Is there a link between elevated atmospheric carbon dioxide concentration, soil water repellency and soil carbon mineralization?

We hypothesized that elevated atmospheric carbon dioxide concentration [CO2] as a feature of climate change promotes the occurrence of soil water repellency (SWR) which reduces soil carbon mineralization and thus increases carbon sequestration. Soil surface transects under elevated (475 μL L−1) and ambient atmospheric [CO2] in a long-term Free Air Carbon Dioxide Enrichment experiment were sampled at a high spatial resolution. All samples were hydrophobic at the time of the sampling. At the micro-scale, the differences in degree and persistence of SWR, soil organic matter (SOM) content, microbial respiration rates (MRR) and water content between the treatments were not significant. SWR was not correlated with SOM or MRR. A strong correlation between water contents and SWR parameters demonstrated the importance of SWR for water redistribution. At the meso-scale of disc infiltrometry, infiltration rates were reduced by SWR, and were higher under ambient than under elevated [CO2]. This corroborates the tendency of reduced SWR under elevated [CO2] observed at the micro-scale. SWR showed a spatial structure, exhibiting short ranges. SOM and MRR showed no spatial pattern at the scale analyzed, emphasizing that SWR did not contribute to an increase of the long-term terrestrial C sink in response to increased atmospheric [CO2].

Research highlights▶ Soil water repellency (SWR) was found important for local topsoil water distribution. ▶ Infiltration was reduced by SWR and was higher under ambient than elevated [CO2]. ▶ Degree and persistence of SWR had short, similar correlation lengths. ▶ SWR did not increase the soil's C sink in response to elevated atmospheric [CO2].