Fine-tuning root exudation sampling procedures– evaluating the effect of sampling solution volume and the suitability of Micropur as microbial activity inhibitor

Abstract

Background and aim: Root exudates are the main drivers of plant-microbes-soil interactions. There are several approaches to collect root exudates, but critical methodological evaluation remains limited. The goal of this study was to assess the effect of the applied sampling solution volume and to test the suitability of Micropur as microbial activity inhibitor during the exudate sampling process. Methods: Using Zea mays L. as model plant and the soil-hydroponic hybrid exudate sampling approach, we tested the effect of different sampling solution volumes and different Micropur concentrations on maize root exudation. Additionally, a sterile hydroponic-only experiment was conducted to monitor potential effects of Micropur on maize physiology. Photometric and LC-TOF-MS analyses were used to reveal the effect of different conditions on root exudation and plant stress response. Results: Our results demonstrated that both, the sampling volume as well as the presence or absence of microbial activity inhibitor can significantly affect obtained exudation results. Carbon exudation rates were underestimated when using a small sampling volume relative to the root biomass. Even though the overall C exudation was minimally affected by microbial degradation, the addition of Micropur (≥ 5 mg L−1) significantly reduced the decomposition of 14C citric acid. Maize plants did not show any stress symptoms upon exposure to different concentrations of MP but root membrane permeability and exudation were negatively affected when using MP concentrations >5 mg L−1. Conclusion: Our findings highlight the importance of thoroughly evaluating experimental procedures and delivers relevant insights supporting future experimental designs targeting root exudates.