The partitioning of litter carbon fates during decomposition under different rainfall patterns: a laboratory study

During litter decomposition, three major fates of litter carbon (C) are possible: emission as carbon dioxide (CO₂) into the atmosphere, leaching of dissolved organic carbon (DOC), and translocation and transformation into soil organic carbon (SOC). Soil moisture, one of the key drivers of litter decomposition, is predicted to change in the future due to shifts in precipitation patterns. We explored the effects of low, medium and high rainfall intensities on the partitioning of litter carbon fates in a 6-month long laboratory experiment. We tracked carbon in ¹³C-labeled tulip poplar litter in a laboratory mesocosms by measuring respiration rates, dissolved organic carbon in the leachate, and soil organic carbon at the end of the experiment. Mesocosms with the same three rainfall intensities but without leaf litter were also set up. Leaching of labile carbon caused priming, but the effect was stronger in the low intensity treatment. Transport of litter-derived carbon also differed: in high intensity treatment there was more total carbon in the surface soil and more litter-derived carbon in in the deep soil layers. The cumulative CO₂ efflux was not significantly different. Our results highlight that extreme rainfall events, as projected by most climate models, may lead to altered carbon cycling in temperate forest soils.