Probability distributions of nonstructural carbon ages and transit times provide insights into carbon allocation dynamics of mature trees.

David Herrera‐Ramírez,Henrik Hartmann,Jan Muhr,Carlos A Sierra,Susan Trumbore,Christine Römermann

doi:10.1111/nph.16461

Abstract

●In trees, the use of nonstructural carbon (NSC) under limiting conditions impacts the age structure of the NSC pools. We compared model predictions of NSC ages and transit times for Pinus halepensis, Acer rubrum and Pinus taeda, to understand differences in carbon (C) storage dynamics in species with different leaf phenology and growth environments. ●We used two C allocation models from the literature to estimate the NSC age and transit time distributions, to simulate C limitation, and to evaluate the sensitivity of the mean ages to changes in allocation fluxes. ●Differences in allocation resulted in different NSC age and transit time distributions. The simulated starvation flattened the NSC age distribution and increased the mean NSC transit time, which can be used to estimate the age of the NSC available and the time it would take to exhaust the reserves. Mean NSC ages and transit times were sensitive to C fluxes in roots and allocation of C from wood storage. ●Our results demonstrate how trees with different storage traits are expected to react differently to starvation. They also provide a probabilistic explanation for the 'last-in, first-out' pattern of NSC mobilization from well-mixed C pools.

Highlights

The availability and mobility of the nonstructural carbon (NSC) reserves, mostly sugars and starch, determine trees’ ability to survive photosynthetic shortages (Dietze et al, 2014; Hartmann & Trumbore, 2016; Martínez‐Vilalta et al, 2016; Overdieck, 2016; Trugman et al, 2018; Wiley et al, 2019)
The structures of the compartmental linear models follow those described in Klein & Hoch (2015) for Pinus halepensis Mill. and in Ogle & Pacala (2009) for Acer rubrum L. and Pinus taeda L. with small variations based on theoretical assumptions (Figs 1, 2)
For P. halepensis, 95% of all NSC in the entire tree was younger than 3.3 yr

Summary

Introduction

The availability and mobility of the nonstructural carbon (NSC) reserves, mostly sugars and starch, determine trees’ ability to survive photosynthetic shortages (Dietze et al, 2014; Hartmann & Trumbore, 2016; Martínez‐Vilalta et al, 2016; Overdieck, 2016; Trugman et al, 2018; Wiley et al, 2019). Trees mobilize NSC from storage to sustain metabolic and growth requirements (Anderegg & Anderegg, 2013; Klein & Hoch, 2015; Mei et al, 2015). C fixed during photosynthesis is transported as NSC from chloroplasts to different plant organs (e.g. leaves, branches, stems, and roots) where it is allocated either to metabolism (respiration, growth, defense, osmotic regulation, among others) or to storage, which may occur passively or actively (Lacointe et al, 2004; Wiley et al, 2013; Huang et al, 2019b). To represent and understand these dynamics, compartmental models have been proposed where NSC is allocated to both organ‐specific compartments (e.g. leaves, stems and roots) and compound‐specific compartments (Richardson et al, 2012; Klein & Hoch, 2015; Ceballos‐Núñez et al, 2018)

Methods

Results

Discussion

Conclusion