Nutrient turnover studies in alpine ecosystems : I. Phytomass and nutrient relations in four mat communities of the Northern Calcareous Alps.

Four plots of alpine meadow communities (mats) of the Northern Calcareous Alps are compared with regard to dry substance (DS), N-, P-, and K-content of living and dead overground and total underground phytomass. The Caricetum firmae F (altitude 2,010 m) produces the least green mass but accumulates the highest amount of dead substance (litter). In all parts it has the lowest content of N, P, K. The opposite is the Caricetum ferrugineae C (1,900 m): Small dead mass, but high production of green mass and high content of N and K in the living overground and total underground phytomass. The Nardetum N (1,930 m) is marked by relatively high amounts of P in living and dead parts. The Seslerio-Semperviretum S (2,150 m) is intermediate but with rather low contents of K.In each plot the average total nitrogen found in the underground phytomass is about 200% of the amount found in the living overground phytomass. This suggests a similar relation of living mass in the two components of the total phytomass.The fluctuations in the phytomass throughout the growing season are represented for S. The green mass increase is about 200g DS with about 3 g N/m2. This amount corresponds to the average mineralization supply of N during the growing season as obtained by the field incubation method (3.3 g/m2, in 0-15 cm depth of the soil). In C the average mineralization is lower whereas the green mass production amounts to 300 g DS/m2 with 5.5 g N/m2. This discrepancy supports again our hypothesis of an "internal nitrogen cycle" in the Carex ferruginea community. In F and N we find a lower incorporation of N into the annual green mass production compared with the N mineralized in the upper soil layers (Table 1).Lactate-soluble P and K were as a rule not accumulated in our soil incubation tests. The actual values and their amplitude during the growing season scarcely coincide with the differences of P and K in the green mass.