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Abstract

Carbonyl sulfide (OCS) plays an important role in the global sulfur cycle and is relevant for climate
change due to its role as a greenhouse gas, in aerosol formation and atmospheric chemistry. The similarities
of the carbon dioxide (CO2) and OCS molecules within chemical and plant metabolic pathways have led to
the use of OCS as a proxy for global gross CO2 fixation by plants (gross primary production, GPP). However,
unknowns such as the OCS exchange from soils, where simultaneous OCS production (POCS) and consumption
(UOCS) occur, currently limits the use of OCS as a GPP proxy. We estimated POCS and UOCS by measuring
net fluxes of OCS, carbon monoxide (CO), and nitric oxide (NO) in a dynamic chamber system fumigated
with air containing different mixing ratios [OCS]. Nine soils with different land use were rewetted and soil–air
exchange was monitored as soils dried out to assess responses to changing moisture. A major control of OCS
exchange was the total amount of available sulfur in the soil. POCS production rates were highest for soils at
WFPS (water-filled pore space) > 60% and rates were negatively related to thiosulfate concentrations. These
moist soils switched from a net source to a net sink activity at moderate moisture levels (WFPS 15% to 37 %).
For three soils we measured NO and CO mixing ratios at different mixing ratios of OCS and revealed that NO
and potentially CO exchange rates are linked to UOCS at moderate soil moisture. High nitrate concentrations
correlated with maximum OCS release rates at high soil moisture. For one of the investigated soils, the moisture
and OCS mixing ratio was correlated with different microbial activity (bacterial 16S rRNA, fungal ITS RNA relative abundance) and gene transcripts of red-like cbbL and amoA.