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Title: Ephemeral microbial responses to pulses of bioavailable carbon in oxic and anoxic salt marsh soils
Roots of salt marsh grasses contribute to soil building but also affect decomposition by releasing bioavailable carbon exudates and oxygen. Disentangling exudate and oxygen effects on decomposition is difficult in the field but essential for marsh carbon models and predicting the impacts of global change disturbances. We tested how pulsed, simulated exudates affect soil metabolism under oxic and anoxic conditions, and whether carbon and oxygen availability facilitate mineralization of existing organic matter (i.e., priming). We conducted a laboratory experiment in flow-through reactors, adding carbon pulses weekly for 84 days and then following starvation under low carbon conditions. Oxygen consumption and sulfide production were inhibited under anoxic and oxic conditions and slowed by 21±10% and 55±8%, respectively, between 1- and 5- days following exudate pulses. Respiration rates immediately following and between pulses increased over time, suggesting that microbes capitalize on and may acclimate to patchy resources. Starvation caused oxygen consumption and sulfide production to fall 28% and 78% in oxic and anoxic treatments. Smaller decreases in oxygen consumption following pulses could suggest greater access to secondary carbon sources and that sulfate reducers were more reliant on exudates. Soil organic carbon was not the likely secondary source because porewater dissolved inorganic carbon 13C values did not change during transit through the reactors, despite a ~26‰ difference between the supplied seawater and marsh soil. Interpretation of oxygen consumption rates is complicated by non-respiratory oxidation of reduced inorganic compounds and possibly significant lithoautotrophy. Exudate pulses elicited rapid and ephemeral respiratory responses, particularly under anoxia, but non-respiratory oxidation of reduced compounds obscured the impact of oxygen availability in our experimental system. Despite this, greater aerobic respiration rates suggest that oxygen availability has more potential to regulate carbon mineralization in coastal wetlands than root exudates.  more » « less
Award ID(s):
2121019 1832178
NSF-PAR ID:
10477178
Author(s) / Creator(s):
; ; ; ;
Corporate Creator(s):
Editor(s):
Blagodatksaya, Evgenia
Publisher / Repository:
Elsevier
Date Published:
Journal Name:
Soil Biology and Biochemistry
Edition / Version:
1
Volume:
185
Issue:
C
ISSN:
0038-0717
Page Range / eLocation ID:
109157
Subject(s) / Keyword(s):
["Salt marsh","rhizosphere","organic carbon","redox","priming","sulfur oxidation"]
Format(s):
Medium: X Size: 5MB Other: pdf
Size(s):
["5MB"]
Sponsoring Org:
National Science Foundation
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