2026-07-22 中国科学院（CAS）
中国科学院（CAS）西双版納熱帯植物園（XTBG）などの研究チームは、東南アジア熱帯雨林の優占樹種であるフタバガキ科Parashorea chinensisの実生成長が、水分条件、個体密度、土壌菌根菌の相互作用によって決まることを明らかにした。研究では、水分（湿潤・乾燥）、実生密度（1・2・8本）、菌根菌（殺菌剤処理の有無）の3要因を組み合わせた1年間の温室実験を実施し、成長量と葉面積、比葉面積、根長など11の機能形質を解析した。その結果、水分条件が最も大きな影響を及ぼす一方、高密度条件では乾燥の悪影響がさらに増幅されることが判明した。また、干ばつの頻発は菌根菌との共生による正のフィードバックを弱め、樹種の競争優位性を低下させる可能性が示された。さらに、高密度では同種間の資源競争が強まり、将来的な大型動物の減少や病害虫の変化も森林更新に影響すると考えられる。研究は、熱帯林の将来予測には単一要因ではなく、気候・生物・土壌要因の相互作用を考慮する必要性を示した。
＜関連情報＞
- https://english.cas.cn/newsroom/research-news/202607/t20260723_1178933.shtml
- https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.70398
水の利用可能性、近隣の密度、外生菌根菌が優占フタバガキ科植物の形質と成長に及ぼす相互作用効果 Interacting effects of water availability, neighbourhood density and ectomycorrhizal fungi on the traits and growth of a dominant Dipterocarp
Libing Pan, Xiaoyang Song, Min Cao, Jie Yang, Nathan G. Swenson
Journal of Ecology Published: 13 July 2026
DOI:https://doi.org/10.1111/1365-2745.70398
Abstract
- Southeast Asian forests are increasingly impacted by global change. Precipitation reduction is a key driver whose effects on tree performance are mediated by biotic contexts such as tree density and altered soil fungal communities. Understanding tree responses to these drivers is central to predicting forest dynamics. However, these drivers are often studied independently despite their potential for interactive effects. Trait-based approaches that ignore these interactions by assuming static trait values may provide limited or biased insights into future forests.
- We manipulated three key variables in a glasshouse experiment: water availability (simulating decreasing precipitation) and two biotic contexts, neighbourhood density and soil ectomycorrhizal (EcM) fungal communities. We assessed their independent and interactive effects on the growth, traits and trait–growth relationships of Parashorea chinensis, a dominant Dipterocarp species in southeast Asian tropical rainforests.
- Our results demonstrate that, while water availability is the dominant driver of seedling growth, the impact is magnified by seedling density. Promotion of seedling growth by soil EcM fungi is observed under wet but not dry conditions. Seedling trait–growth relationships are highly context-dependent, varying across treatments (i.e. water availability, neighbourhood density and fungicide). For instance, while root and stem traits exhibited weak or inconsistent relationships with growth, leaf traits such as leaf area and specific leaf area correlated strongly with growth across treatments. These findings indicate that predictions based upon static species-level trait values will be highly uncertain, revealing that trait–performance relationships are more complex than assumed.
- Synthesis. Our results reveal that trait–growth relationships shift across water availability, neighbourhood density and soil biotas, challenging current vegetation models that rely on mean trait values. These findings highlight the need to move beyond single-driver studies and static trait assumptions by integrating these factors to develop more robust predictions of future forest performance.
