Nutrient turnover studies in alpine ecosystems

Summary

The nutrient relations of five treeless plant communities on acid soils above siliceous rock of the Central Alps are investigated. Three of these communities, situated on Mt. Patscherkofel, are dominated by dwarf shrubs of the Ericaceae family: Loiseleurietum (P 1, 2175 m NN), Loiseleuria heath (P 2, 2000 m NN), and Vaccinium heath (P 3, 1980 m NN). The other two are bound to higher elevations (2500 m NN, at Timmelsjoch): Caricetum curvulae (T 1), forming the mats, and Salicetum herbaceae (T 2), covering the snow-beds.

Phytomass productivity decreases with increasing altitude in the sequence P 3-P 2, P 1-T 1-T 2.

Compared with the turf communities of the Northern Calcareous Alps, nitrogen reserves and experimental net-mineralization of the soils (0–15 cm) are extremely low in P 1, P 2, and P 3 (<0.5 g N/m² mineralized per GS¹). The fluctuation of N in the living above-ground phytomass during the GS is also low (about 1.6 g/m² in P 1 and P 2; 2.2 g/m² in P 3, although it exceeds the values of net mineralization. Additional uptake through mycorrhizal fungi or activation of mineralizing microbes in the rhizosphere by exudation is assumed.

The P- and K-reserves are extremely small in the humic soils of P 2 and P 3, but somewhat higher in the more mineral soil of P 1. Mean lactatesoluble P of the three sites is low (0.3 g/m² or less) whereas K_lact (2.7–3.3 g/m²) is higher than the lowest level found in some turf communities, e.g. Caricetum firmae. The amounts of P in the phytomass are in the range of those of the turf communities and agree with the gradation in the mean P_lact values (P 1 and P 3>P 2). There are, however, almost no discernible fluctuations of P in the phytomass, and the K-fluctuations are far below the mean K_lact level.

The Timmelsjoch communities generally have higher N/C-, P/C-, and K/C-ratios in the soils compared with those of Mt. Patscherkofel, although the N-reserves (g/m²) and the K-reserves (of T 1 only) are lower. The P_lact values are higher than those from Mt. Patscherkofel and also exceed those of the calcareous turf communities. K_lact is low in T 1 whereas in T 2 it is in the range of P 1, P 2, and P 3. Compared with T 1, T 2 has distinctly higher amounts of the three nutrients in the soils and a higher net mineralization of N, as well as higher values in the phytomass components and in the fluctuation of the latter.

In conclusion, a general view is given (Fig. 9) of the most important nutrient parameters of the communities represented in this series, including some others of lower altitudes.