Differences of Nitrogen Flow and Storage Between four Ecosystems in Subalpine Ecotone in the Bavarian Alps

Wien

2002

S. 309-320

2 Abb., 3 Tab., 33 Lit. Ang.

Unselbständiges Werk

200097842

Nitrogen flow and storage were studied in a subalpine ecotone in the Bavarian Alps in order to determine nitrogen budgets, to find possible differences in nitrogen saturation and to estimate future nitrat output into groundwater after climate warming. The following four ecosystems forming a site mosaic on a northerly slope at 1700 m a.s.l. were investigated: (1) Spruce lusters (fragment of Adenostylo glabrae-Piceetum Mayer 69), (2) dwarf pine krummholz (Rhododendro hirsuti-Pinetum mugo Br.-Bl. 39), (3) mat-grass meadow (Geo montani-Nardetum Lüdi 48) and (4) calcareous grassland (Caricetum ferrugineae Lüdi 21). Bulk precipitation, throughfall, litterfall and seepage water were measured fortnightly in summer and monthly in winter. In the spruce cluster ecosystem nitrogen input was elevated by 212 mmol N m ®¬ a®Ü as compared to bulk precipitation. Total nitrogen storage amounts to 213 mmol N m ®¬ a®Ü due to continued biomass accumulation. Under pine krummholz there was a marked vertical gradient of soil chemistry in C/N-ratio pH and base saturation. In the mat-grass meadow a lower annual storage rate of 49 mmol N m ®¬ a®Ü was found. High soil total nitrogen store, a relatively narrow C/N-ratio of 20 and a biomass production of 2.8 t ha®Ü with no current accumulation may indicate N-saturation. The calcareous subalpine grassland, the only community growing on mineral soil, stores nearly the total nitrogen input from precipitation. At a yearly nitrogen storage of 105 mmol N m ®¬ a®Ü this system is far away from nitrogen saturation. Nitrogen cycling in alpine raw humus under changing vegetation types due to climate change is discussed.