Photosynthesis, fluorescence, and nutrition of Zhonglan No. 2, a new alfalfa cultivar

BACKGROUND: The years after planting play an important role in the above-ground biomass and nutritive value of alfalfa. Zhonglan No. 2 (Medicago sativa L. cv. Zhonglan No. 2) is a new breeding alfalfa cultivar characterized by high drought tolerance and high yield. To determine the optimum time for utilization of Zhonglan No. 2, we examined growth traits, chlorophyll content, photosynthetic and fluorescence parameters, and composition and nutritive values at the late vegetative and early flowering stages of the first stubble in the second, third, fourth, sixth, and eleventh years after planting. RESULTS: In general, the height and leaf area decreased with increasing number of years after planting. At the late vegetative stage, the fourth-year alfalfa exhibited higher stomatal conductance (Gs) and intercellular CO₂ concentration (Ci), and better water use efficiency, and at the early flowering stage, the fourth-year alfalfa had the highest (P < 0.05) leaf net photosynthetic rate (Pn) and carboxylation efficiency (CE). Total digestible nutrients did not differ among years, but, in the early flowering stage, crude protein content decreased with years (P < 0.05). Malondialdehyde (MDA) content and total antioxidant capacity did not differ among years after planting, suggesting aging did not impose oxidative stress on this alfalfa cultivar. CONCLUSIONS: Based on height, chlorophyll content, crude protein (CP) content, and photosynthetic and fluorescence parameters, the fourth year after planting, at the early flowering stage, was the best for using Zhonglan No. 2.