Decrease in heathland soil labile organic carbon under future atmospheric and climatic conditions
2017
Thaysen, E. M. | Reinsch, S. | Larsen, K. S. | Ambus, P.
Characterization of the impacts of climate change on terrestrial carbon (C) cycling is important due to possible feedback mechanisms to atmospheric CO₂ concentrations. We investigated soil organic matter (SOM) dynamics in the A1 and A2 horizons (~0–5.1 and ~5.1–12.3 cm depth, respectively) of a shrubland grass (Deschampsia flexuosa) after 8 years of exposure to: elevated CO₂ (CO₂), summer drought (D), warming (T) and all combinations hereof, with TDCO₂ simulating environmental conditions for Denmark in 2075. The mean C residence time was highest in the heavy fraction (HF), followed by the occluded light fraction and the free light fraction (fLF), and it increased with soil depth, suggesting that C was stabilized on minerals at depth. A2 horizon SOM was susceptible to climate change whereas A1 horizon SOM was largely unaffected. The A2 horizon fLF and HF organic C stocks decreased by 43 and 23% in response to warming, respectively. Organic nitrogen (N) stocks of the A2 horizon fLF and HF decreased by 50 and 17%, respectively. Drought decreased the A2 horizon fLF N stock by 38%. Elevated CO₂ decreased the A2 horizon fLF C stock by 39% and the fLF N stock by 50%. Under TDCO₂, A2 horizon fLF C and N stocks decreased by 22 and 40%, respectively. Overall, our results indicate that shrubland SOM will be susceptible to increased turnover and associated net C and N losses in the future.
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