Acclimation of photosynthesis in canopies: models and limitations

Abstract

Within a time-scale of several days photosynthesis can acclimate to light by variation in the capacity for photosynthesis with depth in a canopy or by variation in the stoichiometry of photosynthetic components at each position within the canopy. The changes in leaf photosynthetic capacity are usually related to and expressed as changes in leaf nitrogen content. However, photosynthetic capacity and leaf nitrogen never match exactly the photon flux density (PFD) gradient within a canopy. As a result, photosynthetic light use efficiency, i.e. photosynthetic performance per incident PFD, increases considerably from the top of the canopy to the lower shaded part. Many of existing optimisation models fail to express the actual pattern of nitrogen or photosynthetic capacity distribution within a canopy. This failure occurs because these optimisation models do not consider that the quantitative aspect of photosynthesis acclimation is a whole plant phenomenon. Although turnover models, which describe the distribution of the photosynthetic apparatus within a canopy as a dynamic equilibrium between breakdown and regeneration of apparatus with respect to nitrogen availability, photosynthetic rate and export of carbohydrates, produce realistic results, these models require confirmation. The mechanism responsible for changes in the relative share of light-harvesting apparatus as acclimation to irradiance remains unknown. Ability of the photosynthetic apparatus to balance properly the light harvesting capacity with electron transport and biochemical capacities is limited. As a result of this fundamental limitation, photosynthetic light use efficiency always increases with increasing thickness of the photosynthetic apparatus.

Photosynthetic physiology of eucalypts along a sub-continental rainfall gradient in northern Australia

“…This demonstrates that even though we did not observe a relationship between V cmax and leaf N mass in the present study, leaf N mass is still a useful predictor of V cmax when a larger range of leaf N mass is taken into account. The V cmax -N slope of the relationship obtained from this combined analysis of 41.2 mol CO 2 g −1 N s −1 is in the middle range of V cmax -N slopes observed in a range of previous studies (Kull, 2002).…”

Efficiency of chlorophyll in gross primary productivity: A proof of concept and application in crops

“…Many of these studies analyze the patterns of individual components in isolation, while fewer evaluate the combination of a limited number of components for assessing synergistic relations and trade-offs (Karlsson, 1994;Herppich et al, 2002;Ali et al, 2012;Xu et al, 2013). However, a thorough understanding of the processes behind these optimization patterns is still elusive, mainly due to limitations in the scaling of photosynthesis models from individual leaves to entire canopies (Kull, 2002;Niinemets and Anten, 2009), as well as trade-offs in the use of different resources that may prevent plants from optimizing their efficiencies of use simultaneously (Hirose and Bazzaz, 1998).…”

Modelling the response of yields and tissue C : N to changes in atmospheric CO<sub>2</sub> and N management in the main wheat regions of western Europe

“…During the vegetative phase in which the leaves and roots are expanding, the plant seeks to maximise photosynthetic gain by having a leaf N content that optimises the carboxylation capacity (V max ) (Hirose and Werger, 1987;Kull, 2002). Following Haxeltine and Prentice (1996a) and Smith et al (2014) this is done by calculating the V max that maximises canopy-level net C assimilation given the current temperature, water status and biomass C : N.…”