Matthias, very nice important and thoughtful post. Reminded me of early discussions from my time in Tom Brock's lab that affected my entire career, on the nature of the 'killed' control. As with most things, Tom wrote up his thoughts and published them here (I have not been able to track down article online) -- Brock TD. 1978. The poisoned control in biogeochemical investigations. In: Krumbein, W.E. (editor). Environmental Biogeochemistry and Geomicrobiology. Ann Arbor Science Publishers, Ann Arbor, MI. 3:717-725

I think this is particularly difficult in soils -- autoclaving may change the chemical nature of the soil matrix. We had gone to gamma radiation; but after 30 days there remained some chance that activity would re-emerge.

Best,

Allan