Abstract: Low phosphorus (P) availability is a major constraint for pasture yields in acid soils. In a previous study, a low-P tolerant stylo (Stylosanthes) mutant, TPRC2001-84, was created using space flight mutation. However, the underlying mechanisms of TPRC2001-84 tolerance of P deficiency remain largely unknown. In this study, plant biomass, P acquisition efficiency, P utilization efficiency, soluble inorganic phosphate (Pi) concentration, cell wall P content and acid phosphatase (ACP) activity were investigated in hydroponically grown TPRC2001-84 and a non-mutant control (RY2) in normal P (+P, 250 μmol·L^-1 KH₂PO₄) or low P (-P, 5 μmol·L^-1 KH₂PO₄) solutions. Plant dry weight and P acquisition efficiency were significantly decreased (P<0.05) by P deficiency, while P utilization efficiency was increased (P<0.05) by low P in both accessions, compared to the normal P treatment. Plant dry weight and P utilization efficiency of TPRC2001-84 were 1.6 and 1.4 times those of RY2 under P deficiency, respectively. Although cell wall P content in leaves and roots of TPRC2001-84 were about 70% lower than in RY2 with low P treatment, the soluble Pi concentration in leaves and roots of TPRC2001-84 were 36.8% and 42.6% higher than in RY2 under P deficiency, respectively. Similarly, cell wall ACP activity in leaves and roots of TPRC2001-84 were 46.6% and 53.6% higher than in RY2 under P deficiency, respectively. These results suggest that increased cell wall ACP activity in TPRC2001-84 may contribute to cell wall P scavenging and recycling, increasing P utilization efficiency under P deficiency. Taken together, our results provide a theoretical basis and germplasm resource for selecting and breeding stylo varieties with high P efficiency.

Key words: Stylosanthes, phosphorus deficiency, acid phosphatase, phosphorus efficiency, space flight mutation