2.4. Statistical analyses
The mass remaining of litter (Mr ) (%) during the N and P addition test was calculated using the formula:
Mr =Mt /M0 ⨉100% (1)
Where Mt and M0 refer to the mass (g) of litter at time t of decomposition and the initial mass (g) of litter, respectively.
The value of the rate constant k for decomposition of litter matter was calculated by (Olson, 1963):
Mt /M0 =e kt (2)
Where k refers to the annual decomposition rate constant of litter.
The time to decompose 50% (T0.5 ) and 95% (T0.95 ) of the litter was calculated (Olson, 1963) as:
T0.5 = –ln (1 – 0.5)/k (3)
T0.95 = –ln (1 – 0.95)/k (4)
The lignin, cellulose, total carbon, total nitrogen and total phosphorus remaining rates (Mcr ) (%) during decomposition of litter were calculated as:
Mcr =(CtMt )/(C0M0 )⨉100% (5)
Where Ct and C0 refer to the litter nutrient concentration (g·kg-1) at timet and the initial litter nutrient concentration (g·kg-1), respectively.
The results of the study were processed and analyzed using SPSS 22.0 and R 3.6.3. One-way ANOVA was used to analyze the differences in the decomposition constants (k), the mass remaining of litter, lignin, cellulose, total carbon, total nitrogen and total phosphorus remaining rate, and soil enzyme activities under different treatments at the same decomposition time, and three-way repeated measures ANOVA (RM-ANOVA) was used to investigate the reciprocal effects of N and P addition for each index and their synergistic effects with decomposition time. Pearson correlation analysis and linear regression analysis were preformed to evaluate the correlation between the decomposition rate of litter, litter endogenous nutrient concentration and soil enzyme activity. To compare the relative importance of litter endogenous nutrient concentration and soil enzyme activity on K-value, the relative influence analysis was calculated using the ”gbm” package.The results were plotted by Origin 2022 and R 3.6.3.