EFFECTS OF MODEL ROOT EXUDATES ON SOIL RESPIRATION IN CONTRASTING SALT MARSHES

Salt marshes play a crucial role in the global carbon (C) cycle through efficient sequestration in soils. Yet, the mechanisms that lead to marsh organic C preservation versus microbial degradation remain unclear. Root exudates can help to build new soil organic matter but may also catalyze decomposition of previously buried C through biotic and abiotic priming mechanisms. We hypothesized that priming mechanisms differ between organic and mineral soils, with biotic co-metabolism dominating in the former and abiotic mechanisms in the latter. To test this, we continuously supplied mineral and organic marsh soils with ¹³C-glucose (biotic priming), ¹³C-oxalic acid (abiotic priming), or unamended seawater (control) under oxic or anoxic conditions for 7 days in flow-through reactors, which simulate porewater percolation. Glucose stimulated respiration, as net dissolved inorganic C (DIC) production, more than oxalic acid in both marsh soils. However, after normalizing DIC production to the amount of substrate added, we found proportionally higher respiratory response to oxalic acid than to glucose, particularly in the mineral soils. This was supported by ¹³C-DIC mixing models which estimated greater contributions from existing soil C to net C respiration in oxalic acid treatments. These findings suggest that abiotic priming may more effectively mobilize native soil C than biotic priming (co-metabolism), particularly in mineral salt marshes.

Presentation Preference: Oral

Primary Presenter: Britany Guo, University of Georgia (bg06386@uga.edu)

Authors:

Britany Guo, University of Georgia  (bg06386@uga.edu)

Amanda Spivak, University of Georgia  (aspivak@uga.edu)

Jennifer Pett-Ridge, Lawrence Livermore National Laboratory  (pettridge2@llnl.gov)