Effects of Phosphorus Supply Level on Phosphatase Activity and Phosphorus Absorption and Utilization Efficiency of Young Newhall Navel Orange Trees
The experiment of young Newhall navel orange trees grafted on Poncirus trifoliate (L. ) Raf. in pots were conducted to study the effects of various phosphorus supply levels on the acid phosphatase (APase) activity and phosphorus absorption and utilization efficiency and to provide the scientific basis for soil nutrition diagnosis and determination of suitable phosphorus application quantity in Newhall navel orange garden. The results showed that the APase activity of roots, leaves and soil and SAPase activity of roots were negatively correlated to phosphorus supply levels among 7 phosphorus supply treatments range from 5 to 125 mg/kg. The APase activity of roots, leaves and soil and SAPase activity of roots were the highest and phosphorus utilization efficiency of the whole plant, above-ground part and roots was the maximum under 5 mg/kg phosphorus supply level but leaves displayed the symptoms of phosphorus deficiency. The biomass and phosphorus absorption efficiency of the whole plant, above-ground part and roots under 25 mg/kg phosphorus supply level reached the highest but its phosphorus utilization efficiency was lower than that under 5 mg/kg phosphorus supply level. The growth of young Newhall navel orange trees under above 65 mg/kg phosphorus supply level was inhibited obviously and the APase activity of roots, leaves and soil and SAPase activity of roots, as well as phosphorus absorption and utilization efficiency were reduced significantly. In conclusion,25 -45 mg/kg phosphorus supply level is beneficial to growth and phosphorus absorption and utilization of young Newhall navel orange trees.