Tropical primary forest plants up-regulate root exudation to adapt to long-term high nitrogen deposition

Date: May 27, 2026

Guangzhou, China: A research team led by Prof. Xiankai Lu at the South China Botanical Garden, Chinese Academy of Sciences, investigated tropical forest plant adaptation to 20 years of chronic N addition (up to 150 kg N ha⁻¹ yr⁻¹) in a primary monsoon evergreen broadleaf forest. They found chronic high N addition increased root carbon exudation, stimulating phosphatase activity to mineralize organic P, and enhanced organic acid release to dissolve mineral-bound P. The organic acid pathway contributed ~2-fold more bioavailable P than the phosphatase pathway. This is the first direct evidence that tropical plants actively upregulate root exudation to alleviate P limitation under long-term N enrichment, thereby sustaining productivity and explaining the resilience of tropical forest carbon sinks. These findings reshape predictions of forest carbon dynamics under global change.

Intensifying global nitrogen (N) deposition has disrupted the N-P balance in ecosystems, particularly in tropical and subtropical regions, where soil available P is inherently scarce. Extensive studies in temperate N-limited ecosystems have led to a classic paradigm: N addition alleviates plant competition for N, thereby reducing the allocation of photosynthates belowground, thereby decreasing the release of root exudates. However, whether this paradigm can be directly applied to “N-rich” but P-deficient tropical and subtropical forests has remained untested experimentally for decades, creating a critical knowledge gap in predicting C–P feedbacks and long-term carbon sink stability under chronic N enrichment.

To address this knowledge gap, a research team led by Prof. Xiankai Lu at the South China Botanical Garden, Chinese Academy of Sciences, conducted a 20-year in situ nitrogen addition experiment in a primary tropical forest at Dinghushan National Nature Reserve. Results showed that tropical forest plants deploy an active, carbon-costly adaptation strategy under chronic high N addition: (i) increased root carbon exudation rate to stimulate microbial phosphatase activity and accelerated organic P mineralization; (ii) enhanced the release of organic acids to promote the dissolution of mineral-bound P. More importantly, the organic acid pathway played a dominant role in P-mobilization, driving ~2× more bioavailable P than the phosphatase pathway.

This study provides the first experimental evidence that tropical plants adapt to long-term high N deposition by actively upregulating root exudation, revising the long-standing paradigm that N enrichment universally reduces belowground carbon allocation. This finding not only explains how “N-rich”tropical forests maintain high productivity and stability, but also suggests that ecosystems may possess more complex proactive adaptation strategies when facing chronic environmental stress. This insight is essential for improving predictions of tropical forest carbon sink resilience under accelerating global change.

Original Source：

Zhu X., Zhang Z., Turner B. L., Chen W., Mao Q., Li A., Mo J., Lu X., 2026. Enhanced Root Exudation as an Adaptation Mechanism to Facilitate Phosphorus Mobilization in a Primary Tropical Forest Under Chronic Nitrogen Deposition. Global Change Biology 32(5): e70912

https://doi.org/10.1111/gcb.70912

Keywords: carbon allocation, N-induced P deficiency, nitrogen addition, root exudation, soil P cycling, tropical forests

About the Author

Xiaomin Zhu (First author): South China Botanical Garden, Chinese Academy of Sciences. Research interests include global change ecology, mycorrhizosphere ecology, plant-soil-microbe interactions, and soil carbon sequestration.

Xiankai Lu (Corresponding author): South China Botanical Garden, Chinese Academy of Sciences. His research focuses on responses and adaptative mechanisms of forest ecosystem structure and function to global environmental change.

About the journal

Global Change Biology is an environmental change journal dedicated to shaping the future and solving the world's most challenging problems by tackling sustainability, climate change and environmental protection, food and water security and supply, as well as global health. The journal aims to advance understanding of the impacts of global change on biological systems and solutions. Examples include:

• rising tropospheric ozone, carbon dioxide and sulphur dioxide concentrations
• increasing UV-B irradiation
• global climate change
• biological sinks and sources of atmospheric trace gases
• eutrophication
• land use change
• biodiversity loss
• biological feedback to climate change
• biological mitigation of atmospheric change

About the Institution

Affiliated with the Chinese Academy of Sciences, South China Botanical Garden (SCBG) is one of China's earliest botanical research institutions. It was founded in 1929 by Academician Huan-Yong Chen (Woon-Young Chun) and officially designated as a national botanical garden in 2022. Focusing on South China, it commits to plant conservation, scientific research and science popularization across tropical and subtropical regions, and provides scientific underpinnings for ecological and green development. As a leading institution for plant germplasm conservation, SCBG has attained outstanding achievements since 1988: it has published over 540 monographs, issued more than 6,900 SCI-indexed papers, won over 350 scientific awards, obtained more than 630 patents, and bred over 410 new plant varieties. Its research work is strongly supported by three core academic divisions and a number of field research stations.