The impact of different morphological and biochemical root traits on phosphorus acquisition and seed yield of Brassica napus

Oilseed rape (Brassica nap us L.) is an important crop in China. Although its yields are restricted by phosphorus (P) supply, the response of its root system to P supply has not been explored systematically. This study aimed to investigate the contribution of root morphological and biochemical traits to P acquisition from soils with deficient P (30 kg P2O5 ha(-1)) and sufficient P (90 kg P2O5 ha(-1)) supplies in the field at the leaf development, stem elongation, flowering, pod development and ripening stages. The total root length and root surface area in the surface soil (0-10 cm soil layer) were both reduced significantly by decreasing P supply. However, a larger root/ shoot ratio and root length ratio were observed in plants with the deficient P supply at the flowering stage. Roots of plants with a deficient P supply also secreted more acid phosphatase and organic acid into the rhizosphere from stem elongation to pod development than plants with a sufficient P supply. Seed yield (SY), shoot dry weight (SDW) and total P content (TPC) were strongly correlated with root morphological traits at the leaf development and flowering stages, especially with the coarse root length (CRL) and root surface area in the surface soil. However, there were no correlations between SDW or TPC and root biochemical traits (rhizosphere pH, acid phosphatase activity and organic acid content). It is hypothesized that greater CRL in the surface soil (0-10 cm soil layer) at the leaf development and flowering stages, served as a scaffold for fine roots, enhancing soil exploration and P acquisition, and, thereby, increasing seed yield.