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Morphological Characteristics of Alfalfa Plants Grown at Several Temperatures¹

Three alfalfa (Medicago sativa L.) cultivars, representing a range of environmental adaptation, were grown at 20, 25, 30, or 35 C under controlled environmental conditions to determine what effect growing temperature has on growth and development of alfalfa. Stem and leaf weights per plant were highest for plants grown at 25, followed by those grown at 20, 30, and lowest at 35 C. Leaf area per plant was highest for plants grown at 25 C and lowest at 35 C. Plants grown at 20 or 25 C had larger leaves than plants grown at 30 or 35 C. Specific leaf weight was highest for leaves from plants grown at 35 C, but essentially the same at 20, 25, or 30 C. Leaves of plants at 20 or 25 C had larger cells and more intercellular spaces compared to leaves at 35 C.

These data provide a partial basis for explaining the generally lower alfalfa yields during hot, summer periods. Such plants would have less leaf tissue, lower leaf area, and smaller, more densely packed leaf cells than plants growing during the cooler portions of the season. Large cells in the vascular tissue would facilitate translocation of photosynthates and water, and large intercellular spaces in the parenchyma tissue would enhance CO₂ diffusion.

Key Words: Leaf anatomy • Yield accumulation efficiency • Leaf area

² -Agronomist, PSRD, ARS, USDA, Lafayette, Ind. 47907.

Received for publication March 24, 1972.