Increasing levels of carbon dioxide in the Earth's atmosphere are driving global climate change. Because soils currently hold more organic carbon than is present as carbon in the atmosphere, soil management can affect rates of global climate change. Pyrogenic carbon is a form of soil carbon that is produced naturally during fires that can be difficult for microbes to decompose. Under some circumstance, this pyrogenic carbon ("biochar") may increase carbon storage and thus reduce the amount of carbon that is emitted to the atmosphere from soils. In order to predict the effects of pyrogenic carbon on soil carbon balance, proposed research will expand existing work to look at the importance of microbes and soil type in determining whether addition of pyrogenic carbon increases soil carbon storage. Methods will include a soil incubation experiment, where diverse soil types from across the United States will be mixed with pyrogenic carbon to predict the effects of pyrogenic carbon on soil organic carbon storage under a variety of conditions. This will help improve national and global efforts to model and predict the natural organic carbon cycle and will provide information that can be useful for land management decisions, especially those where prescribed burning is an option. In addition to these impacts, the research will support a PhD student's research, train undergraduate students in research, and engage the public with organic carbon cycle science, through lectures, general interest articles, a research website, and professional meetings.
Pyrogenic C (PyC) can comprise a large fraction of the soil organic carbon (SOC) in soils around the world, with levels up to 50-80% of SOC in some ecosystems. The effects of PyC additions on already existing SOC are still poorly understood. PyC additions to soil have been found to both increase and decrease SOC decomposition, with the magnitude and even direction of these interactions changing over time. These varied responses indicate that multiple mechanisms are occurring, with different mechanisms potentially acting over different timescales. The researchers will use experimental manipulations to determine whether varying the amount of labile OC in PyC and in SOC can predict the magnitude and direction of any priming effects, using 13C-labelled BC. This doctoral dissertation improvement grant will expand current experiments to a nationally representative set of soil types and will test the hypothesis that microbial community composition (analysed using high-throughput sequencing) can be used to predict PyC-SOC interactions. Understanding these mechanisms is essential to predict the impact of natural PyC inputs to soils on the global C cycle, and to quantifying the net climate impact of intentional PyC production and management.
