Doubling agricultural production will be essential by 2050 to satisfy the
demand of food of a constantly growing population, but climate change brings a lot of
uncertainty and complexity to this challenge for agriculture. One of the most important
changes that must be addressed is the increase in atmospheric [CO2], which has
increased from approximately 280 ppm in pre-industrial times to about 400 ppm
nowadays and will further increase to values of 470–570 ppm by 2050 depending on
the climate scenario (IPCC Synthesis report, Climate Change 2007). Although this
increase in [CO2] is expected to have a positive and significant effect on C3 crops
production, it is counteracted by the rise in temperature and the higher evaporative
demand, with the increased risks for drought and heat likely to be progressive in all
regions of our planet. As a matter of fact, the average stimulation of C3 leaf
photosynthesis under field conditions at elevated [CO2] has been reported to be only
14% on average across FACE (550–600 ppm in Free Air CO2 Enrichment)
experiments, much lower than the expected increase of 38%.
Down-regulation of photosynthesis can be ascribe to multiple factors. These include
the limited sink strength of the plants and the consequent accumulation of inhibitory
photo-assimilates, the “hysterical” behavior of photosynthetic organisms to excess
illumination, by either triggering EED (Excess Energy Dissipation) beyond the level
effective for photo-protection or retaining a relevant fraction of quenching for extended
periods after return to limiting light conditions, and the complex and multi-factorial
network that controls CO2 fixation and carbon allocation.
Here we describe the genetic constraints that limit yield potential and prevent it from
being realized on the farm, in order to improve the understanding of plant responses
under elevated [CO2], and provide tentative biotechnological solutions to overcome the
crop yield limitations.
It is worth noting that the huge improvements in agricultural production gained during
the ‘Green Revolution’ were not directly related to manipulation of photosynthesis,
therefore its modification remains an unexplored target for crop improvement.
Keywords: Dark phase efficiency, Improvement strategies, Light phase
efficiency, Photosynthesis, Yield potential.
