[Dynamics of recalcitrant substances in mixed decomposition of indigenous tree species litter in alpine forest burned areas of Northwest Sichuan, China].

Litter decomposition is crucial for restoration of burned areas in the alpine forests of northwestern Sichuan. With the indigenous tree species in the alpine region of Ganzi, Quercus semicarpifolia and Abies fabri, as the research objects, we set up five treatments, including single Q. semicarpifolia litter (Q), single A. fabri litter (A), and 3 mixed treatments (the two were mixed at a ratio of 3:1, 1:1, and 1:3, namely QA3:1, QA1:1, and QA1:3). All the litters were incubated in a 600-day field decomposition experiment in forest burned areas. We explored the decomposition characteristics of recalcitrant substances (lignin, cellulose, and total phenols) during decomposition. The results showed that the lignin degradation rate of mixed litter was generally lower than that of single Q. semicarpifolia (except for QA3:1 decomposed for 600 d), but higher than that of single A. fabri (except for 120 d of decomposition). The degradation rates of cellulose and total phenols in mixed litter were generally higher than those in the two single tree species (except for the cellulose degradation in QA3:1 at 240 d, and the total phenol degradation in QA1:1 and QA1:3 at 120 and 240 d, respectively). During the decomposition process, the observed degradation rates of lignin, cellulose and total phenols were higher than the predicted values in 58.3%, 77.8% and 86.1% of the mixed leaf litter samples, respectively, exhibiting a synergistic trend. For the QA1:3 mixture, both cellulose and total phenol degradation rates exhibited significant synergistic effects throughout the 600-day decomposition. Lignin degradation rate at 240 d of decomposition was significantly correlated with initial lignin and total cellulose content, while it was significantly correlated with initial total phenolic content, total carbon, and total nitrogen content at 480 d of decomposition. Our results showed that litter mixture with a 1:3 ratio of Q. semicarpifolia and A. fabri facilitated the decomposition of the recalcitrant substances, thereby promoting soil organic carbon accumulation.