Drying suppresses fine root production to 1 m depths and alters root traits in four distinct tropical forests.

Drying and drought in tropical forests, which have some of the highest net primary productivity on Earth, are likely to alter root dynamics, ecosystem function, and carbon (C) storage. We used a chronic drying experiment in four lowland Panamanian forests to investigate whether soil drying shifts tropical forest root production from surface to deeper soils, where moisture remains more abundant. Furthermore, we explored whether soil drying promotes resource acquisition strategies in roots, such as outsourcing to arbuscular mycorrhizal fungi (AMF) symbionts or increased specific root length (SRL). We found that chronic drying significantly reduced surface root biomass stocks, production, and turnover rates (0-20 cm soil depth), and increased AMF colonization without changes in SRL. Meanwhile, deep fine root productivity (> 60 cm depth) increased in the dry vs wet season, and in the drying experiment, except in the wettest, most infertile forest. Changes in root characteristics in these tropical forests with drying would likely alter forest-climate feedbacks and long-term soil C storage. At the same time, these results suggest that tropical forests may have an ability to adapt resource acquisition strategies under drying climates.