Effects of Nitrogen and Phosphorus Limitation on the Growth and Phosphorus Allocation of Alfalfa (Medicago sativa L.)

As phosphorus (P) is one of the most limiting elements for crop growth and development, investigating the P allocation strategy of legume species with the nitrogen (N)-fixing functions is particularly important under N and P limitation. In this study, a pot experiment in a greenhouse was conducted in 2021 with three nutrient application treatments including N and P balanced situations, N limitation, and P limitation. The growth, photosynthetic properties, and P content of three organs (leaf, stem, and root P content) and four fractions within leaves (metabolic, nucleic, lipid, and residual P content) were measured for two cultivars of the legume forage crop alfalfa. In our results, plant growth and photosynthetic capacity all decreased under nutrient limitation (P < 0.05), but photosynthetic P-use efficiency was not significantly changed under P limitation. The further analysis showed that P allocation to leaves (ranged from 22