A growing global population and shifts in dietary preferences to plant-based foods mean that crop production will need to increase greatly in the coming decades. Crop growth and yield are ultimately limited by carbohydrate supply from canopy photosynthesis. Efforts to improve crop photosynthesis often focus on increasing leaf photosynthesis rate per unit input, chiefly water, light, and nitrogen. However, photosynthesis at the whole canopy scale depends not only on the rate per unit input, but also on the contributions of leaves with widely varying light levels and nitrogen content. Although the optimal investment of nitrogen should be roughly proportional to how much light each leaf receives, plants tend to underinvest in upper-canopy sunlit leaves and overinvest in lower, more shaded leaves. This may represent an opportunity for crop improvement. Simulations suggest that canopy carbon gain could be increased without additional inputs if canopy profiles of photosynthesis were adjusted to match theoretical optima. Yet, little is known about heritable variability in the optimality of photosynthetic resource distribution across genotypes of crop species.
In our newly published study in AoBP, we examined, for the first time, whether suboptimality differs within crop species, by measuring light capture and photosynthetic capacity in flag and penultimate leaves across 160 wheat genotypes grown in the field. This was achieved using custom-made light sensors, PARbars, and a “high-throughput” photosynthetic gas exchange system with eight leaf chambers, OCTOflux. Using these tools, we found wide variation in the optimality of photosynthetic nitrogen distribution across the population. This was mostly driven by variation in a plants’ ability to move N from penultimate to flag leaves as the canopy develops. Preliminary genome-wide association analysis identified nine strong marker-trait associations with this trait, which should be validated in future work in other environments and/or plant materials. We feel that selecting for less suboptimal nitrogen distribution in plant breeding programs could significantly increase canopy photosynthesis (by up to 5% in our simulations) and in turn, boost crop yield potential. Our results also support recent evidence that efforts to improve crop photosynthesis must look beyond the flag leaf and consider heterogeneity within the canopy.
William (Tam) Salter grew up in Scotland and obtained a BSc in Ecological Science for the University of Edinburgh in 2011. He moved to Australia in 2012 to conduct a PhD in plant ecophysiology at The University of Sydney. Tam was appointed as a postdoc on an International Wheat Yield Partnership project with A/Prof Tom Buckley in 2016 and currently holds a postdoctoral research fellow position with Prof Margaret Barbour in the School of Life and Environmental Sciences and the Sydney Institute of Agriculture at The University of Sydney. He is the Social Media Editor for AoBP and relished the opportunity to finally write about his own work for Botany One.
Tam is a plant ecophysiologist interested in identifying plant phenotypic traits that could be useful for future food security and ecosystem resilience under climate change. He has worked with native Australian plants as well as important crop species. He is also interested in the development of new scientific tools and techniques to understand plant traits that have gone unstudied in the past.