Volatile organic compounds from decomposing leaf litter fuel microbial metabolism and alter community composition

Background/Question/Methods

The current paradigm of soil organic matter formation posits that the majority of stable soil organic matter is derived from labile dissolved organic carbon (C) compounds that are first assimilated by soil microorganisms before being stabilized on soil colloids. However, the role of volatile organic compounds – an abundant source of C in the soil – has largely been ignored in the study of the stabilization of soil organic C. In this study, we sought to determine the effect of volatile organic compounds on soil C cycling and microbial community structure. We used ¹³C labeled leaf litter from 3 species (tulip poplar, switchgrass, and Eucalyptus) to track volatile organic compound-C during leaf litter decomposition into soil C pools. We also used Illumina MiSeq to sequence the bacterial and fungal communities of soils that shared headspace with volatile organic compounds (VOC) from decomposing leaf litter.

Results/Conclusions

Decomposition derived volatile organic compound-C was detected in all of the measured soil C pools. On average, we observed that volatile organic compound-C accounted for 2.0, 0.6, 0.2, and 0.1% of microbial biomass C, dissolved organic C, mineral-associated C, and particulate organic matter C, respectively. We did not see an effect of litter species on the dissolved organic C and particulate organic matter C. However, for microbial biomass, we observed significant differences in the percentage of VOC-C across litters (F_2,9 = 10.4; P < 0.01). For mineral-associated C, we again observed a significant effect of litter species on the percentage of VOC-C observed in that pool (F_2,9 = 5.95; P < 0.05). Lastly, we observed a leaf litter species effect on microbial community composition. Of particular interest were VOC effects on nitrogen transforming microorganisms, implying that volatile organic compounds may also affect nitrogen cycling. This study provides clear evidence that volatile organic compounds play a significant role in soil C-cycling and are a potentially unexamined source of stable organic matter formation in the soil.