Background and aims

Positive relationships between temperature and soil respiration rate are widely observed, but it remains unclear if the relationships are due to increases in soil organic matter mineralisation (R _om), or in root and rhizosphere respiration (R _roots), or increases in both. This study aims to determine the relative sensitivity of R _om and R _roots to temperature in soils with differing properties.

Methods

Taking advantage of the difference in stable carbon isotopic composition provided by C₃ and C₄ plants, we partitioned soil respiration into R _om and R _roots for two soils with contrasting clay mineralogy, pH and carbon content over a 24 °C temperature range (from 12 to 36 °C).

Results

The Chromosol (dominated by illite, with near neutral pH and low organic carbon content) showed an increase in the proportion of R _om with temperature, indicating an increase in the decomposition of soil organic carbon. In contrast, the Ferrosol (dominated by hematite and goethite, with acidic pH and high organic carbon) showed no change in the proportion of R _om with warming, and a negative priming effect at the highest temperature.

Conclusions

The observed positive priming effect for the Chromosol and a negative priming effect for the Ferrosol are consistent with contrasting mineralogy, reflecting the relatively weaker bond strength between soil carbon and illites in the Chromosol compared to the Ferrosol.