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Brunn, M.* ; Hafner, B.D.* ; Zwetsloot, M.J.* ; Weikl, F. ; Pritsch, K. ; Hikino, K.* ; Ruehr, N.K.* ; Sayer, E.J.* ; Bauerle, T.L.*

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

New Phytol., DOI: 10.1111/nph.18157 (2022)
Open Access Green: Postprint online available 04/2023
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, i.e. 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 ~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 threefold. Water-limited P. abies released two-thirds of its exudate-C into the surface soil, whereas it was only one-third in droughted F. sylvatica. 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.
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Publication type Article: Journal article
Document type Scientific Article
Keywords Belowground-carbon Allocation ; Fagus Sylvatica (european Beech) ; Picea Abies (norway Spruce) ; Carbon Partitioning ; Experimental Drought ; Fine-root Exudation ; Rhizosphere ; Temperate-forest C Budget
ISSN (print) / ISBN 0028-646X
e-ISSN 1469-8137
Journal New Phytologist
Publisher Wiley
Reviewing status Peer reviewed