Der Schwermineral-Gehalt von Saale-zeitlichen Moränen- und Schmelzwasser-Ablagerungen des Münsterlandes

This article is a first summary of the heavy-mineral content of moraine and meltwater deposits of the Saalian glaciation in the Münsterland and its northeastern extension (NW Germany). In the beginning the appearance and distribution of both types of sediments are described (E. Speetzen), then the heavy mineral composition of selected outcrops is reported and the results are compared (D. Henningsen). Generally the predominant heavy minerals are garnet, minerals of the epidote group, zircon, and ordinary hornblende. The heavy mineral contents of moraine sediments sometimes are similar to that of meltwater deposits, in other cases they are different. Obviously there exists no relation between the heavy mineral composition and various advances of the Scandinavian ice sheet and their sediments, the content of heavy minerals rather depends on local influences.

Microbial nitrogen dynamics in organic and mineral soil horizons along a latitudinal transect in western Siberia

Soil N availability is constrained by the breakdown of N-containing polymers such as proteins to oligopeptides and amino acids that can be taken up by plants and microorganisms. Excess N is released from microbial cells as ammonium (N mineralization), which in turn can serve as substrate for nitrification. According to stoichiometric theory, N mineralization and nitrification are expected to increase in relation to protein depolymerization with decreasing N limitation, and thus from higher to lower latitudes and from topsoils to subsoils. To test these hypotheses, we compared gross rates of protein depolymerization, N mineralization and nitrification (determined using N-15 pool dilution assays) in organic topsoil, mineral topsoil, and mineral subsoil of seven ecosystems along a latitudinal transect in western Siberia, from tundra (67 degrees N) to steppe (54 degrees N). The investigated ecosystems differed strongly in N transformation rates, with highest protein depolymerization and N mineralization rates in middle and southern taiga. All N transformation rates decreased with soil depth following the decrease in organic matter content. Related to protein depolymerization, N mineralization and nitrification were significantly higher in mineral than in organic horizons, supporting a decrease in microbial N limitation with depth. In contrast, we did not find indications for a decrease in microbial N limitation from arctic to temperate ecosystems along the transect. Our findings thus challenge the perception of ubiquitous N limitation at high latitudes, but suggest a transition from N to C limitation of microorganisms with soil depth, even in high-latitude systems such as tundra and boreal forest.