Abstract: Phosphorus (P) is an important nutrient for plant growth and development. Mixed forests can better maintain the productivity of plantations. Understanding the characteristics and influencing factors of soil P fractions in mixed forests at different developmental stages is of great significance for the sustainable management of plantations. In this study, the Tiessen modified Hedley P fractionation method was used to extract soil samples and investigated the characteristics of soil P fractions with different stand ages (young forest, 15 years old; middleaged forest, 26 years old) and litter manipulation (control, CK; litter removal, NL; litter double, DL; removal of litter and roots, NRL) in Larix principisrupprechtii conifer and broadleaved forest. The results showed that there were significant differences of soil P fraction, soil microbial biomass P and acid phosphatase activity between the young and middle-aged forests (P<0.05). Compared with the 15 years old forest, the contents of soil labile P (Resin-Pi, NaHCO₃-Pi, NaHCO₃-Po) in the 26 years old forest were higher, while the contents of NaOH-Po were lower (P<0.05). Compared with the CK treatment, DL treatment significantly increased the contents of soil labile P (Resin-Pi, NaHCO₃-Pi and NaHCO₃-Po) and middle labile P (NaOH-Pi and NaOH-Po) (P<0.05). NL and NRL treatments significantly reduced the contents of soil Resin-Pi, NaHCO₃-Pi, NaHCO₃-Po, NaOH-Pi and NaOH-Po (P<0.05). There was no significant difference in stable P (dilute HCl-Pi, concentrated HCl-Pi and concentrated HCl-Po) and residual P across different stand ages and litter treatments (P>0.05). The results of redundancy analysis showed that changes in P fractions were mainly driven by soil microbial biomass P, acid phosphatase activity, plant growth (average basal area), and organic carbon content under different aged stands and litter treatments.

Key words: tolerance., phenylalanine ammonia-lyase (PAL), cucumber, inhibitor, low temperature stress