竹林におけるリター分解の制御機構

概要

九州大学学術情報リポジトリ
Kyushu University Institutional Repository

Regulation of litter decomposition in bamboo
stands
マリー オレゴ モラレス

https://hdl.handle.net/2324/7157394
出版情報：Kyushu University, 2023, 博士（農学）, 課程博士
バージョン：
権利関係：

Name

： マリー オレゴ モラレス (Marly Orrego Morales)

Title

：Regulation of litter decomposition in bamboo stands
（竹林におけるリター分解の制御機構）

Category：Kou

Thesis Summary

Litter decomposition is an essential process that regulates the fate of carbon and nutrients in soils
through the progressive breakdown of organic matter, and thus is crucial for the functioning of terrestrial
ecosystems. In East Asia, bamboo invasion is a serious concern due to its ecological and socio-economic
implications, and thus evaluating litter decomposition dynamics in bamboo stands is essential to better
assess their impacts in forest ecosystems.
The aim of this thesis is to further our understanding of litter decomposition and nutrient dynamics in
bamboo stands and explore the controlling factors regulating litter decomposition processes. The first part of
the thesis explored the influence of macroenvironmental, soil and stand structure factors on early-stage litter
decomposition and stabilization in bamboo stands at a regional scale. The results showed that climatic
factors are the main drivers of decomposition processes in Moso bamboo stands. Long-term climate
influences litter stabilization, while the interaction between precipitation and temperature affects litter
decomposition rates at early stages. Stand structure and soil properties have limited direct effects, but
indirect effects from stand density impact litter stabilization through organic matter input and soil bulk
density. These results further suggest that future environmental changes resulting from global climate change
would greatly affect decomposition and soil carbon storage in this region.
The second part of the thesis evaluated the interactive effects litter traits and soil fauna on litter
decomposition processes of above- and below-ground organs. After two years of litter decomposition, the
mass loss followed the order of leaf > fine root > rhizome = branch > culm litter. The results showed that
chemical and structural litter traits were predictors of mass and carbon loss but not nitrogen loss. The
presence of soil fauna did not change the relationship between litter traits and decomposability, indicating
that soil fauna effects were not dependent on litter quality. Soil fauna decreased litter mass and carbon loss
of leaf and branch litter, but had limited effects on fine root, rhizome and culm litter decomposition. The
large disparities in the contribution of soil fauna to litter decomposition and nutrient release suggest that
considering the effects of soil fauna in whole-plant litter decomposition is essential for understanding the
role of soil decomposers in bamboo forest carbon cycling.
The third part of the thesis investigated the chemical and morphological controls on below-ground litter
decomposition following a root functional order classification. The results highlight the morphological and
chemical heterogeneity of fine roots in Hachiku, Madake and Moso bamboo. The analysis of root litter using
13

C-NMR spectroscopy revealed differences in the biochemical composition within the branching root

system. Notably, slower decomposition rates were observed in lower order roots compared to higher order

roots. The results also revealed the limited predictability of litter C/N and lignin/N ratios on fine root litter
decomposition. Furthermore, the recalcitrance of lower order roots was associated with the presence of
aromatic compounds, while the rapid decomposition of higher order roots was linked with the presence of
labile cellulosic compounds. Given that lower order roots are typically short-lived and represent a significant
proportion of the total fine root biomass in bamboo stands, their slower decomposition may have significant
effects in soil carbon cycling through the formation of stable soil organic matter.
The fourth part of the thesis explored the influence of fallen bamboos on the forest floor and soil fauna
on litter decomposition dynamics and discussed whether the removal of these structural components as part
of management practices could potentially affect litter decomposition and nutrient cycling. The results
showed that dead culms in Moso bamboo stands play a crucial role in modifying the soil microenvironment,
enhancing litter biotic activity and accelerating the loss of litter mass, carbon and nitrogen. The dead culms
have a significant impact on mesofauna abundance, diversity and fauna assemblage during litter
decomposition. However, the presence of dead culms does not alter the direct effect of soil fauna on litter
decomposition, suggesting that their influence is mainly through changes in the soil environment and litter
microbial activity. Dead bamboo culms are important structural components that affect decomposer
organisms and the litter nutrient dynamics in bamboo stands. These results further show that the removal of
dead culms from the forest floor could have substantial effects on soil biota and ecosystem processes in
managed stands.
In conclusion, this thesis contributes to the understanding of the interplay among various factors that
regulate litter decomposition, and illustrates how climate, litter quality and soil fauna impact decomposition
processes in bamboo stands. Moreover, the findings on the indirect impacts of dead culms on nutrient
cycling hold practical implications for the management of bamboo stands.

この論文で使われている画像