2025-12-16 森林総合研究所
森林の落葉は、土壌動物にとって「食べ物」であると同時に「住みか」でもある。本研究では、落葉を「お菓子の家(食べ物でできた住みか)」として捉え、その性質を定量的に評価する新たな手法を検証した。従来は窒素濃度やリグニン量など、食物としての化学的性質(Plant Economics Spectrum:PES)のみが重視されてきたが、本研究では落葉の形やサイズに基づく住みかとしての性質(Size and Shape Spectrum:SSS)を新たに導入した。16樹種の落葉を用いた解析と野外メソコズム実験の結果、SSSは土壌動物群集の個体数や多様性をPESよりもよく説明できることが明らかになった。これにより、観察が困難な地下生態系を、地上部の植生特性から推測できる可能性が示され、生物多様性保全や森林管理への応用が期待される。
図1.16樹種の落葉形質の主成分分析(PCA)
落葉の形やサイズに関する多くの形質(青色の字で表示)は第1軸に集約され、Plant Economics Spectrum (PES)に関わる多くの形質(オレンジ色の字で表示)は第2軸に集約された。そこでこのPCA1軸をSize and Shape Spectrum (SSS)、PCA2軸をPESとしてその後の解析に用いた。この2軸を合わせると落葉形質のばらつきの60%以上が説明された。
<関連情報>
- https://www.ffpri.go.jp/press/2025/20251216/index.html
- https://www.ffpri.go.jp/press/2025/20251216/documents/20251216press.pdf
- https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.70187
2つの主要な植物特性スペクトルが落葉層の特性と生息地供給機能に与える影響 Effects of two key plant trait spectra on litter layer properties and habitat provision functions
Saori Fujii, Matty P. Berg, Richard S. P. van Logtestijn, Shun’ichi Makino, Johannes H. C. Cornelissen
Journal of Ecology Published: 03 November 2025
DOI:https://doi.org/10.1111/1365-2745.70187
Abstract
- Plant litter harbours a wide range of organisms, such as soil animals, microbes, vascular plant seeds and seedlings, mosses and lichens. While it is well-recognized that litter drives carbon and nutrient cycling through its traits related to the plant resource economics spectrum (PES), its explanatory power for predicting the litter-dwelling biological community has been very low. In this era of biodiversity change, litter habitat provisioning functions should receive more research attention.
- A conceptual trait space defined by a physical trait axis related to the litter size and shape spectrum (SSS) and a biochemical trait axis (PES) has been proposed, to explain habitat as well as nutrition functions for soil organisms. We aim to improve the explanatory power of litter traits for the litter-dwelling animal communities by testing this concept, and by connecting fundamental traits related to the size and shape of single litter particles with litter layer properties more directly related to habitat quality (e.g. moisture regime, habitat space).
- We tested the concept by using 16 woody species, and examined how different traits or trait axes determine the litter and litter layer properties directly related to habitat quality for soil animals. In addition, we assessed in a field experiment with litter layers in mesocosms how this new trait framework explains the soil invertebrate community.
- The two plant trait spectra together accounted for >60% of the variance in litter quality in a principal component analysis. SSS-related traits strongly explained litter layer habitat-related properties, such as water-holding capacity and litter bulk density. The SSS axis and these SSS-associated properties more strongly determined soil animal communities assembled over 7 weeks in the field experiment, surpassing the effects of the PES axis.
- Synthesis. This study has provided the first empirical evidence for the litter trait space defined by both SSS and PES spectra occupied by wide-ranging plant species, and its utility to explain litter layer properties related to the physical environment and associated habitat provisioning function. We suggest that this trait-based SSS-PES framework will help us to disentangle mechanisms underpinning real-world interactions between above-ground vegetation and below-ground communities.
