Goal:
Root exudates - soluble substances released by plant roots to soil –play a central role in ecosystems. However, there have been few efforts to synthesize exudate research and to discuss critical knowledge gaps. We propose to assemble an international consortium of leading exudation ecologists to discuss sampling and analysis issues/advances, to enhance understanding of how exudates affect plant nutrition, soil microbial communities/activity and ecosystem functioning, and to identify future research priorities.
Rational and scope:
Understanding the role of terrestrial ecosystems in removing CO2 from the atmosphere is critical for predicting future changes in the Earth’s climate. Current estimates of future carbon (C) uptake by the terrestrial biosphere vary by an order of magnitude among global models, indicating high uncertainties in predicting rates of climate change. A primary source of this variability can be attributed to how large-scale models represent carbon (C) and nutrient fluxes in soil. Up to 10% of all C assimilated by plants is released to soil as root exudates. Once in soil, exudates alter belowground processes by 1) increasing the solubility and availability of nutrients, 2) stimulating soil microbial activity, 3) structuring the soil microbiome and fuelling soil food webs 3) enhancing plant pathogen protection and 4) accelerating the formation of deformation of soil organic matter. Moreover, given that exudation rates and exudate composition are sensitive to changes in atmospheric CO2, warming, and drought, an enhanced understanding of exudation is vital for predicting ecosystem responses to (and feedbacks from) global environmental change.
A primary reason we know so little about root exudates relates to methods. Roots exist in the opaque and heterogenous medium of soil, which limits our ability to measure, monitor and manipulate roots in non-destructive ways. Additionally, most exudates are rapidly assimilated by soil microorganisms or adhere to mineral surfaces thereby limiting our ability to track their fate under field conditions. Fortunately, key methodological advances (e.g., widespread use of stable isotopic tracers; cuvette-based methods for trapping exudates; new instruments and bioinformatic pipelines for metabolite analysis) have catalysed field-based research in recent years. Despite such advances, method comparisons and syntheses are rare. Thus, there is a need to discuss how best to further advance these methods, as a means for setting research priorities in the field for the next decade.