Reproducible growth of <i>Brachypodium</i> in EcoFAB 2.0 reveals that nitrogen form and starvation modulate root exudation.

Abstract

Understanding plant-microbe interactions requires examination of root exudation under nutrient stress using standardized and reproducible experimental systems. We grew <i>Brachypodium distachyon</i> hydroponically in fabricated ecosystem devices (EcoFAB 2.0) under three inorganic nitrogen forms (nitrate, ammonium, and ammonium nitrate), followed by nitrogen starvation. Analyses of exudates with liquid chromatography-tandem mass spectrometry, biomass, medium pH, and nitrogen uptake showed EcoFAB 2.0's low intratreatment data variability. Furthermore, the three inorganic nitrogen forms caused differential exudation, generalized by abundant amino acids-peptides and alkaloids. Comparatively, nitrogen deficiency decreased nitrogen-containing compounds but increased shikimates-phenylpropanoids. Subsequent bioassays with two shikimates-phenylpropanoids (shikimic and <i>p</i>-coumaric acids) on soil bacteria or <i>Brachypodium</i> seedlings revealed their distinct capacity to regulate both bacterial and plant growth. Our results suggest that (i) <i>Brachypodium</i> alters exudation in response to nitrogen status, which can affect rhizobacterial growth, and (ii) EcoFAB 2.0 is a valuable standardized plant research tool.