Labile carbon and nitrogen additions affect soil organic matter decomposition more strongly than temperature

- Labile carbon addition induced positive priming effects at 15 °C and 25 °C.
- Labile carbon and nitrogen additions induced negative priming.
- “Mining of nitrogen” from soil organic matter was the main priming mechanism.
- Temperature effect on priming of SOM decomposition was dependent on labile C and N.

Inputs of labile carbon (C) and nitrogen (N) affect the intensity and direction of priming effects (i.e., increase or decrease of soil organic matter (SOM) decomposition caused by labile inputs). Increased temperature is also an important factor affecting SOM decomposition. However, the effects of temperature on priming of SOM decomposition remain unclear. To investigate how temperature affects priming of SOM decomposition through changing microbial composition, we added 13C-labeled glucose with or without NO3− or NH4+ to a subtropical plantation soil in southern China and incubated the soil at 15 °C and 25 °C for 10 days. Soil microbial composition was assessed by analysis of phospholipid fatty acids (PLFAs). Glucose led to positive priming (release of additional CO2) at both temperatures. In contrast, glucose addition with NO3− or NH4+ resulted in negative priming. Temperature did not show a significant effect on SOM decomposition, while the effects of temperature on priming of SOM decomposition were dependent on labile C and N. Labile C addition induced stronger priming at 25 °C than at 15 °C, while combined C and N addition more strongly reduced priming at the high than the low temperature. Although PLFA composition was affected by temperature and labile C and N inputs, changes in PLFA composition were not correlated with priming. We conclude that temperature changes may have limited effects on SOM decomposition in this subtropical soil, while the availability of labile organics has a much stronger effect on priming under warming.

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