Drought re-routes soil microbial carbon metabolism towards emission of volatile metabolites in an artificial tropical rainforest

Abstract

Drought impacts on microbial activity can alter soil carbon fate and lead to the loss of stored carbon to the atmosphere as CO₂ and volatile organic compounds (VOCs). Here we examined drought impacts on carbon allocation by soil microbes in the Biosphere 2 artificial tropical rainforest by tracking ¹³C from position-specific ¹³C-pyruvate into CO₂ and VOCs in parallel with multi-omics. During drought, efflux of ¹³C-enriched acetate, acetone and C₄H₆O₂ (diacetyl) increased. These changes represent increased production and buildup of intermediate metabolites driven by decreased carbon cycling efficiency. Simultaneously,¹³C-CO₂ efflux decreased, driven by a decrease in microbial activity. However, the microbial carbon allocation to energy gain relative to biosynthesis was unchanged, signifying maintained energy demand for biosynthesis of VOCs and other drought-stress-induced pathways. Overall, while carbon loss to the atmosphere via CO₂ decreased during drought, carbon loss via efflux of VOCs increased, indicating microbially induced shifts in soil carbon fate.