Significance of Leaf Phosphorus Remobilization in Yield Production in Soybean

The remobilization of mineral nutrients from vegetative to reproductive structures may influence plant productivity by affecting the timing and/or rate of leaf senescence. Experiments were conducted to ascertain the importance of P remobilizatlon, particularly from leaves, in seed production of soybean ( Glycine max [L.] Merr. cv. McCall). For two separate greenhouse experiments, plants were grown in pots of soil that contained three levels of P fertility (PI, P2, and P3) that provided deficient, optimum, and supraoptimum P nutrition, respectively. Plants were sampled four times from growth stages R5 to RS. For both experiments, P nutrition did not influence plant ontogeny. Plant P accumulation, biomass, and yield were depressed by the P1 treatment. For the P2 and P3 treatments, however, biomass and yield production were similar, even though plant P accumulation was twoto threefold greater for the P3 treatment. Yield decreases for the P1 treatment resulted from a proportional adjustment in the number of seeds and pods per plant. Yield components were similar for the P2 and P3 treatments. Leaf P concentration was similar for the P1 and P2 treatments, even though biomass production and yield were markedly different. There was no net remobilization of P from leaf tissue for the P3 treatment during reproductive growth in either experiment. Additionally, for Exp. 1 there was no net leaf P remobilization from the P1 and P2 treatments. These results indicate that seed development in soybean may occur independently of net P remobilization from the leaves. For all P treatments, N remobilization from leaves was extensive, even though leaf N concentration was increased significantly by the P1 treatment. Thus, N remobilization from leaves was not altered by the internal P or N status of the plants.