3.Results
3.1. Litter mass remaining and
decomposition rate constant
The results showed that N, P and NP additions significantly contributed
to the decomposition of litter matter (Fig.1). At 360 days, the mass
remaining of litter was 53.62%, 62.36% and 65.16% in N1, N2 and N3
treatment; 55.56%, 53.02% and 51.35% in P1, P2 and P3 treatment;
51.05%, 47.72% and 49.23% in NP1, NP2 and NP3 treatment,
respectively. One-way ANOVA showed that compared to CK, there were
significant differences in mass remaining of litter in different
concentrations of N, P and NP treatments, respectively (P <
0.001). Under N addition, N1, N2 and N3 treatments significantly reduced
mass remaining in the early stages of decomposition, and only N1
treatment had a significant effect in the middle and late stages of
decomposition; under P addition, P1, P2 and P3 significantly reduced
mass remaining in each decomposition period; under NP addition, NP1, NP2
and NP3 treatments significantly reduced mass remaining in the middle
and late stages of decomposition, and no significant difference was
found between NP2 and NP3 treatments. The RM-ANOVA showed that the
interaction of N and P additions and their synergistic effect with
decomposition time had a significant effect on the mass remaining of
litter (P < 0.001) (Table S1).
The litter decomposition rate constant (K ) increased
significantly with increasing P addition concentration with the highest
value in the P3 treatment (0.67 year-1), and showed a
trend of increasing and then decreasing with increasing N and NP
addition concentrations with the highest values in the N1 (0.62
year-1) and NP2 (0.73 year-1)
treatments, respectively (Table 2). In the CK treatment, the time
required for 50% (T0.5) and 95%
(T0.95) of litter decomposition was 1.67 and 7.21 years,
respectively. Under N addition, T0.5 and
T0.95 were 1.11 and 4.81 years for the N1 treatment,
1.47 and 6.34 years for the N2 treatment, and 0.62 and 6.99 years for
the N3 treatment, respectively. Under P addition, T0.5and T0.95 were 1.18 and 5.10 years for the P1 treatment,
1.09 and 4.72 years for the P2 treatment, and 4.49 and 1.04 years for
the P3 treatment, respectively. Under NP addition, T0.5and T0.95 were 1.03 and 4.46 years for NP1 treatment,
0.94 and 4.05 years for NP2 treatment, and 0.98 and 4.12 years for NP3
treatment, respectively. The RM-ANOVA showed that the interaction of N
and P additions and their synergistic effect with decomposition time had
a significant effect on the decomposition rate constant (P <
0.001) (Table S1).