XVI International Botanical Congess

The tremendous increases in crop yields in the 20th century have been associated with critical modifications in plant physiological traits. Key traits that are often cited include increased harvest index (grain to total plant weight ratio) and sustained photosynthetic capacity. Erect leaves are sometimes suggested as important contributors. A deeper perspective of plant growth and yield formation indicates, however, that increased capacity to accumulate and store nitrogen (N) is fundamental to each of these traits. Increasing harvest index requires increased N accumulation. The intimate dependence of photosynthetic capacity on N demands a large sequestering of N in leaves. Finally, erect leaves result in little if any benefit for CO2 assimilation, but allow a larger leaf area to be sustained for N storage, which can be subsequently transferred to seeds. Yield potential is closely tied to and limited by N accumulation in the crop. N fertilizer amounts, and hence further yield increases, are being limited by socioeconomic constraints in many industrialized areas. In areas of low yields, yield increases will likely be linked to increased N availability and physiological improvements to optimize N use.