Abstract
Biochar application to soil has been proposed as a promising strategy for carbon (C) sequestration and climatechange mitigation, helping at the same time to maintain soil fertility. However, most of the knowledge on biocharstability is based on short-term lab incubation experiments, as field studies are scarce. Therefore, little is knownabout the interactions between biochar and roots and the related effects on biochar stability in field conditions.The present study aimed to assess the stability of biochar, its effect on original soil organic matter (SOM) decom-position, and the effect of plant roots on biochar stability in field conditions in Northern Italy, for a three-yearmonitoring period within the EuroChar project. The experiment was conducted in a poplar short rotation coppice(SRC). Biochar produced from maize (δ13C = -13.8h) silage pellets in a gasification plant was applied in apoplar short rotation coppice (SRC) plantation in Northern Italy. Root exclusion subplots were established usingthe trenching method to measure heterotrophic respiration. Total (Rtot) and heterotrophic (Rh) respiration weremeasured every 2 hours in control and biochar-treated soil, with a closed dynamic soil respiration system.δ13C ofthe soil-emited CO2was periodically measured using the Keeling plot method. The percentage of biochar-derivedsoil respiration (fB), was calculated using an isotopic mass balance. Results showed that fB varied between 7%and 37% according to the sampling date, and was generally higher in the presence of roots than in trenched plotswhere the root growth was excluded. Without roots, only the 14% of the carbon originally added with biochar wasdecomposed. In the presence of roots, this percentage increased to 21%, suggesting a positive priming effectof roots on biochar decomposition. On the other hand, biochar decreased the decomposition of original SOM byabout 17%, suggesting a protective effect of biochar on SOM