EGU2020-16648
https://doi.org/10.5194/egusphere-egu2020-16648
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Is microbial resilience to drying-rewetting driven by selection for quick colonizers?

Lettice Hicks, Simon Lin, and Johannes Rousk
Lettice Hicks et al.
  • Lund University, Department of Biology, Microbial Ecology, Lund, Sweden

Climate change is exposing terrestrial ecosystems to more extreme drought and rainfall events, resulting in an increased frequency and intensity of drying-rewetting (D/RW) events in soils. Rewetting a dry soil induces enormous dynamics in both microbial growth and biogeochemistry, including a large pulse of COrelease to the atmosphere. Upon D/RW, two different microbial growth responses have been identified; a more resilient response where bacteria start growing immediately with a quick recovery after rewetting and a less resilient response where there is a lag-period of up to 30 hours of near-zero growth before bacteria start to grow. The resilience of microbial growth following D/RW has important implications for the ecosystem C budget, since an extended lag-period of no growth during a time of high COrelease will result in net soil C loss. In natural systems, it has been found that a legacy of drought led to a more resilient bacterial growth response upon rewetting, with a reduced lag-period before the onset of growth. Exposing soils to repeated cycles of D/RW in the laboratory has also been shown to shift bacterial growth responses to a more resilient type. We hypothesised that this shift in response is explained by selection for a microbial community which is quick at colonizing the labile C resources made available upon D/RW.  

In order to test our hypothesis, we pre-treated soils by exposing them to either (i) three cycles of D/RW, (ii) three pulses of glucose addition or (iii) three pulses of litter addition. The substrate additions were used to simulate the labile C release in soils during D/RW, thereby enabling us to investigate if the colonization of new substrate is the causal mechanism explaining the observed shift in bacterial resilience in soils with a history of D/RW. The pre-treated soils – along with an unamended control soil – were then exposed to the same D/RW event, with bacterial growth, fungal growth and respiration responses measured at high temporal resolution over 4 days. As previously reported, exposing the soil to a series of D/RW events resulted in a more resilient bacterial growth response, with the lag-period reduced from ca. 30 hours to an immediate initiation of growth. Pre-treating the soils with glucose reduced the lag-period before the onset of bacterial growth by ca. 50% whereas pre-treatment with litter induced only a marginally (< 10%) more resilient bacterial growth response to D/RW. Interestingly, pre-treatment of the soils with glucose and litter both induced a more resilient fungal growth response, with the responses resembling the shift in fungal resilience induced by exposing the soils to repeated cycles of D/RW. Overall, our results show that selection for quick colonizers partly explains the shift to more resilient microbial growth in soils exposed to repeated D/RW events, but further investigation is required to identify additional factors contributing to the shift in resilience.

How to cite: Hicks, L., Lin, S., and Rousk, J.: Is microbial resilience to drying-rewetting driven by selection for quick colonizers? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16648, https://doi.org/10.5194/egusphere-egu2020-16648, 2020

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