Effect of drought on soil microbial metabolisms driving carbon
allocation and volatile organic compound cycling in the tropical
rainforest at Biosphere 2
Abstract
Droughts are occurring with increased frequency and duration in tropical
rainforests due to climate change, having a significant impact on soil C
dynamics. The role of microbes as drivers of changing C flow,
particularly in relation to volatile organic compound (VOC) cycling,
remains largely unknown. Here, we aimed to characterize microbial
responses to drought using an integrative, multiple ‘omics approach, and
hypothesized that microbial communities will adapt by altering their C
allocation strategies. Specifically, during pre-drought, primary
metabolic pathways will be more active with microbes using C towards
growth, whereas during drought, microbes will divert C to secondary
metabolite (including VOC) production in response to stress. To test
this, we conducted an ecosystem-wide 66-day drought experiment in the
tropical rainforest biome at Biosphere 2, a glass- and steel-enclosed
facility near Tucson, AZ. To track carbon allocation by microbes, we
injected C1 or C2 position-specific 13C-pyruvate solution into a 25 cm2
region within a soil flux chamber collar (n=6 locations) and measured C
isotope ratios of VOC and CO2 emissions. Soil was collected at 0, 6, and
48 hours after pyruvate addition to examine responses in soil
metatranscriptomics, metagenomics, and metabolomics (1H nuclear magnetic
resonance [NMR] and Fourier-transform ion cyclotron resonance
[FTICR]). Our results indicated that 13CO2 (primarily emitted from
C1-13C-pyruvate) fluxes decreased during drought, indicating diminished
microbial activity. 13C-VOCs (primarily emitted from C2-13C-pyruvate)
fluxes also differed between pre-drought and drought. Furthermore,
drought-induced increases in activity of VOC-producing metabolic
pathways, including acetate and acetone biosynthesis, were evident, as
inferred from volatilome, metabolome, and metatranscriptome data.
Overall, these results indicate that integration of multiple ‘omics
datasets reveal specific impacts of drought on microbial activity
affecting carbon flow in the tropical rainforest soil.