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. 2020 Sep 14;126(4):601-614.
doi: 10.1093/aob/mcz163.

Decomposition analysis on soybean productivity increase under elevated CO2 using 3-D canopy model reveals synergestic effects of CO2 and light in photosynthesis

Qingfeng Song  1 , Venkatraman Srinivasan  2   3 , Steve P Long  2   4 , Xin-Guang Zhu  1
Affiliations

Decomposition analysis on soybean productivity increase under elevated CO2 using 3-D canopy model reveals synergestic effects of CO2 and light in photosynthesis

Qingfeng Song et al. Ann Bot. .

Abstract

Background and aims: Understanding how climate change influences crop productivity helps in identifying new options to increase crop productivity. Soybean is the most important dicotyledonous seed crop in terms of planting area. Although the impacts of elevated atmospheric [CO2] on soybean physiology, growth and biomass accumulation have been studied extensively, the contribution of different factors to changes in season-long whole crop photosynthetic CO2 uptake [gross primary productivity (GPP)] under elevated [CO2] have not been fully quantified.

Methods: A 3-D canopy model combining canopy 3-D architecture, ray tracing and leaf photosynthesis was built to: (1) study the impacts of elevated [CO2] on soybean GPP across a whole growing season; (2) dissect the contribution of different factors to changes in GPP; and (3) determine the extent, if any, of synergism between [CO2] and light on changes in GPP. The model was parameterized from measurements of leaf physiology and canopy architectural parameters at the soybean Free Air CO2 Enrichment (SoyFACE) facility in Champaign, Illinois.

Key results: Using this model, we showed that both a CO2 fertilization effect and changes in canopy architecture contributed to the large increase in GPP while acclimation in photosynthetic physiological parameters to elevated [CO2] and altered leaf temperature played only a minor role in the changes in GPP. Furthermore, at early developmental stages, elevated [CO2] increased leaf area index which led to increased canopy light absorption and canopy photosynthesis. At later developmental stages, on days with high ambient light levels, the proportion of leaves in a canopy limited by Rubisco carboxylation increased from 12.2 % to 35.6 %, which led to a greater enhancement of elevated [CO2] to GPP.

Conclusions: This study develops a new method to dissect the contribution of different factors to responses of crops under climate change. We showed that there is a synergestic effect of CO2 and light on crop growth under elevated CO2 conditions.

Keywords: Canopy architecture; SoyFACE; atmospheric change; canopy absorbance; climate change; food security; growth; leaf area index; leaf temperature; light extinction coefficient; photosynthesis; soybean.

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Figures

Fig. 1.
Fig. 1.
Representations of the canopy architectural features for soybean. (A) VU, V1, V2, etc., are nodes of the main stem, Br1 and Br2 are branches from the main stem, and BV1, BV2 and BV3 are branch nodes. (B) The parameters internode length, branch angles, petiole angle 1, petiole angle 2 and mid-leaf angle. (C) Leaf width and length are the maximal width and length of a leaf; leaf angle L, leaf angle R and leaf angle M are shown when the trifoliolate was placed in a plane. (D, E) 3-D models of a single soybean plant at different developmental stages during a growing season under ambient CO2 (D) and elevated CO2 (E). (F–K) 3-D models of soybean canopy under ambient (F, G, H) and elevated CO2 (I, J, K) at stages V4 (DOY 180), V7 (DOY 195) and V11 (DOY 210).
Fig. 2.
Fig. 2.
(A) Daily GPP of a soybean canopy (GPPday) under either elevated or ambient [CO2] conditions. (B) Relative increase of GPP under elevated [CO2] condition as compared to the ambient [CO2] condition. GPP in A and B was model-simulated. (C) Leaf area index (LAI) simulated using the canopy models, as compared to the measured data (Dermody et al., 2006) for soybean grown under elevated [CO2] and ambient [CO2] conditions. (D) Correlation between above-ground biomass (Morgan et al., 2005) and calculated cumulative GPP (cGPP) at different stages. The R2 of linear fitting was > 0.99 for both ambient [CO2] and elevated [CO2] conditions. (E) Correlation between the measured above-ground biomass and model-estimated above-ground biomass from cGPP.
Fig. 3.
Fig. 3.
Venn diagrams showing the contributions of different factors and their interactions to the increase in GPP under elevated CO2 conditions as compared to that under ambient CO2 conditions for the whole growing season (A), dissected contributions on a sunny day during the early developmental stage (195 DOY) (B), dissected contributions on a cloudy day during the later developental stage (231 DOY) (C), and dissected contributions on a sunny day during the later developmental stage (234 DOY) (D).
Fig. 4.
Fig. 4.
Diurnal GPP (A, D, G), diurnal canopy absorbance (B, E, H) and daily averaged canopy absorbance (C, F, I) of soybean canopy on a sunny day during the early developmental stage (A, B, C), on a sunny day during the later developmental stage (D, E, F) and on a cloudy day during the later developmental stage (G, H, I). The error bar shows the standard deviation of six replicates of individual model simulations.
Fig. 5.
Fig. 5.
Distribution of PPFD absorbed by leaves at different depths of a canopy (A, D, G), relative PPFD (PPFD/PPFD0) as a function of cumulative LAI (cLAI) (B, E, H) and canopy absorbance as a function of cLAI (C, F, I) on a sunny day during an earlier developmental stage (195 DOY, A, B, C), on a sunny day during a later developmental stage (234 DOY, D, E, F) and on a cloudy day during a later developmental stage (231 DOY, G, H, I). Relative PPFD and canopy absorbance were calculated based on the distribution of PPFD.
Fig. 6.
Fig. 6.
(A) The relationship between ambient PPFD above the canopy and the contribution of [CO2] to the increase of GPP (ΔGPP) for a mature soybean canopy from the V10 stage to the V18 stage (207 to 264 DOY). Different points show data from different days and the R2 of the linear fitting is 0.727. (B) Light response curves of leaf photosynthetic CO2 uptake rates under elevated [CO2] and ambient [CO2] conditions on the 219 DOY. The curves were drawn based on the Vcmax and Jmax measured on 219 DOY.
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