Phenolic root exudate and tissue compounds vary widely among temperate forest tree species and have contrasting effects on soil microbial respiration
Zwetsloot, Marie J.; Kessler, André; Bauerle, Taryn L.
Root-soil interactions fundamentally affect the terrestrial carbon (C) cycle and thereby ecosystem feedbacks to climate change. This study addressed the question whether the secondary metabolism of different temperate forest tree species can affect soil microbial respiration. We hypothesized that phenolics can both increase and decrease respiration depending on their function as food source, mobilizer of other soil resources, signaling compound, or toxin. We analyzed the phenolic compounds from root exudates and root tissue extracts of six tree species grown in a greenhouse using high-performance liquid chromatography (HPLC). We then tested the effect of individual phenolic compounds, representing the major identified phenylpropanoid compound classes, on microbial respiration through a five-day soil incubation. Phenolic root profiles were highly species-specific. Of the eight classes identified, flavonoids were the most abundant with flavanols being the predominating sub-class. Phenolic effects on microbial respiration ranged from a 26% decrease to a 46% increase, with reduced respiration occurring in the presence of compounds possessing a catechol ring. Tree species variation in root phenolic composition influences the magnitude and direction of root effects on microbial respiration. Our data support the hypothesis that functional group rather than biosynthetic class determines the root phenolic effect on soil C cycling.
We are grateful for the support from the Cornell IGERT Cross-Scale Biogeochemistry and Climate program, David R. Atkinson Center Sustainable Biodiversity Fund, Kieckhefer Adirondack Fellowship, Bartlett Tree Foundation, and Andrew W. Mellon Foundation. We also thank Daniel Buckley, Tim Fahey, Jed Sparks and Kyle Wickings for their advice, Adrian Powell and Tara Webster for discussing HPLC analysis, Leah Rae McEwen for her help with Bio_Rad KnowItAll® 2017 Spectroscopy Software, Stephen Parry from Cornell Statistical Consulting Unit, and Cornell Nutrient Analysis Laboratories (CNAL) and Cornell University Stable Isotope Laboratory (COIL) for soil analysis. Lastly, we thank Juana Muñoz Ucros, Max Heitner, Cari Gostic and Andrew Harner for their help with root exudate collection and respiration measurements.
New Phytologist Trust
phenolics; rhizosphere; root exudates; root priming; secondary metabolism; temperate forest tree species
Previously Published As
Zwetsloot, M.J., Kessler, A., Bauerle, T.L., 2018. Phenolic root exudate and tissue compounds vary widely among temperate forest tree species and have contrasting effects on soil microbial respiration. New Phytologist 218, 530–541. doi:10.1111/nph.15041
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