Abstract
Abstract. Developing a more mechanistic understanding of soil respiration is
hampered by the difficulty in determining the contribution of different
organic substrates to respiration and in disentangling autotrophic-versus-heterotrophic and aerobic-versus-anaerobic processes. Here, we use a
relatively novel tool for better understanding soil respiration: the
apparent respiration quotient (ARQ). The ARQ is the amount of CO2 produced
in the soil divided by the amount of O2 consumed, and it changes
according to which organic substrates are being consumed and whether oxygen
is being used as an electron acceptor. We investigated how the ARQ of soil
gas varied seasonally, by soil depth, and by in situ experimental warming
(+4 ∘C) in a coniferous-forest whole-soil-profile warming
experiment over 2 years. We then compared the patterns in ARQ to those of
soil δ13CO2. Our measurements showed strong seasonal
variations in ARQ, from ≈0.9 during the late spring and summer to
≈0.7 during the winter. This pattern likely reflected a shift from
respiration being fueled by oxidized substrates like sugars and organic
acids derived from root and root respiration during the growing season to
more reduced substrates such as lipids and proteins derived from microbial
necromass during the winter. This interpretation was supported by δ13CO2 values, which were lower, like lipids, in the
winter and higher, like sugars, in the summer. Furthermore,
experimental warming significantly changed how both ARQ and δ13CO2 responded to soil temperature. Wintertime ARQ and δ13CO2 values were higher in heated than in control plots,
probably due to the warming-driven increase in microbial activity that may
have utilized oxidized carbon substrates, while growing-season values were
lower in heated plots. Experimental warming and phenology change the sources
of soil respiration throughout the soil profile. The sensitivity of ARQ to
these changes demonstrates its potential as a tool for disentangling the
biological sources contributing to soil respiration.
Funder
Lawrence Berkeley National Laboratory
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
Cited by
9 articles.
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