Nutrient turnover studies in Alpine ecosystems : II. Phytomass and nutrient relations in the Caricetum firmae.

1. A plot of the Caricetum firmae in the Northern Calcareous Alps (at 2,160 m above sea level) was investigated during the growing season 1973 with regard to dry matter, nitrogen, phosphorus, and potassium content of overground and underground phytomass, including accumulated litter. 2. Compared to another habitat of the same community at 2,010 m a.s.l., the overground phytomass in the state of maximum development (ca.250 g per m2) and the store of nutrients (4 g N, 0.25 g P and 2.4 g K per m2) are nealy, the same, but the primary production is less (ca. 100 g as against ca. 160 g per m2). 3. The accumulation of litter in relation to the annual overground production is nearly 30:1. 4. The content of N, P, and K in the predominant species Carex firma and Dryas octopetala ranks near the inferior limit known for terrestrial plants. The minimum values are attained in the state of maximum development (mid-August). 5. The mineralization of N amounts to about 2 g per m2 during the growing season and thus exceeds the quantity that enters into the overground production. The maximum mineralization is found 5 to 10 cm under the soil surface. In this layer most of the fine roots are concentrated. 6. The lactate-soluble content of P and K in the soil averages ca. 0.3 or 1.5 per m2 and decreases from the beginning to the height of the growing season by ca. 0.35 or 0.5 g per m2 with a slight increase toward the end. In the field incubation experiments losses of P and K, interpreted as microbial incorporation, prevailed during the growing season. It was hardly possible to determine evident relations between the fluctuations of P and K in the soil and those in the phytomass. 7. The Caricetum firmae ranks between the "typical arctic tundra" and the "dwarf-shrub tundra" with regard to the obtained data on phytomass, primary production, and nutrients, except for the underground production which seems to be remarkably higher.