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 =(Ct ⨉Mt )/(C0 ⨉M0 )⨉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.