Non-Foliar Photosynthesis—a Hidden Source of Carbon for Yield Improvement

Abstract In plants, leaves are not the only tissues that fix the CO2 into sugars using the solar energy, and in turn many other tissues perform the same task, which is termed as non-leafy or non-foliar photosynthesis, and this plays an important role in the overall carbon balance of crops. These non-foliar tissues fix both the atmospheric and respiratory carbon dioxide released in these tissues. The photosynthesising non-foliar tissues are very much valuable to the crop plants notably during their late reproductive phase, where the contribution of the foliar photosynthesis declines. In cereals such as wheat and barley, ears and stems remain green for longer duration than leaves and continue to photosynthesize during grain filling stage also. Similarly, the legume pods and maize husks also fix both the atmospheric and respiratory CO2 and that directly supports the seed development. Similarly, flowers, fruits and embryos produce their reserves during their initial stages and minimize their dependency on leaves for photo-assimilates for their development. Non-foliar photosynthesis becomes especially important during drought, heat and nutrient stress where the foliar photosynthesis declines. Thus, the non-foliar tissues refix the carbon dioxide released during respiration, improve water use efficiency and aids in grain/seed filling under harsh conditions. However, most of the crop models and breeding programs still focus mainly on leaves. Understanding and improving the photosynthesis in non-leaf organs could provide a new strategy for increasing crop productivity and resilience in future agricultural systems. This review highlights how stems, ears, pods, fruits, flowers and roots contribute to carbon assimilation and productivity.