Morphological and Anatomical Features of Alfalfa Leaves as Related to CO₂ Exchange¹

Abstract

Cuttings from alfalfa ( Medicago sativa L. cv. ‘Mesa‐Sirsa’) genotypes which exhibited a wide range in leaflet size were grown under spaced‐planted and nonspaced‐planted conditions and used to determine the relation. ships between leaflet anatomy, leaflet morphology, and CO 2 exchange. These same relationships were evaluated under controlled environmental conditions using alfalfa population MSE‐6 which has a broad germplasm base. Area per leaflet and leaflet width were negatively associated with photosynthetic rate per unit leaf area. Specific leaf weight (SLW) was positively correlated with photosynthesis; however, the correlation coefficients were consistently lower than the r values for leaflet size vs photosynthesis. Photosynthesis expressed as total CO 2 uptake per plant was not significantly associated with SLW and leaflet size. Plants with small leaves had the greatest SLW, palisade tissue thickness, and leaf thickness. A positive association was observed between palisade tissue thickness and photosynthesis expressed on a leaf area basis. The significance of leaflet size as a selection tool for photosynthetic rate in alfalfa is discussed.