Photosynthesis and Yield

Abstract

Carbon accumulation seems intuitively to be a major constraint on crop yield. After all, much of the crop mass is constructed of carbon compounds. Yet, there is virtually no evidence that increasing leaf photosynthesis rate has been associated with crop yield increase. The lack of evidence for such a relationship resulted from the fact that in plant growth tissue carbon must be paired with other inputs, particularly nitrogen. These ‘other inputs’ are almost always much more challenging to accumulate than carbon, especially in the large amounts required to grow a high-yielding crop. Nitrogenous compounds are essential components of all growing plant tissues. In leaves, photosynthesis rate and crop mass accumulation are directly limited by leaf nitrogen concentration. In growing seeds, there are quantitative requirements for accumulated nitrogen that must be met for the overall synthesis of new seed mass. In fact, increased carbon accumulation without additional crop nitrogen accumulation can result in yield decrease. Crop yield increases through human history, including the Green Revolution, were based on increased crop access to nitrogen. Photosynthesis activity is rarely a limiting input for increasing crop yield.