Enhanced Root Exudation as an Adaptation Mechanism to Facilitate Phosphorus Mobilization in a Primary Tropical Forest Under Chronic Nitrogen Deposition

Tropical and subtropical forests play a key role in alleviating global climate change by maintaining high ecosystem productivity and carbon (C) sequestration. Elevated atmospheric nitrogen (N) deposition is reshaping ecosystem structure and function in the tropics, yet it remains unclear how N-rich tropical and subtropical ecosystems adapt to chronic N deposition. Using a two-decade N addition experimental platform in a primary tropical forest, we quantified the responses of root exudation and soil P transformation processes. We find that N addition stimulates forest trees to allocate more photosynthates to root exudation and accelerated rhizosphere P mobilization. This finding challenges the paradigm that long-term N addition reduces belowground C allocation. This process represents a critical adaptation mechanism by which trees mitigate decreased P availability induced by long-term N deposition. This study reveals a positive feedback between root exudation and soil P mobilization, supporting high ecosystem C sequestration in N-rich ecosystems under long-term N deposition.