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 above-ground 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 amount 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 below-ground 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.