Sensing the soil: a soil CO2/O2 monitoring network system to study soil processes

• Applicant: Professor Dr. Martin Freudiger
• Subject Area: Soil Sciences
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 559318039

Soil respiration is a key function for many other processes in soil. Although soil respiration is fundamental to understanding carbon turnover in soils, the “forgotten half” of this flux, the counterflow of atmospheric oxygen (O2) into the soil, is rarely studied. The ratio of carbon dioxide (CO2) produced to O2 (qO2) consumed in a soil, qCO2/qO2, is called the respiration quotient RQ. Recent research has shown that the RQ averages around 1.1 and can vary considerably from site to site, which could serve as a key to identifying or possibly even quantifying various other processes. However, there are several abiotic processes that affect CO2 and O2 fluxes and thus mask the biotic RQ signal. While CO2 fluxes can be measured by various methods such as micrometeorological methods or chamber methods, estimating O2 fluxes is more challenging due to the high background of 20.95 % O2 in the atmosphere. In situ monitoring of CO2 and O2 in soil is another method that can be used to study soil-atmosphere and RQ fluxes and provide valuable insights into the ongoing process. As overall aim of the proposed collaboration in the Middle East, we want to conduct a systematic study of CO2-O2 fluxes in the field, and to investigate the suitability of RQ as an ecophysiological key to understanding the spatio-temporal patterns and underlying processes in soils. We aim to develop a sensor network of soil CO2-O2 profile probes and a chamber system to measure CO2-O2 fluxes. In a first semi-controlled study, we want to use these in a large lysimeter system in which we will investigate the effects of groundwater changes. In the subsequent field study, we will map the spatial and temporal patterns at forest sites with a CO2-O2 sensor network and the CO2-O2 fluxes with a mobile respiration chamber. For this purpose, we have selected 4 very different sites, 2 carbonate and 2 acidic soils, one site in a temperate forest and one in a Mediterranean forest.

• DFG Programme: Research Grants
• International Connection: Israel
• International Co-Applicant: Dr. Elad Levintal