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The size and the age of the metabolically active carbon in tree roots
Author(s) -
Hilman Boaz,
Muhr Jan,
Helm Juliane,
Kuhlmann Iris,
Schulze ErnstDetlef,
Trumbore Susan
Publication year - 2021
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/pce.14124
Subject(s) - girdling , botany , respiration , photorespiration , carbon fixation , biology , phloem , horticulture , cellulose , isotopes of carbon , zoology , chemistry , photosynthesis , ecology , total organic carbon , biochemistry
Little is known about the sources and age of C respired by tree roots. Previous research in stems identified two functional pools of non‐structural carbohydrates (NSC): an “active” pool supplied directly from canopy photo‐assimilates supporting metabolism and a “stored” pool used when fresh C supplies are limited. We compared the C isotope composition of water‐soluble NSC and respired CO 2 for aspen roots ( Populus tremula hybrids) cut off from fresh C supply after stem‐girdling or prolonged incubation of excised roots. We used bomb radiocarbon to estimate the time elapsed since C fixation for respired CO 2 , water‐soluble NSC and structural α‐cellulose. While freshly excised roots (mostly <2.9 mm in diameter) respired CO 2 fixed <1 year previously, the age increased to 1.6–2.9 year within a week after root excision. Freshly excised roots from trees girdled ~3 months ago had respiration rates and NSC stocks similar to un‐girdled trees but respired older C (~1.2 year). We estimate that over 3 months NSC in girdled roots must be replaced 5–7 times by reserves remobilized from root‐external sources. Using a mixing model and observed correlations between Δ 14 C of water‐soluble C and α‐cellulose, we estimate ~30% of C is “active” (~5 mg C g −1 ).