How far can the efficiency of photosynthesis be improved?

Crops convert only a small fraction of the sunlight they intercept into biomass. Engineering photosynthesis has recently raised yields in field trials, which makes it timely to ask how much further it can go and where the hard limits lie.

Question

What will be the end point of efforts to improve photosynthetic efficiency? How close can crops come to the theoretical maximum efficiency of converting solar energy into biomass, and which of the losses between light capture and carbohydrate synthesis can be removed, in C3 and C4 crops in the field?

Background

The question is in the category "Molecular Approaches to Fundamental Plant Biology" of the 2023 list of 100 important questions facing plant science, chosen by regional panels from 616 submitted questions. It overlaps a question on the original 2011 list, which the authors say illustrates the time required to address some very important topics [1].

What is known

• The maximum efficiency of converting solar energy to biomass has been estimated at 4.6% for C3 photosynthesis at 30 °C and 380 ppm CO₂, and 6% for C4; the C4 advantage would disappear as CO₂ approaches 700 ppm [2].
• Speeding up the relaxation of photoprotection when leaves pass from sun to shade raised leaf CO₂ uptake and plant dry matter by about 15% in tobacco in fluctuating light [3]; the same change in soybean raised seed yield by up to 33% in replicated field trials, without changing protein or oil content [4].
• Synthetic pathways that recycle the by-products of photorespiration made field-grown tobacco about 40% more productive than wild-type plants [5].
• The same photoprotection change in Arabidopsis impaired growth and biomass in fluctuating light, so gains may not transfer across species [6].

What would count as progress

No single result settles a question like this; contributions like these would move it forward:

• Multi-year, multi-site field trials of photosynthesis-engineered staple cereals (rice, wheat, maize), reporting yield and its stability.
• Measured energy budgets for field crops that show where energy is lost between light capture and harvested biomass, and which losses are largest.
• Surveys of natural variation in photosynthetic traits across crop germplasm, such as the speed of photoprotection relaxation, linked to genetic markers that breeders can use.

References

1. Armstrong, E. M. et al. (2023). One hundred important questions facing plant science: an international perspective. New Phytologist 238(2), 470–481.
2. Zhu, X.-G., Long, S. P. & Ort, D. R. (2008). What is the maximum efficiency with which photosynthesis can convert solar energy into biomass? Current Opinion in Biotechnology 19(2), 153–159.
3. Kromdijk, J. et al. (2016). Improving photosynthesis and crop productivity by accelerating recovery from photoprotection. Science 354(6314), 857–861.
4. De Souza, A. P. et al. (2022). Soybean photosynthesis and crop yield are improved by accelerating recovery from photoprotection. Science 377(6608), 851–854.
5. South, P. F., Cavanagh, A. P., Liu, H. W. & Ort, D. R. (2019). Synthetic glycolate metabolism pathways stimulate crop growth and productivity in the field. Science 363(6422), eaat9077.
6. Garcia-Molina, A. & Leister, D. (2020). Accelerated relaxation of photoprotection impairs biomass accumulation in Arabidopsis. Nature Plants 6(1), 9–12.

Source

Imported from One hundred important questions facing plant science, question 85, curated by Armstrong et al. Listed as open in the source (2023) and still an active research question as of 2026-10-20. The statement above is written in our own words; see the source for the original wording, history and discussion.