OOS 72-7
Macroscale analysis of microbial community homeostasis

Thursday, August 13, 2015: 3:40 PM
315, Baltimore Convention Center
Robert Sinsabaugh, Biology Department, University of New Mexico, Albuquerque, NM
Daryl L. Moorhead, Environmental Sciences, University of Toledo, Toledo, OH
Stuart E.G. Findlay, Cary Institute of Ecosystem Studies, Millbrook, NY
Kevin A. Kuehn, Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, MS
Jennifer Follstad Shah, Watershed Sciences Department, Utah State University, Logan, UT

The capacity of microbial communities to maintain steady state biomass composition and metabolic rates regulates biogeochemical processes.  The elemental C,N and P stoichiometries of organic matter (LC:X) and microbial biomass (BC:X, where X=N or P) are connected through a meta-metabolomic sequence of extracellular digestion, assimilation and cellular metabolism linked by ratios of ecoenzymatic activity (EEAC:X), assimilation efficiency (AC:X) and use efficiency (UEC:X):  BC:X = (EEAC:XŸAC:XŸUEC:E)ŸLC:X.  The dependent relationships among these variables can be described by stoichiometric (S) and elasticity coefficients (ε) estimated from ln-ln regressions.  Using meta-analysis, we calculated S and ε coefficients and frequency distributions for these variables to identify the functional constraints on microbial community organization.  


The abundance of C, N and P substrates in the environment are generally correlated with S ~ 1.0.  The most widely assayed C, N and P-acquiring ecoenzyme activities (EEA) show a similar pattern (S ~ 1.0), as do the relationships between EEA and organic matter and between EEA and microbial production (μ).  Across a broad range of enzymes and ecosystems, catalytic capacity (apparent Vmax) and substrate availability (apparent Km) covary with ε ~ 0.5, a condition optimal for maintenance of steady state. The coefficients for production vs. biomass (B) are similar for fungi and bacteria (ε ~ 0.75), as are the coefficients for respiration (R) and production (S ~ 0.5). Because R lags μ, carbon use efficiency (CUE) increases with B0.25.  Mean CUE for both bacteria and fungi is 0.3.  Median biomass turnover times (B/μ) for bacteria and fungi (112 and 1128 h, respectively), overlap substantially with substrate turnover times (2Km/Vmax) in proportion to the ratio of assimilation efficiency to carbon use efficiency (A/CUE). Collectively, these relationships describe the homeostatic constraints on microbial community organization and merge ecological theory with the microbiome paradigm.