Rapid mineralization of biogenic volatile organic compounds in temperate and Arctic soils

Biogenic volatile organic compounds (BVOCs) are produced by all life forms. Their release into the atmosphere is important with regards to a number of climate-related physical and chemical processes and great effort has been put into determining sources and sinks of these compounds in recent years. Soil microbes have been suggested as a possible sink for BVOCs in the atmosphere; however, experimental evidence for this sink is scarce despite its potentially high importance to both carbon cycling and atmospheric concentrations of these gases. We therefore conducted a study with a number of commonly occurring BVOCs labelled with 14C and modified existing methods to study the mineralization of these compounds to 14CO2 in four different topsoils. Five of the six BVOCs were rapidly mineralized by microbes in all soils. However, great differences were observed with regards to the speed of mineralization, extent of mineralization and variation between soil types. Methanol, benzaldehyde, acetophenone and the oxygenated monoterpene geraniol were mineralized within hours in all soils. The hydrocarbon monoterpene p-cymene was mineralized rapidly in soil from a coniferous forest but was mineralized slower in soil from an adjacent beech stand, while chloroform was mineralized slowly in all soils. From our study it is clear that soil microbes are able to completely degrade BVOCs released by above-ground vegetation as well as BVOCs released by soil microbes and plant roots. In addition to the possible atmospheric implications of this degradation, the very fast mineralization rates are likely important in shaping the net BVOC emissions from soil and it is possible that BVOC formation and degradation may be important but little-recognized parts of internal carbon cycling in soil.