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Explicitly accounting for needle sugar pool size crucial for predicting intra‐seasonal dynamics of needle carbohydrates δ 18 O and δ 13 C
Author(s) -
Leppä Kersti,
Tang Yu,
Ogée Jérôme,
Launiainen Samuli,
Kahmen Ansgar,
Kolari Pasi,
Sahlstedt Elina,
Saurer Matthias,
SchiestlAalto Pauliina,
RinneGarmston Katja T.
Publication year - 2022
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.18227
Subject(s) - sugar , fractionation , scots pine , isotope , chemistry , botany , relative humidity , environmental chemistry , pinus <genus> , biology , chromatography , food science , meteorology , physics , quantum mechanics
Summary We explore needle sugar isotopic compositions (δ 18 O and δ 13 C) in boreal Scots pine ( Pinus sylvestris ) over two growing seasons. A leaf‐level dynamic model driven by environmental conditions and based on current understanding of isotope fractionation processes was built to predict δ 18 O and δ 13 C of two hierarchical needle carbohydrate pools, accounting for the needle sugar pool size and the presence of an invariant pinitol pool. Model results agreed well with observed needle water δ 18 O, δ 18 O and δ 13 C of needle water‐soluble carbohydrates (sugars + pinitol), and needle sugar δ 13 C ( R 2 = 0.95, 0.84, 0.60, 0.73, respectively). Relative humidity (RH) and intercellular to ambient CO 2 concentration ratio ( C i / C a ) were the dominant drivers of δ 18 O and δ 13 C variability, respectively. However, the variability of needle sugar δ 18 O and δ 13 C was reduced on diel and intra‐seasonal timescales, compared to predictions based on instantaneous RH and C i / C a , due to the large needle sugar pool, which caused the signal formation period to vary seasonally from 2 d to more than 5 d. Furthermore, accounting for a temperature‐sensitive biochemical 18 O‐fractionation factor and mesophyll resistance in 13 C‐discrimination were critical. Interpreting leaf‐level isotopic signals requires understanding on time integration caused by mixing in the needle sugar pool.