Root Exudation: An In-Depth Experimental Guide.

Plants exude a wide variety of compounds into the rhizosphere, modulating soil functioning and diversity. The number of studies investigating exudation has exponentially increased over the past decades. Yet, the high inter-study variability of the results is slowing down our understanding of root-soil interactions. This variability is partly due to the absence of harmonized methodologies to collect and characterize exudation. Here, we discuss how various experimental aspects influence exudation profiles by performing a literature review, and we suggest best practices for different experimental setups. We discuss state-of-the-art of spatially resolved exudate collection, collection in controlled versus field conditions and plant growth setups ranging from hydroponics to soil. We highlight the importance of preparing experimental blanks, in situ versus ex situ exudate collection, various collection media and timing of collection, exudate storage and processing and analytical considerations. We summarize best practices for experimental setup and reporting of parameters in an easily accessible table format to facilitate discussion of best practices in the field. An increased standardization in the field together with the systematic studies suggested will improve our knowledge of how plant exudation shapes interactions with organisms in soil.