3 Result

Non-additive effects on litter decomposition were observed of the litter mixtures composed of mangrove species. The water nutrient content, the initial trait dissimilarity, and the CWM of litter mixtures varied with species composition.

3.1 Decomposition rate (k) and mass remaining

Non-additive effects on litter decomposition were detected in the litter mixtures composed of mangrove species, but not in the mixture of A. corniculatum vs. S. alterniflora (Fig. 1ab). The observed mass remaining of the mixture of A. corniculatum vs. K obovata was substantially higher than the expected value (P < 0.01), whereas the observed mass remaining of the mixture of A. corniculatum vs. A. marina was lower than the expected one (P = 0.04), and the mixture of A. corniculatum vs. S. alterniflora did not show a significant difference between the observed and the expected values (P = 0.21; Fig. 1b).
The strength and the direction of the non-additive effect were indicated by the deviation of the non-additive effect from zero (Fig. 2). The mixture of A. corniculatum vs. K. obovata performed a positive and strongest non-additive effect than the other mixtures (P < 0.01). Whereas, A. corniculatum vs. A. marina showed a negative non-additive effect (P = 0.04). The mixture of A. corniculatum vs. S. alterniflora did not show a non-additive effect (P = 0.31).

3.2 Water nutrient content after decomposition

The single litter of A. corniculatum led to lower water content in NH4-N (P < 0.001) than the litters mixed with the other species (Fig. 3a), but did not have differences in total N (P > 0.05), PO3-P (P > 0.10) and total P (P > 0.10) from the mixed litters (Fig. 3ab). The single litter of K. obovata led to lower water content in NH4-N (P = 0.02) than the mixed litter (Fig. 3a), but no differences in the other nutrients (P > 0.10; Fig. 3ab). The single litter of A. marina led to higher water content in all tested nutrients than the mixed litters (P < 0.01 for NH4-N, total N, and PO3-P, P = 0.01 for total P; Fig. 3ab). The single litter of S. alterniflora showed no differences in all the water nutrients from the mixed litter (P > 0.10; Fig. 3ab).
Comparing the three litter mixtures, A. corniculatum vs. K. obovata were lower in all the water nutrients than corniculatum vs. A. marina (P = 0.01 for NH4-N; P = 0.03 for N; P = 0.71 for PO3-P; P = 0.009 for P) and A. corniculatum vs. S. alterniflora (P = 0.11 for NH4-N; P = 0.13 for N; P = 0.95 for PO3-P; P = 0.59 for P) (Fig. 3).

3.3 Trait dissimilarity and CWM of litter mixtures

The litter mixture of A. corniculatum vs. K. obovata had lower dissimilarity in leaf N and P, and greater in LDMC than the other litter mixtures (Fig. 4bce). The litter mixture of A. corniculatum vs. A. marina showed greater dissimilarity in leaf C and P or LDMC than the others (Fig. 4a, c), while A. corniculatum vs. S. alterniflora had lower dissimilarity in leaf C and LDMC but greater in leaf N and SLA than the others (Fig. 4abde).
Among the litter mixtures, A. corniculatum vs. K. obovata had the highest leaf C but lowest leaf nutrients (N and P), A. corniculatum vs. A. marina had the highest leaf nutrients and SLA but the lowest leaf C: N and A. corniculatum vs. S. alterniflora had lower leaf nutrients and SLA but higher LDMC than the others (Fig. 5). Among the single litters, A. corniculatum (100.59 ± 25.47 mg g-1) and K. obovata (162.78 ± 8.00 mg g-1) had higher concentration of condensed tannin than A. marina (1.93 ± 0.33) and S. alterniflora (3.21 ± 0.68 mg g-1).