Plant mediates soil water content effects on soil microbiota independently of its water uptake

Abstract

The on-going climate change impacts soil water distribution and availability, ranging from highly limited during droughts to excessive during rainfalls. While effects of water availability were documented for soil microbiota and plant growth, it remains unclear if the soil microbiota is directly impacted by soil water content (SWC) or via the plant presence and its own response to water fluctuations. Uncoupling these effects is challenging, since the plant alters SWC via its water-uptake and transpiration. We aimed to identify a potential effect of the plant on the soil microbiota, independent of its water uptake. We studied soil microbiota in two contrasting soils exposed to three water levels, either under the presence or absence of Brassica juncea (drought sensitive, waterlogging tolerant) or Brachypodium distachyon (drought tolerant, waterlogging sensitive). Using an automatic high-throughput watering system, we accurately maintained SWC levels to compensate plant water uptake and evapotranspiration, thus enabling the detection of plant effects, independently of its water uptake. Plant traits were measured and the soil bacterial and fungal communities with or without plants were analysed. We highlighted effects of the plant on the microbiota under varying SWC, independently of plant water uptake. These effects were likely instigated by the physiological state of the plant due to SWC, and were dependant on the plant species and the soil considered. While bacterial communities were more sensitive to SWC than fungal communities, we found that the fungal community in the clayey soil was directly affected by SWC, and could opportunistically interact with a drought sensitive plant like Brassica juncea.