Drought-induced soil microbial amino acid and polysaccharide change and their implications for C-N cycles in a climate change world.

High microbial carbon (MBC) demand, a proxy for energy demand (cost), during soil microbial response to stressors such as drought are a major gap in understanding global biogeochemical cycling of carbon (C) and nitrogen (N). The dynamics of two dominant microbial pools (amino acids; AA and exopolymeric substances; EPS) in soils exposed to drying and C and N amendment to mimic both low and high nutrient soil habitats were examined. It was hypothesized that dynamics of EPS and AA (osmolytes) would be greater when soil drying was preceded by a pulse of bioavailable C and N. Drying reduced AA content, even as overall soil MBC increased (~35%). The increase in absolute amounts and mol% of certain AA (eg: Taurine, glutamine, tyrosine, phenylalanine) in the driest treatment (-10 MPa) were similar in both soils regardless of amendment suggesting a common mechanism underlying the energy intensive acclimation across soils. MBC and EPS, both increased ~1.5X and ~3X due to drying and especially drying associated with amendment. Overall major pools of C and N based microbial metabolites are dynamic to drying (drought), and thus have implications for earth's biogeochemical fluxes of C and N, perhaps costing 4-7% of forest fixed photosynthetic C input during a single drying (drought) period.