To sustain food production under accelerating climate change, it is vital to understand how key nutrients respond to the combined effects of rising atmospheric CO₂ and warming. Unlike nitrogen, phosphorus (P) cannot be fixed from the atmosphere. Its availability is governed by finite rock phosphate sources and strongly influenced by soil mineral interactions and microbial activity. In flooded rice paddies, which support over half the world’s population, sharp redox fluctuations induced by irrigation and drainage further complicate P cycling.

In a new study published in Nature Geoscience, researchers from the Institute of Soil Science, Chinese Academy of Sciences—led by Associate Prof. WANG Yu, Prof. ZHANG Jiabao, and Prof. ZHU Chunwu—used a decade-long Free-Air CO₂ Enrichment (FACE) experiment combined with in situ warming to assess how these concurrent climate drivers shape phosphorus dynamics in a typical rice–upland rotation system. The journal also invited the team to prepare an accompanying Research Briefing to highlight the study’s key findings and implications.

Their findings show that elevated CO₂ and warming synergistically reduce soil phosphorus availability, with warming playing a dominant role. Long-term exposure progressively redirects P from plant-available pools into more stabilized organo-mineral complexes and microbial biomass.

By integrating evidence from soil P fractions, iron–organic associations, microbial traits, and crop uptake data, the study reveals a climate-driven shift toward closed P cycling in paddy soils. This raises concerns about the viability of offsetting such imbalances with increased fertilizer use alone—especially in weathered soils with strong P fixation or regions with limited fertilizer access, where added inputs may have limited effect or introduce environmental risks.

This study builds on the team’s earlier Nature Geoscience work: "Reduced phosphorus availability in paddy soils under atmospheric CO2 enrichment", which demonstrated that elevated CO₂ alone reduces soil P availability. Adding field-based warming was technically challenging—maintaining infrared heaters through typhoons and monsoons required constant repairs and recalibration—but proved essential to simulate future climate conditions realistically.

The results point to heightened vulnerability of rice-based food systems, particularly in regions with low adaptive capacity, and underscore the importance of climate-resilient P management strategies. The authors recommend combining precision fertilization with soil amendments that modulate iron–phosphorus interactions to maintain productivity under global change.

Free-Air CO₂ Enrichment (Image by Prof. Zhu Chunwu's team)

Discussing the FACE experiment with Josep Peñuelas (the second from the left) (image by Prof. ZHU Chunwu's team)