Abstract
During recent years, carbonyl sulfide (COS), a trace gas with a similar diffusion pathway into leaves as carbon dioxide (CO2), but with no known “respiration-like” leaf source, has been discussed as a promising new approach for partitioning net ecosystem-scale CO2 fluxes into photosynthesis and respiration. The utility of COS for flux partitioning at the ecosystem scale critically depends on the understanding of non-leaf sources and sinks of COS. This study assessed the contribution of the soil to ecosystem-scale COS fluxes under simulated drought conditions at temperate grassland in the Central Alps. We used transparent steady-state flow-through chambers connected to a quantum cascade laser spectrometer to measure the COS and CO2 gas exchange between the soil surface and the atmosphere. Soils were a source of COS during the day, emissions being mainly driven by incoming solar radiation and to a lesser degree soil temperature. Soil water content had a negligible influence on soil COS exchange and thus the drought and control treatment were statistically not significantly different. Overall, daytime fluxes were large (12.5 ± 13.8 pmol m−2 s−1) in their magnitude and consistently positive compared to the previous studies, which predominantly used dark chambers. Nighttime measurements revealed soil COS fluxes around zero, as did measurements with darkened soil chambers during daytime reinforcing the importance of incoming solar radiation. Our results suggest that abiotic drivers play a key role in controlling in situ soil COS fluxes of the investigated grassland.
Highlights
Land ecosystems presently absorb around 25% of the carbon annually emitted by anthropogenic activities as carbon dioxide (CO2) and beneficially slow down the trend of increasing atmospheric CO2 concentrations and the associated global warming (IPCC 2013; Le Quéré et al 2015; Raupach et al 2011; Schimel et al 2001)
Our results suggest that abiotic drivers play a key role in controlling in situ soil carbonyl sulfide (COS) fluxes of the investigated grassland
The soil water content (SWC), which varied between 5 and 47% and covered almost the entire range of plant extractable soil water at this site, had no significant effect on the COS flux (Fig. 4). This finding is in conflict with results from the literature (Kesselmeier et al 1999; Van Diest and Kesselmeier 2008), especially considering that microbial communities are negatively impacted by droughts (Borken and Matzner 2009; Lavigne et al 2004; Schimel et al 1999) and enzymatic activity within the soil is generally reduced under water stress (Davidson and Janssens 2006; Sardans and Penuelas 2005)
Summary
Land ecosystems presently absorb around 25% of the carbon annually emitted by anthropogenic activities as carbon dioxide (CO2) and beneficially slow down the trend of increasing atmospheric CO2 concentrations and the associated global warming (IPCC 2013; Le Quéré et al 2015; Raupach et al 2011; Schimel et al 2001). Because the net ecosystem exchange of CO2 is the small difference of two large fluxes of opposing sign, gross primary production (GPP) and ecosystem respiration (ER), models typically simulate these two component fluxes separately (Cramer et al 1999). For model calibration and validation, ecosystem-scale observations of GPP and ER are critical; these are characterized by large uncertainties (Wohlfahrt and Gu 2015). A promising new approach is the use of carbonyl sulfide (COS) flux measurements to estimate photosynthesis (Asaf et al 2013; Berry et al 2013; Wohlfahrt et al 2012). In contrast to CO2, COS is not emitted by plants and could, Oecologia (2017) 183:851–860 be used to estimate the gross CO2 uptake by the vegetation
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