Volatile methanol and acetone additions increase labile soil carbon and inhibit nitrification

Recent efforts to understand the contribution of low-molecular weight compounds to carbon dynamics in soil ecosystems has resulted in a framework that suggests that low-molecular weight, labile carbon compounds can be directly assimilated by microbial biomass before being stabilized on soil colloids. However, this model primarily focuses on dissolved organic matter inputs and overlooks the potential importance of volatile organic compounds (VOCs). Here we determined the effects of two VOCs commonly emitted from soil and decomposing leaf litter (methanol, and acetone) on soil respiratory dynamics during a 28-day lab experiment. At the end of the experiment we quantified carbon and nitrogen concentrations in dissolved organic matter, microbial biomass, particulate organic matter, mineral associated organic matter, the labile carbon pool, and we quantified nitrifying microorganism abundance. Our results demonstrate that VOCs (i.e. methanol and acetone) increase soil respiration, contribute to labile soil C, and inhibit nitrification. Our VOC additions resulted in respiration spikes 4.1–5.5-fold greater than the control for acetone and methanol, respectively, though respiration returned back to control levels within 144 h after additions. Our VOC additions resulted in a 1.6–1.7-fold increase in labile soil carbon, suggesting that litter-derived VOCs could enter soil C pools following microbial metabolism. Additionally, soils exposed to VOCs contained ~ 2.25-fold less total dissolved nitrogen, and ~ 34–220-fold less nitrate. Ammonia oxidizing archaea were ~ 1.5 fold less abundant in VOC treated soils than in the control. After VOC additions were ceased, nitrate levels increased at approximately the same rate in all treatments, suggesting an inhibitory effect of methanol and acetone on nitrifying microorganisms. These results indicate that common decomposition derived VOCs play an important yet under-recognized role in driving the formation of soil organic matter as well as increasing the immobilization of nitrogen in soil ecosystems.