A decade-long study has revealed that rising atmospheric CO₂ and warming work together to reduce the availability of phosphorus in rice-upland crop rotation systems, potentially threatening future food security. The research, which was led by scientists from the Institute of Soil Science of the Chinese Academy of Sciences, shows that warming plays a dominant role in redirecting phosphorus into less accessible soil pools.
The findings were published in Nature Geoscience on February 3. The journal also invited the research team to write a Research Briefing highlighting the study's key results and implications.
Understanding how key nutrients respond to the combined effects of rising atmospheric CO₂ and warming is vital to sustaining food production under accelerating climate change. Unlike nitrogen, phosphorus cannot be fixed from the atmosphere. Its availability is governed by finite rock phosphate sources and is greatly affected by interactions involving soil minerals as well as microbial activity. In flooded rice paddies, which support over half the world's population, sharp redox fluctuations induced by irrigation and drainage further complicate phosphorus cycling.
To assess how these concurrent climate drivers shape phosphorus dynamics, researchers led by Associate Prof. WANG Yu, Prof. ZHANG Jiabao, and Prof. ZHU Chunwu conducted a ten-year Free-Air CO₂ Enrichment (FACE) experiment combined with in situ warming in a typical rice-upland rotation system, in which rice and wheat crops are grown sequentially during the same year.
Their findings show that elevated CO₂ and warming synergistically reduced the availability of soil phosphorus, with warming playing a dominant role. Long-term exposure progressively redirected phosphorus from plant-available pools into more stabilized organo-mineral complexes and microbial biomass.
By integrating evidence from soil phosphorus fractions, iron–organic associations, microbial traits, and crop uptake data, the researchers revealed a climate-driven shift toward closed phosphorus cycling in paddy soils. These results raise concerns about offsetting imbalances through increased fertilizer use alone, especially in weathered soils with strong phosphorus fixation or in regions with limited fertilizer access, where added inputs may be ineffective or introduce environmental risks.
The new findings build on the team's earlier Nature Geoscience work, which demonstrated that elevated CO₂ alone reduces soil phosphorus availability. Adding field-based warming posed technical challenges. For example, maintaining infrared heaters through typhoons and monsoons required constant repair and recalibration. Nevertheless, it was essential for realistically simulating future climate conditions.
Overall, the results underscore the importance of climate-resilient phosphorus management strategies and highlight the growing vulnerability of rice-based food systems, particularly in regions with low adaptive capacity. The authors recommend combining precision fertilization with soil amendments that modulate iron–phosphorus interactions to maintain productivity under future climate conditions.
