Below-ground and above-ground production of vegetational organic matter along a climosequence in alpine grasslands

The distribution of vegetational organic matter above- and below ground and its productivity was analyzed in an alpine area along a climosequence ranging from subalpine to alpine climates. Emphasis is placed on the quantification of carbon (C) and nitrogen (N) fixed in the above-ground and below-ground vegetation and its annual input. Annual C-input ranged from 17.9 to 60.2 g m(-2) year(-1) and the N-input from 0.74 to 2.48 g m(-2) year(-1). Above-ground phytomass and the annual production rate of organic matter showed a distinct correlation with the altitude and, thus, the climate. However, the measurement of the above-ground phytomass is bound to methodological problems: the commonly used harvesting method seems to underestimate the real situation. The harvesting method yielded in its average 100 to 300 g m(-2) phytomass which was 35-83% of the values obtained by the soil core method. Thus, the calculation of turnover times of aboveground vegetation greatly depends on the method used. Calculated turnover times based on the harvesting method did not correlate with the climate while a clear tendency of lower turnover times with increasing altitude could be observed using the. soil core method. The a-mount of below-ground phytomass was in the range of 1880 to 2469 g m(-2) and the corresponding annual C-input (fixation in the roots) between 91.1 and 162 g m(-2) year(-1) and the N-input between 2.68 and 4.99 g m(-2) year(-1). The below-ground phytomass and its production rate in high alpine zones are of greater importance and exceed the above-ground ones. With increasing altitude, furthermore, the importance of the belowground phytomass increases with respect to the biomass and to the C- and N-input. For high alpine areas, the phytomass is concentrated in the uppermost soil horizons. About 88.7 to 94.5% of the below-ground phytomass was found in the soil compartment 0-20 cm. The below-ground production rate of phytomass in alpine grassland is fundamental in order to calculate any C or N budgets and potential inputs to SOM: its neglection would introduce most significant errors in modeling any C or N cycles.