EGU General Assembly 2022
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the Creative Commons Attribution 4.0 License.

Effects of rising CO2 concentrations on photosynthetic traits and leaf morphology to test optimality framework

Astrid Odé1, Karin Rebel1, Martine van der Ploeg2, and Hugo de Boer1
Astrid Odé et al.
  • 1Copernicus Institute of Sustainable Development, Environmental Sciences, Utrecht University, Utrecht, the Netherlands
  • 2Environmental Sciences, Hydrology and Quantitative Water Management, Wageningen University, Wageningen, the Netherlands

The eco-evolutionary optimality principle, which states that natural selection rapidly eliminates uncompetitive combinations of traits, has proven to be a powerful source of testable hypotheses and predicting patterns in vegetation structure and composition. In this context, Prentice et al. (2014) proposed an optimality framework for plant functional ecology, which predicts relationships between parameters of photosynthetic biochemistry and stomatal conductance (gs). Leaf morphology plays an essential role herein, as shown by the conservative gs/gsmax ratio (McElwain et al., 2016) and the strong correlation between maximum photosynthesis rate and leaf hydraulic traits (Brodribb et al., 2007). The aim of this research is to determine how such leaf morphological adaptations relate to adaptations of photosynthetic traits, mainly  gs/gsmax and Vcmax, over different timescales. Here we present empirical data to test predicted effects of changing CO2 concentrations on Vcmax, Ci/Ca, Jmax, gs, and leaf morphology, according to the optimality framework.

The effects were tested in two genotypes of Solanum dulcamara (bittersweet) that were grown from seeds to maturity under 200, 400 and 800 ppm CO2 in walk-in growth chambers with tight control on light, temperature and humidity. The genotypes were grown from two distinct natural populations; one adapted to well-drained sandy soil (the 'dry' genotype) and one adapted to poorly-drained clayey soil (the 'wet' genotype). Measurements of photosynthetic traits were obtained with a portable photosynthesis system. Morphological and developmental leaf traits were measured on microscopy images, after plant maturation.

The results show that the optimality framework is suitable to predict changes in the photosynthetic traits under changing atmospheric CO2 concentrations. With higher concentrations, the Vcmax decreased in both S. dulcamara genotypes. Also, at each CO2 growth level, the dry genotype showed a higher Huber value and a lower Vcmax than the wet genotype, indicating that the ‘dry’ genotype combines a relatively high cost of transpiration with a low cost of photosynthesis, and the ‘wet’ genotype vice versa. The down-regulation of Vcmax under high CO2 was strongest in the dry genotype, and the downregulation of gs the strongest in the wet genotype, in line with the predicted trade-off between the costs of transpiration and photosynthesis.

The two leaf morphological traits with the clearest CO2 response were leaf vein density and guard cell length, which were also strongly correlated. Interestingly, stomatal density showed no CO2 response in this species, but is correlated to the guard cell length. Overall, our empirical data support the optimality responses in photosynthetic traits and gs, however, leaf morphological responses appear less consistent with the theory. More research, including experiments over a longer timescale will provide more insight in these relationships.

How to cite: Odé, A., Rebel, K., van der Ploeg, M., and de Boer, H.: Effects of rising CO2 concentrations on photosynthetic traits and leaf morphology to test optimality framework, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9596,, 2022.