Black C Effects On Soil CO2 Emissions: A Methodological Study.

The impact of black carbon (BC) addition to soils on soil CO₂ emissions is poorly understood. Furthermore, in the field setting, partitioning of soil CO₂ emissions from non-BC soil organic carbon (SOC) and BC is confounded by the added effects of changes in root respiration due to BC additions. This pot trial takes a step toward clarifying these issues and examines the effects of BC additions to soil on total soil CO₂ emissions while exploring the relative contributions of CO₂ from plant roots, SOC, and BC. Differences in ¹³C stable isotopes from a C3-derived soil and C4 plant roots (maize, Zea mays L.) are used to differentiate between SOC- versus root-derived CO­­₂. Differences between BC- and SOC-derived CO₂ are determined by using BC produced from ¹³C-labelled sugar maple wood (Acer saccharum) pyrolysed at 350°C for 2 hours. The results of using different proxies for the isotope signature of the CO_­2 sources are also compared. For SOC-derived emissions, the proxies that are used are DOC, total SOC, microbial biomass, and soil without BC additions or plants. For BC-derived emissions, bulk BC, BC volatiles, and soil CO­₂ emissions from a pot with BC in soil that has been combusted to remove SOC are compared as proxies. For root respiration, bulk roots, fine roots, root sugars, and soil CO­₂ emissions from a plant grown in soil combusted to remove SOC  are contrasted. Plants are grown over 2 months, with CO₂ emission rates measured every two weeks. Results are expected to: a) determine optimal proxies for ¹³C signatures of each component when using isotope partitioning techniques b) indicate whether soil CO₂ emissions in plant systems with BC application are additive or if there are other interactions between the components.