The size and the age of the metabolically active carbon in tree roots. (14th June 2021)

• Record Type: Journal Article
• Authors: Hilman, Boaz; Muhr, Jan; Helm, Juliane; Kuhlmann, Iris; Schulze, Ernst‐Detlef; Trumbore, Susan
• Is Part Of: Plant, cell and environment. Volume 44:Number 8(2021)
• Page Start: 2522
• Page End: 2535
• Publication Date: 2021-06-14
• Subjects: fine roots -- girdling -- isotopic fractionation -- nonstructural carbohydrates -- phosphoenolpyruvate carboxylase (PEPC) -- radiocarbon (14C) -- respiration -- storage dynamics -- tree carbon dynamics -- δ13C; Plant physiology -- Periodicals; Plant cells and tissues -- Periodicals; Plant communities -- Periodicals; 581.105
• DOI: 10.1111/pce.14124
• Languages: English
• ISSNs: 0140-7791

Abstract

Abstract: 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 CO2 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 CO2, water‐soluble NSC and structural α‐cellulose. While freshly excised roots (mostly <2.9 mm in diameter) respired CO2 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 ). Abstract : Non‐structural carbohydrates extracted from roots include an "active" pool that supports metabolism and a "stored" pool used when C supplies are limited. Using radiocarbon, we estimate that about a third of NSC in aspen roots is active and demonstrate use of old reserves under C limitation.