Tropical Primary Forest Plants Up-regulate Root Exudation to Adapt to Long-term High Nitrogen Deposition

Intensifying global nitrogen (N) deposition has disrupted the N–phosphorus (P) balance in ecosystems, particularly in tropical and subtropical regions where available P is relatively 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, especially 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 long lacked experimental evidence, becoming a critical knowledge bottleneck for predicting forest carbon (C)–P feedbacks and ecosystem stability under high N deposition.

To address this issue, the term studies investigated how tropical forest plants adapt to chronic high N addition by regulating root exudates and rhizosphere P dynamics in a primary broadleave forest. The results showed that plants evolved an active adaptation mechanism in facing chronic high N addition: (i) increased root C exudation rate to stimulate microbial phosphatase activity and accelerated the mineralization of organic P; (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, driving approximately twice as much P release as the phosphatase pathway.

This study provides the first evidence that tropical plants can adapt to long-term high N deposition by up-regulating root exudation, revising the traditional view that N deposition reduces belowground C 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 crucial for predicting the dynamics of tropical forest carbon sinks under future climate change.

The study, entitled “Enhanced Root Exudation as an Adaptation Mechanism to Facilitate Phosphorus Mobilization in a Primary Tropical Forest Under Chronic Nitrogen Deposition”, was published in Global Change Biology. Associate Professor ZHU Xiaomin and Professor LU Xiankai from South China Botanical Garden (SCBG), CAS, are the first author and the corresponding author, respectively. Other co-authors include Professor MO Jiangming, Associate Professor CHEN Weibin and MAO Qinggong from SCBG; Professor Benjamin L. Turner from Shandong Agricultural University; and Professor ZHANG Ziliang from Northwestern Polytechnical University. Thiswork was supported by Guangdong S&T Program and National Natural Science Foundation of China. Article link：http://dx.doi.org/10.1111/gcb.70912

Figure 1. Effects of long-termN addition on root exudation of dominant tree species in a tropical monsoon evergreen broadleaf forest.（Image by ZHU et al.）

Figure 2. Effects of long-term N addition on soil P fractions in the rhizosphere and bulk soils in a tropical monsoon evergreen broadleaf forest.（Image by ZHU et al.）

Figure 3. A theoretical framework for long-term N deposition promoting root exudation and rhizosphere P cycling in primary tropical forests.（Image by ZHU et al.）