Ecophysiological modeling of photosynthesis and carbon allocation to the tree stem in the boreal forest

Fabio Gennaretti,Frank Berninger,Etienne Boucher,Joel Guiot,Guillermo Gea-Izquierdo,Dominique Arseneault

doi:10.5194/bg-14-4851-2017

Abstract

Abstract. A better understanding of the coupling between photosynthesis and carbon allocation in the boreal forest, together with its associated environmental factors and mechanistic rules, is crucial to accurately predict boreal forest carbon stocks and fluxes, which are significant components of the global carbon budget. Here, we adapted the MAIDEN ecophysiological forest model to consider important processes for boreal tree species, such as nonlinear acclimation of photosynthesis to temperature changes, canopy development as a function of previous-year climate variables influencing bud formation and the temperature dependence of carbon partition in summer. We tested these modifications in the eastern Canadian taiga using black spruce (Picea mariana (Mill.) B.S.P.) gross primary production and ring width data. MAIDEN explains 90 % of the observed daily gross primary production variability, 73 % of the annual ring width variability and 20–30 % of its high-frequency component (i.e., when decadal trends are removed). The positive effect on stem growth due to climate warming over the last several decades is well captured by the model. In addition, we illustrate how we improve the model with each introduced model adaptation and compare the model results with those of linear response functions. Our results demonstrate that MAIDEN simulates robust relationships with the most important climate variables (those detected by classical response-function analysis) and is a powerful tool for understanding how environmental factors interact with black spruce ecophysiology to influence present-day and future boreal forest carbon fluxes.

Highlights

Photosynthetic production is the primary factor affecting growth of trees and other vegetation
As stated in the literature for boreal forests (Gea-Izquierdo et al, 2010; Mäkelä et al, 2004, 1996), we found that the modeling of assimilation/photosynthesis for black spruce is very sensitive to the parameters controlling the temperature dependence of the maximum carboxylation rate (Vcmax; μmol C m−2 of leaves s−1), the water stress level influencing the stomatal conductance and the intercellular CO2 concentration
The ring growth variability at our sites was more linked to temperature than to precipitation variables. The model reproduced this correlation pattern (Fig. 4b) and explained approximately 20–30 % of the observed yearly RWhighF variability, corresponding to correlations of 0.58–0.66. This result is good because the simulated detrended annual gross primary production (GPP) values had only a negative R2 with RWhighF (Fig. 2c; meaning performance was worse than a straight line centered on RWhighF) and much lower correlations

Summary

Introduction

Photosynthetic production is the primary factor affecting growth of trees and other vegetation. Empirical studies have shown that the correlation between photosynthetic production and the diameter growth of trees is far from perfect (Gea-Izquierdo et al, 2014; Rocha et al, 2006; Berninger et al, 2004) This imperfect correlation is due to the fact that plant hydraulics (e.g., turgor pressure) and thermal limitations during very short periods of time can be more important than carbon (C) availability for secondary tree growth (Kirdyanov et al, 2003; Rossi et al, 2016; Zweifel et al, 2016; Fatichi et al, 2014; secondary growth is the increase in the girth of the plant roots and stems). Carbon allocated in different tree components (e.g., canopy, stem or roots) has a specific function and is stored for a different length of time (Moorcroft, 2006)

Methods

Results

Discussion

Conclusion