Short description
(English)
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The project aims at understanding the rates of partitioning and turnover of organic matter in high-elevation grassland sites both below and above the treeline and to specify the role of these soils as potential hot-spots for future emissions of CO2. This will be accomplished by applying physical soil fractionation together with isotope measurements (14C, 15N) and molecular markers. Results will be used to parameterize soil organic matter turnover models for alpine grasslands.
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Partners and International Organizations
(English)
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AT, BA, BE, BG, CH, CZ, DE, DK, EE, ES, FI, GR, HU, IE, IL, IT, LT, NL, NO, PT, RO, SE, SI, SK, TR, UK
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Abstract
(English)
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For decades socio-economic transformations have led to changes in land-use and management throughout the European Alps. The abandonment of less accessible area is the most common trend and broadly perceived as a threat to traditional cultural land. Abandoned grasslands are transitional stages between managed grasslands and forest with undefined temporal dimension. To what extent the current abandonment can contribute to separate carbon (C) from global C cycling, thereby mitigating the atmospheric CO2 increase, remains an open question. The project contributes to elucidate the C sink/source potential of abandoned grasslands. In order to track the response of soil C to management reduction and dare predictions on C sequestration (i) soil organic C distribution, (ii) soil organic carbon dynamics and (iii) soil organic matter stabilization have been analyzed along management intensity gradients (hay meadow, pasture, abandoned grassland) in two typical mountain climates. Physical soil fractionation in combination with bomb radiocarbon modeling revealed that independent of differences in climate between sites the free particulate organic C fractions responded most to grassland abandonment, both in terms of abundance and biogeochemical cycling rates. In contrast, aggregate- and mineral-protected soil organic C fractions did not respond to grassland abandonment <30~yr, but showed higher biogeochemical cycling rates at the warmer mountain site. The C accumulation rates of free soil organic matter fractions were high at the beginning but decreased strongly with time (10, 25, 36~yr) since management reduction. Regression analysis of differences in d15N, an indicator for microbial degradation, and organic C ages between two differently stabilized soil organic matter fractions showed that microbial degradation continues with aging of stabilized organic matter. The comparison of ground- and flux-based estimates of C inputs to soil revealed a discrepancy between the two approaches. Our ground-based approximations yielded in threefold lower C input rates, which is reasonable as flux-based measurement capture rather the active compartments and short time spans of C dynamics in the soil system. From this study it can be concluded that abandonment in its current form does not provide a substantial soil C sink in the European Alps. Furthermore, the stable soil organic C fractions might play an important role in future global warming rather than the short-term responses of labile soil organic C fractions in the Alps.
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