taxus baccata, Stephanandra incisa and Betula pendula were efficient species in capturing PM. Less efficient species were Acer platanoides, Prunus avium and Tilia cordata. Differences among species within the same genus were also observed. Important traits for PM accumulation were leaf properties such as hair and wax cover. The ranking presented in terms of capturing PM can be used to select species for air pollution removal in urban areas. Efficient plant species and planting designs that can shield vulnerable areas in urban settings from polluting traffic etc. can be used to decrease human exposure to anthropogenic pollutants.

His-Asp phosphotransfer possibly involved in the nitrogen signal transduction mediated by cytokinin in maize: molecular cloning of cDNAs for two-component regulatory factors and demonstration of phosphotransfer activity in vitro.

Implication of His-to-Asp and/or Asp-to-His (His-Asp) phosphorelay has been recently reported in signal transduction pathways initiated by ethylene and cytokinin. These signaling systems are generally composed of sensor His-protein kinases, His-containing phosphotransfer (HPt) domains, and response regulator domains. In this study, we isolated maize cDNAs, designated as ZmRR2 and ZmHP2, which encode a response regulator domain and HPt domain, respectively, and we identified their His-to-Asp phosphotransfer activity in vitro. The putative translated product of ZmRR2 was highly similar to that of ZmRR1 (78% identity), a maize response regulator homologue. The putative translated product of ZmHP2 showed similarity to that of HPt domains from Arabidopsis thaliana (AHP1-AHP3: 44 to 47% identity) and Saccharomyces cerevisiae (Ypdlp: 24% identity). In vitro experiments demonstrated that the putative signaling factors can transfer the phosphoryl group from His-80 of ZmHP2 to Asp-90 of ZmRRs. Treating detached leaves with t-zeatin or supplying inorganic nitrogen to the whole plant induced the accumulation of ZmRR1 and ZmRR2 transcripts. On the other hand, the steady-state transcript level of ZmHP2 was not affected by cytokinin or inorganic nitrogen sources. These results indicate that His-Asp phosphotransfer may be involved in the transduction of nitrogen signals mediated by cytokinin, and that multiple response regulators participate in the signaling pathways.