Seasonal Changes in Morphology and Anatomy of Field‐grown Soybean Leaves1

The objective of this study was to examine seasonal changes in specific leaf weight (SLW) of soybean (Glycine max [L.] Merrill) leaves and to compare these with changes in leaf area, thickness, and anatomical features. For individual leaves, SLW generally decreased as leaf area increased, and then increased as leaves thickened. In most cases, leaves thickened after the period of greatest leaf area expansion. Specific leaf weight then decreased as leaves senesced. In general, the maximum SLW achieved by each leaf was successively greater with each successive node. Similarly, leaves at upper nodes were thicker than those of the lower nodes. Leaf thickening was largely the result of concurrent thickening of palisade and spongy mesophyll tissues. An important discovery was that in the uppermost, thickest leaves a third layer of palisade mesophyll cells was formed by periclinal division in the outermost palisade layer. The final SLW and leaf thickness obtained were modified by solar radiation levels during the period of leaf development. Differences in radiation distribution seemed to accentuate differences among leaves in 1976 studies and reduce differences in 1977.