Carbon allocation to root exudates is maintained in mature temperate tree species under drought

Melanie Brunn*, Benjamin D. Hafner, Marie J. Zwetsloot, Fabian Weikl, Karin Pritsch, Kyohsuke Hikino, Nadine K. Ruehr, Emma J. Sayer, Taryn L. Bauerle

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

25 Citations (Scopus)

Abstract

Carbon (C) exuded via roots is proposed to increase under drought and facilitate important ecosystem functions. However, it is unknown how exudate quantities relate to the total C budget of a drought-stressed tree, that is, how much of net-C assimilation is allocated to exudation at the tree level. We calculated the proportion of daily C assimilation allocated to root exudation during early summer by collecting root exudates from mature Fagus sylvatica and Picea abies exposed to experimental drought, and combining above- and belowground C fluxes with leaf, stem and fine-root surface area. Exudation from individual roots increased exponentially with decreasing soil moisture, with the highest increase at the wilting point. Despite c. 50% reduced C assimilation under drought, exudation from fine-root systems was maintained and trees exuded 1.0% (F. sylvatica) to 2.5% (P. abies) of net C into the rhizosphere, increasing the proportion of C allocation to exudates two- to three-fold. Water-limited P. abies released two-thirds of its exudate C into the surface soil, whereas in droughted F. sylvatica it was only one-third. Across the entire root system, droughted trees maintained exudation similar to controls, suggesting drought-imposed belowground C investment, which could be beneficial for ecosystem resilience.

Original languageEnglish
Pages (from-to)965-977
JournalNew Phytologist
Volume235
Issue number3
Early online date11 Apr 2022
DOIs
Publication statusPublished - Aug 2022

Keywords

  • belowground carbon allocation
  • carbon partitioning
  • experimental drought
  • Fagus sylvatica (European beech)
  • fine-root exudation
  • Picea abies (Norway spruce)
  • rhizosphere
  • temperate forest C budget

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