No abstract

In contrast to earlier beliefs, it is now known that boron (B) can be retranslocated complexed with sugar alcohols in some plant species. Conifers had been thought not to translocate sugar alcohols in the phloem. However, 1 d after applying 10 B enriched boric acid to shoots of Scots pine and Norway spruce seedlings, we found increases in both the amount and proportion of 10 B in the root systems in both species. We conclude that B is translocated in the phloem from shoots to roots in spruce and pine, and therefore it is possible that these species retranslocate B.# 2000 Annals of Botany Company

Migration of Hg from black shales to the aquatic ecosystems and local residents was studied comprehensively with samples of black shales (627 samples), surface waters (22), organic stream sediments (40), organic lake sediments (172), noble crayfish (72) and human hair (225). The black shales exhibited elevated C, S, Ni, Cu, Zn, Cd and Hg concentrations. Gneiss granite, mica schist, and quartzite with very low heavy metal contents are encountered just next to the black shales, offering good reference areas for comparison. There are no local anthropogenic Hg sources in the study areas. Black shale areas were reflected as elevated Ni, Cu, Zn and Cd and low Ca in glacial till, surface waters, organic stream sediments and lake sediments. Mercury behaved differently in surface waters than the other heavy metals: there was no correlation between the Hg concentration of the surface waters and the Hg concentration of the underlying bedrock. Median values for total Hg and methyl-Hg in stream water were 1.6 and 0.2 ng/l, respectively, in the black shale area, and 2.0 and 0.3 ng/l in the adjacent reference area with Hg-poor bedrock. Even though Hg concentrations in surface waters were not elevated in the black shale areas relative to the reference areas, mean Hg concentrations of the muscle of noble crayfish (Astacus astacus) were higher in black shale area lakes than in lakes in the reference areas. The explanation of this correlation probably is not Hg flux from the bedrock to watercourses. As a more easily eroded rock than granites, quartzites, and mica schists, black shale tends to occur in topographic depressions in glaciated terrain. Lakes in the black shale areas are typically surrounded by peatlands, and the catchment areas, from which they collect humic material rich in Hg, may be extensive. The total Hg concentrations in hair ranged from 0.04 to 12.1 lg/g. The distribution of hair Hg content did not appear to correlate with the distribution of black shales. In the present study, the main route of Hg to humans was via fish. Even though Hg contents were higher in crayfish and fish in the black-shale-area lakes, people consumed fish not only from the lakes next to their residence, but also from lakes situated in the reference areas. Among the non-fish-eaters in one black shale area, the use of dug well water, as well as the consumption of local potatoes and mushrooms, slightly increased the Hg in hair. This contribution may reflect the heavy metal load of the natural black shale environment.

No abstract

Boron (B) is an essential micronutrient for plants but it is thought not to be essential for fungi. We studied whether the extraradical mycelia of Paxillus involutus in symbiosis with silver birch (Betula pendula) take up B and transport it to the host plant. We grew mycorrhizal plants in flat microcosms with a partitioning wall, below which there was only extraradical mycelium. A boric acid solution enriched in 10B was applied to these mycelia. Increased 10B/11B isotope ratios were subsequently measured in birch leaves, stems, and roots plus mycorrhizas in the upper compartment. Boron was therefore taken up by the mycorrhizal mycelia and transported to the host plant in this species combination.