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 elliottii, a key economic conifer in southern China, requires efficient propagation methods to meet demand for elite germplasm in resin and timber production. While somatic embryogenesis-based plant regeneration has been successfully achieved in Pinus elliottii, large-scale production remains challenging. Our results demonstrate that the genotype of Pinus elliottii significantly influences the induction rate of embryogenic callus. During somatic embryo maturation, the liquid–solid induction method increased the number of mature embryos by 25.85 times. Maturation efficiency was further enhanced by a 3-week pretreatment followed by the application of 9 mg/L ABA, 0.5 mg/L PSK, and 6 mg/L COS. Additionally, the incorporation of activated carbon significantly promoted both the maturation and germination of somatic embryos. In the somatic embryo maturation stage, 1 g/L activated carbon induced 288.67 mature embryos per gram of embryogenic callus, resulting in a total of 1452 embryos. During germination, the application of 4 g/L activated carbon achieved a germination rate of 63%, and the survival rate of somatic embryo-derived seedlings reached 85%. This study not only identifies the optimal conditions for somatic embryogenesis in Pinus elliottii but also establishes an efficient protocol for somatic embryo maturation induction, providing a crucial scientific foundation for the rapid propagation and seedling production of Pinus elliottii.

Pathogenesis-related protein 1 (PR1) plays important roles in plant responses to both biotic and abiotic stresses; however, its role in mediating defense against pine wood nematode in Pinus massoniana remains unclear. In this study, a total of 63 PR1 family members were identified in P. massoniana using bioinformatics approaches and were named PmPR1-1 to PmPR1-63 based on their phylogenetic relationships. Phylogenetic analysis showed that these members were distributed among four of the six subfamilies. Most of the encoded proteins were hydrophilic, with lengths ranging from 131 to 406 amino acids. Their promoter regions contained multiple cis-acting elements associated with phytohormone signaling and stress responses, and some members formed gene clusters on chromosomes 2, 5, and 9. qRT-PCR (quantitative reverse transcription polymerase chain reaction) analysis showed that the clustered genes PmPR1-46, PmPR1-55, PmPR1-56, and PmPR1-61 were significantly upregulated in the early stage of pine wood nematode inoculation in both resistant and susceptible P. massoniana plants, with higher expression levels in resistant plants. Transient overexpression of PmPR1-61 increased SOD and PPO activities as well as proline content while decreasing CAT activity. These results suggest that the PmPR1 family may be involved in the defense response of P. massoniana against pine wood nematode. Among them, PmPR1-55, PmPR1-56, and PmPR1-61 represent candidate resistance genes worthy of further investigation and provide valuable gene resources for elucidating resistance mechanisms and supporting molecular breeding in P. massoniana.

Ubiquitins (Ubs) play a crucial role in plant–pathogen interactions, particularly the RPL40 family, which is essential for protein synthesis. While Pinus massoniana is highly susceptible to pine wilt disease (PWD) caused by Bursaphelenchus xylophilus, the defense mechanisms mediated by RPL40s remain poorly understood. Here, we performed a genome-wide identification of the ubiquitin and ubiquitin-like gene family (PmUBQs) in P. massoniana. We identified 30 PmUBQ genes unevenly distributed across 11 chromosomes, which were classified into six subfamilies based on phylogenetic analysis. An analysis of promoter regions indicated that the PmUBQ genes were enriched with cis-acting elements associated with stress responses, hormone regulation, and development. Specifically, two group II members, PmRPL40-1 and PmRPL40-2, located on chromosomes 12 and 11, respectively, were identified and exhibited distinct responses to B. xylophilus infection in resistant and susceptible P. massoniana. PmRPL40-1 was significantly highly expressed in the 15 days post-inoculation, while PmRPL40-2 was downregulated on day 1 and then upregulated. Moreover, both genes showed peak divergence at 15 days post-inoculation; the expression levels of PmRPL40-1 and PmRPL40-2 in resistant P. massoniana were approximately 1.8- and 3.7-fold higher, respectively, than in susceptible P. massoniana. These patterns suggest that PmRPL40s might be involved in the rapid activation of defense responses and late-stage cell repair. Notably, transient overexpression of PmRPL40-1 in P. massoniana led to a significant 1.6-fold increase in the jasmonic acid (JA) content (p < 0.0001). These findings reveal the key PmUBQ genes and suggest that PmRPL40s contribute to PWD resistance potentially through the modulation of JA signaling, offering potential targets for molecular breeding in P. massoniana.