DISSERTATION RESEARCH: Carbon Cycle Changes in a Changing Climate: Using 13C and 14C to Partition Ecosystem Respiration in Tundra Undergoing Permafrost Thaw

University Of Florida, Gainesville FL

Investigators

Abstract

Permafrost soils, which are soils frozen for two or more consecutive years, store vast quantities of carbon (C). These soils are reservoirs of C because thousands of years of cold temperatures have prevented the microbial decomposition of soil organic carbon (SOC), and thus the subsequent release of carbon dioxide (CO2) from soils to the atmosphere. However, permafrost soils are very vulnerable to warming; as the climate warms, permafrost soils begin to thaw, which allows microbes to access and decompose stored SOC , thereby releasing CO2. Permafrost thaw, therefore, has the potential to become a positive feedback to climate change: CO2 in the atmosphere can increase warming, and warming of permafrost soils can result in more CO2 release to the atmosphere via increased rates of decomposition and ecosystem respiration. However, permafrost thaw can also increase plant growth, which takes CO2 out of the atmosphere via photosynthesis, and may, in the short term, result in a negative feedback to climate change. Thus the relative responses of both soil microbes and plants to permafrost thaw determine whether, on balance, permafrost ecosystems add CO2 to the atmosphere (microbial response and positive feedback) or whether the ecosystem takes CO2 from the atmosphere (plant response and negative feedback.) The main objective of this research is to quantify the response of four components of ecosystem respiration, all of which result in release of CO2 to the atmosphere (aboveground plant structures, belowground plant structures, surface soil microbes, and deep soil microbes) to permafrost thaw in order to determine whether plant or microbial responses are dominating the Alaska tundra's changing carbon cycle. Natural abundances of two carbon isotopes, 13C and 14C, will be used to identify the sources of respired CO2. By measuring the isotopic values of CO2 sources as well as ecosystem respiration, the relative contribution of soil microbes and plants to carbon fluxes can be calculated. This ecosystem respiration partitioning will be performed seasonally in a natural gradient of permafrost thaw, in a tundra warming experiment, and in an area with two different amounts of vegetation and two different soil climates to explore the effects of permafrost thaw on the carbon balance of tundra ecosystems. Throughout the course of this research, undergraduate students will be trained, 8th grade students will be educated, and a layperson's guide to C cycling in permafrost will be created. Finally, the results of this study will be important to climate models; these models do not currently consider biological responses to the physics of climate warming.