Canopy uptake dominates nighttime carbonyl sulfide fluxes in a boreal forestKooijmans, L. M. J., Maseyk, K., Seibt, U., Sun, W., Vesala, T., Mammarella, I., Kolari, P., Aalto, J., Franchin, A., Vecchi, R., Valli, G. & Chen, H. 26-Sep-2017 In : Atmospheric Chemistry and Physics. 17, 18, p. 11453-11465 13 p.
Research output: Scientific - peer-review › Article
Nighttime vegetative uptake of carbonyl sulfide (COS) can exist due to the incomplete closure of stomata and the light independence of the enzyme carbonic anhydrase, which complicates the use of COS as a tracer for gross primary productivity (GPP). In this study we derived night-time COS fluxes in a boreal forest (the SMEAR II station in Hyytiala, Finland; 61 degrees 51 ' N, 24 degrees 17 ' E; 181ma.s.l.) from June to November 2015 using two different methods: eddy-covariance (EC) measurements (FCOS-EC) and the radon-tracer method (FCOS-Rn). The total night-time COS fluxes averaged over the whole measurement period were -6.8 +/- 2.2 and -7.9 +/- 3.8 pmolm (-2) s (-1) for FCOS-Rn and FCOS-EC, respectively, which is 33-38% of the average daytime fluxes and 21% of the total daily COS uptake. The correlation of Rn-222 (of which the source is the soil) with COS (average R-2 = 0.58) was lower than with CO2 (0.70), suggesting that the main sink of COS is not located at the ground. These observations are supported by soil chamber measurements that show that soil contributes to only 34-40% of the total night-time COS uptake. We found a decrease in COS uptake with decreasing nighttime stomatal conductance and increasing vapor-pressure deficit and air temperature, driven by stomatal closure in response to a warm and dry period in August. We also discuss the effect that canopy layer mixing can have on the radon-tracer method and the sensitivity of (FCOS-EC) to atmospheric turbulence. Our results suggest that the nighttime uptake of COS is mainly driven by the tree foliage and is significant in a boreal forest, such that it needs to be taken into account when using COS as a tracer for GPP.
|Number of pages||13|
|Journal||Atmospheric Chemistry and Physics|
|State||Published - 26-Sep-2017|