Abstract. Land-use change (LUC) and management are among the major driving forces of soil carbon (C) storage. Abandonment of mountain grassland promotes accumulation of aboveground biomass and litter, but related responses of soil organic matter (SOM) dynamics are uncertain. To determine SOM-C turnover we sampled 0–10 cm of soils along land-use gradients (hay meadows, grazed pastures and abandoned grasslands) in the European Alps varying in management intensity at Stubai Valley (MAT: 3 °C, P: 1097 mm) in Austria and Matsch Valley (MAT: 6.6 °C, P: 527 mm) in Italy. We determined C input and decomposition rates of labile water-floatable and free particulate organic matter (wPOM, fPOM <1.6 g cm−3) and stable aggregate-occluded particulate and mineral-associated organic matter (oPOM <1.6 g cm−3, mOM >1.6 g cm−3) using bomb radiocarbon. At both sites C turnover decreased from w- and fPOM (4–8 yr) to oPOM (76–142 yr) to mOM (142–250 yr). Following abandonment C input pathways shifted from root-derived towards litter-derived C. The decomposition rates of labile wPOM-C declined with a decrease in litter quality, while both C input and C decomposition rates of labile fPOM increased with an increase in litter quantity. In contrast, protected stable SOM-C (oPOM-C, mOM-C) dynamics remained relatively unaffected by grassland abandonment. Carbon accumulation rates of labile POM fractions decreased strongly with time since LUC (10, 25 and 36 yr). For wPOM-C, for example, it decreased from 7.45 &pm; 0.99 to 2.18 &pm; 1.06 to 0.82 &pm; 0.21 g C m−2 yr−1. At both sites, most C was sequestered in the first years after LUC and labile SOM fractions reached new steady state within 20–40 yr. We concluded that w-and fPOM-C vs. oPOM-C dynamics respond differently to grassland management change and thus POM does not represent a homogeneous SOM fraction. Sequestered C is stored in the labile readily decomposable POM fractions and not stabilized in the long-term. Thus it is unlikely that abandonment, the dominant form of LUC in the European Alps, provides a substantial net soil C sink.
Hydrological dynamics of tropical streams on a gradient of land-use disturbance and recovery: A multi-catchment experiment