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| Titel |
Investigating the legacy effect of drought on microbial responses to drying and rewetting along a Texan precipitation gradient |
| VerfasserIn |
Lettice Hicks, Ainara Leizeaga, Christine Hawkes, Johannes Rousk |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250152345
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| Publikation (Nr.) |
 EGU/EGU2017-17172.pdf |
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| Zusammenfassung |
| Hydrological regimes will intensify due to climate change, thus increasing the duration and
intensity of drought and rainfall events. Rewetting of dry soil is known to stimulate dramatic
CO2 releases. A clear understanding of the mechanisms that determine the dynamics of CO2
loss upon rewetting is therefore required to characterise ecosystem C-budgets and predict
responses to climate change. Laboratory studies have identified two distinct responses upon
rewetting; bacterial growth either increases linearly immediately, with maximal respiration
also occurring immediately and decreasing exponentially with time (“Type 1”), or bacterial
growth increases exponentially after a period of near-zero growth, with a sustained period of
elevated respiration, sometimes followed by a secondary increase in respiration coinciding
with the onset of bacterial growth (“Type 2”). A shift from a Type 1 to a Type 2
response has been observed with increasing duration and intensity of drying prior to
rewetting. The size of the surviving microbial community after drying, relative to
resources available after rewetting, is suggested to dictate whether a Type 1 or 2
response occurs, with more ‘harsh’ (i.e. longer or more severe) drying reducing
microbial biomass such that carbon available upon rewetting is sufficient to support
exponential growth (leading to Type 2 response). However, this is yet to be tested in intact
ecosystems.
We investigated the legacy of drought on microbial responses to drying and rewetting
using grassland soils from a natural precipitation gradient in Texas. Mean annual
precipitation spanned a 500 mm range (400-900 mm year−1) across the 400 km gradient,
while mean annual temperature was constant. Soil properties (pH, SOM) did not vary
systematically across the gradient, with differences reflecting land-use history rather
than rainfall. Air dried soils from 18 sites were rewetted to 50 % water holding
capacity with bacterial growth, fungal growth and respiration measured at high
temporal resolution over 7 days. We predicted that there would be a shift in the type of
response to rewetting (Type 1 to Type 2) across the gradient, as a consequence
of exposure to harsher drying. Further, given the lack of systematic variation in
other factors with rainfall, we expected levels of maximal growth and respiration
as well as the level of steady state growth and respiration to be similar across the
gradient.
All soils exhibited a Type 1 response, with respiration, bacterial and fungal growth
increasing immediately upon rewetting and typically stabilising after c. 20 hours. There were,
however, differences in the magnitude of CO2 release and microbial growth among soils,
whereby rewetting of historically wetter soils stimulated higher rates of microbial
growth and a greater release of CO2, compared to rewetting of historically drier
soils.
Contrary to expectations, there was no difference in the type of microbial response to
rewetting, but instead a systematic dependence of overall microbial rates, depending on the
legacy of drought. This contrasted with previous laboratory studies, suggesting that exposure
to drought across the natural gradient was not perceived as ‘harsh’ by the microbial
communities. This may be explained by either (i) differences in resource availability (i.e.
plant input) mitigating the microbial susceptibility to drought in intact ecosystems or (ii)
microbial tolerance to drought. |
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