Abstract:
Recenttechnologicaladvanceshaveenabledthewiderapplicationofautomatedchambers for soil greenhouse gas (GHG) ?ux measurements, several of them commercially available. However, only few studies addressed the di?culties and challenges associated with operating these systems. In this contribution we compared two commercial5 soil GHG chamber systems–the LI-8100A Automated Soil CO2 Flux System and the Greenhouse Gas Monitoring System AGPS. From April 2014 until August 2014, the two systems monitored in parallel soil respiration (SR) ?uxes at a recently harvested poplar plantation, which provided a bare ?eld situation directly after the harvest as well as a closed canopy later on. For the bare ?eld situation (15 April–30 June 2014),10 the cumulated average SR obtained from the un?ltered datasets of the LI-8100A and the AGPS were 520 and 433g CO2 m?2, respectively. For the closed canopy phase (01 July–31 August 2014), which was characterized by a higher soil moisture content, the cumulated average SR estimates were not signi?cantly di?erent with 507 and 501g CO2 m?2 for the AGPS and the LI-8100A, respectively. Flux quality control and ?ltering15 did not signi?cantly alter the results obtained by the LI-8100A, whereas the AGPS SR estimates were reduced by at least 20%. The main reasons for the observed di?erences in the performance of the two systems were (i) a lower data coverage provided by the AGPS due to technical problems; (ii) incomplete headspace mixing in the AGPS chambers; (iii) lateral soil CO2 di?usion below the collars during AGPS chamber mea-20 surements; (iv) increased root growth within the LI-8100A collars; and (v) a possible overestimation of nighttime SR ?uxes by the LI-8100A. In contrast to the LI-8100A, the AGPS had the gas sample inlets installed inside the collars and not the chambers. This uniquedesignfeatureenabledforthe?rsttimethedetectionofdisturbedchambermeasurements during nights with a strati?ed atmosphere, resulting in unbiased nighttime25 SR estimates. Thus besides providing high temporal frequency ?ux data, automated chamber systems o?er another possibility to greatly improve our understanding of SR ?uxes.
