Merging Ecological Theory with Organic Geochemistry and Environmental Metabolomics

In recent years there have been significant advances in understanding organic geochemistry and its interaction with environmental microbiomes. New tools have also emerged that enable quantitative descriptions of underlying mechanisms that couple microbes with the diverse suite of organic molecules that environmental microbes transform and produce. Linking this understanding to systems-scale biogeochemical function is a major challenge. Recent evidence from the hyporheic zone indicates that ultra-high resolution organic carbon profiles—here broadly interpreted as environmental metabolomes—explain nearly 80% of the variation in measured biogeochemical rates, while metaproteomic and metagenomic profiles explain virtually none. Here we will discuss an opportunity to meld microbial ecology with organic geochemistry by bringing ecological theory to bear on understanding spatiotemporal patterns of environmental metabolomes. A quantitative approach will be demonstrated using surface water, the hyporheic zone, and groundwater systems. This approach can be readily extended to other components of the Earth system such as terrestrial, coastal, and marine ecosystems. The merging of ecology with organic geochemistry via metabolomics has potential to reveal when coupled physical-chemical-biological systems are in a state of transition and when they are in relative stasis. This is critical for understanding and ultimately predicting the influences of environmental perturbation. In addition, the ecology-metabolomics linkage has potential to reveal the relative influences of hydrologic transport versus reaction rates on in situ biogeochemical activity. This outcome can therefore tie metabolomics and organic geochemistry to the Damkohler number, thereby indicating when, where, and why biogeochemical hotspots occur.