Under the context of global climate change, Southeast Asian tropical rainforests face multiple stressors including reduced precipitation, altered population density, and shifts in soil microbial communities. However, systematic experimental evidence on how these factors interact to affect tree regeneration remains scarce.
In a study published in Journal of Ecology, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and their collaborators revealed the growth and functional traits of Parashorea chinensis, a keystone dipterocarp tree in Southeast Asian rainforests, are shaped by the interplay of drought, neighbourhood density, and beneficial soil fungi.
The researchers conducted a year-long greenhouse experiment in Yunnan, China, manipulating three factors: water availability (wet vs. dry conditions), seedling density (one, two, or eight individuals per pot), and soil fungal communities (with or without fungicide to disrupt ectomycorrhizal associations). They monitored seedling growth and measured 11 functional traits (from leaf area and specific leaf area to root length and stem density) to understand how these stressors jointly affect seedling performance.
Their findings revealed that seedling growth is collectively regulated by water, density, and mycorrhizal fungi. While water availability emerged as the primary driver, its impact was substantially amplified by seedling density: the combined effect of low water and high density was multiplicative. Ectomycorrhizal fungi promoted growth under well-watered conditions but conferred no benefit under drought. Under stress (drought, high density, or fungicide), seedlings exhibited adaptive shifts, including higher leaf dry matter content, increased root-to-shoot ratios, and reduced leaf size.
They further found that increasing drought frequency may disrupt positive feedback between Parashorea chinensis and soil fungi, potentially undermining the species’ competitive dominance. Additionally, high density intensifies intraspecific resource competition, while future reductions in large vertebrates (altered herbivory patterns) and pest-disease accumulation will increase complexity in population dynamics.
The study emphasizes that drought, changes in neighbourhood density, and alterations to soil fungal communities occur simultaneously in natural forests, making single-driver studies insufficient for understanding forest responses to global change.
“Our results reveal that trait-growth relationships shift across water availability, neighbourhood density, and soil biotas,” said YANG Jie of XTBG. “Ignoring these context dependencies could lead to misleading predictions of how tropical forests will respond to future droughts and defaunation.”
First published: 13 July 2026
