Comparative assessment of root exudation in maize: Influence of experimental setup, growth conditions and root hairs

A major challenge in root exudation research is obtaining exudate samples that accurately reflect exudation processes under natural soil growth conditions, as both the growth environment and the experimental setup can significantly influence root exudation dynamics. This study investigated the effects of different experimental systems and growth conditions on carbon (C) exudation in maize (Zea mays L.) roots, and whether these factors affect the ability to resolve genotypic differences between the wild type (B73) and its root hairless mutant (rth3). 
Plants were cultivated under various experimental conditions, including soil-based and hydroponic systems, and root exudates were collected using a combination of traditional and innovative sampling approaches. Carbon exudation rates were compared across systems and genotypes, and laboratory results were additionally evaluated against data from a separate field experiment.
Carbon exudation rates varied greatly with experimental design and environmental context, whereas the contribution of root hairs to total C exudation was minor in comparison. Notably, exudation rates measured in soil-based laboratory systems were consistent with those obtained in the field when growth temperatures were similar, indicating that soil-based laboratory experiments can provide ecologically relevant estimates of C exudation when designed to match field-relevant conditions. However, large differences in root biomass introduced systematic bias into exudation measurements, especially when the root-to-sampling volume ratio (RSVR) differed substantially among systems or genotypes. These findings demonstrate how experimental setup and environmental conditions influence measured exudation rates and can potentially outweigh genotypic effects. 
Overall, these results provide methodological guidance for reliably quantifying root carbon exudation in maize. Specifically, soil-based laboratory systems that closely replicate field conditions, particularly temperature, together with maintaining a consistent RSVR, can provide comparable estimates of maize root carbon exudation for field experiments.