Abstract
• Root exudates are thought to play an important role in plant-microbial interactions. In return for nutrition, soil bacteria can increase the bioavailability of soil nutrients. However, root exudates typically decrease in situations such as drought, calling into question the efficacy of solvation and bacteria-dependent mineral uptake in such stress. • Here we tested the hypothesis of exudate-driven microbial priming on Cupressus saplings grown in forest soil in custom-made rhizotron boxes. A 1-month imposed drought and concomitant inoculations with a mix of Bacillus subtilis and Pseudomonas stutzeri, bacteria species isolated from the forest soil, were applied using factorial design. • Direct bacteria counts and visualization by confocal microscopy showed that both bacteria associated with Cupressus roots. Interestingly, root exudation rates increased 2.3-fold with bacteria under drought, as well as irrigation. Forty four metabolites in exudates were significantly different in concentration between irrigated and drought trees, including phenolic acid compounds and quinate. When adding these metabolites as carbon and nitrogen sources to bacterial cultures of both bacterial species, 8 of 9 metabolites stimulated bacterial growth. Importantly, soil phosphorous bioavailability was maintained only in inoculated trees, mitigating drought-induced decrease in leaf phosphorus and iron. • Our observations of increased root exudation rate when drought and inoculation regimes were combined, support the idea of root recruitment of beneficial bacteria, especially under water stress.
| Original language | American English |
|---|---|
| Article number | e79679 |
| Journal | eLife |
| Volume | 11 |
| DOIs | |
| State | Published - Jul 2022 |
| Externally published | Yes |
Bibliographical note
Funding Information:The project was funded by The Edith and Nathan Goldenberg Career Development Chair; Mary and Tom Beck-Canadian Center for Alternative Energy Research; Larson Charitable Foundation New Scientist Fund; Angel Faivovich Foundation for Ecological Research; Yotam Project; Dana and Yossie Hollander; Estate of Emile Mimran; and Estate of Helen Nichunsky.We thank The Weizmann Tree Lab members for support, advice and helpful discussions throughout. We also thank Guy Shmuel for providing us with a protocol of ICP-MS; Nir Galili for help with earlier experiments; Roee Ben Nissan for assistance with programing of bacteria growth curve; Ron Rotkopf for guidance with statistical analysis; and Sergey Kapishnikov for coordinating the elemental mapping experiments (Weizmann Institute of Science). We thank SH Lau and the engineers of Sigray (San Francisco, CA, USA) for performing the elemental mapping on our samples; Robert Fluhr (Weizman Institute of Science), Daniel Dar (Caltech, CA, USA), and Sophie Obersteiner (Ben Gurion University, Israel), for providing helpful comments on earlier versions of this paper.
Funding Information:
The project was funded by The Edith and Nathan Goldenberg Career Development Chair; Mary and Tom Beck-Canadian Center for Alternative Energy Research; Larson Charitable Foundation New Scientist Fund; Angel Faivovich Foundation for Ecological Research; Yotam Project; Dana and Yossie Hollander; Estate of Emile Mimran; and Estate of Helen Nichunsky.
Publisher Copyright:
© 2022, eLife Sciences Publications Ltd. All rights reserved.
Keywords
- Drought
- leaf elements
- metabolomics
- microbial priming
- root exudation