Seasonal variations of nickel concentrations in annual xylem rings of beech trees ( Fagus sylvatica L.)

Abstract

Seasonal variations of Ni concentrations in stem wood of mature beech trees ( Fagus sylvatica L.) were detected. Wood samples were collected at monthly intervals between April and December from trees of two sites in Germany. Radial distribution patterns of Ni were similar in all trees. Highest contents were found in the sapwood. Lower concentrations occurred in the outer heartwood. Towards the stem center, Ni levels increased. The general profile of such radial patterns did not change substantially during the period investigated. However, the concentration levels of Ni varied significantly with the season. Highest Ni concentrations were found in April. Variations between June and December were less significant. The presented results suggest, that radial distribution patterns of Ni in xylem rings of beech trees do not contain a reliable record of the Ni availability during the life span of the trees. The reasons are: (a) The distribution patterns showing high levels near the sapwood-heartwood transition indicate the possibility of a radial transport of Ni and a subsequent accumulation in the inner sapwood. (b) Seasonal variations of Ni concentrations in wood render the analytical data useless for the reconstruction of pollution levels in the past.