Concurrent measurement of atmospheric oxygen (O2) and carbon dioxide (CO2) concentrations have been used to derive the global terrestrial and ocean carbon sinks. A basic assumption in the derivation is that the oxidative ratios (O2:CO2) are distinct for terrestrial and ocean fluxes. A fixed oxidative ratio (approximately 1.1) of the terrestrial carbon sink was used in these estimations. However, the oxidative ratios of microbial and root respiration and their spatial and temporal variations are uncertain. Partitioning of soil respiration into microbial and root components is therefore difficult and there are no satisfactory methods available to date. The objectives of this project are 1) to develop a novel method to continuously and concurrently measure CO2 fluxes and O2 fluxes in soils, and calculate the oxidative ratios of microbial respiration and root respiration; and 2) to develop a novel method to partition soil respiration into microbial respiration and root respiration based on the different oxidative ratios for the two processes.
A field study will be conducted at the Harvard Forest in central Massachusetts, a Long Term Ecological Research site. To address the above objectives concurrent CO2 and O2 flux measurements will be made with newly developed high-frequency CO2 and O2 sensors and the oxidative ratios for microbial and root respiration will be calculated with both in situ sensor measurement and chemical extraction of soil carbon compounds in the laboratory. The different oxidative ratios between microbial respiration and root respiration will be used to partition total soil respiration into root and microbial respiration.
By exploring the transformative concept of the oxidative ratio, the work will provide new insight into the carbon cycle, and potentially shape future research in the field of biogeochemistry. New information on the carbon and oxygen cycles will be incorporated into undergraduate teaching provided by the Marine Biological Laboratory (MBL). It will also help shape graduate curricula and help training graduate students enrolled at Brown University through the joint MBL/Brown graduate program. The results drawn from this project will be presented at national meetings and published in the scientific literature.
Concurrent measurement of atmospheric O2 and CO2 concentration and its ratio has been used to derive the global terrestrial and ocean carbon sinks. The basic assumption is that the oxidative ratios (O2:CO2) are different for terrestrial and ocean fluxes. A fixed oxidative ratio (~1.1) of the terrestrial carbon sink was used in these estimations. The detailed information of this ratio, such as O2 and CO2 fluxes from soils, remains unclear. This information will help to separate CO2 fluxes from soils that are sourced from microbes and from plant roots. We designed a new custom-made automated chamber system to concurrently measure CO2 and O2 fluxes in soils. This system was tested at Harvard Forest in central Massachusetts. It successful recorded CO2 and O2 concentration changes and thus enabled us to calculate CO2 and O2 fluxes from soils. We obtained diel and seasonal patterns of CO2 and O2 fluxes and their ratio (O2:CO2). We found the ratio was not fixed as 1.1. This EAGER (EArly-concept Grants for Exploratory Research) project explored a transformative concept of the oxidative ratio, provided a new insight to studying the carbon cycle, and potentially shaped the field of biogeochemistry. It has broader impacts on the scientific community. We are currently writing a full proposal to further this project.
