The biodiversity of litter can regulate carbon and nutrient cycling during mixed decomposition. It is common knowledge that the decomposition rates of mixed litters frequently deviate from those predicted for these component litter species. However, the direction and magnitude of the nonadditive effects on the degradation of mixed litters remain difficult to predict. Previous studies have reported that the different carbon fractions of leaf litters responded to litter mixture differently, which may help to explain the ambiguous nonadditive effect of diversity on bulk litter decomposition. Therefore, we conducted decomposition experiments on 32 litter mixtures from seven common tree species to test the responses of different carbon fractions to litter diversity in subtropical forests. We found that the overall mass loss of the mixed litter was faster than that estimated from single species. The relative mixing effects (RMEs) of different carbon fractions exhibited different patterns to litter diversity and were driven by different aspects of litter functional dissimilarity. Soluble carbon fractions decomposed more slowly than expected from single species, while lignin fractions decayed more quickly. Moreover, we found that the RMEs of bulk litter decomposition may be determined by the lignin fraction decomposition. Our findings further support that distinguishing the response of different carbon fractions to litter diversity is important for elucidating the nonadditive effects of total litter decomposition.

Pinus taeda is a key timber species, and extensive research has been conducted on its wood formation. However, a comprehensive investigation into the biosynthetic pathways of lignin, cellulose, and hemicellulose in P. taeda is lacking, resulting in an incomplete understanding of secondary cell wall (SCW) formation in this species. In this study, we systematically analyzed transcriptomic data from previously published sources and constructed detailed pathways for lignin, cellulose, and hemicellulose biosynthesis. We identified 188 lignin-related genes and 78 genes associated with cellulose and hemicellulose biosynthesis. An RT-qPCR highlighted 15 key lignin biosynthesis genes and 13 crucial genes for cellulose and hemicellulose biosynthesis. A STEM analysis showed that most essential enzyme-coding genes clustered into Profile 14, suggesting their significant role in SCW formation. Additionally, we identified seven NAC and six MYB transcription factors (TFs) from atypical evolutionary clades, with distinct expression patterns from those of the previously characterized NAC and MYB genes, indicating potentially unique functions in SCW formation. This research provides the first comprehensive overview of lignin, cellulose, and hemicellulose biosynthetic genes in P. taeda and underscores the importance of non-canonical NAC and MYB TFs, laying a genetic foundation for future studies on SCW regulatory mechanisms.