Reproducible growth of Brachypodium distachyon in fabricated ecosystems (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 Brachypodium distachyon hydroponically in novel fabricated ecosystem devices (EcoFAB 2.0) under three inorganic nitrogen forms (NO3-, NH4+, NH4NO3), followed by nitrogen starvation. Analyses of exudates with LC-MS/MS, biomass, medium pH, and nitrogen uptake showed EcoFAB 2.0s low intra-treatment data variability. Furthermore, the three inorganic nitrogen forms caused differential exudation, generalized by abundant amino acids/peptides and alkaloids. Comparatively, N-deficiency decreased N-containing compounds but increased shikimates/phenylpropanoids. Subsequent bioassays with two shikimates/phenylpropanoids (shikimic and p-coumaric acids) on the rhizobacterium Pseudomonas putida or Brachypodium seedlings revealed that shikimic acid promoted bacterial and root growth, while p-coumaric acid stunted seedlings. Our results suggest: (i) Brachypodium alters exudation in response to nitrogen status, which can affect rhizobacterial growth; and (ii) EcoFAB 2.0 is a valuable standardized plant research tool. TeaserEcoFAB 2.0, a novel fabricated ecosystem device, has low data variability in studies of plant traits.