Black Carbon

Project Summary: A critical knowledge gap exists in understanding the role of incompletely combusted plant biomass remaining after fires (black carbon) in soil organic C (SOC) cycling. Most currently used climate models predict that temperate forests will experience greater fire frequency under a warmer future climate, thereby increasing the inputs of black carbon (BC) to soils. Recent evidence from field and laboratory studies indicates that previous estimates of BC decomposition rates in soils may have been unrealistically low, and that a significant amount of BC degrades in decades to centuries, mainly by biologically mediated soil processes. Consequently, the dynamics of BC, a substantial portion of soil C (7-45%), may significantly affect soil C stocks and net ecosystem C exchange. However, direct, quantitative information on the long-term fate of BC in terrestrial ecosystems is scarce. Through integrated field and laboratory studies, this proposed research will explore the fundamental biological, chemical and physical controls on BC degradation and transport processes. This research will link he combustion temperature of BC materials to their chemical and physical structures and their resulting in situ decay rates, the activity of the main fauna and microbial degraders, oxidative and hydrolytic enzyme activities, transport dynamics, and its stabilization mechanisms in mineral soils. This project will also quantify the stimulation/inhibition of native SOC turnover from BC additions and the co-metabolic controls on BC degradation. The proposed experimental approach will use highly 13C/15N-enriched BC materials produced over a range of combustion temperatures (200 to 600ºC) and its precursor wood of jack pine (Pinus banksiana L.), a fire-prone and abundant tree species in eastern North America, to elucidate the physiochemical structures of BC materials and track the multiple fates of these materials when added to soil. This approach will permit a direct assessment of the transformation and utilization pathways by indigenous soil fauna and microbial communities. The fates of 13C and 15N will be tracked into CO2, DOC and DON, microbial biomarkers, macro- and meso-fauna, and stabilized products in soil fractions using advanced molecular and spectroscopic techniques. This work will provide the first look at the roles of specific groups of microorganisms and soil fauna involved in the decomposition of BC and wood in soils. To test the effects of plant species on BC chemical and physical structures, highly 13C/15Nenriched BC from Red maple (Acer rubrum L.) will be compared with the Jack pine. The resulting data and knowledge base will be an important contribution to ongoing efforts to robustly predict terrestrial C cycling and to inform both ecosystem and climate modelers and land use managers.