Seed reserve dependency of Leucaena leucocephala seedling growth for nitrogen and phosphorus.

Mineral elements stored in seed reserves meet the nutrient demands of seedlings during their initial development and growth. We experimentally examined when seed reserves become insufficient to meet demands for nitrogen (N) and phosphorus (P) of seedlings of Leucaena leucocephala (Lam.) de Wit, a tropical woody legume. Seedlings were grown from seeds with four nutrient treatments: receiving all nutrients; all nutrients except N, all nutrients except P or deionised water. Growth curves were compared to quantify the time course of the onset of N and P deficiency during 8 weeks. N deficiency became significant for leaf area and biomass growth after 11 and 16 days, respectively, whereas P deficiency became significant after 31 days for both leaf area and biomass growth. Thus, seed reserves alone could support the P demands of seedlings for more than twice as long as N demands. As nutrient deficiency developed, seedlings adjusted increased relative biomass allocation to roots, diluted organ N and P concentrations but conserved 100% of the initial nutrient pool derived from the seed.