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Growth Rate and Physiology of Alfalfa as Influenced by Canopy and Light¹

Specific leaf weight (SLW) and net C exchange (NCE) of alfalfa (Medicago sativa L.) leaves were measured in very sparse canopies that allowed about the same light intensity to all plant heights. With 100% normal daylight SLW and NCE values remained high throughout a growth cycle; however, these values declined sharply with light intensities of 27 and 45% of normal daylight. Concurrently, for natural dense alfalfa canopies under field environments with normal daylight, the SLW and NCE values of upper young leaves increased until they were fully expanded; thereafter, these values declined sharply because of diminishing and low light intensities in the lower layers of accumulating canopies. The data suggest that the decline of photosynthetic efficiency and SLW of the basal leaves was caused by low light intensities in the lower layers of normal dense canopies.

Key Words: Specific leaf weight • Photosynthesis • Leaves

² Associate Professor and Professor of Agronomy, respectively.

Received for publication May 7, 1971.