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Purpose: Root exudates are key components driving belowground interaction between plant, microbes and soil. High-end analytical approaches provide advanced insights into exudate metabolite diversity, however, the amount of total carbon (C) released by roots should always be determined as the most basic parameter when characterizing root exudation as it (i) provides quantitative information of C exuded into the surrounding soil and (ii) allows to relate the abundance of individual exudate compounds to total C released. Here we propose a simple and quick, spectrophotometry-based method to quantify total dissolved organic carbon (DOC) concentration in exudation samples that is based on measuring the absorption of a pre-filtered but otherwise untreated exudate sample at 260 nm (DOC260). Method: Exudate samples collected from different grass genotypes (Zea mays, Oryza sativa, Hordeum vulgare) grown in various experimental settings (soil, hydroponic) were analysed with the DOC260 assay and results were compared with C concentrations obtained by liquid TOC-analyser. Conclusion: We demonstrated that the DOC260 method allowed for quick and inexpensive measurements of total dissolved organic carbon concentrations in exudate samples from grass species grown under nutrient sufficient as well as under P deficient conditions. Interestingly, DOC260 failed to predict DOC concentrations in exudate samples from plants grown under Zn and Fe deficiency suggesting a strong shift in metabolite composition under micronutrient deficiency. Even though the applicability of the DOC260 method remains to be tested on exudate samples originating from dicots and plants exposed to other environmental stresses (e.g. pathogen attack, heavy metal stress, etc), it will help to increase our understanding of root exudation and related rhizosphere processes in the future. [ABSTRACT FROM AUTHOR]

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.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.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.Our findings highlight the importance of thoroughly evaluating experimental procedures and delivers relevant insights supporting future experimental designs targeting root exudates.Methods: 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.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.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.Our findings highlight the importance of thoroughly evaluating experimental procedures and delivers relevant insights supporting future experimental designs targeting root exudates.Results: 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.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.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.Our findings highlight the importance of thoroughly evaluating experimental procedures and delivers relevant insights supporting future experimental designs targeting root exudates.Conclusion: 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.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.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.Our findings highlight the importance of thoroughly evaluating experimental procedures and delivers relevant insights supporting future experimental designs targeting root exudates. [ABSTRACT FROM AUTHOR]