Assessing photosynthetic limitation to grain yield in a field crop

Abstract

A method is proposed for assessing the degree to which the availability of photosynthate during grain filling limits the yield of a cereal ('source limitation'). The technique uses shading and carbon dioxide enrichment to alter photosynthesis after anthesis, and may be applied in the field. From only final dry weight determinations, the degree of source limitation of grain yield is quantified on a 0 to 1 scale by relating differences in grain weight to differences in plant weight. For a crop of barley (cv. Resibee) on which the method was tried, the degree of source limitation was about one-half, which suggested that for this particular crop neither the source nor the sink presented an overriding limitation to grain yield. This was so for four stands of the cultivar produced by different levels of shading and carbon dioxide enrichment before anthesis. A yield component analysis indicated that kernel weight was the major component changed by post-anthesis treatments. Pre-anthesis treatments, which also affected grain yield, mainly influenced the numbers of ears produced.