Partners and International Organizations
(English)
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A, B, BG, CY, CZ, DK, FIN, F, D, GR, H, IRL, I, NL, N, PL, P, RO, SK, E, S, CH, GB
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Abstract
(English)
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Thirty two model ecosystems were established in April 2000 with deciduous trees, Pices abies, and understory plants in 16 large OTCs, each split in a acidic and a calcareous subsoil compartment and twenty model ecosystems in field plots (FPs) with acidic subsoil. Four treatments were applied: control (CO), heavy metals (HM) with 2700 Zn, 385 Cu, 63 Pb and 10 Cd mg/kg, acid rain (AR), and their combination (HMAR). Visible leaf symptoms induced in Populus tremula (juvenile leaf morphology) by the HM appeared as light-green stipples on the adaxial leaf side and developed to leaf edge necroses, allowing a symptom rating scale. The slower growing young Betula pendula and Acer pseudoplatanus only developed clear visible leaf symptoms in the third year. Cell wall reactions were observed along the pathway of HM from the veins through the leaf blade. They included cell wall thickenings, protrusions and inlays of polyphenolics all indicative of extra cellular oxidative stress. Inside the cells, the changes suggested an acceleration of cell senescence. Discrete groups of necrotic cells in the assimilative tissue surrounded by degenerating cells filled with antioxidative compounds including proanthocyanidines indicated the induction of the plant defences resulting in a frequent plant reaction called the 'hypersensitive-like response'. Total content of phenolic substances and proanthocyanidine were significantly increased in leaves of P. tremula from the HM treatment vs. the control. The cellular symptoms together with the development of a microscopical method to visualise Zn in plant tissues will in future allow us to differentiate HM effects from that of other stress factors. Transpiration, like photosynthesis, was significantly increased by the HM treatment in the leaves of Salix viminalis, but decreased in those of P. tremula and P. abies. P. abies with a low rooting system showed a physiological avoidance of HM by reducing water uptake (or root injury), whereas S. viminalis partly avoided the HM in the topsoil by forming a deeper rooting system. In all species, including understory plants, HM concentrations were significantly increased for the HM treatment vs. CO, in the leaves/needles as well as in the wood (on average a third of the leaf conc.) with large interspecific differences. The species rating was different for Zn and Cd concentration in the HM treatment (P. tremula Zn 1050, Cd 9.5 > S. viminalis > T. vulgare > C. sylvatica > P. abies Zn 110, Cd < 0.6 mg/kg) vs. Cu (T. vulgare Cu 26 > C. sylvatica > P. tremula > S. viminalis > P. abies Cu 4.5 mg/kg) and for FP < OTC. Pb was below the detection limit of 3 mg/kg. On a model ecosystem level total Zn extraction in the first year in above ground plant parts reached a maximum of 1g in the FPs HM treatment. As expected in the first year of a reafforested system, the light demanding understory plants were dominating the extraction process. The effect of the AR was negligible whereas the subsoil acidity modified HM uptake and growth parameters. When only considering the tree biomass per model ecosystem, more HM were taken up in the OTCs acidic subsoil (500 mg) than in the FPs (180mg), and AR became a significantly modifying factor for HM uptake in P. tremula and in P. abies wood. Compared to Zn, Cu was less mobile in the topsoil and less extracted by the plants in the first year (2000). Given a roughly initial Zn:Cu content of 7:1 in the HM treatment, the resulting total uptake in aboveground biomass per model ecosystems was about 20:1 respectively. Most Cu (42 mg per FP) was extracted by the understory plants. In the second year stem diameter increment per inidvidual tree was significantly decreased in trees under heavy metal influence particularly on acidic subsoil. Aboveground biomass was increased on calcareous subsoil for deciduous trees and understory plants but not for the P. abies relative to acidic subsoil. The combination of HM treatment and different subsoil acidity showed, that in the second year the deciduous trees have a significant biomass reduction by the HM treatment on calcareous subsoil, in favour of the herbaceous understory plants.
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