Effects of Low Phosphorus Stress on Leaf Physiological and Biochemical Characteristics of Tripterygium wilfordii Hook. f. Seedlings

Phosphorus (P) is a very important element that controls the processes of plant life,especially during its growth phase. Low-P in the soil usually leads to adaptive changes in plants in aspects such as photosynthesis,respiration and biosynthesis,and low available P is one of the major limitations to plant production. Tripterygium wilfordii Hook. f. is an important traditional Chinese medicine,widely used in medical treatment of diabetes,rheumatism,and nephropathy. Tripterygium wilfordii is distributed in southeastern China in poor P and available P red soil. Low-P in the soil may lead to reduced T. wilfordii production. Usually,chemical fertilization and soil improvement are the primary measures used to meet the P demands of crops in traditional agriculture and trees in forestry management,but these measures still fail to increase T. wilfordii yield to meet good manufacturing practice (GAP) standards. Recently,plants with high P use efficiency have been discovered and used to replace traditional measures for improving P use efficiency of plants. Therefore,studying the effect of different P stresses on T. wilfordii will help to reveal the mechanism of low-P adaptation,and breed T. wilfordii with high-P use efficiency. Therefore,we analyzed the physiological and biochemical responses (such as peroxidase (POD),catalase (CAT),malondialdehyde (MDA),superoxide dismutase (SOD),acid phosphatase (APA),and proline (Pro)) during one growing season of one-year-old and three-year-old seedlings (T. wilfordii clones) to six P stresses under soil culture:normal P supply (25 mg/kg,CK),slight P deficiency (20 mg/kg),medium P deficiency (15 mg/kg,10 mg/kg),and heavy P deficiency (5 mg/kg,0 mg/kg). The results indicated that under low phosphorus stress,the leaves of both seedling types were higher in SOD,MDA,Pro,APA than in CK,and these values increased with concentration and time of stress. In contrast,CAT and POD values were lower than CK values in the leaves of both seedling types,and decreased with the concentration of low P stress. The protective enzymes,MDA,Pro and APA of seedling leaves were sensitive to low-P stress and worked well,especially at the treatments of 15 and 20 mg/kg. As mentioned above,T. wilfordii was adapted well in the environments of slight and medium P deficiency by self physiological regulation. The adaptability of three-year-old T. wilfordii seedlings was better than that of one-year-old seedlings in oxidation resistance,osmoregulation and low-P tolerance. Consequently,the three-year-old seedlings were preferred for interplantation in low P conditions. The APA levels can serve as a reference to the breeding of T. wilfordii with low P tolerance,but more research is needed to determine whether APA levels are an important index for evaluating and selecting T. wilfordii clones with high P use efficiency.