Dynamics of initial carbon allocation after drought release in mature Norway spruce—Increased belowground allocation of current photoassimilates covers only half of the carbon used for fine‐root growth

Abstract

After drought events, tree recovery depends on sufficient carbon (C) allocation to the sink organs. The present study aimed to elucidate dynamics of tree-level C sink activity and allocation of recent photoassimilates (C new ) and stored C in c. 70-year-old Norway spruce (Picea abies) trees during a 4-week period after drought release. We conducted a continuous, whole-tree 13 C labeling in parallel with controlled watering after 5 years of experimental summer drought. The fate of C new to growth and CO 2 efflux was tracked along branches, stems, coarse-and fine roots, ectomycorrhizae and root exudates to soil CO 2 efflux after drought release. Compared with control trees, drought recovering trees showed an overall 6% lower C sink activity and 19% less allocation of C new to aboveground sinks, indicating a low priority for aboveground sinks during recovery. In contrast, fine-root growth in recovering trees was seven times greater than that of controls. However, only half of the C used for new fine-root

Closing in on the last frontier: C allocation in the rhizosphere

“…Furthermore, this experimental approach, applied at a large scale, facilitated the characterization of novel mechanisms in tree eco-physiology, such that belowground allocation of current photoassimilates covers only half of the C used for fine-root growth. Another enlightening example from the same research regards the sustained C allocation to root exudation, despite drought (Brunn et al, 2022). This finding corroborates observations from a more drought-exposed forest (Jakoby et al, 2020).…”

“…After drought release in the combined rain exclusion-13 C labeling experiment, fine root growth increased; however, no change in root exudation or ectomycorrhizae was found (Hikino et al, 2022).…”

“…As demonstrated well in Hikino et al (2022), it is crucial to consider tree C allocation to predict C sequestration in the soil. Abiotic and warming are already influencing tree C fluxes.…”

“…Global Change Biology published by John Wiley & Sons Ltd. This is a commentary onHikino et al, 2022Hikino et al, , https://onlinelibrary.wiley.com/doi/full/10.1111…”

“…In this issue, Hikino et al (2022) combine a rain exclusion experiment and a 13 C labeling experiment performed on mature trees in the field, representing a new achievement in tree eco-physiology research.…”