Characteristics of phosphorus absorption and utilization in five apple rootstocks under low phosphorus stress

【Objectives】As an essential mineral element in the plants, phosphorus can facilitate the differentiation of flower bud. However， phosphorus is easily fixed in soils when applied to soil, and mostly transferred to occluded P, which is not available to plants. Therefore，it has great significance to excavate phosphorus efficient apple rootstocks under low phosphorus stress. In this study，five one-year-old wild apple rootstocks were used as materials and their phosphorus absorption and utilization characteristics under the condition of low phosphorus stress wereanalyzed. 【Methods】The five one-year-old apple rootstocks ［M. micromalus Makino, Malus hupehensis Rehd., M. baccata Borkh., M. prunifolia（Willd）Borkh. and M. sievesii（Ledeb.）Roemer］ were grown in low phosphorus group（LP）and control group（CK）in pots with 6 replication. The root surface area and length were determined by WinRHIZO root analysis software, and the plant phosphorus content by vanadium molybdate yellow colorimetric method. The the kinetic parameters of H2PO-4 absorption of seedlings were determined with a water culture experiment. Firstly, the seedlings were P\|starved in black bottle for 24 h and then put into the solutions of different P\|concentrations for 24 h, and finally, 10 mL solutions were collected to determine the phosphorus content with Mo-Sb colorimetry. 【Results】The relative phosphorus efficiencies of five rootstocks from high to low are in order of M. prunifolia（Willd）Borkh.（93.66%） Malus hupehensis Rehd.（87.69%） M. baccata Borkh.（83.44%） M. micromalus Makino.（74.54%） M. sievesii（Ledeb.）Roemer.（74.01%）. The phosphorus absorption efficiencies（PAE） from high to low are in order of M. prunifolia（Willd）Borkh. Malus hupehensis Rehd. M. baccata Borkh. M. sievesii（Ledeb.）Roemer. M. micromalus Makino, while the phosphorus utilization efficiencies （PUE）are in order of Malus hupehensis Rehd. M. prunifolia（Willd）Borkh. M. micromalus Makino M. sievesii（Ledeb.）Roemer M. baccata Borkh. Considering the kinetic parameters of H2PO-4, the values of the Vmax of the five rootstocks are in the order of M. prunifolia（Willd）Borkh.［101.81 mol/(gh) ］ Malus hupehensis Rehd. ［66.40 mol/(gh) ］ M. baccata Borkh. ［45.00 mol/(gh) ］ M. sievesii（Ledeb.）Roemer［44.32 mol/(gh) ］ M. micromalus Makino［41.28 mol/(gh) ］. The values of Km are arranged in turn by the following order，Malus hupehensis Rehd. (4.05 mol/L) M. prunifolia（Willd）Borkh.（8.68 mol/L） M. baccata Borkh.（12.29 mol/L） M. sievesii（Ledeb.）Roemer（12.64 mol/L） M. micromalus Makino（13.57 mol/L）. The total absorption surface area and length of root are highest in M. prunifolia（Willd）Borkh, lowest in M. micromalus Makino. 【Conclusions】M. prunifolia（Willd）Borkh has the highest relative phosphorus efficiency and phosphorose absoprtion efficiency under phosphorus stress, exhibiting the highest growth vigor and the strongest P absorption capacity. M. prunifolia（Willd）Borkh. has the best adaptation to low phosphorus stress. Malus hupehensis Rehd has lower relative phosphorus efficiency relative to M. prunifolia（Willd）Borkh, and has the highest PUE, and its capacity to low phosphorus stress ranks after M. prunifolia（Willd）Borkh. Further analysis showed that the values of PAE in the five rootstocks were significantly and positively correlated with the surface area and length of absorption root, indicating that the root absorption area enlargement of plants could promote the acquisition of P by increasing the root surface area and length under low phosphorus stress.