Optimal photosynthetic nitrogen partitioning in
cucumber leaves for maximizing canopy photosynthesis
Y. C. Pao, Tsu Wei Chen, Hartmut Stützel
To cite this version:
Y. C. Pao, Tsu Wei Chen, Hartmut Stützel. Optimal photosynthetic nitrogen partitioning in cucumber
leaves for maximizing canopy photosynthesis. iCROPM 2016 International Crop Modelling Sympo-
sium, Leibniz-Zentrum für Agrarlandschaftsforschung = Leibniz Centre for Agricultural Landscape
Research, Leibniz Association (ZALF). DEU., Mar 2016, Berlin, Germany. 437 p. �hal-02741476�
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International Crop Modelling Symposium 15-17 March 2016, Berlin
Optimal photosynthetic nitrogen partitioning in cucumber leaves for
maximizing canopy photosynthesis
1 1,2 1
Y.-C. Pao – T.-W. Chen – H. Stützel
1
Institute of Horticultural Production Systems, Faculty of Natural Sciences, Leibniz University Hanover,
Herrenhäuser Str. 2, D-30419 Hanover, Germany, e-mail: pao@gem.uni-hannover.de
2
INRA, UMR759 Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, Place Viala,
F-34060 Montpellier, France
Introduction
In response to considerable variation in light intensity within the canopy, the partition-
ing of nitrogen (N) to various photosynthetic functions should vary to achieve efficient
utilization of light. Here, photosynthetic N partitioning (PNP) is defined as optimum
when the whole canopy photosynthesis is maximized. The objective of this work is to
identify the optimal PNP in cucumber leaves as dependent on light conditions, and to
determine the discrepancy between actual and optimum at both leaf and canopy level.
Materials and Methods
Cucumber cv. ‘Aramon’ was grown hydroponically in a growth chamber to determine
the empirical PNP (ENP). Twenty-four leaves, which had been positioned perpendicu-
-2 -1
larly to constant light intensities ranging from 5-40 mol m d daily photon irradiance
(DPI). The PNP of these leaves was determined based on Niinemets and Tenhunen
(1997) and Buckley et al., (2013). PNP fractions for carboxylation (fv) and electron
transport (fj) were calculated from their maximum rates, Vcmax and Jmax, respectively.
The fraction in light harvesting (fc) was calculated from leaf chlorophyll content. fv and
fj were described depending on DPI using monomolecular functions with three param-
eters, fx,max, dx and ax:
𝑓x = 𝑓x,max [1 − 𝑑x × 𝑒𝑥𝑝−𝑎x × 𝐼d ] (1)
fc was calculated as:
𝑓c = 1 − 𝑓v − 𝑓j (2)
To test the optimal PNP, a multi-layer model representing a canopy with 25 layers was
constructed to simulate daily canopy CO2 assimilation (DCA) depending on PNP in each
layer and DPI above the canopy. Each layer was different in leaf area, specific leaf area,
N content, local light intensity (Id) and PNP, which is used to determine the photosyn-
thetic variables, Vcmax, Jmax and chlorophyll content, in the layer. Layer structural char-
acteristics and total N content were determined by a greenhouse experiment. PNP was
calculated by Eqn 1 and 2 depending on Id, which was simulated for each layer in the
canopy using Lambert-Beer law. The diurnal irradiance above the canopy was simulat-
ed by a simple cosine bell function (Kimball and Bellamy, 1986).
-2 -1
Using this model, the dependency of DCA on DPI above the canopy (5-50 mol m d )
was simulated and compared between ENP, the theoretically optimal PNP (TNP) pro-
119
International Crop Modelling Symposium 15-17 March 2016, Berlin
posed by Buckley et al., (2013), and several different optimal PNP patterns. These
optimal PNP patterns were derived from ENP by changing the three parameters in
Eqn 1 by which maximum DCA was obtained under a given DPI above the canopy. The
variation of the parameters were constrained between 0 and two-fold of the original
values in ENP functions.
Results and Discussion
DCA simulated with TNP is up to 16 % higher than ENP under various DPI above the
canopy. This suggests that developmental acclimation of PNP to light intensity in cu-
cumber cv. ‘Aramon’ is not optimal. fv of ENP is higher and fj of ENP is lower than those
of TNP throughout the whole range of Id, suggesting that N might be over-invested in
carboxylation and under-invested in electron transport .
With the optimal PNP patterns derived from ENP, up to 20 % DCA can be theoretically
increased over the typical light regimes in the greenhouse. To improve PNP in cucum-
ber leaves, a higher proportion of photosynthetic N should be invested into electron
transport instead of into carboxylation under low Id, while under high Id, more photo-
synthetic N should be partitioned into electron transport instead of into light harvest-
ing function. In the actual canopy, chlorophyll content is higher than optimum
throughout the canopy. Vcmax exceeds optimum below middle layers, while Vcmax and
Jmax are both considerably lower than optimum in the upper layer.
Conclusions
20 % higher DCA could be obtained with optimal PNP. At leaf level, a higher proportion
of photosynthetic N should be partitioned into electron transport from carboxylation
and light harvesting functions. At canopy level, photosynthetic variables are not opti-
mal. In the upper canopy, a higher proportion of photosynthetic N should be parti-
tioned from light harvesting to carboxylation and electron transport. Below middle
canopy, a higher proportion of photosynthetic N should be partitioned from light har-
vesting and carboxylation to electron transport.
Acknowledgements
Many thanks to Ilona Napp, Marlies Lehmann, and Dr. Dany Pascal Moualeu.
References
Buckley, T.N., A. Cescatti A. and G.D. Farquhar (2013). Plant, Cell & Environment, 36: 1547–1563.
Niinemets, Ü. and J.D. Tenhunen (1997). Plant, Cell & Environment, 20: 845–866.
Kimball, B.A. and Bellamy L.A. (1986). Energy in Agriculture, 5: 185–197.
120
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