Carbon inputs from riparian vegetation limit oxidation of physically-bound organic carbon via biochemical and thermodynamic processes

1 In light of increasing terrestrial carbon (C) transport across aquatic boundaries, the 2 mechanisms governing organic carbon (OC) oxidation along terrestrial-aquatic interfaces are 3 crucial to future climate predictions. Here, we investigate the biochemistry, metabolic pathways, 4 and thermodynamics corresponding to OC oxidation in the Columbia River corridor using ultra5 high resolution C characterization. We leverage natural vegetative differences to encompass 6 variation in terrestrial C inputs. Our results suggest that decreases in terrestrial C deposition 7 associated with diminished riparian vegetation induce oxidation of physically-bound OC. We 8 also find that contrasting metabolic pathways oxidize OC in the presence and absence of 9 vegetation and—in direct conflict with the ‘priming’ concept—that inputs of water-soluble and 10 thermodynamically favorable terrestrial OC protects bound-OC from oxidation. In both 11 environments, the most thermodynamically favorable compounds appear to be preferentially 12 oxidized regardless of which OC pool microbiomes metabolize. In turn, we suggest that the 13 extent of riparian vegetation causes sediment microbiomes to locally adapt to oxidize a particular 14 pool of OC, but that common thermodynamic principles govern the oxidation of each pool (e.g., 15 water-soluble or physically-bound). Finally, we propose a mechanistic conceptualization of OC 16 oxidation along terrestrial-aquatic interfaces that can be used to model heterogeneous patterns of 17 OC loss under changing land cover distributions. 18 19 20 21 . CC-BY-NC-ND 4.0 International license peer-reviewed) is the author/funder. It is made available under a The copyright holder for this preprint (which was not . http://dx.doi.org/10.1101/105486 doi: bioRxiv preprint first posted online Feb. 2, 2017;