Ecosystem gross CO2 fluxes in a tropical rainforest estimated from carbonyl sulfide (COS)

Wednesday, 17 December 2014: 5:45 PM
Ulrike H Seibt1, Kadmiel S Maseyk2, Celine Lett3, Sabrina Juarez4 and Wu Sun1, (1)University of California Los Angeles, Los Angeles, CA, United States, (2)Open University, Milton Keynes, MK7, United Kingdom, (3)NERC British Antarctic Survey, Cambridge, United Kingdom, (4)BIOEMCO Biogéochimie et Ecologie des Milieux Continentaux, Thiverval-Grignon, France
Carbonyl sulfide (COS) is a promising new tracer to constrain the gross CO2 fluxes of land ecosystems, particularly in tropical forests where CO2 flux partitioning is often problematic due to the absence of turbulent flow at night. Since vegetation COS and CO2 uptake during photosynthesis is closely coupled, the gross fluxes of photosynthesis and respiration can be quantified through the concurrent measurements of COS and CO2. We measured ecosystem COS and CO2 exchange over four months in a tropical rainforest at La Selva, Costa Rica. We observed a strong ecosystem uptake of COS with a diel signal that was similar but not identical to net CO2 fluxes. Soils at the site mostly acted as COS sinks, correlated with soil moisture. The COS and CO2 data were used to calculate canopy photosynthesis (approx. GPP) from net ecosystem CO2 exchange (NEE) based on the empirical relationship of leaf relative uptake of COS and CO2. Mid-day COS-based GPP estimates ranged from -10 to -15 μmol m-2 s-1, compared to NEE of -5 to -10 μmol m-2 s-1. Ecosystem respiration, calculated as the difference of NEE and GPP, ranged from 5 to 10 μmol m-2 s-1, similar to previous estimates of 5 to 9 μmol m-2 s-1 from CO2 flux partitioning and respiration component measurements at the site. Our results support the application of COS as a new tool in ecosystem flux partitioning that may be particularly useful in tropical forests.