Abiotic condition plays an important role and shapes the amplitude or the direction of the plant - microbe interaction, on plant-phenotype and molecular level, in studies of elevated temperature or nitrogen limitation

Plant roots grow in a changing environment in every stage of soil exploration [1]. Studying the root in its native conditions is challenging, but non-invasive phenotyping can help to understand the space-time interaction between root growth, soil and microbes [2].Elevated temperature is a rising agricultural problem. We show that Paraburkholderia phytofirmans (PsJN) improved plant performance in Arabidopsis at 30°C, using an advanced version of GrowScreen-Agar [3]. Root responses to PsJN were dynamic, and included increases in lengths and growth rates of roots and changes in root angles under both temperatures. The onset of beneficial interaction was at day 12 post inoculation and the growth promotion was greater in plants with PsJN at ambient temperature vs. 30°C. Importantly, the improvement at 30°C significantly reduced heat stress responses. Analysis of shoot biomass correlated to the root results. Lipidomic measurements will compare systemic changes e.g. of membrane lipids.Overuse of fertilizers is a serious environmental problem, and recent regulations limit Nitrogen (N) fertilizers per unit arable land impacting yield. Thus, we study the plant response to N-fixing bacteria. In two projects, the cereal model Brachypodium dystachion (Bd) shows different response to N-fixing bacteria based on N availability. Inoculation with Herbaspirillum seropedicae (Hs) in EcoFABs [4] resulted in longer primary roots and shorter root hairs regardless of N, with stronger changes at low N. A mass-balance calculation showed that at high N, Hs provided 11% total plant N from sources other than seed or nutrient solution, correlated to N-metabolism transcript expression. Time-resolved phenotypic and molecular data indicates two modes of action: At 5 mM Bd benefits through Hs N-fixation; at 0.5 mM Hs promotes N-uptake from the root medium