Decomposition and nutrient release of eucalyptus harvest residues in southeast Brazil

ABSTRACT Background: Background: Eucalypt harvest residues are critical to nutrient balances and forest soil productivity mainly in areas with consecutive forest rotations. However, nutrient release and their relations over decomposition are still poorly understood in tropical sites. We aimed to understand how nutrients are released from leaves, branches, and bark (as harvest residues), and how nutrient concentrations could be limiting the decomposition of each fraction. We measured mass loss and nutrient release of Eucalyptus urophylla x Eucalyptus grandis harvest residues for 365 days in Southeast Brazil. Results: Results: Leaves fraction showed a faster decomposition rate than branches and bark, but nutrient accumulation was observed for all harvest residues, especially bark and branches at later stages of the decomposition. Decomposition of all harvest residues seemed to be P-limited with a stronger limitation occurring for leaf litter decomposers. The decomposition of more lignified residues such as bark and branches was less influenced by climatic variables than leaf decomposition. Conclusion: Conclusion: Eucalypt harvest residues had a great contribution to soil fertility, and retaining them in the soil systems will enhance soil fertility in the short (leaves) and long-term (branches and bark) and can partially supply the nutrients for the next rotation.

摘要
背景：在连续轮伐的林区中，桉树采伐剩余物（Eucalypt harvest residues）对养分平衡与森林土壤生产力至关重要。然而在热带区域，分解过程中的养分释放及其内在关联机制仍未得到充分解析。本研究旨在明确叶片、枝条与树皮（作为采伐剩余物）的养分释放规律，以及养分浓度如何限制各组分的分解进程。我们于巴西东南部开展了为期365天的试验，测定尾叶桉（Eucalyptus urophylla）×巨桉（Eucalyptus grandis）采伐剩余物的质量损失与养分释放情况。
结果：叶片组分的分解速率显著快于枝条与树皮，但所有采伐剩余物均出现养分累积现象，其中以分解后期的树皮与枝条表现尤为突出。所有采伐剩余物的分解过程均受到磷（P）限制，且枯落叶分解者受到的磷限制更强。相较于叶片分解，木质化程度更高的树皮与枝条分解受气候变量的影响更小。
结论：桉树采伐剩余物对土壤肥力具有重要贡献，将其留存于土壤系统中，可在短期（叶片组分）与长期（枝条与树皮组分）维度提升土壤肥力，并可为下一茬造林周期提供部分养分补给。