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| Titel |
Disentangling the drivers of soil organic matter decay as temperature changes by integrating reductionist systems with soil data |
| VerfasserIn |
Sharon Billings, Ford Ballantyne, Kyungjin Min, Christoph Lehmeier, Susan Ziegler |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092646
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| Publikation (Nr.) |
 EGU/EGU2014-7004.pdf |
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| Zusammenfassung |
| Accurately predicting decomposition rates of soil organic matter (SOM) as temperature
increases is critical for projecting future atmospheric [CO2]. SOM decay is catalyzed by
exo-enzymes (EEs) produced by microorganisms and secreted into the soil. Microbes take up
liberated resources for metabolic processes and release diverse compounds, including CO2.
Historically, investigations of the influence of temperature on heterotrophic CO2 release have
focused on CO2 response, including its isotopic composition; recent studies also assess EE
activity and microbial community composition. However, it is difficult to generalize from
such studies how temperature will influence SOM decay and CO2 release because
the responses of EEs, microbial resource demand, biomass production rates, and
respiration rates are not parsed. Quantifying the individual temperature responses
of all of these processes in unaltered soil is not tractable. However, we can use
experimentally simplified systems to quantify fundamental biochemical and physiological
responses to temperature and compare these results to those from environmental
samples. For example, we can quantify the degree to which EE kinetics in isolation
induce changes in availability of microbially assimilable resources as temperature
changes and calculate associated changes in relative availability of assimilable
carbon and nitrogen (C:N flow ratio), in isolation from altered microbial resource
demand or uptake. We also can assess EE activity and CO2 release at different
temperatures in diverse soils, integrating temperature responses of EE kinetics and
microbial communities. Discrepancies in the temperature responses between real
soils and isolated enzyme-substrate reactions can reveal how adaptive responses of
microbial communities influence the temperature responses of soil heterotrophic CO2
release.
We have shown in purified reactions that C:N flow ratios increase with temperature at pH 4.5,
but decline between pH 6.5 and 8.5. If soil microbes exhibited no change in resource demand
or C allocation with altered C:N flow ratios and if relative C availability was tightly
coupled to respiration, we would expect variation in C:N flow ratios predicted by
purified solutions to be expressed in analogous, relative patterns of C mineralization.
However, the positive response of heterotrophic CO2 release to similar temperature
increases in five strongly acidic forest soils (three boreal, one cool temperate, and one
warm temperate) was much smaller than in a neutral-pH grassland or an alkaline
desert, the opposite of what we might predict if C:N flow ratio was the only driver
of respiratory responses to temperature. We also observe distinct d13C of CO2
respired from pure cultures in which substrate composition and availability are strictly
controlled as temperature changes, reflecting fundamental shifts in C flux through
metabolic pathways. These changes in d13C-CO2 with warming are greater than
those observed in soils. Combined, these CO2 and d13C-CO2 data suggest that
soil microbial adaptation to temperature is a meaningful driver of heterotrophic
respiratory responses to temperature. We highlight the utility of reductionist experimental
systems for characterizing fundamental SOM decay rates and changes in microbial C
metabolism at different temperatures, and integrating them with analogous data
derived from soils to quantify the role of microbial adaptation as a driver of SOM
decay. |
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