Drought induces soil microbial stress responses and emissions of volatile organic compounds in an artificial tropical rainforest

Drought impacts microbial carbon cycling, and thus the fate of carbon in soils. Carbon allocation to energy via CO2 producing respiration and to biosynthesis via volatile organic compound (VOC) emissions both represent consequent carbon loss to the atmosphere, although only the former is well studied. Here, we examined drought impacts on carbon allocation by soil microbes to CO2 and VOCs using position-specific 13C-labeled pyruvate and multi-omics in an artificial tropical rainforest. During drought, 13C-VOCs efflux increased, driven by increased production and buildup of intermediate metabolites due to decreased interconnectivity between central carbon metabolism pathways, and 13C-CO2 efflux decreased, driven by an overall decrease in microbial activity. However, internal carbon allocation to energy relative to biosynthesis did not change, signifying maintained energy demand toward biosynthesis of VOCs and drought-stress induced biosynthesis pathways. Therefore, while carbon loss to the atmosphere via CO2 decreases during drought, carbon loss via VOCs may increase.