There is substantial variation in estimates of the respiratory quotient (RQ) which is defined as the molar ratio of produced CO₂  and consumed O₂ during microbial mineralization of organic matter (OM). The resulting RQ value of microbial metabolism is usually dependant upon the composition of the organic matter and the properties of the microbial degrading communities. While several studies have examined the controlling factors and the magnitude of RQ, in either terrestrial or in aquatic ecosystems, broader cross-ecosystem comparisons are missing, and universal insights into the extrinsic (environmental) and intrinsic (organic matter composition) controls on RQ are lacking. In this study, we calculated the RQ across a broad range of environmental samples, including soils, aquatic sediments, peat, lake and marine water by measuring CO₂ production and O₂ consumption in the headspace of incubation vials using membrane inlet mass spectrometry (MIMS). We also assessed the microbial metabolic profiles using BIOLOG Ecoplates and determined the energy content of the natural OM with bomb calorimetry. Our findings show that 1) RQ values differ significantly between the ecosystem types, 2) the extent of microbial respiration across the different studied ecosystems is correlated with the bulk energy content of the OM (kJ per g organic carbon) and 3) RQ is regulated by other environmental parameters which constrain the energetic controls on OM decomposition. We argue that cross-system comparison of a wider range of ecosystems will help us understand the persistence and decay of OM.

Primary Presenter: Konstantinos-Marios Vaziourakis, Uppsala University (konstantinos.vaziourakis@ebc.uu.se)

Authors:

Konstantinos Vaziourakis, Uppsala University  (konstantinos.vaziourakis@ebc.uu.se)

Liam Heffernan, Uppsala University  (liam.heffernan@ebc.uu.se)

Lars Tranvik, Uppsala University  (Lars.Tranvik@ebc.uu.se)