Inundation and drought affect soil eukaryote dominance but not occurrence in Australian floodplain soils

Background/Question/Methods

Sustained inundation and drought are significant disturbance events for most soil systems, yet floodplain biota must be able to regularly survive such extremes.  A unique series of flood events occurring within a decade of extreme drought in semi-arid southern Australia’s Yanga National Park has enabled us to explore the combined long-term effects of flood return interval and drought on floodplain soil biodiversity. Here, human manipulation of minor flooding events across a lowland floodplain in Yanga National Park combined to create a mosaic of flood histories, many separated only by narrow levee banks. High-throughput barcoded pyrosequencing was used to define the chronosequence of soil eukaryotic community structures in this floodplain from sites submersed for over a year to nine years since last inundation. 

Results/Conclusions

Using space for time substitution we show that eukaryotic biodiversity on this floodplain shifts within two years of a flood event to become dominated by terrestrial organisms. However, less than a tenth of the total biota were restricted to long-term drought locations while a quarter of the biota were present across inundated to drought soils, suggesting that most of the biota are adapted to frequent disturbance intervals.  Analysis of soil eukaryote betadiversity patterns showed that communities transitioned from inundated to drought states primarily through changes in the relative abundance of organisms.  Such a core of persistent organisms may be fundamental to the viability and underpin resitance of floodplain soils during disturbance events, suggesting that this biota can be used to detect important changes in floodplain condition in the long-term.