Decomposition characteristics of bark litter in subtropical Eucalyptus plantations

Senesced bark litter of Eucalyptus collected from pure Eucalyptus plantation was placed in four stand types, including pure Eucalyptus urophylla plantation (control), E. urophylla-Cunninghamia lanceolata mixed plantation (Eucalyptus-Cunninghamia), E. urophylla-Fokienia hodginsii mixed plantation (Eucalyptus-Fokienia), and E. urophylla-C. lanceolata-F. hodginsii mixed plantation (Eucalyptus-Cunninghamia-Fokienia). During a 540-day decomposition period, litterbags were retrieved every 60 days to measure remaining dry mass and the contents of carbon (C), nitrogen (N), phosphorus (P), cellulose, and lignin. We analyzed decomposition characteristics, home-field advantage (HFA), nutrient release, and key drivers in mixed plantations. The results showed that decomposition rates in the mixed plantations were significantly higher than in the pure plantation, with negative HFA indices. Decomposition was fastest in the Eucalyptus-Cunninghamia mixed plantation, followed by the Eucalyptus-Cunninghamia-Fokienia mixed plantation and the Eucalyptus-Fokienia mixed plantation, which slightly exceeded the pure plantation. The three Eucalyptus-conifer mixed plantations promoted the mineralization of C, N, P, and the degradation of cellulose during bark litter decomposition, but had little effect on lignin degradation, accompanied by decreases in C/N, C/P, N/P and an increase in lignin/N. During the decomposition process, C and cellulose showed a continuous release pattern in both home and away fields, while N and P exhibited a "release-accumulation-release" pattern. Nutrient remaining amounts, stoichiometric ratios, and recalcitrant compound contents collectively explained 76.6% of the variation in bark litter decomposition. Higher C remaining amount is positively related with decomposition, while higher P remaining rate, C/N, and N/P negatively related with decomposition. The Eucalyptus-Cunninghamia mixed plantation significantly enhanced the decomposition of Eucalyptus bark litter. In future structural transformations of Eucalyptus plantations, it is recommended that Eucalyptus-Cunninghamia mixed plantation be prioritized.