A new study has revealed how elevated CO₂ and nitrogen deposition, two key drivers of global change, interact to affect the rhizosphere priming effect (RPE) of Chinese fir, a major plantation tree species in China.

Soil organic matter (SOM) is a major reservoir of carbon in terrestrial ecosystems, and its decomposition by soil microbes releases carbon dioxide (CO2) into the atmosphere. Plant roots can enhance or mitigate this process by altering the availability of nutrients and substrates for microbes, a phenomenon known as the rhizosphere priming effect (RPE).

Researchers from the Chinese Academy of Sciences conducted a 543-day chamber experiment to investigate the RPE of Chinese fir seedlings under two concentrations of atmospheric CO₂ (400 and 800 ppm) and two levels of nitrogen addition (0 and 100 kg N ha^-1 yr^-1). They used a stable isotope tracer technique to measure the RPE, which is the difference in SOM decomposition between planted and unplanted soil.

They found that the RPE stimulated SOM decomposition. The priming intensity ranged from 27% to 390%, which was within the range reported by previous studies. Elevated CO₂ significantly decreased the RPE but only at the later stage of the experiment.

The researchers also discovered an interaction between elevated CO₂ and nitrogen addition on the RPE. Nitrogen addition reduced plant-microbe competition for nitrogen under ambient CO2, but not under elevated CO2, where the competition was more intense.

The study was published in the journal Soil Biology & Biochemistry, with the title "Elevated CO2 and nitrogen interactively affect the rhizosphere priming effect of Cunninghamia lanceolata".